Capturing rapid land surface dynamics with Collection V006 MODIS BRDF/NBAR/Albedo (MCD43) products

Abstract

MODIS BRDF/NBAR/Albedo products (MCD43) have been widely used for a variety of land surface studies since 2000 (e.g., for climate and biosphere modeling, radiative forcing, phenology, and classification schemes). In the past, limitations in computing and archive capacity had restricted the MCD43 retrievals to only once every eight days. The latest reprocessing of the entire archive of Terra and Aqua MODIS BRDF/NBAR/Albedo products (Collection V006) provide retrievals each day and therefore represent a major improvement for phenological and surface monitoring efforts. Compared to the previous retrieval which occurred every 8-days based on a 16-day retrieval period for Collection V005 MODIS BRDF/NBAR/Albedo, this study demonstrates that the Collection V006 MODIS BRDF/NBAR/Albedo product retrieved every day captures significantly more seasonal vegetation dynamics and rapid land surface changes. The Collection V006 product still utilizes the 16-days of directional reflectances surrounding the day of interest (9th day) to retrieve the model of the surface anisotropy but assigns the highest temporal weight to the day of interest (the center date of the retrieval period). Furthermore, the Collection V006 retrievals utilize the day of interest snow/snow-free status to capture snow albedo (an improvement over the previous Collection V005 strategy which based the retrieval on the predominant snow/snow-free status of the majority of the observations over the 16-day retrieval period). All valid clear sky observations from Terra and Aqua are now used for each retrieval, which improves the inversion quality. This is especially true at high latitudes, where up to nine observations from each sensor can be observed per day. Thus, although the high quality full inversion Collection V006 albedo retrieval values are consistent with the Collection V005 results, the overall number of high quality results retrieved has increased. Furthermore, the accuracy of the poorer quality magnitude inversions (which rely on a back-up algorithm) has improved due to utilization of the latest high quality full inversion retrievals as pixel-specific a priori knowledge. The ability of the latest Collection V006 MODIS BRDF/NBAR/Albedo products to capture land surface dynamics is evaluated by using a globally-distributed record of spatially representative tower measurements. The RMSE of broadband shortwave blue-sky albedo at these sites is <0.0318 and the bias is within ±0.0076 for all quality results.