Uncertainties in Satellite Passive Microwave Observations of Cloud Liquid Water Path

Observations of cloud liquid water path (CLWP) provided by satellite microwave radiometers are greatly underutilized in climate studies mainly because they are perceived as having very large uncertainties. While there is some truth to this, these uncertainties can be identified and quantified with the help of measurements from other satellite sensors to improve the accuracy of these observations.

This study makes use of Advanced Microwave Scanning Radiometer-EOS (AMSR-E) CLWP L2 data collocated with MODIS L2 cloud products over the full 9-year record of the AMSR-E, as well as collocated with CloudSat Cloud Profiling Radar (CPR) L2 cloud/rain data and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) L2 cloud layer data for 2008, to quantify systematic CLWP errors for strictly warm clouds, conditions under which these errors can be more readily determined. The new merged MODIS/AMSR-E L2 products are produced using a rigorous but fast collocation method to ensure that the higher spatial resolution MODIS cloud data are matched precisely with the coarser resolution AMSR-E footprints. Four types of systematic errors are considered: Clear sky bias, cloud/rain partition bias, cloud-fraction-dependent-bias, and cloud temperature bias.

Our ultimate goal is to make these error estimates more accessible to climate researchers in order to encourage greater use of satellite microwave CLWP data.