BackInstrument:  GEMS2 

Instrument details
Acronym GEMS2
Full name Global Environmental Monitoring System – 2nd Generation
Purpose Temperature and humidity sounding in most weather conditions. Precipitation and cloud characterization.
Short description
  • 24 channel radiometer including 118 and 183 GHz bands (see below)
  • Cross-track scanning
Background
  • Developed as a commercial instrument to provide global data services with US DoD and private funding support
Scanning Technique

Cross-track and Along-track Nyquist spatial sampling at 16 km SSP. Swath ~1800-2200 km altitude dependent. Scan rate ~1 Hz
Resolution 16 km SSP for channels 104-125 GHz, 12 km SSP for channels 155-185 GHz
Coverage / Cycle Near-global coverage twice/day
Mass 3 kg Power 15 W Data Rate 300

 

Providing Agency Weatherstream
Instrument Maturity Flown on an R&D satellite
Utilization Period: 2025 to 2028
Last update: 2025-04-23
Detailed characteristics
No. Central Frequency (GHz) Bandwidth (MHz) Polarisation NeDT Nadir IFOV
1 108.6003 7700 QH 0.22K 16 km
2 118.7503 ± 5 2600 QH 0.27K 16 km
3 118.7503 ± 3.1 1200 QH 0.43K 16 km
4 118.7503 ± 2.1 800 QH 0.57K 16 km
5 118.7503 ± 1.5 400 QH 0.57K 16 km
6 118.7503 ± 1.1 400 QH 0.52K 16 km
7 118.7503 ± 0.7 400 QH 0.68K 16 km
8 118.7503 ± 0.4 200 QH 0.91K 16 km
9 118.7503 ± 0.2 100 QH 1.07K 16 km
10 118.7503 ± 0.1 50 QH 1.51K 16 km
11 118.7503 ± 0.05 25 QH 2K 16 km
12 118.7503 ± 0.025 12.5 QH 3K 16 km
13 118.7503 ± 0.0125 6 QH 4.4K 16 km
14 118.7503 ± 0.006 3 QH 5.7K 16 km
15 118.7503 ± 0.003 1.5 QH 9K 16 km
16 160.31 10000 QV 1.4K 12 km
17 169.31 8000 QV 1K 12 km
18 175.81 4500 QV 1.3K 12 km
19 178.61 1000 QV 2.1K 12 km
20 179.61 1000 QV 1.8K 12 km
21 180.71 1000 QV 1.5K 12 km
22 183.31 ± 1.5 1000 QV 1.5K 12 km
23 183.31 ± 0.7 500 QV 1.7K 12 km
24 183.31 ± 0.3 300 QV 1.9K 12 km
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
  • Passive microwave radiometer
  • Cross-track, special or non-scanning microwave radiometer
WIGOS Subcomponents
  • Subcomponent 1
  • MW sounders [in SSO]
  • MW sounder [in SSO]
Mission objectives
Primary mission objectives
  • Atmospheric temperature
  • Specific humidity
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*2 - very highCoarse vertical resolution.. Inaccurate in low troposphere.Many MW channels in the 118 GHz band. Nearly all-weather sounding
Cloud drop effective radius5 - marginalHighly indirect.MW channels around 90 GHz, and in 183 GHz band
Cloud ice3 - highNo specific limitation.MW channels around 90 GHz, and in 118 and 183 GHz bands
Cloud ice Total Column3 - highNo specific limitation.MW channels around 90 GHz, and in 118 and 183 GHz bands
Cloud ice effective radius2 - very highNo specific limitation.MW channels around 90 GHz, and in 118 and 183 GHz bands
Cloud liquid water (CLW)3 - highNo specific limitation.MW channels around 90 GHz, and in 118 and 183 GHz bands
Cloud liquid water (CLW) total column3 - highNo specific limitation.MW channels around 90 GHz, and in 118 and 183 GHz bands
Downward long-wave irradiance at Earth surface5 - marginalHighly indirect.MW channels in 118 and 183 GHz bands to account for downward cloud radiation
Precipitation intensity at surface (liquid or solid)4 - fairNo specific limitation.MW channels in the 118 and 183 GHz bands. Suitable for solid and, to a less extent, liquid precipitation over sea and land, Insensitive to surface emissivity
Specific humidity*2 - very highCoarse vertical resolution.MW channels in the 183 GHz band, and 118 GHz for temperature and ice water corrections
Integrated Water Vapour (IWV)2 - very highNo specific limitation.MW channels in the water vapour band around 183 GHz
Upward long-wave irradiance at Earth surface5 - marginalHighly indirect.MW channels is the 118 and 183 GHz bands to infer the impact of clouds on the upward LW radiation