Lidar In-space Technology Experiment measurements of sea surface directional reflectance and the link to surface wind speed

Abstract

The dependence of sea surface directional reflectance on surface wind stress suggests a method for deriving surface wind speed from space-based lidar measurements of sea surface backscatter. In particular, lidar measurements in the nadir angle range from 10 degrees to 30 degrees appear to be most sensitive to surface wind-speed variability in the regime below 10 m/s. The Lidar In-space Technology Experiment (LITE) shuttle lidar mission of September 1994 provided a unique opportunity to measure directional backscatter at selected locations by use of the landmark track maneuver and to measure fixed-angle backscatter from the ocean surfaces on a global scale. During the landmark track maneuver the shuttle orbiter orientation and roll axis are adjusted continuously to maintain the lidar footprint at a fixed location for a duration of ~1 min. Several data sets were converted to calibrated reflectance units and compared with a surface reflectance model to deduce surface wind speeds. Comparisons were made with ERS-1 scatterometer data and surface measurements.

Sea surface wind speed estimation from space-based lidar measurements

“…The dependence of the lidar/radar backscatter cross section on the angle of incidence was proposed in theory by Barrick (1968), and verified qualitatively by measurements from airborne lidar (Bufton et al, 1983) and space-based lidar (Menzies et al, 1998).…”

Airborne lidar reflectance measurements at 1.57 μm in support of the A-SCOPE mission for atmospheric CO<sub>2</sub>

“…The surface reflectance characteristics are quite different for land and water. In general the reflectivity of the sea is caused by specular reflection on the water surface, by backscattering due to whitecaps, and by subsurface backscattering (Menzies et al, 1998). As well-known from previous studies, over the ocean the lidar reflectance will strongly be anticorrelated to the surface wind speed which effects the possibility for Published by Copernicus Publications on behalf of the European Geosciences Union.…”

The CALIPSO Mission

“…iii) The retrieval of ocean surface roughness from spaceborne lidar observations was demonstrated using observations from LITE (Menzies et al 1998), but CALIOP data have allowed progress in the analysis of ocean surface and subsurface signals (Hu et al 2008). Recent work combining CALIOP, CloudSat, and passive microwave measurements points toward the use of lidar ocean surface returns to improve the retrievals of column aerosol optical depth and extinction profiles (Josset et al 2008).…”