- Email: [email protected]
U.S. operational space program for climate observations
Adv. Space ties. Vol. 5, No. 6 , p p . 3 1 - 3 8 , 1985 Printed in Great Britain. All rights reserved.
0 2 7 3 - 1 1 7 7 / 8 5 $0.00 + .50 Copyright © COSPAR
U.S. OPERATIONAL SPACE P R O G R A M FOR CLIMATE OBSERVATIONS H. W. Yates
National Environmental Satellite, Data, and Information Service (NESDIS), NOAA, Washington, DC 20233, U.S.A.
ABSTRACT Satellites provide two important characteristics to earth climate studies not available from other, conventional sources: (I) full global coverage, and (2) consistency within the data set. This latter arises from the fact that the satellite data are usually derived from one instrument (or at least from a small number) whereas other sources involve large numbers of separate instruments and hence exhibit a substantial standard deviation. Satellite data, of course, are more subject to bias and must therefore be carefully validated, usually via ground truth. The ISCCP and ISLSCP are examples of the increasing reliance on satellite data for climate studies. In addition to the multispectral images, quantitative products of importance are: (I) atmospheric temperature structure, (2) snow cover, (3) precipitation, (4) vegetation index, (5) maximum/minimum temperature, (6) insolation, and (7) earth radiation balance. The U.S. civil space program is presently committed to its current geostationary (GOES) and polar (NOAA) programs through this decade and to continue both programs into the next decade with spacecraft carrying improved and augmented instrumentation. GOES VISSR Atmospheric Sounder (VAS) data, presently in research status and available only for special observation periods, will become available operationally in 1987 from the current spacecraft series. GOES-Next will provide additional spectral channels, simultaneous imaging, atmospheric soundings, and possibly increased resolution starting in 1990. The NOAA follow-on spacecraft, in the same time frame, is expected to provide additional spectral channels, improved passive microwave radiometry, and possibly increased spatial resolution. The Landsat program is expected to be continued by a commercial operator following the useful life of Landsat-5. All three follow-on programs are presently at various stages of definition and procurement. Final definition may not be completed until late in 1984. However, their status as of the time of this presentation will be reviewed in detail. INTRODUCTION The study of climate and climate mechanisms requires access to a wide range of data on a global scale with continuous coverage for extended periods of time. The only systems capable of providing truly global coverage are the environmental satellites and although they have some weaknesses, they will probably continue to be the primary source of some classes of data for the foreseeable future. Sea surface temperature, for example, an extremely important datum for climate studies, is provided from satellite data with uniform coverage and high internal consistency (the observations are all derived from one instrument, or at least from a small number of essentially identical instruments). Ship-ofopportunity and buoy data are not well distributed globally and are derived from a large number of different types of instruments, many of which are poorly maintained. The classes of data important to climate research provided currently from environmental satellites are: o o o o o o o o
Sea surface temperature Snow cover Cloud type, distribution and dynamics Atmospheric water vapor distribution and movement Atmospheric temperature structure and winds Insolation Ozone distribution and dynamics Earth radiation balance (extrapolated from narrow-band measurements). 31
32
H.W. Yates
Classes are:
of data which are anticipated
o Improved atmospheric
with the availability
temperature
of new generations
of satellites
and water vapor observations
o Global precipitation o Earth radiation balance o Improved ozone observations The International Satellite Cloud Climatology Project (ISCCP) and the International Satellite Land Surface Climatology Project (ISLSCP) are recently created programs capitalizing on the data available from satellites. The latter represents a recognition of the importance of the interaction between the atmosphere and the earth's surface in understanding climate. In the ISLSCP several products, not previously connected to climate studies in any consistent manner, have been identified and are being exploited. Among these are: o Global vegetation o Maximum/minimum
index (a measure of the extent and vigor of vegetation)
temperatures
over land
POLAR ORBITING SPACECRAFT The current NOAA series of polar-orbiting spacecraft will continue through 1990 with five more spacecraft, NOAA-F, G, H, I and J maintaining a two satellite operational system. There is a proposal to reduce this to a one satellite system as an economy measure and if this decision is made the remaining spacecraft should last through 1992. The follow-on to these satellites, NOAA K, L, and M, will be basically the same except for the substitution of a more advanced sounding system for the present TOVS and the addition of one more channel to the AVHRR imaging instrument. Following NOAA M it is expected that NESDIS will procure a new spacecraft system. In order to maintain a high probability of continuity of service this procurement will be initiated in 1985. Any additions or changes to the present complement of instruments must be considered and approved before the procurement cycle begins. The imaging instrument, the AVHRR on NOAA K, L, and M, will be a 6-channel radiometer having the same resolution as the present instrument, l.l km at the sub-satellite point. Table I summarizes the characteristics of the new radiometer. The new channel at 1.6 micrometers will aid in discriminating between snow and clouds. Since this channel is useless at night and the 3.7 micrometer channel is heavily contaminated with fluorescence and scattered sunlight by day, they share a single data channel with the 1.6 switched on in daylight and the 3.7 switched on at night.
TABLE I
CHANNEL
High Resolution
SPECTRAL DEFINITION (MICROMETERS)
Radiometer
- NOAA K, L, M
SENSITIVITY
1
0.58 -
0.68
S/N 3:1 AT 0.5% ALBEDO
2
0.82
-
0.87
S/N 3:1 AT 0.5% ALBEDO
3a*
1.57
-
1.78
3b*
3.55 -
3.93
0.12K AT 300K SCENE
4
10.30 - 11.30
0.12K AT 300K SCENE
5
11.50 - 12.50
0.12K AT 300K SCENE
*Data system will select either 3a or 3b with 3a normally used in daytime and 3b at night.
U.S. Operational Space Program
33
The current TIROS Operational Vertical Sounder (TOVS) Consists of three instruments: the 20-channel HIRS, an infrared radiometer; the 4-channel MSU, a microwave radiometer; and the 3-channel SSU, an infrared stratospheric sounder provided by the British Meteorological Office. NOAA K, L, and M will carry two instruments: an improved version of the 20-channel, infrared HIRS and an Advanced Microwave Sounding Unit (AMSU) which in turn consists of two units, A and B. The AMSU-A is a 15-channel radiometer designed for temperature sounding. The AMSU-B is a 5-channel, high-frequency unit designed for vastly improved water vapor soundings. The British Meteorological Office, continuing the successful and mutually beneficial cooperative program of providing the SSU for the current spacecraft, has agreed to supply the AMSU-B. The definition of the channels and their specifications for the HIRS, AMSU-A and AMSU-B are given in Tables 2, 3, and 4 respectively.
TABLE 2
CHANNEL
High-Resolutlon Infra-Red Sounder - NOAA K, L, M
N~A~
SPECTRAL DEFINITION (MICROMETERS)
MAXIMUM BRIGHTNESS TEMPERATURE
(mW/M2,sr,cm- I )
FUNCTION
(x) I
14.95
0.75
280
2
14.71
0.25
265
3
14.49
0.25
240
ATMOSPHERIC
4
14.22
0.20
250
TEMPERATURE
5
13.97
0.20
265
SOUNDING
6
13.64
0.20
280
7
13.35
0.20
290
8
11.11
0.I0
330
SURFACE TEMPERATURE
9
9.71
0.15
270
03 CORRECTION
I0
8.16
0.15
290
11
7.33
0.20
275
12
6.72
0.I0
260
13
4.57
0.002
300
14
4.52
0.002
290
ATMOSPHERIC
15
4.46
0.002
280
TEMPERATURE
16
4.40
0.002
260
SOUNDING
17
4.24
O. 002
280
18
4.00
O. 002
340
LOW CLOUDS
19
3.76
0.001
340
SURFACE TEMPERATURE
20
0.69
WATER VAPOR SOUNDING
.
.
.
.
.
.
.
.
.
.
.
CLOUDS
GROUND RESOLUTION 20 km AT SUB-SATELLITE POINT ALL CHANNELS
34
H.W. Yates
TABLE 3
CHANNEL
Advanced Microwave Sounding Hnit-A - NOAA K, L, M
SPECTRAL DEFINITION
SENSITIVITY
(GHz)
(X)
23.80
0.3
31.40
0.3
FUNCTION
TROPOSPHERIC H20 VAPOR PRECIPITATION,
SEA-ICE
SNOW 3
50.30
0.35
4
52.80
O. 25
5
53.33
O. 25
6
54.40
0.25
7
54.94
0.25
8
55.50
0.25
9
57.29
0.25
i0
57.290344
0.4
II
57.290561 ± 48 MHz
0.4
12
57.290561 ± 22 MHz
0.6
13
57.290561 ± i0 MHz
0.8
14
57.290561 ± 4.5 MHz
1.20
15
89.0
0.5
ATMOSPHERIC TEMPERATURE SOUNDING
TROPOSPHERIC H20 VAPOR PRECIPITATION, SEA-ICE SNOW
RESOLUTION AT SUB-SATELLITE POINT = 50 km ALL CHANNELS
U.S. Operational Space Program
TABLE 4
35
Advanced Microwave Sounding Unit-B - NOAA K, L, M
SPECTRAL
CHANNEL
DEFINITION (GHz)
SENSITIVITY
16
89.0
O.6
17
166.0
0.6
FUNCTION
TROPOSPHERIC
18
183.31 + 1.0
0.8 H20 VAPOR
19
183.31
+ 3.0
0.8
20
183.31
+ 7.0
0.8
GROUND RESOLUTION AT SUB-SATELLITE POINT " 15 km ALL CHANNELS
The AMSU replaces the MSU and SSU in TOVS and also represents an important change in procedures. In TOVS, HIRS is the primary instrument and the MSU and SSU secondary instruments. In NOAA K, L, M the AMSU is the primary instrument and the HIRS the secondary instrument. Some consideration had been given to eliminating the HIRS and relying entirely on microwave radiometry but it has been shown that in clear areas the infrared instruments still provide superior soundings and it will be retained. The AMSU is especially important to the climate research program. It will provide atmospheric temperature profiles superior to those now flowing from TOVS in accuracy, vertical resolution and coverage, especially in cloudy areas and below extensive, solid cloud cover. With added channels peaking in the lower troposphere, soundings below clouds will be significantly improved and with higher spatial resolution it will be better able to recognize precipitation below clouds and reject temperature soundings there. Useful soundings in the presence of precipitation below clouds cannot be made and the coarser resolution MSU may not recognize small cells of precipitation and turn out a bad sounding as a result. AMSU will also provide temperature measurements in the stratosphere up to 45 km, an important data source for climate research. Current numerical models do not use data in this region of the atmosphere so that it is not presently available from operational systems. More importantly, perhaps, is the improvement expected in water vapor profiles. The TOVS water vapor output is only marginally useful. The AMSU product should provide accurate and truly useful water vapor data. Presently there is no useful source of data on precipitation over the global oceans, particularly the tropical oceans where cells tend to be small. The AMSU, with its enhanced capability to recognize--and to a certain extent quantify--precipitation below clouds will provide a truly useful global data source for this important mechanism of energy exchange in the atmosphere-ocean system. GEOSTATIONARY SPACECRAFT The current GOES series will continue with two additional spacecraft, GOES-G and H scheduled for delivery and available for launch in 1986. There is some concern that the currently operational spacecraft, GOES-5 and 6, may not last that long. GOES-5 will be nearly two years past its design life-expectancy by then and there is a distinct possibility that we will have only one operational satellite for some period of time. GOES-G and H are expected to carry through until 1989 at which time GOES-Next, currently in the procurement cycle, will be available. GOES-Next will have significantly greater capability than the present GOES spacecraft. The most important feature will be the ability to provide the by-now-familiar images and do atmospheric temperature and water vapor soundings simultaneously. These soundings will not have either the quality or the coverage of those produced from the polar-orbiting NOAA
36
H.W. Yates
spacecraft, but they will have t h e advantage of providing greatly improved temporal resolution needed to study rapidly developing atmospheric conditions. The NOAA satellites provide four soundings per day (two from each spacecraft) for any given point on the earth---currently at 0130, 0730, 1330, and 1930 local time--whereas the GOES-Next will be capable of a sounding every 40 minutes or, in special circumstances, even more frequently. GOES-Next will be capable of sounding the portion of the earth it views from 0 ° to 50 ° latitude in 4 hours or any 3000 km x 3000 km area in 40 minutes. It will, however, provide soundings only in clear areas or between clouds since it has only infrared channels. It is possible to produce soundings down to the tops of clouds and that capability may be implemented. It is not currently done operationally. The NOAA spacecraft, which have microwave channels as well as infrared, will be the primary source of sounding data providing global coverage in cloudy as well as clear areas. The definition and characteristics of the infrared sounding channels planned for GOES-Next are given in Table 5. They are very similar to many of the channels of the current HIRS instrument on the polar-orbiting NOAA spacecraft. GOES-Next will have five imaging channels representing a major improvement over the current spacecraft. In addition to the present visible and thermal infrared channels, a near-infrared, a water vapor, and a "split-window" thermal infrared channel will be added. Further, the resolution of the infrared channels (except for the water vapor channel) will be increased from the current 8 km to 4 km. The definition and specifications of these five imaging channels are given in Table 6. Channels 4 and 5, the so-called "split-window" channels, function together to provide a measure of the radiometric influence of water vapor in the atmosphere. In measuring surface temperatures from space with infrared radiometers, correcting for the influence of atmospheric water vapor is the major factor determining the accuracy. Channels 4 and 5 are spectrally very close differing only in their sensitivity to water vapor. Channel 3, the water vapor channel, will provide data on the distribution of water vapor in the upper troposphere. The value and utility of this important data have been dramatically demonstrated by similar channels on both Meteosat and the current GOES spacecraft. GOES-Next will be capable of imaging the earth below it from 60°N to 60°S in 25 minutes and will produce images consecutively. It will not have the retrace and inter-frame delays of the current spin-stabilized spacecraft. Smaller areas can be covered in proportionately reduced times. Further, it is the objective to have the earth location accuracy of any image element be 2 km or less with a probability of 0.68 km. The g e o s t a t i o n a r y s p a c e c r a f t a r e p r i m a r i l y u s e f u l i n p r o v i d i n g c o n t i n u o u s c o v e r a g e i n t i m e . T h e i r g r e a t d i s t a n c e , 3 7 , 0 0 0 km, from t h e e a r t h makes i t d i f f i c u l t f o r them t o compete w i t h the polar orbiter in precision or resolu tion so tha t they are not the prim a ry s ourc e of data important to the climate programs. However t h e r e a r e some p r o d u c t s whose a c c u r a c y and utility are dependent on the continuous coverage they provide and they will remain an important data source. Typical of this type of data are cloud cover and precipitation. The four observations per day provided by the polar orbiter may provide a distorted sample of the diurnal characteristics. Thus the five geostationary satellites equally distributed around the equatorial belt are the primary source of data for the International Satellite Cloud Climatology Project with the polar orbiters covering the polar regions, filling any gaps that may occur and providing an intercomparison which can serve as a calibration check.
U.S. Operational
TABLE 5
Proposed Specifications
SPECTRAL DEFINITION (MICROMETERS)
CHANNEL
Space Program
37
- GOES-Next Atmospheric Sounder
NEAN (mW/m 2, s r ,
cm- 1 )
MAXIMUM BRIGHTNESS TEMPERATURE
FUNCTION
(K) 14.73
0.87
255
14.47
0.67
255
14.29
0.72
265
ATMOSPHERIC TEMPERATURE
14.08
0.70
278
13.60
0.56
288
13.37
0.44
300
12.00
0.16
330
II.00
0.16
335
7.33
0.18
290
SOUNDING
SURFACE TEMPERATURE AND CLOUD DETECTION
H20 VAPOR 6.82
0.074
270
11
4.52
0.0086
300
TEMPERATURE SOUNDING
12
3.97
0.0033
340
13
3.74
0.0036
340
SURFACE TEMPERATURE AND LOW CLOUD DETECTION
14
0.70
I0
SOUNDING
%
ATMosPHERIC
10 -3 ALBEDO
CLOUD DETECTION
CHANNEL
Specifications
0.35 AT 300K
4.0
11.50
12.50
0.35 AT
4.0
10.20 - 11.20
-
1.0 A T
8.0
6.50 - 7.00
300K
230K
1.4 A T 3 0 0 K
4.0
0.55
3.80 - 4 . 0 0
NEAT (K)
- GOES-Next
NOT APPLICABLE S / N = 150 AT 100% A L B E D O
(K~)
SPATIAL R E S O L U T I O N FROM GEOSTATIONARY ALTITUDE
Proposed
1.0
6
- 0.75
SPECTRAL DEFINITION (MICROMETERS)
TABLE
Instrument
L O W CLOUDS N I G H T TIME
WATER VAPOR (UPPER T R O P O S P H E R E )
SURFACE TEMPERATURE
C O R R E C T I O N OF SURFACE TEMPERATURE FOR H20 VAPOR
4 - 320K
4 - 320K
4 - 320K
4 - 420K
CLOUDS
CLOUD COVER SURFACE FEATURES
APPLICATION
1.6 - 100Z ALBEDO
USEFUL D Y N A M I C RANGE
Imaging
m=
0 2 7 3 - 1 1 7 7 / 8 5 $0.00 + .50 Copyright © COSPAR
U.S. OPERATIONAL SPACE P R O G R A M FOR CLIMATE OBSERVATIONS H. W. Yates
National Environmental Satellite, Data, and Information Service (NESDIS), NOAA, Washington, DC 20233, U.S.A.
ABSTRACT Satellites provide two important characteristics to earth climate studies not available from other, conventional sources: (I) full global coverage, and (2) consistency within the data set. This latter arises from the fact that the satellite data are usually derived from one instrument (or at least from a small number) whereas other sources involve large numbers of separate instruments and hence exhibit a substantial standard deviation. Satellite data, of course, are more subject to bias and must therefore be carefully validated, usually via ground truth. The ISCCP and ISLSCP are examples of the increasing reliance on satellite data for climate studies. In addition to the multispectral images, quantitative products of importance are: (I) atmospheric temperature structure, (2) snow cover, (3) precipitation, (4) vegetation index, (5) maximum/minimum temperature, (6) insolation, and (7) earth radiation balance. The U.S. civil space program is presently committed to its current geostationary (GOES) and polar (NOAA) programs through this decade and to continue both programs into the next decade with spacecraft carrying improved and augmented instrumentation. GOES VISSR Atmospheric Sounder (VAS) data, presently in research status and available only for special observation periods, will become available operationally in 1987 from the current spacecraft series. GOES-Next will provide additional spectral channels, simultaneous imaging, atmospheric soundings, and possibly increased resolution starting in 1990. The NOAA follow-on spacecraft, in the same time frame, is expected to provide additional spectral channels, improved passive microwave radiometry, and possibly increased spatial resolution. The Landsat program is expected to be continued by a commercial operator following the useful life of Landsat-5. All three follow-on programs are presently at various stages of definition and procurement. Final definition may not be completed until late in 1984. However, their status as of the time of this presentation will be reviewed in detail. INTRODUCTION The study of climate and climate mechanisms requires access to a wide range of data on a global scale with continuous coverage for extended periods of time. The only systems capable of providing truly global coverage are the environmental satellites and although they have some weaknesses, they will probably continue to be the primary source of some classes of data for the foreseeable future. Sea surface temperature, for example, an extremely important datum for climate studies, is provided from satellite data with uniform coverage and high internal consistency (the observations are all derived from one instrument, or at least from a small number of essentially identical instruments). Ship-ofopportunity and buoy data are not well distributed globally and are derived from a large number of different types of instruments, many of which are poorly maintained. The classes of data important to climate research provided currently from environmental satellites are: o o o o o o o o
Sea surface temperature Snow cover Cloud type, distribution and dynamics Atmospheric water vapor distribution and movement Atmospheric temperature structure and winds Insolation Ozone distribution and dynamics Earth radiation balance (extrapolated from narrow-band measurements). 31
32
H.W. Yates
Classes are:
of data which are anticipated
o Improved atmospheric
with the availability
temperature
of new generations
of satellites
and water vapor observations
o Global precipitation o Earth radiation balance o Improved ozone observations The International Satellite Cloud Climatology Project (ISCCP) and the International Satellite Land Surface Climatology Project (ISLSCP) are recently created programs capitalizing on the data available from satellites. The latter represents a recognition of the importance of the interaction between the atmosphere and the earth's surface in understanding climate. In the ISLSCP several products, not previously connected to climate studies in any consistent manner, have been identified and are being exploited. Among these are: o Global vegetation o Maximum/minimum
index (a measure of the extent and vigor of vegetation)
temperatures
over land
POLAR ORBITING SPACECRAFT The current NOAA series of polar-orbiting spacecraft will continue through 1990 with five more spacecraft, NOAA-F, G, H, I and J maintaining a two satellite operational system. There is a proposal to reduce this to a one satellite system as an economy measure and if this decision is made the remaining spacecraft should last through 1992. The follow-on to these satellites, NOAA K, L, and M, will be basically the same except for the substitution of a more advanced sounding system for the present TOVS and the addition of one more channel to the AVHRR imaging instrument. Following NOAA M it is expected that NESDIS will procure a new spacecraft system. In order to maintain a high probability of continuity of service this procurement will be initiated in 1985. Any additions or changes to the present complement of instruments must be considered and approved before the procurement cycle begins. The imaging instrument, the AVHRR on NOAA K, L, and M, will be a 6-channel radiometer having the same resolution as the present instrument, l.l km at the sub-satellite point. Table I summarizes the characteristics of the new radiometer. The new channel at 1.6 micrometers will aid in discriminating between snow and clouds. Since this channel is useless at night and the 3.7 micrometer channel is heavily contaminated with fluorescence and scattered sunlight by day, they share a single data channel with the 1.6 switched on in daylight and the 3.7 switched on at night.
TABLE I
CHANNEL
High Resolution
SPECTRAL DEFINITION (MICROMETERS)
Radiometer
- NOAA K, L, M
SENSITIVITY
1
0.58 -
0.68
S/N 3:1 AT 0.5% ALBEDO
2
0.82
-
0.87
S/N 3:1 AT 0.5% ALBEDO
3a*
1.57
-
1.78
3b*
3.55 -
3.93
0.12K AT 300K SCENE
4
10.30 - 11.30
0.12K AT 300K SCENE
5
11.50 - 12.50
0.12K AT 300K SCENE
*Data system will select either 3a or 3b with 3a normally used in daytime and 3b at night.
U.S. Operational Space Program
33
The current TIROS Operational Vertical Sounder (TOVS) Consists of three instruments: the 20-channel HIRS, an infrared radiometer; the 4-channel MSU, a microwave radiometer; and the 3-channel SSU, an infrared stratospheric sounder provided by the British Meteorological Office. NOAA K, L, and M will carry two instruments: an improved version of the 20-channel, infrared HIRS and an Advanced Microwave Sounding Unit (AMSU) which in turn consists of two units, A and B. The AMSU-A is a 15-channel radiometer designed for temperature sounding. The AMSU-B is a 5-channel, high-frequency unit designed for vastly improved water vapor soundings. The British Meteorological Office, continuing the successful and mutually beneficial cooperative program of providing the SSU for the current spacecraft, has agreed to supply the AMSU-B. The definition of the channels and their specifications for the HIRS, AMSU-A and AMSU-B are given in Tables 2, 3, and 4 respectively.
TABLE 2
CHANNEL
High-Resolutlon Infra-Red Sounder - NOAA K, L, M
N~A~
SPECTRAL DEFINITION (MICROMETERS)
MAXIMUM BRIGHTNESS TEMPERATURE
(mW/M2,sr,cm- I )
FUNCTION
(x) I
14.95
0.75
280
2
14.71
0.25
265
3
14.49
0.25
240
ATMOSPHERIC
4
14.22
0.20
250
TEMPERATURE
5
13.97
0.20
265
SOUNDING
6
13.64
0.20
280
7
13.35
0.20
290
8
11.11
0.I0
330
SURFACE TEMPERATURE
9
9.71
0.15
270
03 CORRECTION
I0
8.16
0.15
290
11
7.33
0.20
275
12
6.72
0.I0
260
13
4.57
0.002
300
14
4.52
0.002
290
ATMOSPHERIC
15
4.46
0.002
280
TEMPERATURE
16
4.40
0.002
260
SOUNDING
17
4.24
O. 002
280
18
4.00
O. 002
340
LOW CLOUDS
19
3.76
0.001
340
SURFACE TEMPERATURE
20
0.69
WATER VAPOR SOUNDING
.
.
.
.
.
.
.
.
.
.
.
CLOUDS
GROUND RESOLUTION 20 km AT SUB-SATELLITE POINT ALL CHANNELS
34
H.W. Yates
TABLE 3
CHANNEL
Advanced Microwave Sounding Hnit-A - NOAA K, L, M
SPECTRAL DEFINITION
SENSITIVITY
(GHz)
(X)
23.80
0.3
31.40
0.3
FUNCTION
TROPOSPHERIC H20 VAPOR PRECIPITATION,
SEA-ICE
SNOW 3
50.30
0.35
4
52.80
O. 25
5
53.33
O. 25
6
54.40
0.25
7
54.94
0.25
8
55.50
0.25
9
57.29
0.25
i0
57.290344
0.4
II
57.290561 ± 48 MHz
0.4
12
57.290561 ± 22 MHz
0.6
13
57.290561 ± i0 MHz
0.8
14
57.290561 ± 4.5 MHz
1.20
15
89.0
0.5
ATMOSPHERIC TEMPERATURE SOUNDING
TROPOSPHERIC H20 VAPOR PRECIPITATION, SEA-ICE SNOW
RESOLUTION AT SUB-SATELLITE POINT = 50 km ALL CHANNELS
U.S. Operational Space Program
TABLE 4
35
Advanced Microwave Sounding Unit-B - NOAA K, L, M
SPECTRAL
CHANNEL
DEFINITION (GHz)
SENSITIVITY
16
89.0
O.6
17
166.0
0.6
FUNCTION
TROPOSPHERIC
18
183.31 + 1.0
0.8 H20 VAPOR
19
183.31
+ 3.0
0.8
20
183.31
+ 7.0
0.8
GROUND RESOLUTION AT SUB-SATELLITE POINT " 15 km ALL CHANNELS
The AMSU replaces the MSU and SSU in TOVS and also represents an important change in procedures. In TOVS, HIRS is the primary instrument and the MSU and SSU secondary instruments. In NOAA K, L, M the AMSU is the primary instrument and the HIRS the secondary instrument. Some consideration had been given to eliminating the HIRS and relying entirely on microwave radiometry but it has been shown that in clear areas the infrared instruments still provide superior soundings and it will be retained. The AMSU is especially important to the climate research program. It will provide atmospheric temperature profiles superior to those now flowing from TOVS in accuracy, vertical resolution and coverage, especially in cloudy areas and below extensive, solid cloud cover. With added channels peaking in the lower troposphere, soundings below clouds will be significantly improved and with higher spatial resolution it will be better able to recognize precipitation below clouds and reject temperature soundings there. Useful soundings in the presence of precipitation below clouds cannot be made and the coarser resolution MSU may not recognize small cells of precipitation and turn out a bad sounding as a result. AMSU will also provide temperature measurements in the stratosphere up to 45 km, an important data source for climate research. Current numerical models do not use data in this region of the atmosphere so that it is not presently available from operational systems. More importantly, perhaps, is the improvement expected in water vapor profiles. The TOVS water vapor output is only marginally useful. The AMSU product should provide accurate and truly useful water vapor data. Presently there is no useful source of data on precipitation over the global oceans, particularly the tropical oceans where cells tend to be small. The AMSU, with its enhanced capability to recognize--and to a certain extent quantify--precipitation below clouds will provide a truly useful global data source for this important mechanism of energy exchange in the atmosphere-ocean system. GEOSTATIONARY SPACECRAFT The current GOES series will continue with two additional spacecraft, GOES-G and H scheduled for delivery and available for launch in 1986. There is some concern that the currently operational spacecraft, GOES-5 and 6, may not last that long. GOES-5 will be nearly two years past its design life-expectancy by then and there is a distinct possibility that we will have only one operational satellite for some period of time. GOES-G and H are expected to carry through until 1989 at which time GOES-Next, currently in the procurement cycle, will be available. GOES-Next will have significantly greater capability than the present GOES spacecraft. The most important feature will be the ability to provide the by-now-familiar images and do atmospheric temperature and water vapor soundings simultaneously. These soundings will not have either the quality or the coverage of those produced from the polar-orbiting NOAA
36
H.W. Yates
spacecraft, but they will have t h e advantage of providing greatly improved temporal resolution needed to study rapidly developing atmospheric conditions. The NOAA satellites provide four soundings per day (two from each spacecraft) for any given point on the earth---currently at 0130, 0730, 1330, and 1930 local time--whereas the GOES-Next will be capable of a sounding every 40 minutes or, in special circumstances, even more frequently. GOES-Next will be capable of sounding the portion of the earth it views from 0 ° to 50 ° latitude in 4 hours or any 3000 km x 3000 km area in 40 minutes. It will, however, provide soundings only in clear areas or between clouds since it has only infrared channels. It is possible to produce soundings down to the tops of clouds and that capability may be implemented. It is not currently done operationally. The NOAA spacecraft, which have microwave channels as well as infrared, will be the primary source of sounding data providing global coverage in cloudy as well as clear areas. The definition and characteristics of the infrared sounding channels planned for GOES-Next are given in Table 5. They are very similar to many of the channels of the current HIRS instrument on the polar-orbiting NOAA spacecraft. GOES-Next will have five imaging channels representing a major improvement over the current spacecraft. In addition to the present visible and thermal infrared channels, a near-infrared, a water vapor, and a "split-window" thermal infrared channel will be added. Further, the resolution of the infrared channels (except for the water vapor channel) will be increased from the current 8 km to 4 km. The definition and specifications of these five imaging channels are given in Table 6. Channels 4 and 5, the so-called "split-window" channels, function together to provide a measure of the radiometric influence of water vapor in the atmosphere. In measuring surface temperatures from space with infrared radiometers, correcting for the influence of atmospheric water vapor is the major factor determining the accuracy. Channels 4 and 5 are spectrally very close differing only in their sensitivity to water vapor. Channel 3, the water vapor channel, will provide data on the distribution of water vapor in the upper troposphere. The value and utility of this important data have been dramatically demonstrated by similar channels on both Meteosat and the current GOES spacecraft. GOES-Next will be capable of imaging the earth below it from 60°N to 60°S in 25 minutes and will produce images consecutively. It will not have the retrace and inter-frame delays of the current spin-stabilized spacecraft. Smaller areas can be covered in proportionately reduced times. Further, it is the objective to have the earth location accuracy of any image element be 2 km or less with a probability of 0.68 km. The g e o s t a t i o n a r y s p a c e c r a f t a r e p r i m a r i l y u s e f u l i n p r o v i d i n g c o n t i n u o u s c o v e r a g e i n t i m e . T h e i r g r e a t d i s t a n c e , 3 7 , 0 0 0 km, from t h e e a r t h makes i t d i f f i c u l t f o r them t o compete w i t h the polar orbiter in precision or resolu tion so tha t they are not the prim a ry s ourc e of data important to the climate programs. However t h e r e a r e some p r o d u c t s whose a c c u r a c y and utility are dependent on the continuous coverage they provide and they will remain an important data source. Typical of this type of data are cloud cover and precipitation. The four observations per day provided by the polar orbiter may provide a distorted sample of the diurnal characteristics. Thus the five geostationary satellites equally distributed around the equatorial belt are the primary source of data for the International Satellite Cloud Climatology Project with the polar orbiters covering the polar regions, filling any gaps that may occur and providing an intercomparison which can serve as a calibration check.
U.S. Operational
TABLE 5
Proposed Specifications
SPECTRAL DEFINITION (MICROMETERS)
CHANNEL
Space Program
37
- GOES-Next Atmospheric Sounder
NEAN (mW/m 2, s r ,
cm- 1 )
MAXIMUM BRIGHTNESS TEMPERATURE
FUNCTION
(K) 14.73
0.87
255
14.47
0.67
255
14.29
0.72
265
ATMOSPHERIC TEMPERATURE
14.08
0.70
278
13.60
0.56
288
13.37
0.44
300
12.00
0.16
330
II.00
0.16
335
7.33
0.18
290
SOUNDING
SURFACE TEMPERATURE AND CLOUD DETECTION
H20 VAPOR 6.82
0.074
270
11
4.52
0.0086
300
TEMPERATURE SOUNDING
12
3.97
0.0033
340
13
3.74
0.0036
340
SURFACE TEMPERATURE AND LOW CLOUD DETECTION
14
0.70
I0
SOUNDING
%
ATMosPHERIC
10 -3 ALBEDO
CLOUD DETECTION
CHANNEL
Specifications
0.35 AT 300K
4.0
11.50
12.50
0.35 AT
4.0
10.20 - 11.20
-
1.0 A T
8.0
6.50 - 7.00
300K
230K
1.4 A T 3 0 0 K
4.0
0.55
3.80 - 4 . 0 0
NEAT (K)
- GOES-Next
NOT APPLICABLE S / N = 150 AT 100% A L B E D O
(K~)
SPATIAL R E S O L U T I O N FROM GEOSTATIONARY ALTITUDE
Proposed
1.0
6
- 0.75
SPECTRAL DEFINITION (MICROMETERS)
TABLE
Instrument
L O W CLOUDS N I G H T TIME
WATER VAPOR (UPPER T R O P O S P H E R E )
SURFACE TEMPERATURE
C O R R E C T I O N OF SURFACE TEMPERATURE FOR H20 VAPOR
4 - 320K
4 - 320K
4 - 320K
4 - 420K
CLOUDS
CLOUD COVER SURFACE FEATURES
APPLICATION
1.6 - 100Z ALBEDO
USEFUL D Y N A M I C RANGE
Imaging
m=