Clear-sky Planetary Boundary Layer Characterisation Using Near- and Thermal-infrared Observations from Satellite-based Imagers

The planetary boundary layer (PBL) contains the majority of moisture and links solar surface heating to increased convection  through vertical redistribution of heat and moisture. Such changes can influence the initiation and life cycle of convective clouds. Remote sensing of these parameters could be beneficial to short-range forecasting, nowcasting and process studies.

In a previous study we analysed the sensitivity of various channels to changes in boundary layer height (BLH) and moisture (BLM). Clear-sky, day-time observations in the near-infrared (NIR) at 0.9µm and thermal infrared (TIR) at 12 µm are primarily sensitive to total column water vapour (TCWV) and in the TIR to the skin temperature and emissivity. But they also exhibit distinct sensitivities to changes to BLH and BLM, respectively. The Flexible Combined Imager (FCI) onboard Meteosat-12 carries both these channels.

In an effort to exploit these sensitivities we build a look-up-table which ties BLH and BLM to the split window difference (SWD, brightness temperature difference between 11 and 12 µm) and the water vapour optical depth (calculated from the ratio of 0.865 and 0.914 µm). With an optimal-estimation inversion scheme, BLH and BLM may be retrieved at 10 minute intervals for clear-sky, day-time pixels.

Currently our effort lies on integrating these complementary NIR and TIR measurements to improve retrievals of TCWV and to derive additional information on the vertical moisture structure in the lower levels of the atmosphere.