During December 1993 a microwave radiometer belonging to the Central Aerological Observatory (CAO) Moscow was operated at the Meteorological Research Unit, Cardington, UK. The radiometer has a single channel with a central frequency of 61.0 GHz, bandwidth of 2 GHz and sensitivity 0.04 K for a 1 s integration time. The antenna (beam-width 6°) was scanned from nadir to horizontal in 9°s teps. Calibration was done every scan cycle using an electrically switched load. The information potentially available from such a radiometer is discussed. The measurements made at Cardington are compared with in situ observations made by radiosondes and by the Meteorological Office's tethered balloon system. Microwave brightness temperatures calculated from the radiosonde ascents are compared with observations. These were found to agree with a mean difference of 0.1 K and with a standard deviation of < 0.3 K. Similarly retrieved temperature profiles up to 500 m were found to agree with the radiosonde profiles within 1 K rms. During the comparison period there were no strong lowlevel inversions to test fully the radiometer's retrieval capability.

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Observations made by the temperature sounders on the Tiros N series of operational meteorological satellites are being used for generating routine analyses for the stratosphere. One component of the sounder, the stratospheric sounding unit, is described. The methods being used for retrieving stratospheric temperatures and the available products are presented.

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SUMMARYA radiometer sonde has been constructed to observe radiation from the atmosphere above the radiometer in the spectral region 5-7 p with a spectral resolution of about 0.3 p. The results from a fight of the instrument at night up to a height of 25 km are presented. Emission from water-vapour indicates a dry stratosphere with a mass mixing ratio of about 3 x An energy flux originating above 25 km amounting to about 2 pW cm-2 has been observed near 5.7 p. Various possible sources for this additional radiation are discussed.