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Remote sensing applications of the earth's surface: an outlook into the future
Photogrammetria, 41 (1987) 59-71
59
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Remote Sensing Applications of the Earth's Surface: An Outlook into the Future* HERMAN Th. VERSTAPPEN
International Institute for Aerospace Survey and Earth Sciences ( ITC), Enschede, The Netherlands (Received 31 August 1986; revised and accepted 29 September 1986)
ABSTRACT Verstappen, H. Th., 1987. Remote sensing applications of the Earth's surface: an outlook into the future. Photograrnmetria, 41: 59-71. To minimize the risk that predictions on the future of remote sensing applications are mere speculations, the author first analyzes the developments in this field during the last few decades and specifies present trends. Thereafter, some extrapolations to a period of approximately equal length in the future are given. In the context of this 7th symposium of Commission VII, ISPRS, it is considered appropriate to use the 1st symposium, held in Delft 1962, as a starting point and to look forward to the 14th symposium in the year 2014. The author tries to weigh the future role in resource surveying of high-resolution satellites, lowresolution satellites and aircraft of various kinds. Recording systems in the photographic, thermographic and microwave bands are treated separately and the changing relationships between resource surveyors and photogrammetrists also are touched upon. The growing importance of optimal organization and utilization of the massive amount of data gathered by means of geographic information systems (GIS) is indicated and finally the necessity of matching space technology with the immediate and future needs of the human race is emphasized.
INTRODUCTION
Summarizing the outcome of a large symposium, like the present 7th symposium of Commission VII of the International Society of Photogrammetry and Remote Sensing (ISPRS), is a difficult task, particularly if it has to be done at the closing session and thus without the possibility of data analysis, selection and compression provided by the filtering process of quiet contemplation. Venturing an outlook for the future may even be considered hazardous under such conditions if there are no clear-cut trends of development. Fortu*Abbreviated closing keynote paper of the Symposium on Resources Development and Environmental Management of ISPRS Commission VII held 25-29 August 1986.
0031-8663/87/$03.50
© 1987 Elsevier Science Publishers B.V.
60 nately, in the field of remote sensing applications at least some indications can be detected that may serve as a basis for extrapolation into the future. Although this fact makes my task today somewhat easier, I prefer to take two precautions to limit the chances of arriving at erroneous conclusions. First, I think it is wise to briefly view the developments during the last quarter century by comparing the state-of-the-art in 1962 when the 1st symposium of Commission VII was held at ITC, then in Delft, with the present situation as reflected in the papers presented and the discussions held during this 7th symposium in Enschede, 1986. I will then, as a second precaution, limit my attempt to extrapolate these trends to another period of similar length, as will be reflected - assuming that my guesswork is correct - in the proceedings of the 14th symposium of Commission VII in the year 2014. A longer prediction period seems rather unrealistic. Thereafter, I will try to refine the extrapolation by introducing present technological trends and users' needs as factors affecting directly the future course of development. Not all of us will play an active part in that 14th symposium. Some may even already be engaged in an interesting study on "angelo photogrammetry" and - although ! have high hopes for the technological advances of the next century - I am strongly convinced that in that case oral presentation will be a major obstacle. IN RETROSPECT The 1962 symposium was still just in the era dominated by stereoscopic interpretation of aerial photographs using simple conventional methods that had been established three or four decades earlier. This is clearly reflected in the papers presented as only five of the 75 papers of the transactions deal with technical and methodologic matters, whereas the remainder are straightforward applications to specific fields and areas. The winds of change, however, were already beginning to blow and in part were also reflected in the programme. Airborne geophysical surveying, particularly ~nagnetometer surveys, but also electromagnetic and scintillometer surveys using low-flying aircraft had become common practice in the 1950s, but these non-imaging remote sensing methods had developed independently and had rather escaped the attention of photo-interpreters. There was no paper presented about this subject during the 1962 symposium. Some textbooks on photointerpretation in those days already pointed to the fact that the visible spectrum, in which aerial photography is rooted, is only a small portion of the electromagnetic spectrum and that other wavelengths, particularly the microwave and thermal IR bands, awaited exploration. Although vertical PPI (plan position indicator) radar had been extensively used during World War II, the strip-wise sensing by SLAR was developed only in the 1950s and was not yet commercially available in 1962. Thermographic
61 remote sensing had just made its entry in the scene and although airborne applications were not referred to during the symposium, two papers dealt with early satellite applications of this type of sensor installed in the TIROS (Television and Infra-Red Observation Satellite) low-resolution weather satellites. These two papers thus also mark the advent of satellite remote sensing and it is of interest to note that each of them highlighted a subject that is still a focus of interest, namely surveillance and monitoring through repetitive satellite passes, and computer applications in semiautomatic satellite image interpretation systems (mentioning, for example, pattern recognition, man-machine communication and the need of a (photo) data base). Obviously, in 1962 photointerpretation was on the threshold of the new era of "remote sensing" that in the past 24 years has stunned the professional world by a mushrooming of new tools, methods and applications. While air photography evolved into remote sensing, the field of photointerpretation widened to become image interpretation. These developments are clearly mirrored in the subject matter presented at this, the seventh symposium of Commission VII. The number of contributions is almost tripled compared to 1962, a fact that is indicative of the growing importance of remote sensing for resource assessment. About one-third of these contributions (as compared to 4% in 1962) relate to technical aspects concerning, e.g., the hard- and software used for the job. This trend is indicative of the spectacular technological growth in the field of space research and remote sensing in the past 24 years. When looking at the fields of applications, the marked increase of papers related to remote sensing of renewable resources deserves mention. This fact is readily explained by the introduction of multispectral remote sensing techniques which allow for reliable and even semiautomatic detection of crops, vegetation types, etc. This field has expanded substantially in recent years. The same techniques have also furthered remote sensing of surface water features including water pollution. Contributions on the use of remote sensing for surveying nonrenewable resources are distinctly less numerous. Although this may in part be due to competition with other conferences, it is certainly also related to the fact that these resources normally cannot be directly detected on the basis of their spectral characteristics, although they may ( or may not ) be reflected in the spectral signatures of their vegetation or soil cover. Advances in this field are thus less distinct and await the impulses provided by the stereoscopic satellite images that recently have become available and that are essential for earth science application of satellite imagery. While in 1962 emphasis was on detailed surveys, many papers of 1986 deal with small-scale and medium-scale resource mapping projects. This is quite logical taking into account the fact that in 1962 aerial photographs were practically the only available tool, whereas the imagery of the first-generation highresolution resource satellites, with a spatial resolution of about 80 m, invites
62 reconnaissance studies of large areas. More detailed studies require the additional use of aerial photographs in multiphase approaches. It is of considerable interest in this context that earlier this year the first operational second-generation high-resolution satellite ( S P O T ) has been launched. The merits of these images, with a spatial resolution of 10 m panchromatic and 20 m colour and the potential of the stereoscopy that can be obtained, have been amply discussed during this symposium. One may thus say with justification that also this seventh symposium of Commission VII is taking place on the threshold of a new era of satellite remote sensing in much the same way as the first one coincided with an earlier major threshold. Monitoring and updating of maps using recurrent passes of high-resolution sun-synchronous satellites is the subject of several papers and relate to matters such as coastal development, river floods, etc. A number of authors have made use of images/data recorded by (NOAA) weather satellites which characteristically have a low spatial resolution and a high temporal resolution. These images have lured meteorologists and oceanographers into the use of satellite imagery, thus considerably widening the circle of scientists engaged in remote sensing applications. In addition, these images serve a variety of other purposes, such as the monitoring of vegetation changes, drought and desertification, and they are even used in the context of locust control. Although not all these subjects may have received equal weight during this symposium, the applicability of low-resolution satellite imagery as a counterpart of the second-generation high-resolution, stereoscopic S P O T satellite data is fully realized by the participants. There has been made no mention of applications of extraterrestrial remote sensing during this symposium, although this imagery is now available from the moon, a number of planets and planetoids and some of the moons of other planets. Some may consider this a lack of scientific imagination from the side of the participants while others may see it as reflecting a (too) low assessment of extraterrestrial ( e.g., mineral ) resources. MAIN TRENDS When considering the developments of the last few decades in a more general sense the following main trends emerge: (a) A great diversification of sensors that has freed us from the limitations of the narrow visible spectrum and that now enable recording in all usable parts of the electromagnetic spectrum from the micro waves, through the thermal infrared zone and the visible spectrum to the ultraviolet. (b) A great diversification of recording altitudes which - leaving for a moment the extraterrestrial recordings - now range from an altitude of 36,000 km for the geostationary (weather) satellites and an altitude of approximately 700-900
63 km for orbiting (e.g., sun-synchronous) satellites to 250-300 km for the space shuttle and approximately 18,000-200 m for survey aircraft that include superaltitude (stratospheric), conventional, low-flying reconnaissance and ultralight planes. ( c ) Repeated recording at regular relatively short intervals became common practice. The possibilities for sequential interpretation of aerial photographs limited by a recording interval of usually years or decades is surpassed by the orbiting resource satellites giving a temporal resolution of less than one to several weeks (or, if cloud cover interferes, months) and by the geostationary satellites that record near-continuously (interval of a few hours or days ). There is, of course, a trade-off here between spatial resolution and temporal resolution, which makes high- and low-resolution systems complementary. (d) Rapid introduction of digitalization methods covering digital data recording, telemetering of data to groundstations and the subsequent data processing, and (semi) automatic interpretation techniques are envisaged. Image enhancement ranks high in this respect and can be subdivided into digital methods for restoration of the images through geometric and radiometric corrections, for contrast improvement through histogram equalization, density slicing, spatial frequency filtering, etc., and for (feature space) information extraction purposes by way of automatic classification, maximum likelihood approaches, intensity mapping and ratioing, principal component transformations, etc. (e) A cascade of topographic and thematic information is being constantly poured down over our heads from satellites and other sources. Since the satellite remote sensing data are mostly digitized and give the precise geographical location of the recordings in X, Y ( and Z) coordinates, storing the information in a data base and its subsequent classification and retrieval by way of a geographical (or land) information system (GIS/LIS) has become feasible. In the context of planned development, there is a great need all over the world for rapid data acquisition and presentation and thus GIS/LIS hold a good promise for the future. The resource surveyors have become part of a larger community. As I have already mentioned, several scientific disciplines that never really were using aerial photographs, such as meteorology and oceanography, have developed a great interest in satellite remote sensing, particularly in low-resolution imagery. The field of application of aerospace data for resource development and related subjects thus has grown substantially. This, however, is only one and an even relatively minor aspect of the matter. Resource surveyors share their interest in aerospace technology with photogrammetrists making and updating topographic maps, with geodesists and geophysicists measuring the shape of the Earth, and with astronomers exploring our planetary system and even the universe. The breakthrough of space technology has the effect of rapidly pushing forward the frontiers of science. In fact, although nowadays entire satellite
64 systems are devoted to resource studies of our planet, very substantial sums are spent on other, quite different, aspects of space research (telecommunications for example ). Cynical people will say that governments do not usually spend such vast amounts of money for the sake of pure science and that the military potentials of rockets and spacecraft are the reasons behind it. These potentials undeniably exist but need not worry us unduly as resource surveyors. There is, in fact, nothing new in this respect as aircraft development has in the past hardly been influenced by considerations of resource surveying, but through the years photogrammetrists and photointerpreters alike have nevertheless greatly benefitted from it. Also, I feel that the military potentials are just a part - and probably not even the most crucial part - of the engine pushing space research. A space-industrial complex is developing and technological breakthroughs in fields such as supercomputers and microchips are triggered. We are moving quickly to the post-industrial space era with its inherent problems related to advanced technology, economic growth, employment, utilization of human resources, social discrepancies between various parts of the globe, preservation of our cultural heritage, etc. We resource surveyors nowadays are like the small sucker fish that is attached to the skin of a whale (or shark), while being thrust forward by the whale of space technology, we - living in symbiosis with it - have to find applications that are justifiable from an economic, scientific and social point of view. THE CHANGINGFACEOF RESOURCESURVEYINGFOR DEVELOPMENT The rise of aerospace technology has affected resource surveying in various ways by making images of different types and scales available. Nevertheless, the same basic methods of image interpretation still apply throughout - the essence of which is indicated in Fig. 1. An eye-brain interactive system based on visible image density (greytone, colour) and relief elements leads to an assessment of the (usually) invisible resources, through a reiterative process of observation deduction, induction and verification that generates hypotheses, interpretations and conclusions. Obviously, technologically perfected data acquisition and scientifically well-trained interpreters are of equal importance for obtaining optimum results, in much the same way as refined equipment and a skilled watchmaker are required to produce a good watch. The density can be pictured in grey tones or in colours and relates specifically to the vegetal cover, to surface water, ice and snow and to barren soil or rock. The relief can best be pictured stereoscopically, although also monoscopically some data can be obtained through shadow (density) patterns. It is particularly important as an indicator of terrain forms. While in stereoscopic photointerpretation both density and relief criteria played a rather balanced part, the development of airborne satellite remote sensing during the last decades has strongly emphasized the analysis of density patterns. Image interpre-
65
Fig. 1. The reiterative process of eye-brain interaction in image interpretation.
tation, especially in the fields of the "green" and "blue" sciences (vegetation, land use, surface hydrology, oceanography), has benefitted from this. Although "brown" (earth) sciences have also been positively affected by improved density analysis, a stronger impetus for them can be expected in the years to come. With the advent of SPOT and also metric camera/large format camera, etc., stereoscopic relief has been introduced as a criterion in the interpretation of orbital imagery. When briefly outlining the increased capacity of image interpretation the following picture emerges. Multispectral recordings have considerably improved both qualitative and quantitative image interpretation methods. The possibilities for recognition and identification of objects by visual, qualitative means have increased distinctly but the scope in the context of quantitative studies of spectral signatures and digital data processing is enormous. Quantitative relief analysis using satellite remote sensing is as yet much less advanced and is a promising area of research now that stereoscopic satellite imagery has come on the market. Multitemporal recordings have given new impetus to the field of dynamic image interpretation. It may relate to monitoring of daily/hourly changes in cloud patterns, of seasonal changes in vegetation patterns, of sea-water temperatures and of sudden or gradual changes in the land surface, such as coastlines and river courses. The requirements for spatial and temporal resolution vary with the type of phenomenon concerned and the affected surface area. Generally there is a trade-off between low-resolution images/data obtained at
66 short intervals and high-resolution images taken at larger intervals. In this respect, there is ample scope for both high- and low-resolution satellite data. A special case is the monitoring of sudden and often catastrophic natural disasters, such as floods. Time-specific recordings are then required and the present problem is that low-resolution data are inadequate and high-resolution imagery from orbiting satellites may not be available either because there is no pass at the required time or because of cloud cover. More frequent satellite passes and/or all-weather (radar) systems are thus badly needed. An often insufficiently understood characteristic of disaster surveying using satellite imagery as a tool is that the hazard zoning usually has to be established in advance on the basis of the terrain configuration visualized on earlier, predisaster, images which are then to be matched with the time-critical images taken during the disaster. Multiphase recording has been advocated as a method in resource surveys using Landsat satellite images. These have proved very useful for static mapping of the major terrain types, large structural elements, etc., but the spatial resolution of 80/30 m is insufficient for more detailed analysis. Thus a stepwise "zooming-in" approach was introduced starting from satellite images, e.g., at a scale of 1:1,000,000 through Landsat blow-ups and/or digital images at a scale of, e.g., 1:250,000 to photographic mosaics and aerial photographs in scales ranging from 1:100,000 to 1:10,000. Ground-truth gathering is a final step, but can also be implemented in various levels of detail such as rapid traversing of the whole area and detailed site analysis of selected, characteristic areas of limited size. Only for small-scale reconnaissance mapping is the multiphase approach not necessary because the spatial resolution of Landsat data is sufficient for this purpose. Thus the entirely new possibility for direct small-scale mapping was created, avoiding the conventional procedures of scale reduction with connexed cartographic and conceptual generalization. This applies also to topographic mapping and the method has been used in particular also for updating of maps. An important breakthrough in the field of small-scale surveying and mapping thus was generated. THE WAYAHEAD Since the beginning of this year, SPOT-1 satellite data are available with a spatial resolution of 10 m (panchromatic). This means that this kind of satellite imagery can be used directly for detailed resources surveying in scales of 1:25,000-1:50,000. The multiphase approach, just mentioned in the context of Landsat imagery, is not required and this method will, in likelihood, be obsolete in the near future. Satellite imagery that up to the present could be considered complementary to aerial photography in resource surveying now has become competitive. Most
67 types of resource survey work can technically now be implemented using satellite imagery alone. Only for geophysical surveys and for very detailed surveys e.g., for engineering sites, for assessment of the timber volume, urban studies etc., aerial photographs will remain indispensible also in the forthcoming decades. The air-photography companies thus are bound to lose many of their resource survey customers in the next decades. There is, of course, the matter of cost, but since the gigantic expenditures for developing space technology do not have to be paid by the resource surveyor alone, who - in contrast - will be charged for the full cost (including overhead, stand-by cost of crew/aircraft, etc. ) by the air-survey companies, the outcome is not difficult to guess. The space industry will be wise enough to keep their prices at a competitive level. Another interesting consequence of the advent of satellite imagery having this high spatial resolution is that secrecy with even detailed topographic and other maps, and with aerial photographs (and any restriction in their free availability) is completely outdated. It will be a blessing that resource surveyors at last have got rid of the sometimes staggering and frustrating problems of getting the imagery and further information required to efficiently perform their duties of resource inventory and environmental management for purposes of development. One may wonder - and the question has been put during this symposium whether, given the potentials of existing and future satellite remote sensing systems, we do not risk gathering more data than are actually required for specific purposes. This would mean getting swamped with unneccessary information and an undue increase of the already gigantic problems of data handling. As an example, I mention the equipment developed for simultaneous multispectral recording in 10 or 16 spectral bands. This may be of use in a number of cases, but most of our multispectral needs are satisfied by recording in three or four bands only. Thus, systems developed along these lines have a much greater feasibility for application in orbiting resource satellites for world needs. It is, of course, also a matter of cost. One could economize and optimize by collecting only the amount and type of information that we need and want. Clear specification of users' needs, therefore, ranks high among the tasks/duties of those applying aerospace technology to resource studies and environmental management. I am convinced the space industry will listen to our voices because it is generally understood that the budgets required for further technological advances will be considerably more willingly allocated by the various governments if operational and economically sound applications can be found immediately or are within reach in the near future. One may object that if all aerospace and other data on environmental resources were stored in a geographical information data handling and retrieval system, procedures could be adjusted to accomodate the needs of detailed, largescale surveying and the needs of more generalized information for mediumand small-scale mapping. Consequently, we should gather as much informa-
68 tion as possible. This concept is certainly realistic and it is our goal for the future. Until such sophisticated information systems have been implemented on a world-wide scale, however, there is scope for several types of satellite observation systems operating simultaneously and each serving specific fields of application. This will be the reality for several decades to come. This development, by the way, illustrates the great weight now put on resource surveying and mapping as compared to a few decades ago when it was common practice to make a hole in any more or less suitable and available aircraft and mount a camera in it. In many cases surveys even had to be based on aerial photographs made previously for other purposes, even if they were not optimally suitable because of scale, acquisition season, emulsion or up-to-dateness. A first type of resource satellite systems comprises high-resolution satellites with multispectral capacity in at least a few channels for recording the reflection/emission of the Earth surface and with stereoscopic capacity and/or other means for analysing the vertical dimension of the terrain configuration. The Landsat satellites were the forerunners in this field. In the present context, it is evident, however, that a non-stereoscopic system with a spatial resolution of 80 or even 30 m (Landsat/TM) is no match for a stereoscopic system with a spatial resolution of 10/20 m ( SPOT-1 ). The future will certainly bring further developments in this type of resource satellite system which will cater for thematic mapping in scales of 1:25,000 to 1:100,000. A second type of resource satellites are the (geostationary) low-resolution satellites. Their characteristics of covering very large parts of the globe with a very high temporal resolution render them suitable for very small (multimillion) scale monitoring and mapping. Meteorology and oceanography are important, but certainly not the only fields of application. The present systems of NOAA, GOES and ESA Meteosat satellites are operational and will remain so, unaffected by the recent launch of the SPOT-1 satellite. Further improvements of the systems can be expected for the future, including the development of zooming-in facilities for temporarily depicting specific parts of the Earth surface in greater detail. There may be scope for a third type of resource satellite, catering for resource mapping at scales in the order of 1:250,000 to 1:500,000. While maintaining the multispectral and stereoscopic capacities of the first type already mentioned, lower spatial resolution and the coverage of a larger surface area per frame should be aimed at, possibly in combination with a higher temporal resolution. Thorough exploration of the market for such products should precede future developments in this area. In addition to these three main types, satellites serving specific areas may prove viable, such as the Tropical Earth Resources (TERS) satellite concept studied by Indonesia and The Netherlands for applications in equatorial countries. In the overview on current trends in remote sensing and programmes under-
69 way, the Earth Observation Programme of the European Space Agency should be mentioned. During the opening session of this symposium, European cooperation in the field of remote sensing from space has been highlighted as a paramount example of successful international programmes. European countries together with Canada decided to develop the ERS-1 programme. The objectives are to transfer experimental use of microwave techniques to operational use for applications in global ocean and ice monitoring. This programme offers a challenge for both global climate research, sea state forecasting and near-future operational and commercial applications. In this respect data continuity is an essential condition. After ERS-1 {to be launched in 1990) with an expected lifetime of three years, the duration of the mission will be expended by the launch of ERS-2 in 1993. The ESA Earth Observation Preparatory Programme which started this year will define future missions dedicated to meteorology, land observation, ocean and ice observation and solid earth studies. With regard to land observation a major contribution is expected from the acquisition of synthetic aperture data on a regular basis. The ERS-1 programme will offer a first opportunity to collect SAR images in C-band overland, with the constraints related to regional coverage over Europe and North America and its experimental character. A possible future land-oriented mission can provide us in the 90-ties with a capability for frequent observation by means of an advanced SAR system suited to develop operational use of polarorbiting platforms for monitoring of agriculture and land use. TRENDS OF FUTUREDEVELOPMENTSIN SATELLITEREMOTE SENSING The spectral recording systems in the visible and near-infrared spectrum at present include: ÷ Multispectral sensing ( MSS ) ; probably the most widely used system when satellites are concerned, such as Landsat MSS and SPOT-3 band scanner. ÷ Multispectral photography (MSP) with multilens cameras or multispectral imaging with TV cameras; known from aerial survey and satellites such as Soyuz (MKF-6) and Landsat 1 and 2 (RBV-3). ÷ Panchromatic black and white imaging. Under this category come the RBV of Landsat 3, the linear array, "pushbroom" SPOT configuration, and the long focal length photography of manned spacecraft, Stereosat and Mapsat. Air photography (panchromatic/colour) also comes under this heading. Multispectral sensing from satellites has a great promise for the future in studies of the Earth's cover. Panchromatic imaging from aircraft, orbiters and satellites will be the main field of interest of photogrammetrists. Earth scientists share with the latter the need for stereoscopy, but their metrical requirements are of a lower level. In the microwave zone, the recording systems comprise side-looking air-
70 borne radar (SLAR) and synthetic aperture radar (SAR) systems used in orbiters. Because of the need for all-weather capacity, especially for purposes of monitoring and time-critical data-gathering, e.g., in the context of flood disasters, microwave recording will become increasingly important. Once the technical problems have been solved, a great future exists for satelliteborne microwave observation. After the Seasat (1978) and the space-shuttle SIR-A and B (1981 and 1984) new developments are eagerly expected, such as the ERS 2 satellite of ESA (1989), the Japanese MOS 1-3 satellites (19..) and the Canadian Radarsat (1992). Whether the - at present rather erratic - airborne microwave (SLAR) recording can compete with such operational satellite microwave systems is doubtful. Thermographic recording in the middle and far infrared, using aircraft as a platform, though very useful for specific purposes, has always been a rather rare bird in remote sensing. From satellites, to the contrary, it has found wide applications in Landsat 3, the short-lived Seasat and particularly in the NOAA satellites (heat capacity mapping mission - HCMM). Since the technology for recording all usable parts of the electromagnetic spectrum has already been developed, further perfections rather than spectacular new breakthroughs can be expected for the future, although, of course, the satellite systems will further evolve. The relief recording methods range from the conventional but very important stereoscopic imagery radar altimetry and scatterometry to laser-altimetry. The precision of the latter is such that deformations of the sea surface caused by gravitational anomalies can be recorded and information about the submarine relief consequently can be obtained. The methods have been developed, but since this is a fairly recent occurrence further developments are likely. Stereoscopic imagery from space is in its infancy and will soon be widely applied, particularly for purposes of earth sciences and photogrammetry. Methodological developments in interpretation, however, will be minor. The diverse requirements of the various users of satellite imagery make it likely that several types of sensors will be installed in future spacecraft in addition to dedicated satellites launched for specific purposes. These developments are, in fact, already underway and are rooted in the emphasis put on: ÷ Spectral characteristics - for the study of vegetation, sea and ice. ÷ Relief characteristics - for earth science applications. + Relief and high metric qualities - for photogrammetric purposes. ÷ Temporal resolution - for monitoring. ÷ All-weather capability - for monitoring, disaster surveying, etc. Beyond doubt, a wide array of satellites having different configurations will be launched in the years to come. Quo VADIS? The cost involved in implementing satellite technology in the next few decades will be very high. In a recent report of the U.S. Commission on Space,
71 entitled "Pioneering the Space Frontier", an annual expenditure of US$ 20 billion is expected around the year 2000. The annual expenditure by the FRG is estimated at DM 1.6 billion (approximately US$ 0.75 billion). Adding to this the considerable space efforts of the ESA and of countries like France, Japan, Canada, Brazil, etc., astronomical figures are reached. These figures assume continuous economic growth in the coming decades. Since this is quite uncertain, possibly less funds will in fact become available. Various countries would like to take the lead in space research, :resulting in a centralized administration. This seems hardly feasible to me. Many countries want to develop their own satellites and administrative structures, fully participating in the high technology of the future and enhancing their national prestige. Personally, I feel that such competition is very desirable because only this way will challenges be mutually presented that will yield optimum results. Good international cooperation will, of course, be required to avoid major inefficiencies and undue duplications. The best solution may prove to be joint efforts of groups of countries. This could be a very important aspect of space technology. Bringing the nations together because there is a job at hand that cannot be done by any country individually. This job, I think, is to study, map and monitor the globe with the aim of safeguarding our threatened environment, "mother earth", for the generations to come and to give them the quality of life required for economic, social and spiritual development. We should not pursue technology for its own sake but put it to use for the study of the "ordinary business of life", a term I quote from a recent issue of the UN University periodical WORK IN PROGRESS. Only this way will the costly efforts of space research in the long run be justified.
REFERENCE Damen, M.C.J., Sicco Smit, G. and Verstappen, H.Th., 1986. Remote Sensing for Resources Developmentand EnvironmentalManagement(3 volumes).Balkema,Rotterdam.
59
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Remote Sensing Applications of the Earth's Surface: An Outlook into the Future* HERMAN Th. VERSTAPPEN
International Institute for Aerospace Survey and Earth Sciences ( ITC), Enschede, The Netherlands (Received 31 August 1986; revised and accepted 29 September 1986)
ABSTRACT Verstappen, H. Th., 1987. Remote sensing applications of the Earth's surface: an outlook into the future. Photograrnmetria, 41: 59-71. To minimize the risk that predictions on the future of remote sensing applications are mere speculations, the author first analyzes the developments in this field during the last few decades and specifies present trends. Thereafter, some extrapolations to a period of approximately equal length in the future are given. In the context of this 7th symposium of Commission VII, ISPRS, it is considered appropriate to use the 1st symposium, held in Delft 1962, as a starting point and to look forward to the 14th symposium in the year 2014. The author tries to weigh the future role in resource surveying of high-resolution satellites, lowresolution satellites and aircraft of various kinds. Recording systems in the photographic, thermographic and microwave bands are treated separately and the changing relationships between resource surveyors and photogrammetrists also are touched upon. The growing importance of optimal organization and utilization of the massive amount of data gathered by means of geographic information systems (GIS) is indicated and finally the necessity of matching space technology with the immediate and future needs of the human race is emphasized.
INTRODUCTION
Summarizing the outcome of a large symposium, like the present 7th symposium of Commission VII of the International Society of Photogrammetry and Remote Sensing (ISPRS), is a difficult task, particularly if it has to be done at the closing session and thus without the possibility of data analysis, selection and compression provided by the filtering process of quiet contemplation. Venturing an outlook for the future may even be considered hazardous under such conditions if there are no clear-cut trends of development. Fortu*Abbreviated closing keynote paper of the Symposium on Resources Development and Environmental Management of ISPRS Commission VII held 25-29 August 1986.
0031-8663/87/$03.50
© 1987 Elsevier Science Publishers B.V.
60 nately, in the field of remote sensing applications at least some indications can be detected that may serve as a basis for extrapolation into the future. Although this fact makes my task today somewhat easier, I prefer to take two precautions to limit the chances of arriving at erroneous conclusions. First, I think it is wise to briefly view the developments during the last quarter century by comparing the state-of-the-art in 1962 when the 1st symposium of Commission VII was held at ITC, then in Delft, with the present situation as reflected in the papers presented and the discussions held during this 7th symposium in Enschede, 1986. I will then, as a second precaution, limit my attempt to extrapolate these trends to another period of similar length, as will be reflected - assuming that my guesswork is correct - in the proceedings of the 14th symposium of Commission VII in the year 2014. A longer prediction period seems rather unrealistic. Thereafter, I will try to refine the extrapolation by introducing present technological trends and users' needs as factors affecting directly the future course of development. Not all of us will play an active part in that 14th symposium. Some may even already be engaged in an interesting study on "angelo photogrammetry" and - although ! have high hopes for the technological advances of the next century - I am strongly convinced that in that case oral presentation will be a major obstacle. IN RETROSPECT The 1962 symposium was still just in the era dominated by stereoscopic interpretation of aerial photographs using simple conventional methods that had been established three or four decades earlier. This is clearly reflected in the papers presented as only five of the 75 papers of the transactions deal with technical and methodologic matters, whereas the remainder are straightforward applications to specific fields and areas. The winds of change, however, were already beginning to blow and in part were also reflected in the programme. Airborne geophysical surveying, particularly ~nagnetometer surveys, but also electromagnetic and scintillometer surveys using low-flying aircraft had become common practice in the 1950s, but these non-imaging remote sensing methods had developed independently and had rather escaped the attention of photo-interpreters. There was no paper presented about this subject during the 1962 symposium. Some textbooks on photointerpretation in those days already pointed to the fact that the visible spectrum, in which aerial photography is rooted, is only a small portion of the electromagnetic spectrum and that other wavelengths, particularly the microwave and thermal IR bands, awaited exploration. Although vertical PPI (plan position indicator) radar had been extensively used during World War II, the strip-wise sensing by SLAR was developed only in the 1950s and was not yet commercially available in 1962. Thermographic
61 remote sensing had just made its entry in the scene and although airborne applications were not referred to during the symposium, two papers dealt with early satellite applications of this type of sensor installed in the TIROS (Television and Infra-Red Observation Satellite) low-resolution weather satellites. These two papers thus also mark the advent of satellite remote sensing and it is of interest to note that each of them highlighted a subject that is still a focus of interest, namely surveillance and monitoring through repetitive satellite passes, and computer applications in semiautomatic satellite image interpretation systems (mentioning, for example, pattern recognition, man-machine communication and the need of a (photo) data base). Obviously, in 1962 photointerpretation was on the threshold of the new era of "remote sensing" that in the past 24 years has stunned the professional world by a mushrooming of new tools, methods and applications. While air photography evolved into remote sensing, the field of photointerpretation widened to become image interpretation. These developments are clearly mirrored in the subject matter presented at this, the seventh symposium of Commission VII. The number of contributions is almost tripled compared to 1962, a fact that is indicative of the growing importance of remote sensing for resource assessment. About one-third of these contributions (as compared to 4% in 1962) relate to technical aspects concerning, e.g., the hard- and software used for the job. This trend is indicative of the spectacular technological growth in the field of space research and remote sensing in the past 24 years. When looking at the fields of applications, the marked increase of papers related to remote sensing of renewable resources deserves mention. This fact is readily explained by the introduction of multispectral remote sensing techniques which allow for reliable and even semiautomatic detection of crops, vegetation types, etc. This field has expanded substantially in recent years. The same techniques have also furthered remote sensing of surface water features including water pollution. Contributions on the use of remote sensing for surveying nonrenewable resources are distinctly less numerous. Although this may in part be due to competition with other conferences, it is certainly also related to the fact that these resources normally cannot be directly detected on the basis of their spectral characteristics, although they may ( or may not ) be reflected in the spectral signatures of their vegetation or soil cover. Advances in this field are thus less distinct and await the impulses provided by the stereoscopic satellite images that recently have become available and that are essential for earth science application of satellite imagery. While in 1962 emphasis was on detailed surveys, many papers of 1986 deal with small-scale and medium-scale resource mapping projects. This is quite logical taking into account the fact that in 1962 aerial photographs were practically the only available tool, whereas the imagery of the first-generation highresolution resource satellites, with a spatial resolution of about 80 m, invites
62 reconnaissance studies of large areas. More detailed studies require the additional use of aerial photographs in multiphase approaches. It is of considerable interest in this context that earlier this year the first operational second-generation high-resolution satellite ( S P O T ) has been launched. The merits of these images, with a spatial resolution of 10 m panchromatic and 20 m colour and the potential of the stereoscopy that can be obtained, have been amply discussed during this symposium. One may thus say with justification that also this seventh symposium of Commission VII is taking place on the threshold of a new era of satellite remote sensing in much the same way as the first one coincided with an earlier major threshold. Monitoring and updating of maps using recurrent passes of high-resolution sun-synchronous satellites is the subject of several papers and relate to matters such as coastal development, river floods, etc. A number of authors have made use of images/data recorded by (NOAA) weather satellites which characteristically have a low spatial resolution and a high temporal resolution. These images have lured meteorologists and oceanographers into the use of satellite imagery, thus considerably widening the circle of scientists engaged in remote sensing applications. In addition, these images serve a variety of other purposes, such as the monitoring of vegetation changes, drought and desertification, and they are even used in the context of locust control. Although not all these subjects may have received equal weight during this symposium, the applicability of low-resolution satellite imagery as a counterpart of the second-generation high-resolution, stereoscopic S P O T satellite data is fully realized by the participants. There has been made no mention of applications of extraterrestrial remote sensing during this symposium, although this imagery is now available from the moon, a number of planets and planetoids and some of the moons of other planets. Some may consider this a lack of scientific imagination from the side of the participants while others may see it as reflecting a (too) low assessment of extraterrestrial ( e.g., mineral ) resources. MAIN TRENDS When considering the developments of the last few decades in a more general sense the following main trends emerge: (a) A great diversification of sensors that has freed us from the limitations of the narrow visible spectrum and that now enable recording in all usable parts of the electromagnetic spectrum from the micro waves, through the thermal infrared zone and the visible spectrum to the ultraviolet. (b) A great diversification of recording altitudes which - leaving for a moment the extraterrestrial recordings - now range from an altitude of 36,000 km for the geostationary (weather) satellites and an altitude of approximately 700-900
63 km for orbiting (e.g., sun-synchronous) satellites to 250-300 km for the space shuttle and approximately 18,000-200 m for survey aircraft that include superaltitude (stratospheric), conventional, low-flying reconnaissance and ultralight planes. ( c ) Repeated recording at regular relatively short intervals became common practice. The possibilities for sequential interpretation of aerial photographs limited by a recording interval of usually years or decades is surpassed by the orbiting resource satellites giving a temporal resolution of less than one to several weeks (or, if cloud cover interferes, months) and by the geostationary satellites that record near-continuously (interval of a few hours or days ). There is, of course, a trade-off here between spatial resolution and temporal resolution, which makes high- and low-resolution systems complementary. (d) Rapid introduction of digitalization methods covering digital data recording, telemetering of data to groundstations and the subsequent data processing, and (semi) automatic interpretation techniques are envisaged. Image enhancement ranks high in this respect and can be subdivided into digital methods for restoration of the images through geometric and radiometric corrections, for contrast improvement through histogram equalization, density slicing, spatial frequency filtering, etc., and for (feature space) information extraction purposes by way of automatic classification, maximum likelihood approaches, intensity mapping and ratioing, principal component transformations, etc. (e) A cascade of topographic and thematic information is being constantly poured down over our heads from satellites and other sources. Since the satellite remote sensing data are mostly digitized and give the precise geographical location of the recordings in X, Y ( and Z) coordinates, storing the information in a data base and its subsequent classification and retrieval by way of a geographical (or land) information system (GIS/LIS) has become feasible. In the context of planned development, there is a great need all over the world for rapid data acquisition and presentation and thus GIS/LIS hold a good promise for the future. The resource surveyors have become part of a larger community. As I have already mentioned, several scientific disciplines that never really were using aerial photographs, such as meteorology and oceanography, have developed a great interest in satellite remote sensing, particularly in low-resolution imagery. The field of application of aerospace data for resource development and related subjects thus has grown substantially. This, however, is only one and an even relatively minor aspect of the matter. Resource surveyors share their interest in aerospace technology with photogrammetrists making and updating topographic maps, with geodesists and geophysicists measuring the shape of the Earth, and with astronomers exploring our planetary system and even the universe. The breakthrough of space technology has the effect of rapidly pushing forward the frontiers of science. In fact, although nowadays entire satellite
64 systems are devoted to resource studies of our planet, very substantial sums are spent on other, quite different, aspects of space research (telecommunications for example ). Cynical people will say that governments do not usually spend such vast amounts of money for the sake of pure science and that the military potentials of rockets and spacecraft are the reasons behind it. These potentials undeniably exist but need not worry us unduly as resource surveyors. There is, in fact, nothing new in this respect as aircraft development has in the past hardly been influenced by considerations of resource surveying, but through the years photogrammetrists and photointerpreters alike have nevertheless greatly benefitted from it. Also, I feel that the military potentials are just a part - and probably not even the most crucial part - of the engine pushing space research. A space-industrial complex is developing and technological breakthroughs in fields such as supercomputers and microchips are triggered. We are moving quickly to the post-industrial space era with its inherent problems related to advanced technology, economic growth, employment, utilization of human resources, social discrepancies between various parts of the globe, preservation of our cultural heritage, etc. We resource surveyors nowadays are like the small sucker fish that is attached to the skin of a whale (or shark), while being thrust forward by the whale of space technology, we - living in symbiosis with it - have to find applications that are justifiable from an economic, scientific and social point of view. THE CHANGINGFACEOF RESOURCESURVEYINGFOR DEVELOPMENT The rise of aerospace technology has affected resource surveying in various ways by making images of different types and scales available. Nevertheless, the same basic methods of image interpretation still apply throughout - the essence of which is indicated in Fig. 1. An eye-brain interactive system based on visible image density (greytone, colour) and relief elements leads to an assessment of the (usually) invisible resources, through a reiterative process of observation deduction, induction and verification that generates hypotheses, interpretations and conclusions. Obviously, technologically perfected data acquisition and scientifically well-trained interpreters are of equal importance for obtaining optimum results, in much the same way as refined equipment and a skilled watchmaker are required to produce a good watch. The density can be pictured in grey tones or in colours and relates specifically to the vegetal cover, to surface water, ice and snow and to barren soil or rock. The relief can best be pictured stereoscopically, although also monoscopically some data can be obtained through shadow (density) patterns. It is particularly important as an indicator of terrain forms. While in stereoscopic photointerpretation both density and relief criteria played a rather balanced part, the development of airborne satellite remote sensing during the last decades has strongly emphasized the analysis of density patterns. Image interpre-
65
Fig. 1. The reiterative process of eye-brain interaction in image interpretation.
tation, especially in the fields of the "green" and "blue" sciences (vegetation, land use, surface hydrology, oceanography), has benefitted from this. Although "brown" (earth) sciences have also been positively affected by improved density analysis, a stronger impetus for them can be expected in the years to come. With the advent of SPOT and also metric camera/large format camera, etc., stereoscopic relief has been introduced as a criterion in the interpretation of orbital imagery. When briefly outlining the increased capacity of image interpretation the following picture emerges. Multispectral recordings have considerably improved both qualitative and quantitative image interpretation methods. The possibilities for recognition and identification of objects by visual, qualitative means have increased distinctly but the scope in the context of quantitative studies of spectral signatures and digital data processing is enormous. Quantitative relief analysis using satellite remote sensing is as yet much less advanced and is a promising area of research now that stereoscopic satellite imagery has come on the market. Multitemporal recordings have given new impetus to the field of dynamic image interpretation. It may relate to monitoring of daily/hourly changes in cloud patterns, of seasonal changes in vegetation patterns, of sea-water temperatures and of sudden or gradual changes in the land surface, such as coastlines and river courses. The requirements for spatial and temporal resolution vary with the type of phenomenon concerned and the affected surface area. Generally there is a trade-off between low-resolution images/data obtained at
66 short intervals and high-resolution images taken at larger intervals. In this respect, there is ample scope for both high- and low-resolution satellite data. A special case is the monitoring of sudden and often catastrophic natural disasters, such as floods. Time-specific recordings are then required and the present problem is that low-resolution data are inadequate and high-resolution imagery from orbiting satellites may not be available either because there is no pass at the required time or because of cloud cover. More frequent satellite passes and/or all-weather (radar) systems are thus badly needed. An often insufficiently understood characteristic of disaster surveying using satellite imagery as a tool is that the hazard zoning usually has to be established in advance on the basis of the terrain configuration visualized on earlier, predisaster, images which are then to be matched with the time-critical images taken during the disaster. Multiphase recording has been advocated as a method in resource surveys using Landsat satellite images. These have proved very useful for static mapping of the major terrain types, large structural elements, etc., but the spatial resolution of 80/30 m is insufficient for more detailed analysis. Thus a stepwise "zooming-in" approach was introduced starting from satellite images, e.g., at a scale of 1:1,000,000 through Landsat blow-ups and/or digital images at a scale of, e.g., 1:250,000 to photographic mosaics and aerial photographs in scales ranging from 1:100,000 to 1:10,000. Ground-truth gathering is a final step, but can also be implemented in various levels of detail such as rapid traversing of the whole area and detailed site analysis of selected, characteristic areas of limited size. Only for small-scale reconnaissance mapping is the multiphase approach not necessary because the spatial resolution of Landsat data is sufficient for this purpose. Thus the entirely new possibility for direct small-scale mapping was created, avoiding the conventional procedures of scale reduction with connexed cartographic and conceptual generalization. This applies also to topographic mapping and the method has been used in particular also for updating of maps. An important breakthrough in the field of small-scale surveying and mapping thus was generated. THE WAYAHEAD Since the beginning of this year, SPOT-1 satellite data are available with a spatial resolution of 10 m (panchromatic). This means that this kind of satellite imagery can be used directly for detailed resources surveying in scales of 1:25,000-1:50,000. The multiphase approach, just mentioned in the context of Landsat imagery, is not required and this method will, in likelihood, be obsolete in the near future. Satellite imagery that up to the present could be considered complementary to aerial photography in resource surveying now has become competitive. Most
67 types of resource survey work can technically now be implemented using satellite imagery alone. Only for geophysical surveys and for very detailed surveys e.g., for engineering sites, for assessment of the timber volume, urban studies etc., aerial photographs will remain indispensible also in the forthcoming decades. The air-photography companies thus are bound to lose many of their resource survey customers in the next decades. There is, of course, the matter of cost, but since the gigantic expenditures for developing space technology do not have to be paid by the resource surveyor alone, who - in contrast - will be charged for the full cost (including overhead, stand-by cost of crew/aircraft, etc. ) by the air-survey companies, the outcome is not difficult to guess. The space industry will be wise enough to keep their prices at a competitive level. Another interesting consequence of the advent of satellite imagery having this high spatial resolution is that secrecy with even detailed topographic and other maps, and with aerial photographs (and any restriction in their free availability) is completely outdated. It will be a blessing that resource surveyors at last have got rid of the sometimes staggering and frustrating problems of getting the imagery and further information required to efficiently perform their duties of resource inventory and environmental management for purposes of development. One may wonder - and the question has been put during this symposium whether, given the potentials of existing and future satellite remote sensing systems, we do not risk gathering more data than are actually required for specific purposes. This would mean getting swamped with unneccessary information and an undue increase of the already gigantic problems of data handling. As an example, I mention the equipment developed for simultaneous multispectral recording in 10 or 16 spectral bands. This may be of use in a number of cases, but most of our multispectral needs are satisfied by recording in three or four bands only. Thus, systems developed along these lines have a much greater feasibility for application in orbiting resource satellites for world needs. It is, of course, also a matter of cost. One could economize and optimize by collecting only the amount and type of information that we need and want. Clear specification of users' needs, therefore, ranks high among the tasks/duties of those applying aerospace technology to resource studies and environmental management. I am convinced the space industry will listen to our voices because it is generally understood that the budgets required for further technological advances will be considerably more willingly allocated by the various governments if operational and economically sound applications can be found immediately or are within reach in the near future. One may object that if all aerospace and other data on environmental resources were stored in a geographical information data handling and retrieval system, procedures could be adjusted to accomodate the needs of detailed, largescale surveying and the needs of more generalized information for mediumand small-scale mapping. Consequently, we should gather as much informa-
68 tion as possible. This concept is certainly realistic and it is our goal for the future. Until such sophisticated information systems have been implemented on a world-wide scale, however, there is scope for several types of satellite observation systems operating simultaneously and each serving specific fields of application. This will be the reality for several decades to come. This development, by the way, illustrates the great weight now put on resource surveying and mapping as compared to a few decades ago when it was common practice to make a hole in any more or less suitable and available aircraft and mount a camera in it. In many cases surveys even had to be based on aerial photographs made previously for other purposes, even if they were not optimally suitable because of scale, acquisition season, emulsion or up-to-dateness. A first type of resource satellite systems comprises high-resolution satellites with multispectral capacity in at least a few channels for recording the reflection/emission of the Earth surface and with stereoscopic capacity and/or other means for analysing the vertical dimension of the terrain configuration. The Landsat satellites were the forerunners in this field. In the present context, it is evident, however, that a non-stereoscopic system with a spatial resolution of 80 or even 30 m (Landsat/TM) is no match for a stereoscopic system with a spatial resolution of 10/20 m ( SPOT-1 ). The future will certainly bring further developments in this type of resource satellite system which will cater for thematic mapping in scales of 1:25,000 to 1:100,000. A second type of resource satellites are the (geostationary) low-resolution satellites. Their characteristics of covering very large parts of the globe with a very high temporal resolution render them suitable for very small (multimillion) scale monitoring and mapping. Meteorology and oceanography are important, but certainly not the only fields of application. The present systems of NOAA, GOES and ESA Meteosat satellites are operational and will remain so, unaffected by the recent launch of the SPOT-1 satellite. Further improvements of the systems can be expected for the future, including the development of zooming-in facilities for temporarily depicting specific parts of the Earth surface in greater detail. There may be scope for a third type of resource satellite, catering for resource mapping at scales in the order of 1:250,000 to 1:500,000. While maintaining the multispectral and stereoscopic capacities of the first type already mentioned, lower spatial resolution and the coverage of a larger surface area per frame should be aimed at, possibly in combination with a higher temporal resolution. Thorough exploration of the market for such products should precede future developments in this area. In addition to these three main types, satellites serving specific areas may prove viable, such as the Tropical Earth Resources (TERS) satellite concept studied by Indonesia and The Netherlands for applications in equatorial countries. In the overview on current trends in remote sensing and programmes under-
69 way, the Earth Observation Programme of the European Space Agency should be mentioned. During the opening session of this symposium, European cooperation in the field of remote sensing from space has been highlighted as a paramount example of successful international programmes. European countries together with Canada decided to develop the ERS-1 programme. The objectives are to transfer experimental use of microwave techniques to operational use for applications in global ocean and ice monitoring. This programme offers a challenge for both global climate research, sea state forecasting and near-future operational and commercial applications. In this respect data continuity is an essential condition. After ERS-1 {to be launched in 1990) with an expected lifetime of three years, the duration of the mission will be expended by the launch of ERS-2 in 1993. The ESA Earth Observation Preparatory Programme which started this year will define future missions dedicated to meteorology, land observation, ocean and ice observation and solid earth studies. With regard to land observation a major contribution is expected from the acquisition of synthetic aperture data on a regular basis. The ERS-1 programme will offer a first opportunity to collect SAR images in C-band overland, with the constraints related to regional coverage over Europe and North America and its experimental character. A possible future land-oriented mission can provide us in the 90-ties with a capability for frequent observation by means of an advanced SAR system suited to develop operational use of polarorbiting platforms for monitoring of agriculture and land use. TRENDS OF FUTUREDEVELOPMENTSIN SATELLITEREMOTE SENSING The spectral recording systems in the visible and near-infrared spectrum at present include: ÷ Multispectral sensing ( MSS ) ; probably the most widely used system when satellites are concerned, such as Landsat MSS and SPOT-3 band scanner. ÷ Multispectral photography (MSP) with multilens cameras or multispectral imaging with TV cameras; known from aerial survey and satellites such as Soyuz (MKF-6) and Landsat 1 and 2 (RBV-3). ÷ Panchromatic black and white imaging. Under this category come the RBV of Landsat 3, the linear array, "pushbroom" SPOT configuration, and the long focal length photography of manned spacecraft, Stereosat and Mapsat. Air photography (panchromatic/colour) also comes under this heading. Multispectral sensing from satellites has a great promise for the future in studies of the Earth's cover. Panchromatic imaging from aircraft, orbiters and satellites will be the main field of interest of photogrammetrists. Earth scientists share with the latter the need for stereoscopy, but their metrical requirements are of a lower level. In the microwave zone, the recording systems comprise side-looking air-
70 borne radar (SLAR) and synthetic aperture radar (SAR) systems used in orbiters. Because of the need for all-weather capacity, especially for purposes of monitoring and time-critical data-gathering, e.g., in the context of flood disasters, microwave recording will become increasingly important. Once the technical problems have been solved, a great future exists for satelliteborne microwave observation. After the Seasat (1978) and the space-shuttle SIR-A and B (1981 and 1984) new developments are eagerly expected, such as the ERS 2 satellite of ESA (1989), the Japanese MOS 1-3 satellites (19..) and the Canadian Radarsat (1992). Whether the - at present rather erratic - airborne microwave (SLAR) recording can compete with such operational satellite microwave systems is doubtful. Thermographic recording in the middle and far infrared, using aircraft as a platform, though very useful for specific purposes, has always been a rather rare bird in remote sensing. From satellites, to the contrary, it has found wide applications in Landsat 3, the short-lived Seasat and particularly in the NOAA satellites (heat capacity mapping mission - HCMM). Since the technology for recording all usable parts of the electromagnetic spectrum has already been developed, further perfections rather than spectacular new breakthroughs can be expected for the future, although, of course, the satellite systems will further evolve. The relief recording methods range from the conventional but very important stereoscopic imagery radar altimetry and scatterometry to laser-altimetry. The precision of the latter is such that deformations of the sea surface caused by gravitational anomalies can be recorded and information about the submarine relief consequently can be obtained. The methods have been developed, but since this is a fairly recent occurrence further developments are likely. Stereoscopic imagery from space is in its infancy and will soon be widely applied, particularly for purposes of earth sciences and photogrammetry. Methodological developments in interpretation, however, will be minor. The diverse requirements of the various users of satellite imagery make it likely that several types of sensors will be installed in future spacecraft in addition to dedicated satellites launched for specific purposes. These developments are, in fact, already underway and are rooted in the emphasis put on: ÷ Spectral characteristics - for the study of vegetation, sea and ice. ÷ Relief characteristics - for earth science applications. + Relief and high metric qualities - for photogrammetric purposes. ÷ Temporal resolution - for monitoring. ÷ All-weather capability - for monitoring, disaster surveying, etc. Beyond doubt, a wide array of satellites having different configurations will be launched in the years to come. Quo VADIS? The cost involved in implementing satellite technology in the next few decades will be very high. In a recent report of the U.S. Commission on Space,
71 entitled "Pioneering the Space Frontier", an annual expenditure of US$ 20 billion is expected around the year 2000. The annual expenditure by the FRG is estimated at DM 1.6 billion (approximately US$ 0.75 billion). Adding to this the considerable space efforts of the ESA and of countries like France, Japan, Canada, Brazil, etc., astronomical figures are reached. These figures assume continuous economic growth in the coming decades. Since this is quite uncertain, possibly less funds will in fact become available. Various countries would like to take the lead in space research, :resulting in a centralized administration. This seems hardly feasible to me. Many countries want to develop their own satellites and administrative structures, fully participating in the high technology of the future and enhancing their national prestige. Personally, I feel that such competition is very desirable because only this way will challenges be mutually presented that will yield optimum results. Good international cooperation will, of course, be required to avoid major inefficiencies and undue duplications. The best solution may prove to be joint efforts of groups of countries. This could be a very important aspect of space technology. Bringing the nations together because there is a job at hand that cannot be done by any country individually. This job, I think, is to study, map and monitor the globe with the aim of safeguarding our threatened environment, "mother earth", for the generations to come and to give them the quality of life required for economic, social and spiritual development. We should not pursue technology for its own sake but put it to use for the study of the "ordinary business of life", a term I quote from a recent issue of the UN University periodical WORK IN PROGRESS. Only this way will the costly efforts of space research in the long run be justified.
REFERENCE Damen, M.C.J., Sicco Smit, G. and Verstappen, H.Th., 1986. Remote Sensing for Resources Developmentand EnvironmentalManagement(3 volumes).Balkema,Rotterdam.