The Polar Radiant Energy in the Far Infrared Experiment: A New Perspective on Polar Longwave Energy Exchanges

Abstract

The Earth’s climate is strongly influenced by energy deficits at the poles that emit more thermal energy than they receive from the sun. Energy exchanges between the surface and atmosphere influence the local environment while heat transport from lower latitudes drives midlatitude atmospheric and oceanic circulations. In the Arctic, in particular, local energy imbalances induce strong seasonality in surface-atmosphere heat exchanges and an acute sensitivity to forced climate variations. Despite these important local and global influences, the largest contributions to the polar atmospheric and surface energy budgets have not been fully characterized. The spectral variation of far-infrared radiation that makes up 60% of polar thermal emission has never been systematically measured impeding progress toward consensus in predicted rates of Arctic warming, sea ice decline, and ice sheet melt.Enabled by recent advances in sensor miniaturization and CubeSat technology, the Polar Radiant Energy in the Far InfraRed Experiment (PREFIRE) mission will document, for the first time, the spectral, spatial, and temporal variations of polar far-infrared emission. Selected under NASA’s Earth Ventures Instrument (EVI) program, PREFIRE will utilize new light weight, low-power, ambient temperature detectors capable of measuring at wavelengths up to 50 micrometers to quantify Earth’s far-infrared spectrum. Estimates of spectral surface emissivity, water vapor, cloud properties, and the atmospheric greenhouse effect derived from these measurements offer the potential to advance our understanding of the factors that modulate thermal fluxes in the cold, dry conditions characteristic of the polar regions.

Retrieval of Surface Spectral Emissivity in Polar Regions Based on the Optimal Estimation Method

“…The PREFIRE mission, scheduled to launch no earlier than December 2022, will employ two CubeSats to operate in near‐polar orbits (82°–98° inclination) and collect observations of polar spectral emission in both mid‐IR and far‐IR on hourly to seasonal timescales (L’Ecuyer et al., 2021). Each spacecraft will carry a Thermal InfraRed Spectrometer (TIRS), a grating spectrometer with 64 channels covering 0–54 μm at a spectral resolution of 0.84 μm and a field of view comparable to AIRS (L’Ecuyer et al., 2021). TIRS will record spectral radiances over eight cross‐track pixels, all within near nadir view.…”

“…These two studies were restricted to observations in March 2015 over a limited region in the Greenland Plateau. The PREFIRE mission, on the other hand, aims to measure in both mid‐IR and far‐IR (5–45 μm, with a resolution of 0.84 μm) over polar regions at hourly to seasonal scales for the first time (L’Ecuyer et al., 2021). PREFIRE will provide an unprecedented opportunity in this decade for retrievals of far‐IR surface emissivity in the polar regions.…”

“…(2018) further evaluated surface emissivity feedback in response to the doubling of CO 2 and concluded that such surface emissivity feedback is smaller than the surface albedo feedback by at least 1 order of magnitude. These studies have directly motivated observational efforts to measure and monitor far‐IR surface spectral emissivity, especially in the polar regions, which then encouraged the selections of two satellite missions dedicated to far‐IR observations, that is, PREFIRE (Polar Radiant Energy in the Far InfraRed Experiment; L’Ecuyer et al., 2021) by NASA and FORUM (Far‐infrared Outgoing Radiation Understanding and Monitoring; Palchetti et al., 2020) by ESA.…”

Synergistic Use of Far‐ and Mid‐Infrared Spectral Radiances for Satellite‐Based Detection of Polar Ice Clouds Over Ocean

“…The far‐IR has been historically underutilized for spaceborne remote sensing due to technological limitations. However, two upcoming missions will measure the far‐IR radiances, namely the Polar Radiant Energy in the Far Infrared Experiment (PREFIRE; L’Ecuyer et al., 2021) and the Far‐infrared‐Outgoing‐Radiation Understanding and Monitoring (FORUM) missions (Palchetti et al., 2020). The planned spectral range for the sensors used in these missions is 5–54 μm for PREFIRE and 100–1,600 cm −1 for FORUM, respectively.…”

Retrieval of Tropospheric Water Vapor From Airborne Far‐Infrared Measurements: A Case Study

“…Despite constituting a large percentage of the Earth's OLR, there are currently no space‐based instruments capable of measuring spectrally resolved radiances across the far‐ir However, two upcoming satellite missions, the European Space Agency (ESA) Far‐infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission (Palchetti et al., 2020) and the NASA Polar Radiant Energy in the Far Infrared Experiment (PREFIRE) mission (L’Ecuyer et al., 2021) aim to fill this gap.…”