Thermal Infrared Remote Sensing of Dust Aerosols based on the Combined CALIOP and IIR Observations

Abstract:

Mineral dust aerosol has significant longwave thermal infrared (LW) direct radiative effect (DRE) due to its large size. However, unlike the well-agreed cooling effect of the shortwave solar (SW) DRE of dust aerosol, the LW DRE remains uncertain because of the poor understanding of the LW radiative properties, especially the optical depth. From the observations of Infrared Imaging Radiometer (IIR) and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard CALIPSO, dust aerosol optical depth (AOD) is retrieved using the brightness temperature difference (dBT) between clear-sky and dust-laden scenarios based on the Lookup-Table (LUT) method. In contrast to thermal infrared hyperspectral observations with a coarse spatial resolution leading to sub-grid cloud contaminations, this method takes advantage of the accurate cloud-free dust vertical distribution provided by CALIOP. With the pre-calculated dust models by particle size distributions and refractive indices of dust samples from worldwide deserts, we can further retrieve the dust particle size based on the split-window signatures of BT provided by three IIR bands centered at 8.7, 10.6 and 12 μm. The pixel-to-pixel comparison will be applied to the retrieved thermal infrared dust AOD with that from AIRS and IASI observations. The retrieved dust particle size will be compared with the AERONET observations and the measurements during the Fennec campaign.