METimage is a multi-spectral (visible and IR) imaging passive radiometer which will provide detailed information on clouds, wind, aerosols and surface properties which are essential for meteorological and climate applications.
METimage will provide continuity to the AVHRR (Advanced Very High Resolution Radiometer) series on board the Metop and NOAA satellites, and VIIRS on board NOAA satellites. METimage is expected to have a great improvement with respect to AVHRR and comparable performance with respect to VIIRS.
The primary objective of the VII mission is to provide high quality imagery data for global and regional Numerial Weather Prediction, nowcasting, and climate monitoring through the provision of:
- High horizontal resolution cloud products including microphysical analysis
- Sea surface temperature
- Vegetation, snow coverage, and fire monitoring products
- Aerosol products
- Polar atmospheric motion vectors
The mission objectives also include providing information on aerosols, cloud size, surface albedo, fire, land and ice surface temperature, snow cover and soil moisture. An important objective of Metimage is to support the sounders on-board EPS-SG A satellite for their geolocation, cloud characterisation and Scene inhomogeneity quantification for correction of the spectral response.
Compared to its predecessor AVHRR, METimage will have many more channels for the benefit of measuring far more geophysical variables. This combined with on-board radiometric calibration of solar channels and the enhanced spatial sampling (500 m compared to 1 km at nadir) will provide a breakthrough in several application areas: numerical weather forecast, very short-range forecast and now-casting, oceanography, hydrology, land-surface applications, and climate monitoring.
This imaging radiometer measures the thermal radiance emitted by the earth and solar backscattered radiation. It, thus, covers a broad spectral range in 20 spectral bands from 443 to 13.345 µm. METimage provides images in a number of spectral channels as listed below.
|VII-4||0.443 µm||Aerosol, ‘true colour imagery’ (blue channel), vegetation|
|VII-8||0.555 µm||Clouds, vegetation, ‘true colour imagery’ (green channel)|
|VII-12||0.668 µm||Clouds, vegetation, ‘true colour imagery’ (red channel)|
|VII-15||0.752 µm||Atmospheric corrections (aerosol), optical cloud top height assignment, vegetation|
|VII-16||0.763 µm||Atmospheric corrections (aerosol), optical cloud top height assignment, vegetation|
|VII-17||0.865 µm||Vegetation, aerosol, clouds, surface features|
|VII-20||0.914 µm||Water vapour imagery
Water vapour total column
|VII-22||1.24 µm||Vegetation, aerosol|
|VII-23||1.375 µm||Aerosol, ‘true colour imagery’ (blue channel), vegetation|
|VII-24||1.63 µm||Cloud phase, snow and ice, vegetation, aerosol, fire|
|VII-25||2.25 µm||Cloud microphysics at cloud top, vegetation, aerosol over land, fire (effects)|
|VII-26||3.74 µm||Cloud variables, cloud microphysics at cloud top, absorbing aerosol, Sea Surface temperature (SST), Land Surface Temperature (LST), fire, sea and land ice, snow|
|VII-28||3.959 µm||SST, LST, fire|
|VII-30||4.05 µm||SST, LST, fire|
|VII-33||6.725 µm||Water vapour imagery (including wind in polar regions), water vapour profile (coarse vertical resolution)|
|VII-34||7.325 µm||Water vapour imagery (including wind in polar regions), water vapour profile (coarse vertical resolution)|
|VII-35||8.54 µm||Cirrus clouds, cloud emissivity|
|VII-37||10.69 µm||Cloud variables including cirrus detection, surface temperatures and other radiative variables, surface imagery (snow, ice etc.)|
|VII-39||12.02 µm||Cloud variables including cirrus detection, surface temperatures and other radiative variables, surface imagery (snow, ice etc.)|
|VII-40||13.345 µm||Carbon Dioxide (CO2) slicing for accurate cloud top height. Temperature profile (coarse vertical resolution)|
Spectral Characteristics of METimage
The following table shows the central wavelength of the 20 channels of METimage, their bandwidth, and signal to noise ratio.
|Channel number||Central Wavelength
|FWHM (in micrometres)
||SNR or NEδT* & specified input|
|VII-4||0.443 µm||0.03||221 (at 42 W m-2 sr-1 µm-1)|
|VII-8||0.555 µm||0.02||215 (at 22 W m-2 sr-1 µm-1)|
|VII-12||0.668 µm||0.02||66 (at 9.5 W m-2 sr-1 µm-1)|
|VII-15||0.7515 µm||0.01||400 (at 28 W m-2 sr-1 µm-1)|
|VII-16||0.7627 µm||0.0115||400 (at 20 W m-2 sr-1 µm-1)|
|VII-17||0.865 µm||0.02||60 (at 6.04 W m-2 sr-1 µm-1)|
|VII-20||0.914 µm||0.02||250 (at 15 W m-2 sr-1 µm-1)|
|VII-22||1.24 µm||0.02||75 (at 5.4 W m-2 sr1 µm-1)|
|VII-23||1.375 µm||0.04||300 (at 6 W m-2 sr-1 µm-1)|
|VII-24||1.63 µm||0.02||300 (at 7.3 W m-2 sr-1 µm-1)|
|VII-25||2.25 µm||0.05||110 (at 1 W m-2 sr-1 µm-1)|
|VII-26||3.74 µm||0.18||0.050 (at 300 K)|
|VII-28||3.959 µm||0.06||0.074 (at 300 K)|
|VII-30||4.05 µm||0.06||0.074 (at 300 K)|
|VII-33||6.725 µm||0.37||0.215 (at 238 K)|
|VII-34||7.325 µm||0.29||0.200 (at 250 K)|
|VII-35||8.54 µm||0.29||0.050 (at 300 K)|
|VII-37||10.69 µm||0.5||0.050 (at 300 K)|
|VII-39||12.02 µm||0.5||0.050 (at 300 K)|
|VII-40||13.345 µm||0.31||0.2 (at 260 K)|
*NEΔT — Noise Equivalent Temperature change
METimage Scanning Characteristics
Derived from a whisk-broom scanner principle, the instrument records 24 image lines simultaneously during each scan across-track with a swath width of ±54 degrees. By proper selection of rotation frequency, the scanner produces a gap-free scan pattern on ground. Output is an image sampled at discrete locations. The sampling within each line is performed at constant scan angle increments.
METimage has an across track swath of ~2670 km, corresponding to a scan angle of ±53deg, with a constant spatial sampling angle across the swath and a spatial resolution of 500 m at nadir. The scan period of 1.729 s is defined by the satellite orbit (sun synchronous, average altitude of 830 km) and the spatial resolution.