Polar Radiant Energy in the Far InfraRed Experiment (PREFIRE) Surface Emissivity from PREFIRE Satellite 2 COG19um R01

Polar Radiant Energy in the Far InfraRed Experiment (PREFIRE) Surface Emissivity from PREFIRE Satellite 2 COG19um (PREFIRE_SAT2_2B-SFC_COG19um) is derived from data collected by the PREFIRE Thermal Infrared Spectrometer (TIRS-PREFIRE) aboard PREFIRE-SAT2. Dual CubeSats each carry a PREFIRE Thermal Infrared Spectrometer (TIRS-PREFIRE), a push broom spectrometer with 63 channels measuring mid- and far-infrared (FIR) radiation from approximately 5 to 53 µm. Most polar emissions are in the FIR but have not been measured on a large scale. PREFIRE aims to fill knowledge gaps in the global energy budget by more accurately characterizing polar emissions. This information will then be assimilated into global circulation and other models to predict future conditions more accurately. PREFIRE_SAT2_2B-SFC_COG19um contains Cloud-Optimized GeoTIFF (COG) files that each contain a georeferenced rendering of retrieved surface emissivity values for channel 21 (centered at about 18.6 µm). Those surface emissivity data values are computed from a single granule of PREFIRE Spectral Radiance (PREFIRE_SAT2_1B-RAD) data using an Optimal Estimation retrieval via a radiative transfer model with inputs from PREFIRE_SAT2_2B-MSK (cloud mask), and PREFIRE_SAT2_AUX-MET. The retrieved surface emissivity values are only available for clear-sky conditions. As part of the rendering process, mean retrieved surface emissivity values are computed for a global grid of raster elements (each approximately 2.23 km in width), based on which raster elements each PREFIRE ground footprint overlaps. This procedure is done in order to better visualize the PREFIRE data despite substantial overlap of adjacent along-track ground footprints – but it is important to remember that the individual PREFIRE ground footprints are much bigger (by about 80x, in terms of area) than each of the GeoTIFF raster elements. These cloud-optimized GeoTIFF images may be viewed using many geographic information systems (GIS), such as the freely available QGIS. Science data retrieval started June 29, 2024 and is ongoing. Currently, the geographic coverage is for latitudes between approximately 60° to 84° in both polar regions, although future releases may include data for all latitudes equatorward of about 84°. Within the orbital swath there are eight distinct tracks of data associated with the eight separate spatial scenes for each TIRS-PREFIRE. At the beginning of the mission, the approximate scene footprint sizes were 11.8 km x 34.8 km (cross-track x along-track), with gaps between each scene of approximately 24.2 km. The entire swath was about 264 km across. Note that the scene footprint and swath sizes quoted here are for the orbit altitude soon after launch. However, the footprint and swath sizes will slowly become smaller as the orbit altitude decreases with time. Similar surface emissivity GeoTIFF renderings for the sister instrument aboard PREFIRE-SAT1 can be found in the PREFIRE_SAT1_2B-SFC_COG19um collection.

Tags: earth-science-atmospheric-radiation-atmosphere-earth-radiation-budget, earth-science-atmospheric-radiation-atmosphere-longwave-radiation-upwelling-longwave-radiation, earth-science-surface-radiative-properties-land-surface-emissivity
Organization: National Aeronautics and Space Administration