MWI A Spot

Microwave Imager


Providing all-weather surface imagery

MWI A Spot
MWI A Spot

The Microwave Imager (MWI) is a conically scanning radiometer, capable of measuring thermal radiance emitted by the Earth, at high spatial resolution in the microwave region of the electromagnetic spectrum.

Last Updated

20 June 2022

Published on

19 May 2020

EPS-SG MicroWave Imager Instrument
Figure 1: The MWI radiometer (Credit: OHB-Italia)

MWI has heritage from microwave imaging missions such as SSM/I (Special Sensor Microwave Imager) and SSMI/S (Special Sensor Microwave Imager Sounder), which have been flown as part of the US Defence Meteorological Satellite Program, and the NASA/JAXA Global Precipitation Measurement’s Microwave Imager (GMI), TRMM-TMI Tropical Rainfall Measuring Mission’s (TRMM) Microwave Imager (TMI) and The Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E).

The primary objective of the MWI is to support numerical weather prediction (NWP) at regional and global scales by providing cloud and precipitation products and all weather surface imagery.

It will provide all-weather surface imagery, including sea ice coverage and type, snow coverage and water equivalent. The primary objective of MWI is also to obtain sea surface winds and total column water vapour above oceans.

Other mission objectives include water vapour and temperature gross profiles, plus providing continuity of other key microwave imager channels (e.g. SSM/I, TRMM TMI, SSMIS, AMSR-E) in support of long-term climate records.

For nowcasting and very short-range forecasting at regional scales, MWI mission is foreseen to fulfil key requirements on cloud liquid water and ice estimates, and precipitation estimates.

MWI frequency coverage is from 18GHz up to 183GHz. The table below shows the MWI channel specifications, NEΔT and footprint size. All MWI channels up to 89GHz are measured with both *V- and **H polarisations. Channels above 89GHz are measured at V polarisation only.

Channel Frequency Bandwidth Polarisation Radiometric Sensitivity (***NEΔT) Footprint Size at 3dB
MWI-1 18.7GHz 200MHz V, H 0.8 50km
MWI-2 23.8GHz 400MHz V, H 0.7 50km
MWI-3 31.4GHz 200MHz V, H 0.9 30km
MWI-4 50.3GHz 400MHz V, H 1.1 30km
MWI-5 52.61GHz 400MHz V, H 1.1 30km
MWI-6 53.24GHz 400MHz V, H 1.1 30km
MWI-7 53.75GHz 400MHz V, H 1.1 30km
MWI-8 89.0GHz 4000MHz V, H 1.1 10km
MWI-9 118.7503±3.2GHz 2x500MHz V 1.3 10km
MWI-10 118.7503±2.1GHz 2x400MHz V 1.3 10km
MWI-11 118.7503±1.4GHz 2x400MHz V 1.3 10km
MWI-12 118.7503±1.2GHz 2x400MHz V 1.3 10km
MWI-13 165.5±0.75GHz 2x1350MHz V 1.2 10km
MWI-14 183.31±7.0GHz 2x2000MHz V 1.3 10km
MWI-15 183.31±6.1GHz 2x1500MHz V 1.2 10km
MWI-16 183.31±4.9GHz 2x1500MHz V 1.2 10km
MWI-17 183.31±3.4GHz 2x1500MHz V 1.2 10km
MWI-18 183.31±2.0GHz 2x1500MHz V 1.3 10km

*V — Vertical Polarisation
**H — Horizontal Polarisation
***NEΔT — Noise Equivalent Temperature change

Scanning characteristics

The conically scanning MWI collects radiation coming from the Earth by means of a rotating offset parabolic reflector antenna and feed-horn cluster rotating together. The rotation of the slanted antennas allows conical scans with constant incidence angles of about 53°, depending on the channel frequency.

The observations are acquired within an angle of ± 65° in azimuth for the fore view, equivalent to a swath of about 1700km from the altitude of the nominal orbit. MWI has a moderate antenna size providing on ground footprints ranging from 50km down to 10km, depending on frequency. The observation geometry can be seen in the figure.

MicroWave Imager instrument scanning pattern
Figure 2: MWI viewing geometry