An improved IASI temperature and humidity retrieval method based on double channel differences

Due to surface emissivity, the retrieval accuracy of hyperspectral infrared temperature and humidity profiles is typically poor in the lower atmosphere. To solve this problem, we use the double channel differences method (DCDM) to retrieve the temperature and humidity profiles of the Infrared Atmospheric Sounding Interferometer (IASI) with different surfaces, zenith angles, and data sources. Results show that DCDM can effectively improve IASI retrieval performance. The root mean square error (RMSE) reductions are large and exhibit no marked change with the zenithal angle. Compared with prior profiles, prior near-surface temperatures can markedly improve the retrieval performance of temperature profiles. Humidity profile retrieval using both humidity and temperature channels can reduce the RMSE and the dependence on the precision of the prior inputs. The DCDM can markedly reduce errors in temperature and relative humidity retrievals, and the retrievals agree with ERA-Interim better than IASI L2. With the DCDM, the lower temperature and relative humidity RMSE can be similar to 3.5 K/14% (land), similar to 3 K/13% (coast), similar to 1.4 K/7% (sea). Compared with radiosonde observations and ERA-Interim, the DCDM can reduce errors in temperature and humidity retrievals, and the improvement in performance is equivalent.