About GRAS
GRAS (Global Navigation Satellite System Receiver for Atmospheric Sounding) is a new European GNSS (Global Navigation Satellite System) receiver that operates as an atmospheric sounder. It will provide unprecedented observations ...
19 VEEBR. 2002
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Measured temperature accuracy | 1K |
|---|---|
Number of occultation channels (set + rise) | 4 |
Number of navigation channels | 8 |
Number of occultations per day | 500 |
Horizontal resolution | 100 to 300 km |
Vertical resolution Fresnel zone (stratosphere, troposphere) | 300 to 1500 m |
High Vertical resolution (troposphere) | 100 m |
Navigation solution accuracy | 100 m |
USO frequency stability | 1 x 10-12 |
Bending angle budget @ 30 km | 0.42 mrad |
Mass | 26 kg |
|---|---|
Power | 37 W |
Data rate (mean, max) | 27 kb/s 60 kb/s |
Occultation antennas | |
Gain | 9 to 10 dBi |
Elevation angle | -25.5 to -28.3° |
Azimuth angle | ± 55° |
Navigation antenna | |
Gain | -4 to +7 dBi |
Elevation angle | 15 to 90° |
Azimutz angle | 360° |
keep text in case it is needed later on. The mass budget for the whole GRAS instrument is around 30 kg, including the harness and deployment mechanism for the anti-velocity antenna. The power consumption in full operation (navigation and occultation signals) is 38 W. The average GRAS data rate is 22 kbit/s, with peaks of up to 60 kbit/s.
The meteorological community calls for a 1° Kelvin accuracy in the temperature profiles provided by the instrument. This requirement is met in the stratosphere using the Geometrical Optics method. For the troposphere, where the temperature gradient is higher, a more advanced technique such as Back Propagation method will be used.
The best performance will be obtained between 5 km and 30 km altitude.
The horizontal resolution is of the order of 100 km to 300 km; inherent to the limb-sounding technique. A key element to reach these performances is the high value of the occultation antennas gain (10dB).
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Description
Flown on MetOp, the new GRAS (Global Navigation Satellite System Receiver for Atmospheric Sounding) instrument will, through the technique of radio occultation, provide very accurate information about the temperature and ...
Instrument design
The entire GRAS (Global Navigation Satellite System Receiver for Atmospheric Sounding) instrument weighs about 30 kg and comprises three antenna-receivers positioned separately on MetOp. One of the antennae, the GVA ...
Performance
Measured temperature accuracy1KNumber of occultation channels (set + rise)4Number of navigation channels8Number of occultations per day500Horizontal resolution100 to 300 kmVertical resolution Fresnel zone(stratosphere, troposphere)300 to 1500 mHigh Vertical resolution (troposphere)100 mNavigation solution accuracy100 mUSO frequency stability1 x 10-12Bending ...
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Instrument overview
The MetOp satellites carry a set of seven 'heritage' instruments provided by the United States’ National Oceanic and Atmospheric Administration (NOAA) and the French Space Agency (CNES) and a new generation of five European instruments offering improved sensing capabilities to both meteorologists and climatologists.
About A-DCS
The Advanced Data Collection System (A-DCS), also known as ARGOS, is to provide a worldwide in-situ environmental data collection and Doppler-derived location service with the basic objective of studying and ...
About AMSU-A1
The Advanced Microwave Sounding Unit – A1 (AMSU-A1) is one of the complement of American instruments provided by NOAA to fly on MetOp-A, -B and –C.
About AMSU-A2
The Advanced Microwave Sounding Unit – A2 (AMSU-A2) is one of the complement of American instruments provided by NOAA to fly on MetOp-A, -B and –C.
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