A research team led by Prof. CHEN Cheng from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has used two polarimetric instruments to retrieve cloud optical and microphysical properties at high spatial resolution.
The Directional Polarimetric Camera (DPC) and the Particulate Observing Scanning Polarimeter (POSP), both independently developed by the team, are onboard the GaoFen-5(02) (GF-5(02)) satellite.
The results have been published in Journal of Quantitative Spectroscopy and Radiative Transfer and IEEE Transactions on Geoscience and Remote Sensing.
Cloud particle size is an important factor in understanding cloud formation, optical properties and their impact on climate. However, obtaining accurate cloud particle size information from satellite observations remains challenging, especially at high spatial resolution.
For the DPC instrument, the team worked on a way to make better use of the polarization signals captured from different viewing angles. The method brings together information from nearby pixels and adjusts the area used for analysis according to cloud conditions. This allows the cloudbow signals, which contain information about cloud particle size, to be used more effectively.
The resulting cloud particle size products have a spatial resolution of about 3.3 km, close to the original resolution of DPC observations. The method provides global maps of cloud effective radius (CER) and cloud effective variance (CEV) for water clouds at a much finer spatial scale.
For POSP, the team combined observations at two infrared wavelengths and corrected the influence of cloud reflectance on the measurements. This increased the proportion of pixels with valid retrievals by 52.06%.
Using POSP observations, the team retrieved global cloud optical thickness (COT) and cloud effective radius (CER) for water and ice clouds. The results were consistent with widely used cloud products from Moderate Resolution Imaging Spectroradiometer (MODIS) and the Visible Infrared Imaging Radiometer Suite (VIIRS).
The results could help improve understanding of cloud processes and their effects on climate，according to the team.
Global retrieval results and comparative validation of CER and COT from POSP/GF-5(02). (Image by YU Haixiao)
