For more than a decade, the remote sensing community has called for longwave spectral measurements of the Earth system to facilitate closing the radiation budget. In an effort to address this large gap in Earth-observing capability, NASA has supported the development and implementation of the Polar Radiant Energy in the Far-Infrared (FIR) Experiment (PREFIRE), which realizes two miniaturized thermal IR spectrometers (TIRSs), one on each of two polar orbiting small satellites with different ascending node crossing times. The spectral radiances measured by the TIRS instruments are utilized to extract cloud presence, atmospheric state, surface properties, and the associated top-of-atmosphere (TOA) spectral fluxes at both poles. This article describes the major system and algorithm components and introduces the geophysical products. PREFIRE data will be used to inform and improve ice-sheet and coupled-Earth system models to better predict the future state of the Earth’s poles.

Small-scale glaciological processes can drive large-scale ice sheet behavior but remain underreported due to a paucity of surface elevation measurements in remote polar regions. Satellite images provide a relatively long record of spatially dense surface observations, which allow us to investigate changes in ice sheet topography on the spatial scales of 1-10 km. Inferring surface topography from satellite images is an established technique, but in previous efforts, strict requirements for illumination conditions and image quality have led to a great quantity of discarded data. Relaxing quality requirements and fitting linear trends to the time series of image-derived surface topography allow inclusion of more total signal and enable blending data from multiple platforms. As a proof of concept, we combine 121 MODerate-resolution Imaging Spectroradiometer images to develop a 250-m resolution map of surface elevation change at Totten Glacier, Antarctica achieving a 1-σ uncertainty of 0.22 m a-1for a 15-year period. Our method of repeat photoclinometry agrees with repeat laser altimetry while revealing clear patterns of surface elevation change associated with ice advection, channelized ice shelf basal melt, subglacial lake activity, and possible grounding line migration.