Abstract:Far-infrared radiation (that occurring at wavelengths longer than 15 microns) constitutes half of Earth’s emission. However, while far-infrared spectra have been collected from every planet in the solar system, Earth’s far-infrared emission spectrum has not been systematically documented. Filling this gap could offer powerful new insights into the key processes at work in the rapidly changing polar regions as well as shedding light on variations in temperature, humidity, and thin cirrus clouds in the cold, dry, upper troposphere at lower latitudes. In an effort to fill this observing gap, NASA’s Polar Radiant Energy in the Far Infrared Experiment (PREFIRE) mission, consisting of two CubeSats that launched in summer 2024, is now mapping Earth’s emission spectra from 5 to 53 m with 0.84 m sampling. The near-complete spectra from PREFIRE’s Thermal InfraRed Spectrometers (TIRS) provide the first far-infrared measurements of Earth since early experimental missions in the 1970’s and 80’s.
This presentation will introduce the PREFIRE mission and provide a first look at data acquired during the first six months in orbit. When processed using modern remote sensing techniques, PREFIRE’s spectra are providing the insights into spectral surface emissivity, water vapor, cloud properties, and the atmospheric greenhouse effect needed to advance models of thermal fluxes in the cold, dry conditions characteristic of the polar regions and upper atmosphere. For example, preliminary results suggest significant differences in the far infrared emissivities of common polar surfaces that are not represented in current models. However, potential applications of PREFIRE measurements extend far beyond the polar regions. Strong absorption from the water vapor rotation band at far-infrared wavelengths provides temperature and humidity profile information in clear skies. As a result, assimilating far-infrared radiances from the unique 3:45 am/pm and 8 am/pm PREFIRE overpass times may fill temporal gaps in information gleaned from current operational sounders that sample at different times of day. Progress toward adapting an observational operator to simulate TIRS spectral responses that could be used to explore this PREFIRE application to numerical weather prediction will be discussed.
