1. Bryan HUNEYCUTT (NASA/JPL) WMO, Geneva, Switzerland 20-21 March 2006
Earth Exploration-Satellite Service (Active) Active Spaceborne Remote Sensing
Bryan HUNEYCUTT (NASA/JPL)
WMO, Geneva, Switzerland
20-21 March 2006

2. Active Sensor Types
SYNTHETIC APERTURE RADARS - Sensors looking to one side of nadir track, collecting phase and time history of coherent radar echo from which typically can be produced a radar image or topographical map of the Earth surface
ALTIMETERS - Sensors looking at nadir, measuring the precise time between a transmit event and receive event to extract the precise altitude of ocean surface
SCATTEROMETERS - Sensors looking at various aspects to the sides of the nadir track, using the measurement of the return echo power variation with aspect angle to determine wind direction and speed on Earth ocean surface
PRECIPITATION RADARS - Sensors scanning perpendicular to nadir track, measuring the radar echo from rainfall to determine the rainfall rate over Earth surface, usually concentrating on the tropics
CLOUD PROFILE RADARS - Sensors looking at nadir, measuring the radar echo return from clouds, to determine cloud reflectivity profile over Earth surface
20-21 March 2006

3. ACTIVE SENSOR AND SERVICE DEFINITIONS
Active Sensor: a measuring instrument in the Earth exploration-satellite service or in the space research service by means of which information is obtained by transmission and reception of radio waves (RR)
Earth Exploration-Satellite Service: a radiocommunication service between earth stations and one or more space stations, which may include links between space stations, in which:
-      information relating to the characteristics of the Earth and its natural phenomena including data relating to the state of the environment is obtained from active sensors or passive sensors on earth satellite;
-      similar information is collected from airborne or earth-based platforms;
-      such information may be distributed to earth stations within the system concerned
Space Research Service: a radiocommunications service in which spacecraft or other objects in space are used for scientific or technological research purposes
20-21 March 2006

4. Active Sensors Applications by Sensor Type
20-21 March 2006

5. Active Sensor Characteristics
20-21 March 2006

6. Active Sensor Examples
SAR-Radar Image Bora Bora, French Polynesia
Altimeter-Sea Level
Scatterometer-Wind Speeds
Precipitation Radar-Rain Rates
Cloud Radar-Cloud Reflectivity Profile
20-21 March 2006

7. Synthetic Aperture Radars (SARs)
Provide radar images and topographical maps of the Earth’s surface
RF center frequency depends on the Earth’s surface interaction with the EM field
RF bandwidth affects the resolution of the image pixels
Allowable image pixel quality degradation determines allowable interference level
SAR Illumination Swath
Chirp Spectrum
20-21 March 2006

8. Synthetic Aperture Radars (SARs) (contd)
Shuttle RadarTopography Mission (SRTM) Synthetic Aperture Radar (SAR)
SIR-C L,C band interferograms Ft. Irwin, CA
SRTM perspective with Landsat overlay, Antelope Valley, CA
SRTM France, shaded relief and colored height
20-21 March 2006

9. Illustration of Altimeter Return
Altimeters
Provide altitude of the Earth’s ocean surface
RF center frequency depends on the ocean surface interaction with the EM field
Dual frequency operation allows ionospheric delay compensation
JASON-1 uses frequencies around GHz and 5.3 GHz
Allowable height accuracy degradation determines the allowable interference level
Illustration of Altimeter Return
20-21 March 2006

10. Altimeters (contd) Jason Sea Level Residuals
TOPEX/POSEIDON maps of sea surface height relative to normal
Sea Topography
20-21 March 2006

11. Jason 1-TOPEX/Poseiden Tandem Mission
Altimeters (contd)
Jason 1-TOPEX/Poseiden Tandem Mission
Ocean Surface Topography Mission (OSTM) follow-on to Jason to launch in 2008
20-21 March 2006

12. Variation of Backscatter with Aspect Angle
Scatterometers
Provide the wind direction and speed over the Earth’s ocean surface
RF center frequency depends on the ocean surface interaction with the EM field and its variation over aspect angle
Narrow RF signal bandwidth provides the needed measurement cell resolution
Allowable wind speed accuracy degradation determines the allowable interference level
Variation of Backscatter with Aspect Angle
20-21 March 2006

13. Scatterometers (contd)
SEAWINDS scanning pencil beam illuminates scans at two different look angles from nadir, and scans 360 degrees about nadir in azimuth
NSCAT illuminated the Earth’s surface at several different fixed aspect angles
20-21 March 2006

14. Scatterometers (contd)
NSCAT illustration
Synoptic View of Ocean Surface Wind by NASA Scatterometer
On-orbit satellite overview of NSCAT
20-21 March 2006

15. Scatterometers (contd)
QuickSat SeaWinds
Ocean Surface Winds by QuickSat
ADEO II SeaWinds
20-21 March 2006

16. Precipitation Radars
Provide precipitation rate over the Earth’s surface, typically concentrating on rainfall in the tropics
RF center frequency depends on the precipitation interaction with the EM field
Narrow RF signal bandwidth provides the needed measurement cell resolution
Tropical Rainfall Measurement Mission (TRMM) uses only 0.6 MHz RF bandwidth
Allowable minimum precipitation reflectivity degradation determines the allowable interference level
20-21 March 2006

17. Precipitation Radars (contd)
TRMM Precipitation Radar Latest Tropical Cyclone data
TRMM Average Precipitation ’98-’04 (combined with gauge information)
TRMM Latest Week of Global Rainfall Accumulation data
Mosaic of TRMM overpasses of Hurricane Isabel crossing the Atlantic (Sept ’04)
20-21 March 2006

18. Cloud Profile Radars
Provide three dimension profile of cloud reflectivity over the Earth’s surface
RF center frequency depends on the ocean surface interaction with the EM field and its variation over aspect angle
Antennas with very low sidelobes so as to isolate the cloud return from the higher surface return illuminated by the sidelobes
Narrow RF signal bandwidth provides the needed measurement cell resolution
Allowable reflectivity accuracy degradation determines the allowable interference level
20-21 March 2006

19. Cloud Profile Radars (contd)
Cloudsat
Formation flying of Cloudsat with Calipso to overlap lidar footprint with CPR footprint
Time-height cross section of radar reflectivity from 94 GHz radar
20-21 March 2006

20. Active Sensor Interference And Performance Criteria
20-21 March 2006

21. Typical Interference Levels at Earth’s Surface
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22. Compatibility Studies
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23. Compatibility Studies
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24. WRC’06 Issues/Concerns
20-21 March 2006

25. 9.3-9.5 GHZ BAND CURRENT STUDIES
The WRC-2006 resolution 747 resolves to consider the possible extension of up to 200 MHz in the band of GHz to the EESS (active) and SRS (active).
Agreement from the spaceborne active sensor community to use extension band for wideband applications only such as for wideband SARs; ongoing studies analyze the interference from spaceborne SARs in the band GHz into radiodetermination systems; studies analyzing the interference into SARs showed about a 4 dB margin from the interference threshold from a worldwide deployment of radiodetermination transmitters.
Another study by the the spaceborne active sensor community analyzes the compatibility between spaceborne SARs and fixed systems in the band GHz; simulation results showed that the worst case interference levels from SARs was dB exceeded 1% of the time for an FS station at 45 deg latitude; studies analyzing the interference into SARs showed about a 5.3 dB margin from the interference threshold from a worldwide deployment of FS stations.
20-21 March 2006

26. OTHER CURRENT STUDIES
JRG 1A-1C-8B: major issue of the “design objective” in ITU-R Rec SM Annex 8 for primary radars (includes EESS (active)) with the possibility of making more stringent the “roll-off” of out-of-band emissions from the current 20 dB/decade to 40 dB/decade
GHz band: PDNR on the “Mutual planning between the EESS (active) and the RAS in the 94 GHz and 130 GHz bands” to ensure that the RAS receivers are not damaged by the EESS (active) CPRs, but no undue burden is put on the EESS (active) CPR operations
Approved Revised recommendations in SG7:
ITU-R Rec SA.577 “Preferred frequencies and necessary bandwidths for spaceborne active remote sensors”
ITU-R Rec SA.1166 “Performance and interference criteria for active spaceborne sensors”
Approved New recommendation in SG7:
ITU-R SA.[MITIGATE] “Mitigation technique to facilitate the use of the MHz band by the Earth exploration-satellite service (active) and the space research service (active)”
20-21 March 2006