BackForwardInstrument:  GRAS 

Instrument details
Acronym GRAS
Full name GNSS Receiver for Atmospheric Sounding
Purpose Atmospheric temperature/humidity sounding with highest vertical resolution. Also ionospheric total electron content along slant path.
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 to 2027
Last update: 2024-03-04
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
WIGOS Subcomponents
  • Subcomponent 1
  • GNSS radio occultation (basic constellation)
  • GNSS radio occultation sounder (basic constellation)
Mission objectives
Primary mission objectives
  • Atmospheric temperature
  • Height of the top of PBL
  • Height of the tropopause
  • Ionospheric Total Electron Content (TEC)
  • Specific humidity
  • Temperature of the tropopause
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
Note: * Primary mission objective.
VariableRelevance for measuring this variableOperational limitationsExplanation
Atmospheric temperature*3 - 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 PBL*3 - 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 tropopause*3 - highNo specific limitation.Two directional antennas, one GNSS system tracked, about 500 soundings/day. Tropopause height measured as discontinuity of the refraction index
Specific humidity*3 - highInaccurate in high troposphere.Two directional antennas, one GNSS system tracked, about 500 soundings/day
Temperature of the tropopause*3 - highNo specific limitation.Two directional antennas, one GNSS system tracked, about 500 soundings/day
Atmospheric density1 - primaryNo specific limitation.Measuring atmospheric density
Electron Density1 - primaryNo specific limitation.Two directional antennas, one GNSS system tracked, about 500 soundings/day
Ionospheric Total Electron Content (TEC)*3 - highNo specific limitation.Two directional antennas, one GNSS system tracked, about 500 soundings/day
Ionospheric Scintillation4 - fairNo specific limitation.Two directional antennas, one GNSS system tracked, about 500 soundings/day