NPP VIIRS Land Surface Temperature EDR validation using NOAA's observation networks

NOAA will soon use the new Visible Infrared Imager Radiometer Suite (VIIRS) on the Joint Polar Satellite System (JPSS) as its primary polar-orbiting satellite imager. Employing a near real-time processing system, NOAA will generate a series of Environmental Data Records (EDRs) from VIIRS data. For example, the VIIRS Land Surface Temperature (LST) EDR will estimate the surface skin temperature over all global land areas and provide key information for monitoring Earth surface energy and water fluxes. Because both VIIRS and its processing algorithms are new, NOAA is conducting a rigorous calibration and validation program to understand and improve product quality. This work presents a new validation methodology to estimate the quantitative uncertainty in the LST EDR, and contribute to improving the retrieval algorithm. It employs a physically-based approach to scaling up point LST measurements currently made operationally at many field and weather stations around the world. The scaling method consists of the merging information collected at different spatial resolutions within a land surface model to fully characterize large area (km x km scale) satellite products. The approach can be used to explore scaling issues over terrestrial surfaces spanning a large range of climate regimes and land cover types, including forests and mixed vegetated areas. First results show that VIIRS and MODIS (collection 5) LST products are very consistent. Over vegetated areas, VIIRS LST EDRs verify JPSS program quality requirements - bias and precision specifications of VIIRS LST EDRs are 1.5K and 2.5K. However, VIIRS agrees better with scaled-up field data than with non-scaled field observations. Over desert areas, current VIIRS LST EDRs do not verify JPSS specifications. VIIRS and MODIS LST products tend to underestimate surface temperature at night. Ultimately, this validation approach should lead to an accurate and continuously-assessed VIIRS LST products suitable to support weather forecast, hydrological applications, or climate studies. It is readily adaptable to other moderate resolution satellite systems.