Information content assessment of hyperspectral microwave radiometer for temperature and humidity sounding in a numerical weather prediction context

Abstract We present the preliminary results of an information content study to assess the potential of a proposed hyperspectral microwave satellite instrument, the Bureau of Meteorology (the Bureau) microwave‐sounding mission (MSM), to provide atmospheric temperature and humidity profile information under clear‐sky conditions in the context of the Bureau's global numerical weather prediction (NWP) system. First, we conducted a user survey that allowed us to develop the requirements for the mission, which indicated a desire to prioritise 50–60‐GHz band capability and noise performance. To examine trade‐offs between band availability and spectral resolution versus noise, we used a one‐dimensional optimal estimation technique to calculate the information content of clear‐sky temperature and humidity vertical profiles from the hyperspectral MSM in the context of NWP. The degrees of freedom for signal (DFS) are computed for temperature and water vapour using the column representation of the Bureau's operational background error covariance matrix ( B ) for different combinations of observation errors ( R ) and spectral resolutions. The results show that the information content is highest when the instrument is configured to a 10‐MHz bandwidth in the 50–60‐GHz band, and with single‐sideband 20‐MHz and 40‐MHz bandwidths in the 118‐ and 183‐GHz bands respectively. The information content can be considerably improved by using a 3 × 3 averaging of adjacent footprints, similar to the preprocessing of the advanced technology microwave sounder (ATMS) in operational use at the Bureau, indicating that spatial oversampling is a desirable feature of such an instrument. The study indicates that the hyperspectral MSM would provide considerably increased information content relative to ATMS and other existing operational microwave sounders. This finding is consistent with other studies into the benefits of hyperspectral microwave instrumentation, and in line with the impact provided by operational hyperspectral infrared sounders such as the infrared atmospheric sounding interferometer (IASI).