WMO OSCAR | Details for Instrument GEMS2

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Instrument: 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

Global Environmental Monitoring System – 2nd Generation (Weatherstream)
- GEMS2- Amethyst (see instrument status) 2025 - 2027
- GEMS2- Beryl (see instrument status) 2025 - 2028

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.

Search:

Variable	Relevance for measuring this variable	Operational limitations	Explanation
Atmospheric temperature*	2 - very high	Coarse vertical resolution.. Inaccurate in low troposphere.	Many MW channels in the 118 GHz band. Nearly all-weather sounding
Cloud ice effective radius	2 - very high	No specific limitation.	MW channels around 90 GHz, and in 118 and 183 GHz bands
Specific humidity*	2 - very high	Coarse vertical resolution.	MW channels in the 183 GHz band, and 118 GHz for temperature and ice water corrections
Integrated Water Vapour (IWV)	2 - very high	No specific limitation.	MW channels in the water vapour band around 183 GHz
Cloud ice	3 - high	No specific limitation.	MW channels around 90 GHz, and in 118 and 183 GHz bands
Cloud ice Total Column	3 - high	No specific limitation.	MW channels around 90 GHz, and in 118 and 183 GHz bands
Cloud liquid water (CLW)	3 - high	No specific limitation.	MW channels around 90 GHz, and in 118 and 183 GHz bands
Cloud liquid water (CLW) total column	3 - high	No specific limitation.	MW channels around 90 GHz, and in 118 and 183 GHz bands
Precipitation intensity at surface (liquid or solid)	4 - fair	No 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
Cloud drop effective radius	5 - marginal	Highly indirect.	MW channels around 90 GHz, and in 183 GHz band
Downward long-wave irradiance at Earth surface	5 - marginal	Highly indirect.	MW channels in 118 and 183 GHz bands to account for downward cloud radiation
Upward long-wave irradiance at Earth surface	5 - marginal	Highly indirect.	MW channels is the 118 and 183 GHz bands to infer the impact of clouds on the upward LW radiation

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