BackForwardInstrument:  GRAS 

Instrument details
Acronym GRAS
Full name GNSS Receiver for Atmospheric Sounding
Purpose Temperature/humidity sounding with highest vertical resolution
Short description Measuring the phase delay due to refraction during occultation between GPS and LEO
Background Consolidated technology
Scanning Technique Limb scanning from 80 km altitude to close-to-surface by time sampling – Azimuth: 90° sectors fore- and aft-
Resolution About 300 km horizontal, 0.5 km vertical
Coverage / Cycle 1 GNSS constellation tracked. About 650 soundings/day - Average spacing 880 km - Global coverage (300 km spacing) in 8.5 days
Mass 30 kg Power 30 W Data Rate 27 kbps

 

Providing Agency ESA
Instrument Maturity Flown on operational programme
Utilization Period: 2007-05-15 to ≥2024
Last update: 2013-07-02
Detailed characteristics
Satellites this instrument is flying on

Note: a red tag indicates satellites no longer operational, a green tag indicates operational satellites, a blue tag indicates future satellites

Instrument classification
  • Earth observation instrument
  • Active and radio-occultation sensor
  • GNSS radio-occultation
Mission objectives
Primary mission objectives
  • Atmospheric temperature
  • Height of the top of PBL
  • Height of the tropopause
  • Specific humidity
  • Temperature of the tropopause
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Tentative Evaluation of Measurements

The following list indicates which measurements can typically be retrieved from this category of instrument. To see a full Gap Analysis by Variable, click on the respective variable.

Note: table can be sorted by clicking on the column headers
VariableRelevance for measuring this variableOperational limitationsExplanation
Atmospheric temperature3 - highInaccurate in low troposphere.Two directional antennas, one GNSS system tracked, covering about 500 soundings/day
Geoid4 - fairHighly indirect.Radio-occultation processing implies precise orbitography. Geoid derived from multi-temporal analysis
Gravity field5 - marginalHighly indirect.Radio-occultation processing implies precise orbitography. Gravity field derived from multi-temporal analysis
Height of the top of PBL3 - highNo specific limitation.Two directional antennas, one GNSS system tracked, about 500 soundings/day. PBL top measured as discontinuity of the refraction index
Height of the tropopause3 - highNo specific limitation.Two directional antennas, one GNSS system tracked, about 500 soundings/day. Tropopause height measured as discontinuity of the refraction index
Specific humidity3 - highInaccurate in high troposphere.Two directional antennas, one GNSS system tracked, about 500 soundings/day
Temperature of the tropopause3 - highNo specific limitation.Two directional antennas, one GNSS system tracked, about 500 soundings/day