Satellite Oceanic remote sensing

Coring Operations: Procedures for Sampling and Analysis of Bottomhole and Sidewall Cores EXLOG. Ed. Alun Whittaker D. Reidel, 1985; ISBN 90-277-1980-2; Dfl. 115,00/£31.95 This book is aimed at the practising logging geologist for whom it is intended as reference handbook. In this respect it succeeds admirably, providing in four well-illustrated chapters the background information to the requirement for cores, the practical considerations involved in their collection, the procedures to be used when logging and sampling and finally the equipment and methods to be employed if wellsite evaluation is to be carried out. The introductory chapter explains the necessity for core sampling and the reasoning behind wellsite analysis. The importance of careful handling and curation is emphasized and there is a concise and well illustrated summary of the physical properties of a rock reservior. Measurement of the main physical properties, porosity, permeability and saturation are illustrated in relation to collected cores and the limitations of these measurements are also clearly stated. Chapter two notes the costs associated with bottomhole and sidewall coring, then continues with a comprehensive summary of the various bottomhole corebarrels and core bit types available. Particular emphasis is placed on explaining the different parameters required for bottomhole coring as opposed to straightforward drilling. The collection technique for sidewall cores is only briefly mentioned here. The next chapter deals with the recovery of the cores and how to sample them for analysis. A simple site check on core curation supplies and the precautions necessary to retain those supplies is followed by the criteria generally used for picking a core point. Logging parameters to be observed while coring is progressing are explained and discussed, together with the pitfalls present in the measurement of rate penetration, core depths, the evaluation of gas and oil content, lithology of cuttings, salinity and nitrate ion content assuming stable mud conditions. Rigfloor preparation for

receiving the recovered core is explained, together with the precautions necessary for safety, and ease of working. The necessity to ensure proper and meticulous curation as the core leaves the corebarrel is clearly set out, together with a schedule for the core logging work. A comprehensive sampling procedure and encoding of data for shipping notes completes the bottomhole coring section. Sidewall core techniques are then reviewed, their collection points explained, handling precautions noted and their limitations for sampling for analysis noted. The final chapter deals with the core analysis methods and the equipment required to undertake the quantative measurements of porosity, permeability and saturation. The principles behind the methods are followed by the sample preparation, analytical procedure and calibration of the equipment used to process the bottomhole cores. The calculation of results, optional further tests and presentation of data are followed by the methods used during sidewall core analysis and the care, maintenance and shipping details for all the on-site testing equipment. While the book does not take the place of the logging geologist's brief from his employer, it is invaluable for a comprehensive summary of background information, stores, equipment and methods checks. In particular it puts the important work of collection and evaluation into its precise setting within the overall drilling programme and gives the logging geologist a useful insight into the roles of the specialist coring crew. It may also assist in monitoring laboratory testing staff under some circumstances.

A. C. Skinner

British Geological Survey

Satellite Oceanic Remote Sensing Advances in Geophysics, Vol. 27 Ed. Barry Saltzman, Academic Press, 1985 This is the latest in what has become a fairly steady flow of books on remote sensing of the oceans. In several respects it is very good - - one of the best - - despite a certain uneveness in content. It is curious for instance, that there is no real treatment of sea surface topography; its precise measurement from satellites, and the implications of that for large-scale ocean circulation studies, remains one of the greatest hopes of the future. Less curious perhaps is the fact that all 37 authors live and work in one country - - since that country was responsible for the launch of the satellites described here. 1978 was a good year for marine remote sensing - - a year that saw the launch of Nimbus 7, TIROS-N and Seasat. An analysis of their sensor data soon confirmed that satellite technology could now match many of the scientists' aspirations expressed at the first 'Oceanography from Space' Symposium held in 1964. Of the triumvirate of satellites Nimbus-7 still survives as do the operational follow-up spacecraft (the N O A A series) to TIROS-N. Seasat, on the other hand, functioned for little more than 10(1 days before being snuffed out and it is a measure of its impact on marine science that the major part of this book is given over to a description of its performance (despite several earlier books and journal publications on the subject).

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Jack Sherman has been a familiar figure on the ocean remote sensing scene for a number of years and few can be more familiar with the details of the programmes presented here. In the opening chapter he provides a useful review of the 6 ocean sensors carried on the 3 satellites, though some of his diagrams are similar to (and in one case identical to) those used in later chapters. The summary tables are concise and informative, and provide good reference material. There then follow 4 chapters covering the measurement of wind and waves which are amongst the most comprehensive reviews made to date on the subject. The treatment of the analysis and interpretation of the altimeter sea echo by Barrick and Lipa, in particular, is essential reading for anyone wishing to understand the relationship between altimetry and the measurement of surface wave height, and includes descriptions of the contributions made by rain, pointing errors and electromagnetic bias on the measurement of the surface slopes. Equally informative is the review of the measurement of surface winds (in chapter 4) made by Seasat's scatterometer system (SASS). Estimates of wind speed to +2 m/s and wind direction to +20' are now accepted as entirely feasible though there is a suggestion that accuracy is reduced in extreme conditions. The juxtaposition of three separate subjects in one chapter

Book Reviews (5) - - the measurement of surface wave heights by the radar altimeter, the treatment of a synthetic aperture radar's ability to image ocean surface waves, and a separate description of internal waves as revealed by the Seasat SAR record - appears contrived even if the idea of moving away from the more conventional sensor-oriented approach is not without merit. What is evident in this chapter (and throughout the book) is the lack of cross-reference. (Here, for instance, there is no reference to the treatment of the altimeter sea echo two chapters before). The imaging of internal wave trains by SAR is now more or less well understood. The greatest surprise in the SAR record is that it revealed internal waves to be so ubiquitous. The imaging of surface waves is quite a different problem. At a data rate of about 100 mbits/s one has no hesitation in accepting the author's contention that a SAR image contains the greatest amount of information on waves but what is still unresolved is the exact nature of the interaction of SAR with a dynamic sea surface and the extent to which images of azimuth-travelling waves (those moving along the flight direction) have been smeared. The nub of the problem, highlighted by the authors, is that the modulation transfer function becomes non-linear which limits the extraction of the correct directional wavenumber spectra from SAR. There follows (Chapter 6) a multi-author treatment of the performance of the Seasat suite of microwave sensors in monitoring tropical cyclones. Considering the short operating life of the spacecraft it comes as a surprise to learn that measurements were made over 21 separate hurricanes and 20 tropical storms. The authors concentrate largely on assessing the satellite's performance over hurricanes Fico, Ella and Greta plus the QEII storm. In general the scatterometer underestimated high winds compared to in situ observations possibly because of the relatively coarse spatial resolution. The SMMR errors were greater. The treatment of the SMMR's measurement of sea surface temperatures is relatively short and this is followed in the same chapter (7) by a description of the Advanced Very High Resolution Radiometer. The microwave's all weather operation compared to the IR's inability to penetrate cloud is compensated to an extent by the higher spatial and spectral resolution ( - 1 km and '0.5 k) of the AVHRR. Future mission planners might like to note the problem brought out again here of comparing in situ spot measurements with

spatially averaged satellite measurements of 'skin temperature'. The scatter in the in situ observations is usually greater than differences between satellite and surface buoy. The chapter on ocean colour is credited to a small host of US experts in the field. Their main conclusion that the CZCS can provide estimates of pigment concentration to + 30% in the range 0 to 5 mg/m 3 for case 1 waters, is encouraging and, at global ocean scales, represents an improvement over any other method of estimation. Satellite monitoring is particularly valuable over the earth's more hostile environments and there is an understandable enthusiasm from the bevy of glaciologists who, in chapter 9, convincingly demonstrate the great potential of microwave sensors over polar regions. This is an exhaustive review and describes in some detail the performance of SAR, SASS, SMMR and the altimeter (all from Seasat) and the SMMR carried on Nimbus-7. The final two comparatively short chapters are given over to a description of precipitation in tropical cyclones as measured by the VIRR, and to the application of remote sensoring in fisheries research. Proof that stellite reconaissance could form an important input into the management of fish stocks would fulfil a cherished hope of space planners seeking to demonstrate commercial benefits from expensive space missions, and this final chapter goes some way to nourishing that hope. The book carries a number of short appendices. Conscious of the fact that many newcomers entering the field of marine remote sensing have little idea of where to turn for their data and images, the editor has inserted a short appendix on data availability which is a compendium of useful addresses. There is much of value in this book though, as previously noted, each chapter appears to have been conceived and written as a separate entity. Clearly the editor has tried to call in as many US experts as possible (5 out of 11 chapters are credited to 27 different authors). This approach is more successful in some chapters than in others where the joins are rather obvious. But there are enough good things in the book to compensate, and some chapters are almost compulsory reading for anyone entering the field.

T. D. Allan

Institute of Oceanographic Sciences Wormley, Surrey

Velocities in reflection seismology Jean-Pierre Cordier

D. Reidel Publishing Company; ISBN 90-277-2024-X; £30.50 A clear understanding of the basic physics of the propagation of seismic waves and in particular of the causes of variations in seismic velocities is essential to the geophysicist involved in processing seismic data. Increasingly, the interpreter of seismic data is being required to participate in specification of seismic processing routes, to construct and validate geological models which depend on conversion of time sections to depth sections, and in some circumstances invert the process. Thus the topic of velocities in reflection seismology is of wider interest today than a few years ago with more routine use now of modelling techniques and of interactive manipulation of seismic data by interpreters using seismic workstations, also in the use of VSP surveys conducted using three component detectors and in the utilization of seismic attributes and offset amplitude variation in the attempt to map lithological variations directly from seismic data. It is thus most timely that a book on velocities in reflection seismology should be published. The author, a specialist in seismic data processing, approaches the subject in a logical manner, developing the theoretical and mathematical concepts by stages through the book yet at the same time allowing the reader to consult a

chapter on a specific topic without finding undue reference to previously developed arguments and derivations. Each chapter serves well as a stand-alone exposition of the topic it addresses. The book commences with a chapter on basic ideas on the propagation of seismic waves, then a chapter on general considerations on the recording of seismic waves in prospecting for petroleum: both very concise giving in note form only the essential details required as introduction to the more specific topics to be covered later in the book. Chapter 3 treats the theory of seismic wave velocities in relationship to the theory of elasticity and discusses factors which influence velocity variations. This is followed by a chapter on the calculation of travel times of seismic signals and the definition of AT. The first four chapters thus cover the basic theory: the rest of the book is mainly concerned with practical applications, although at each stage mathematical theory is fully treated in explanation of the techniques being described. Chapters 5 and 6 describe the principal sources of velocity information: (5) measurement of velocities in boreholes; sonic logs,

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