Empirical assessment of "lidar albedo" as a proxy for local, planetary albedo

Details Empirical assessment of "lidar albedo" as a proxy for local, planetary albedo Empirical assessment of "lidar albedo" as a proxy for local, planetary albedo

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.a51e0110a&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #A51E-0110

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0305 Aerosols And Particles (0345, 4801, 4906), 0360 Radiation: Transmission And Scattering, 0394 Instruments And Techniques, 1640 Remote Sensing (1855), 3311 Clouds And Aerosols

Scientific paper

The variability of Earth's albedo (A) - i.e. the fraction of incident solar energy reflected back to space - has emerged as a major source of uncertainty in regard to both anthropogenic climate forcing and natural climate stability. There is a need for improved methods of observing albedo variations over the full range of relevant time and space scales. Spaceborne lidar offers a novel approach to this problem in the form of an albedo proxy which we dub the "lidar albedo" (AL). This parameter (otherwise known as integrated attenuated backscatter) is readily and accurately measured by spaceborne lidar with no required retrieval assumptions and no dependence on surface type or solar zenith angle. Thus, AL represents a globally-uniform satellite product that responds exclusively to variations atmospheric reflectivity. Before using this product, however, it is important to assess whether variations in AL actually correspond to atmospherically-induced variations in A. Here, we address this question empirically by comparing data on AL with retrieved values of A from the CERES broadband radiometers. Comparisons are made over the ice-free ocean in order to remove surface albedo as a spurious source of variation. An initial comparison using monthly-mean, 2-degree resolution data from instruments on different orbits (GLAS lidar and CERES on Terra) showed a strong relationship but considerable scatter (r-squared correlation coefficient of 0.38). The A-Train constellation of satellites provides an opportunity for a far more definitive comparison. We will compare AL values from the CALIPSO lidar to spatially matched values of A retrieved from CERES on Aqua. Perfect correlation is not expected because the lidar samples only a narrow line across each of the 20-km CERES pixels. Nevertheless, we expect the correlation to be strong and to reveal the atmospheric conditions over which the relationship is linear. The CALIPSO mission is expected to acquire three years of AL measurements at spatial resolution down to 0.3 km. The results of this study will guide future applications of these data to assessing the nature and atmospheric causes of albedo variability.

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