Algorithm for the Estimation of Continental Scale Land-Surface Broadband Albedo from INSAT-3D Imager Data

Land surface albedo (LSA) is an important parameter in surface-energy budget studies and process-based models. Availability of LSA on a continental scale from the geostationary platform can be very useful in various applications and modelling activities. A study has been carried out to develop a narrow to broadband albedo conversion algorithm for estimating broadband LSA over India and surrounding from INSAT-3D (I3D) Imager observations. An atmospheric radiative transfer model was used to simulate the at-sensor reflectivity corresponding to two spectral bands of I3D Imager located in visible (0.55–0.75 μm) as well as shortwave infrared (1.55–1.70 μm) regions and a shortwave broadband spectral region (0.40–2.5 μm) for diverse land-atmospheric characteristics by assuming the surfaces as Lambertian targets. Then a mathematical relationship between reflectivity of two Imager bands and a shortwave broadband was developed based upon radiative transfer model simulation results, which yielded narrow-to-broadband conversion coefficients. A separate set of narrow to broadband conversion coefficients for major land covers were generated for I3D Imager sensor. Using the proposed method and coefficients, broadband LSA maps were generated over India and surrounding regions. Daily and 15-Day composite LSA products have also been successfully generated on continental scale. The broadband LSA derived from I3D captured the albedo range successfully for various land covers, including water (0.03–0.07), desert (0.30–0.55), crop (0.12–0.18), forest (0.11–0.17), soil (0.09–0.26) and snow (0.41–0.65). Comparison of I3D-derived LSA by the proposed algorithm with the Moderate Resolution Imaging Spectroradiometer (MODIS) albedo product showed a very good match (R2=0.88 and root mean square error, RMSE=0.046). The proposed algorithm is being successfully used for operational retrieval of Daily and 15-Day composite LSA on Indian Space Research Organisation’s MOSDAC (Meteorological and  Oceanographic Data Archival Centre) and India Meteorology Department’s IMDPS (IMD Processing System) sites.