Finding Surface Reflectivity in a Coastal Area

Kassianov, E., Pacific Northwest National Laboratory

Radiation Processes

Warm Boundary Layer Processes

Kassianov E, J Barnard, C Flynn, L Riihimaki, L Berg, and D Rutan. 2017. "Areal-Averaged Spectral Surface Albedo in an Atlantic Coastal Area: Estimation from Ground-Based Transmission." Atmosphere, 8(7), 123, 10.3390/atmos8070123.

Science

Accurate measurements of surface albedo—or surface reflectivity—in coastal regions with complex mixtures of distinctive surface types (land and ocean) present a great challenge for conventional approaches based on data from tower-mounted instruments and satellites. Frequently, these data are limited or unavailable. Researchers from the U.S. Department of Energy (DOE) helped demonstrate feasibility of a new ground-based method—using clouds as a mirror—for measuring surface reflectivity in a highly heterogeneous coastal region. Such measurements are based on sunlight “bounced up” from a surface and then “bounced down” by a cloud deck.

Impact

Compared with conventional satellite-based and composite methods, results showed that the new ground-based method produced similar spectral signatures of surface reflectivity. Because the ground-based data required for the new method can be obtained at locations around the globe with various degrees of surface heterogeneity, the new method can provide spectral surface reflectivity at cli­­matically important regions and is a valuable complementary tool to conventional approaches.

Summary

Surface reflectivity substantially affects the variability of the Earth’s radiation balance. This variability is sensitive to multiple natural and man-made factors, and accurate measurements from the ground, air, and space are important for data sets used in atmospheric models. Assessing surface variability, however, is extremely challenging in regions with complex landscapes and different types of surface cover. In this study, researchers used an integrated data set collected during a 19-month period (June 2009–December 2010) at the DOE Atmospheric Radiation Measurement (ARM) Facility observatory on Graciosa Island in the Azores, a small archipelago off the coast of Portugal. This data set was developed using both ground-based and satellite observations. Scientists compared the areal-averaged surface reflectivity obtained by the new method to those derived from satellite observations and estimated by a conventional composite approach combining satellite- and ground-based data. Comparisons showed that the new method can effectively estimate the spectral surface reflectivity in a coastal area at spatial scales needed to validate and improve model simulations of surface reflectivity.