Combining Data from Ground-based Microwave Radiometers and Other Instruments in Temperature and Humidity Profile Retrievals

Ground-based microwave radiometry offers a new opportunity to automate upper air observations by providing information on temperature and humidity profiles as well as the integrated water vapour and liquid water amounts with high time resolution. To improve their relatively poor vertical resolution and provide a more complete picture of the vertical profile, radiometer observations can be combined with other instruments making up an Integrated Profiling Station. This paper describes a variational method of combining observations from different instruments with background from Numerical Weather Prediction (NWP) models in a statistically optimal way, accounting for their error characteristics. This method is illustrated using microwave and infrared radiometers and surface sensors as an example showing the requirement for a forward model of each observation and an estimate of their error covariance. Methods to exploit the high timeresolution of ground-based observations while assimilating them into NWP are discussed, as these may compensate for the geographic sparsity of a future network of Integrated Profiling Stations.