METimage A Spot

METimage

 

Supporting numerial weather prediction, nowcasting, and climate monitoring

METimage A Spot
METimage A Spot

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.

Last Updated

29 June 2022

Published on

19 May 2020

EPS-SG METImage Instrument
Figure 1: METimage instrument. Credit: DLR

METimage will provide continuity to the AVHRR (Advanced Very High Resolution Radiometer) series on board the EPS 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 (NWP), 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 (500m compared to 1km 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 13.345µm. METimage provides images in a number of spectral channels as listed below.

Channel Central Wavelength
(in micrometres)
Primary Use
VII-4 0.443µm Aerosol, ‘true colour imagery’ (blue channel), vegetation
VII-8 0.555µm Clouds, vegetation, ‘true colour imagery’ (green channel)
VII-12 0.668µm Clouds, vegetation, ‘true colour imagery’ (red channel)
VII-15 0.752µm Atmospheric corrections (aerosol), optical cloud top height assignment, vegetation
VII-16 0.763µm Atmospheric corrections (aerosol), optical cloud top height assignment, vegetation
VII-17 0.865µm Vegetation, aerosol, clouds, surface features
VII-20 0.914µm Water vapour imagery
Water vapour total column
VII-22 1.24µm Vegetation, aerosol
VII-23 1.375µm High level aerosol, cirrus clouds, water vapour imagery
VII-24 1.63µm Cloud phase, snow and ice, vegetation, aerosol, fire
VII-25 2.25µm Cloud microphysics at cloud top, vegetation, aerosol over land, fire (effects)
VII-26 3.74µm 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 3.959µm SST, LST, fire
VII-30 4.05µm SST, LST, fire
VII-33 6.725µm Water vapour imagery (including wind in polar regions), water vapour profile (coarse vertical resolution)
VII-34 7.325µm Water vapour imagery (including wind in polar regions), water vapour profile (coarse vertical resolution)
VII-35 8.54µm Cirrus clouds, cloud emissivity
VII-37 10.69µm Cloud variables including cirrus detection, surface temperatures and other radiative variables, surface imagery (snow, ice etc.)
VII-39 12.02µm Cloud variables including cirrus detection, surface temperatures and other radiative variables, surface imagery (snow, ice etc.)
VII-40 13.345µm Carbon dioxide (CO2) slicing for accurate cloud top height. Temperature profile (coarse vertical resolution)

Spectral characteristics

The following table shows the central wavelength of the 20 channels of METimage, their bandwidth, and signal to noise ratio.

Channel number Central Wavelength
(in micrometres)
FWHM (in micrometres)
 
SNR or NEδT* & specified input
VII-4 0.443µm 0.03 221 (at 42W m-2 sr-1 µm-1)
VII-8 0.555µm 0.02 215 (at 22W m-2 sr-1 µm-1)
VII-12 0.668µm 0.02 66 (at 9.5W m-2 sr-1 µm-1)
VII-15 0.7515µm 0.01 400 (at 28W m-2 sr-1 µm-1)
VII-16 0.7627µm 0.0115 400 (at 20W m-2 sr-1 µm-1)
VII-17 0.865µm 0.02 60 (at 6.04W m-2 sr-1 µm-1)
VII-20 0.914µm 0.02 250 (at 15W m-2 sr-1 µm-1)
VII-22 1.24µm 0.02 75 (at 5.4W m-2 sr1 µm-1)
VII-23 1.375µm 0.04 300 (at 6W m-2 sr-1 µm-1)
VII-24 1.63µm 0.02 300 (at 7.3W m-2 sr-1 µm-1)
VII-25 2.25µm 0.05 110 (at 1W m-2 sr-1 µm-1)
VII-26 3.74µm 0.18 0.050 (at 300K)
VII-28 3.959µm 0.06 0.074 (at 300K)
VII-30 4.05µm 0.06 0.074 (at 300K)
VII-33 6.725µm 0.37 0.215 (at 238K)
VII-34 7.325µm 0.29 0.200 (at 250 K)
VII-35 8.54µm 0.29 0.050 (at 300K)
VII-37 10.69µm 0.5 0.050 (at 300K)
VII-39 12.02µm 0.5 0.050 (at 300K)
VII-40 13.345µm 0.31 0.2 (at 260K)

*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 ~2670km, corresponding to a scan angle of ±53deg, with a constant spatial sampling angle across the swath and a spatial resolution of 500m at nadir. The scan period of 1.729s is defined by the satellite orbit (sun-synchronous, average altitude of 830km) and the spatial resolution.