Ocean and Land Surface Studies Using CALIPSO Lidar Measurements
Yongxiang
Hu, NASA LaRC, yongxiang.hu-1@nasa.gov
(Presenting)
Mike
Behrenfeld, Oregon State Univ., behrenfeldm@science.oregonstate.edu
Carl
Weimer, Ball Aerospace Corp., cweimer@ball.com
Charles
McClain, NASA GSFC, charles.r.mcclain@nasa.gov
Jacques
Pelon, CNES, France, jacques.pelon@aero.jussieu.fr
CALIPSO&rsquos main mission objective is studying the climate impact of clouds and aerosols in the atmosphere. CALIPSO also collects information about other components of the Earth&rsquos climate system, such as land surface and ocean.
CALIPSO measures the ocean surface wind speed product using clear sky CALIPSO 1064nm ocean surface backscatter. CALIPSO lidar backscatter from ocean surface is primarily a result of specular reflection of the laser beam from surface. For weak winds, the surface is smooth and specular reflection is a narrow beam with little divergence. As wind speed increases, the surface roughens and the divergence of the same 2% specularly reflected energy increases. As a result, Lidar backscatter intensity reduces as wind increases.
CALIPSO also provide the most direct global measurements of column atmospheric optical depth from space. Atmospheric two-way transmittance, and thus optical depth, can be accurately estimated from the collocated ocean surface CALIPSO lidar backscatter and AMSR-E wind speed measurements. These aerosol and ice cloud optical depths are derived without making assumptions about microphysical properties such as phase function and single scattering albedo.
The 532nm CALIPSO perpendicular polarization measurement provides a direct measure of phytoplankton backscatter in water, since backscatter by ocean surface glint, density fluctuation of water, and dissolved matters hardly depolarize. The ocean sub-surface backscatter can be measured for ocean surface under non-opaque cirrus clouds and aerosols. The atmospheric attenuation can be accurately accounted for using collocated AMSR-E wind and ocean surface parallel polarization measurements.
A technique we refer to as Elevation Information in Tail (EIT) has been developed to provide improved lidar altimetry from CALIPSO lidar data. The EIT technique is demonstrated using CALIPSO data and is applicable to other similar lidar systems with low-pass filters. The technique relies on an observed relation between the shape of the surface return signals (peak shape) and the detector photo-multiplier tube transient response (transient response tail). Application of the EIT to CALIPSO data resulted in an order of magnitude or better improvement in the CALIPSO land surface 30-meter elevation measurements. The results of EIT compared very well with the National Elevation Database (NED) high resolution elevation maps, and with the elevation measurements from the Shuttle Radar Topography Mission (SRTM).
NASA Carbon Cycle & Ecosystems Active Awards Represented by this Poster: