Developing NASA’s VIIRS LST and Emissivity EDRs using a physics based Temperature Emissivity Separation (TES) algorithm

Abstract:

Land Surface Temperature and Emissivity (LST&E) data are acknowledged as critical Environmental Data Records (EDRs) by the NASA Earth Science Division. The current operational LST EDR for the recently launched Suomi National Polar-orbiting Partnership’s (NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) payload utilizes a split-window algorithm that relies on previously-generated fixed emissivity dependent coefficients and does not produce a dynamically varying and multi-spectral land surface emissivity product. Furthermore, this algorithm deviates from its MODIS counterpart (MOD11) resulting in a discontinuity in the MODIS/VIIRS LST time series.

This study presents an alternative physics based algorithm for generation of the NASA VIIRS LST&E EDR in order to provide continuity with its MODIS counterpart algorithm (MOD21). The algorithm, known as temperature emissivity separation (TES) algorithm, uses a fast radiative transfer model - Radiative Transfer for (A)TOVS (RTTOV) in combination with an emissivity calibration model to isolate the surface radiance contribution retrieving temperature and emissivity. Further, a new water-vapor scaling (WVS) method is developed and implemented to improve the atmospheric correction process within the TES system. An independent assessment of the VIIRS LST&E outputs is performed against in situ LST measurements and laboratory measured emissivity spectra samples over dedicated validation sites in the Southwest USA. Emissivity retrievals are also validated with the latest ASTER Global Emissivity Database Version 4 (GEDv4). An overview and current status of the algorithm as well as the validation results will be discussed.