WMO OSCAR | Details for Instrument MERSI-LL

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Instrument: MERSI-LL

Instrument details

Acronym	MERSI-LL
Full name	Medium Resolution Spectral Imager - Low-Light
Purpose	Multi-purpose imagery with low-level light capability
Short description	7-channel VIS/IR spectro-radiometer, with one VIS operable with low-level illumination and 6 MWIR/TIR [see details in table below] Calibration monitoring here
Background	Derivative of the 25-channel MERSI-2 flown on FY-3D, replacing the 19 SW channel by a Low-light VIS channel, for use in a dawn-dusk orbit
Scanning Technique	Cross-track: 2048 samples for channels at 1000 m resolution at nadir, or 8192 samples for channels at 250 m resolution, swath 2900 km - Along-track: ten 1-km lines every 1.5 s.
Resolution	500 m or 1.0 km at s.s.p.
Coverage / Cycle	Global coverage twice/day (including VIS).
Mass		Power	Data Rate

Providing Agency	CMA
Instrument Maturity	Flown on operational programme
Utilization Period:	2021 to 2035
Last update:	2024-09-09

Detailed characteristics

Center wavelength	Bandwidth	SNR or NEΔT @ specified input	IFOV at s.s.p.
0.70 μm	0.5-0.9 μm	7.0 @ 4.0e-5 W m^-2 sr^-1 μ^-1(LowLight) 200 @ 50.0e-5 W m^-2 sr^-1 μ^-1 (daytime)	1000 m
3.80 μm	0.18 μm	0.25 K @ 300 K	1000 m
4.05 μm	0.155 μm	0.25 K @ 300 K	1000 m
7.20 μm	0.50 μm	0.30 K @ 270 K	1000 m
8.55 μm	0.30 μm	0.25 K @ 270 K	1000 m
10.8 μm	1.0 μm	0.3 K @ 300 K	250 m
12.0 μm	1.0 μm	0.3 K @ 300 K	250 m

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

Feng-Yun - 3 (CMA)
- FY-3E (see instrument status) Oct 2021 - 2027
- FY-3J (see instrument status) Jan 2027 - 2035

Instrument classification

Earth observation instrument
Passive optical radiometer or spectrometer
Moderate resolution optical imager

WIGOS Subcomponents

Subcomponent 1
VIS/IR imagery; realisation of a Day/Night band [in SSO]
VIS/IR imager [in SSO]
VIS/IR imager with day/night capability [in SSO]]

Mission objectives

Primary mission objectives

Cloud cover
Cloud top height
Cloud top temperature
Fire fractional cover
Sea surface temperature

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
Cloud top temperature*	2 - very high	No specific limitation.	TIR channels in window and water vapour band (for emissivity)
Fire radiative power	2 - very high	Cloud sensitive.. Coarse spatial resolution.	MWIR and TIR channels
Fire temperature	2 - very high	Cloud sensitive.. Coarse spatial resolution.	MWIR and TIR channels
Sea surface temperature*	2 - very high	Cloud sensitive.	MWIR and TIR window channels around 3.7 and 11 micrometers (cloud impact reduction, water vapour correction)
Integrated Water Vapour (IWV)	2 - very high	Cloud sensitive.	TIR channels around 6.3 micrometers and in the 11 micrometers split window
Cloud cover*	3 - high	No specific limitation.	VIS, MWIR and TIR channels
Cloud top height*	3 - high	No specific limitation.	TIR channels in window and water vapour band (for emissivity) to estimate cloud top height from its temperature
Cloud type	3 - high	No specific limitation.	VIS, MWIR and TIR channels
Land surface temperature	3 - high	Cloud sensitive.	MWIR and TIR window channels (high sensitivity to high temperature, cloud impact reduction, water vapour correction)
Downward long-wave irradiance at Earth surface	4 - fair	Cloud sensitive.. Highly indirect.	MWIR and TIR channels including the water vapour band
Fire fractional cover*	4 - fair	Cloud sensitive.. Coarse spatial resolution.	VIS, MWIR and TIR channels
Sea-ice cover	4 - fair	Cloud sensitive.	VIS, MWIR and TIR channels
Soil moisture at surface	4 - fair	Cloud sensitive.. Index only.	VIS and TIR window channels. Soil moisture inferred from thermal inertia
Upward long-wave irradiance at Earth surface	4 - fair	Cloud sensitive.. Highly indirect.	MWIR and TIR channels in windows around 3.7 and 11 micrometers, and in the water vapour band around 6.3 micrometers
Wind (horizontal)	4 - fair	Limited to high latitudes.. Cloud or water vapour tracers needed.	TIR channels in the 11 micrometers window and the 6.3 micrometers water vapour band
Snow cover	5 - marginal	Cloud sensitive.. Daylight only.	VIS channel(s)
Upward long-wave irradiance at TOA	5 - marginal	Spectral interpolation needed.	MWIR and TIR channels in windows around 3.7 and 11 micrometers, and in the water vapour band around 6.3 micrometers

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