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.

Surface emissivity (ϵ) plays a critical role in Earth’s radiation budget and climate. The Polar Radiant Energy in the Far-InfraRed Experiment (PREFIRE) and the Far-Infrared Outgoing Radiation Understanding and Monitoring (FORUM) satellite missions aim to estimate surface spectral emissivities in mid-IR and far-IR regions. This study presents a neural network (NN)-based surface spectral emissivity retrieval algorithm under clear-sky that offers comparable performance to optimal-estimation (OE)-based methods but reduces computation time by a factor of 105. The NN-based method has achieved a mean relative retrieval error (|∆ϵ|) of 0.0028 with a standard deviation of 0.0013. Shapley values are employed to interpret the algorithm’s results and assess the relative importance of input features. The results derived from the Shapley values analysis are in good agreement with the physical understanding. The study highlights the effectiveness of the proposed neural network approach for surface emissivity estimation in forthcoming satellite missions.

This letter describes a general solution to the parallax correction issue concerning the collocation of measurements of the same object from different satellites that use different viewing geometries. Two examples in cloud remote sensing are described with case studies. The applicability of the parallax correction is also discussed. Correct collocation of data collected by multiple satellites is needed in order to avoid introducing incorrect information in the data fusion of multiple sensors on different satellite platforms.