Retrieval of tropospheric water vapour profiles by using spectra from a microwave spectro-radiometer at 22 GHz

Abstract

We present an approach to retrieve the tropospheric water vapour content from spectra observed at 22 GHz by the groundbased microwave radiometer MIAWARA (Middle Atmospheric Water Vapour Radiometer), located in the south of Bern (CH) and operated by the Institute of Applied Physics in the frame of NDACC. Our retrieval approach uses the entire bandwidth of 1 GHz of the spectrometer to additionally retrieve tropospheric water vapour profiles. Thereby total power spectra from tipping curve calibration (usually used to determine tropospherical opacity) are used. In addition to a standard a priori profile, we try to improve the performance of our retrieval approach by using external informations as additional retrieval constraints. One attempt is to use informations about cloud coverage delivered by a Ceilometer (installed close to the instrument) and an infrared sensor, which is attached to the instrument with the same line-of-sight. Thereby the cloud-base height together with an assumed relative humidity of 100% deliver a "fixed-point" with known profile value as additional a-priori information.