Microwave Airborne Radiometer Scanning System (MARSS)

A scanning microwave radiometer operating at AMSU-B channels 16-20 (89-183GHz) and pointing both upward and downward.

Used for satellite intercomparisons, radiative transfer model validation, temperature and humidity profiling, column liquid water retrievals, precipitation, ice cloud and surface emissivity studies, etc.


Microwave radiometry can provide a unique insight into the state of the atmosphere, as well as land and sea surface properties.

To exploit this, a number of Advanced Microwave Sounding Units (AMSU) instruments have been flown aboard satellites since 1998, and are still producing global observations of the temperature and humidity structure of the atmosphere for forecasting applications.

In order to investigate ways of improving the use of data from these and similar instruments, the Met Office has developed and operates two microwave radiometers. These instruments have been flown on both the MRF C-130 and the FAAM BAe 146 aircraft as well as being used to make ground-based measurements.


MARSS (Microwave Airborne Radiometer Scanning System) is an along-track scanning, total power microwave radiometer which measures in five channels, two window channels at 89 and 157 GHz and three channels centred on the water vapour absorption line at 183.31 GHz. MARSS is able to view in nine upward and nine downward directions during each three second scan. Each scan also incorporates views of both a hot and ambient calibration target.

Schematic overview of the MARSS instrument The MARSS pod fitted to the FAAM aircraft.

The microwave spectrum lies roughly between 3 and 300 GHz (10 cm to 1 mm) and within this region there is atmospheric absorption due to oxygen and water vapour depending on the exact frequency selected.

Channels are chosen with different levels of absorption in order to make them sensitive to different layers of the atmosphere. For example, by choosing a number of channels with differing levels of absorption by oxygen (which is assumed to be well mixed in the atmosphere) it is possible to build up an idea of the temperature structure in the atmosphere.

Instrument Deimos MARSS
AMSU Channel
1 3 16 17 18 19 20
Frequency (GHz)
24 50 59 157 183±1 183±3 183±7
View angles
along track
Up or down
+35° to -5°
Up and down
+40° to -40°
Beamwidth (FWHM)
11° 11° 12° 11°
Sensitivity NEDT (K)
0.6 0.6 0.5 0.7 0.6 0.4 0.3
Calibration Accuracy (K)
3 3 0.9 1.1 1.0 0.9 0.8

Further Details

Contact Stuart Fox, MetOffice


Additional information