Abstract
Land surface albedo (LSA), one of the Visible Infrared Imaging Radiometer Suite (VIIRS) environmental data records (EDRs), is a fundamental component for linking the land surface and the climate system by regulating shortwave energy exchange between the land and the atmosphere. Currently, the improved bright pixel sub-algorithm (BPSA) is a unique algorithm employed by VIIRS to routinely generate LSA EDR from VIIRS top-of-atmosphere (TOA) observations. As a product validation procedure, LSA EDR reached validated (V1 stage) maturity in December 2014. This study summarizes recent progress in algorithm refinement, and presents comprehensive validation and evaluation results of VIIRS LSA by using extensive field measurements, Moderate Resolution Imaging Spectroradiometer (MODIS) albedo product, and Landsat-retrieved albedo maps. Results indicate that: (1) by testing the updated desert-specific look-up-table (LUT) that uses a stricter standard to select the training data specific for desert aerosol type in our local environment, it is found that the VIIRS LSA retrieval accuracy is improved over a desert surface and the absolute root mean square error (RMSE) is reduced from 0.036 to 0.023, suggesting the potential of the updated desert LUT to the improve the VIIRS LSA product accuracy; (2) LSA retrieval on snow-covered surfaces is more accurate if the newly developed snow-specific LUT (RMSE = 0.082) replaces the generic LUT (RMSE = 0.093) that is employed in the current operational LSA EDR production; (3) VIIRS LSA is also comparable to high-resolution Landsat albedo retrieval (RMSE < 0.04), although Landsat albedo has a slightly higher accuracy, probably owing to higher spatial resolution with less impacts of mixed pixel; (4) VIIRS LSA retrievals agree well with the MODIS albedo product over various land surface types, with overall RMSE of lower than 0.05 and the overall bias as low as 0.025, demonstrating the comparable data quality between VIIRS and the MODIS LSA product.
Highlights
Land surface albedo (LSA), defined as the ratio between solar radiation reflected by Earth’s land surface and solar radiation incident at the surface, is a function of both solar illumination and the reflective properties of land [1]
Intercomparisons are performed among Visible Infrared Imaging Radiometer Suite (VIIRS) LSA, Moderate Resolution Imaging Spectroradiometer (MODIS) albedo product, and albedo retrieved from Landsat Enhanced Thematic Mapper Plus (ETM+) and Operational Land Imager (OLI) data
In this study, considering that the operational LSA environmental data records (EDRs) product experienced several code changes and the data might not be consistent since its publication, the validation results given in Section 3 are based on the LSA data retrieved from our local infrastructure by employing improved bright pixel sub-algorithm (BPSA) on the original moderate resolution bands
Summary
Land surface albedo (LSA), defined as the ratio between solar radiation reflected by Earth’s land surface and solar radiation incident at the surface, is a function of both solar illumination and the reflective properties of land [1]. Preliminary validations were conducted in our earlier works by comparing the VIIRS LSA retrieval with the field albedo measurements over seven SURFRAD sites and with MODIS albedo product [15]. The V1 stage is a critical milestone in the JPSS EDR production; it is defined as “using a limited set of samples, the algorithm output is shown to meet the threshold performance attributes identified in the JPSS level 1 requirements.” It has been over three years since. VIIRS LSA EDR started its operation in 2012, leading to the collection of sufficient data to perform further validation and evaluation of the quality and accuracy of this product. Intercomparisons are performed among VIIRS LSA, MODIS albedo product, and albedo retrieved from Landsat Enhanced Thematic Mapper Plus (ETM+) and Operational Land Imager (OLI) data.
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