Developing Ocean Subsurface Data Record from CALIPSO Depolarization Ratio Measurements

CALIOP, the dual wavelength, polarization sensitive lidar flying aboard the CALIPSO satellite, has been operating since June 2006 and is expected to continue for several more years. CALIOP's depolarization ratio is one of the best calibrated measurements made by the A-Train sensors. Over the life of the CALIPSO mission, the stability of the CALIOP depolarization ratio calibration has remained within 1%. CALIOP's depolarization ratio measurements can be used for studying changes in the backscatter of ocean subsurface particulates. The ocean surface/subsurface depolarization ratio measurements from CALIOP together with collocated A-train instruments can be used for estimating the subsurface particulate backscatter coefficient (bbp) and the cross polarization component of the column integrated ocean subsurface backscatter signal. To derive the cross component of inte¬grated ocean subsurface backscatter signal from the depolarization ratio of CALIOP integrated ocean surface/subsurface range bins, we need theoretical estimates of the ocean surface back¬scatter cross section, which can be derived accurately from CloudSat ocean surface backscatter measurements or from AMSR-E wind speeds. Using the CALIOP cross component of the integrated ocean subsurface backscatter together with diffuse attenuation coefficient derived from MODIS, bbp can be estimated. Preliminary CALIOP data analysis shows that in the Southern Oceans, ocean subsurface backscatter has increased by about 5% since the beginning of the CALIPSO mission in June 2006. This study will: (1) introduce the CALIPSO ocean subsurface backscatter data products; (2) assess the uncertainties in the data products and comparing with in situ optics measurements, radiative transfer modeling and aircraft lidar measurements; and (3) summarize the global and regional (e.g., Gulf of Mexico region) statistics and temporal variations of the ocean subsurface backscatter from CALIPSO measurements.