PREFIRE (Polar Radiant Energy in the Far-InfraRed Experiment)
The Polar Radiant Energy in the Far Infrared Experiment (PREFIRE) will fly a pair of 6U CubeSat satellites to probe a little-studied portion of energy emitted by Earth for clues about Arctic warming, sea ice loss, and ice-sheet melting. The mission is a collaboration between the National Aeronautics and Space Administration Jet Propulsion Laboratory (NASA/JPL) and the University of Wisconsin-Madison Space Science Engineering Centre (UW SSEC) and is due to be launched in 2023.
|Launch date||August 2023|
|Measurement category||Radiation budget|
|Instrument type||Hyperspectral imagers|
|CEOS EO Handbook||See PREFIRE (Polar Radiant Energy in the Far-InfraRed Experiment) summary|
Each of the two PREFIRE satellites will carry one Thermal InfraRed Spectrometer (TIRS), a pushbroom spectroradiometric imager that measures mid and far-infrared radiation. TIRS will provide measurements of spectral fluxes, column-water vapour, surface emissivity and broadband radiances over the majority of thermal wavelengths. The measurements from TIRS will be integrated into current models to enable further understanding of Arctic thermal radiation which is key to understanding the rate of climate change.
TIRS will measure in the mid and Far InfraRed (FIR) wavelengths between 4 µm and 53 µm over 64 channels with a channel width of 0.86 µm. It will have a maximum swath width of 300 km and will have a resolution of 10 m over a 10 - 15 km sampling area. TIRS will have measurement noise less than 0.33 K for a 300 K unit emissivity scene, in each channel between 6 and 11 microns, and scene measurement noise less than 1.1 K for a 300 K unit emissivity scene, in each channel between 12 and 24 microns.
The PREFIRE satellites will be in a sun-synchronous orbit with a period of 95 minutes and an orbital inclination of 98°.
Space and Hardware Components
The PREFIRE satellites are under development by NASA JPL and UW SSEC. They will be identical small 6U CubeSats with dimensions of approximately 300 mm x 200 mm x 100mm. In order to meet the mass, power and cost constraints imposed by a CubeSat platform, an uncooled focal plane is required by TIRS which is thermally isolated from the spacecraft and regulated through controlled dissipation of its steady-state power.
The Polar Radiant Energy in the Far Infrared Experiment (PREFIRE) will fly a pair of small CubeSat satellites to probe a little-studied portion of energy emitted by Earth for clues about Arctic warming, sea ice loss, and ice-sheet melting. PREFIRE will fly miniaturised thermal infrared spectrometers on two 6U CubeSat platforms. The sensors are based on technology previously flown on the Mars Climate sounder. PREFIRE satellites will orbit Earth’s poles to measure far-infrared emissions and how they change throughout the day and over the seasons.
The observations will allow scientists to assess how changes in the thermal infrared emission at the top of Earth’s atmosphere are related to changes in cloud cover and surface conditions below, such as the amount of sea ice and meltwater on the surface of the ice.
PREFIRE measures variations in Far-Infrared (FIR) emissivity and the greenhouse effect via thermal radiometric sampling at the top of the polar atmosphere. These measurements are integrated with models to understand the role of FIR radiation in the Arctic climate. The Arctic is the Earth’s thermostat and it regulates the climate by venting excess energy received within the tropics. Therefore, it is important to study the Arctic thermal radiation. Nearly 60% of Arctic emission occurs at wavelengths greater than 15 μm that have never been systematically measured. PREFIRE fills this gap in measurements and improves climate prediction by anchoring spectral far-infrared emission and atmospheric greenhouse effects.
The baseline mission consists of two 6U CubeSat spacecraft in two different 470-650 km altitude, near-polar (82°-98° inclination) orbits, each with a heritage miniaturised IR spectrometer, covering the 0-54 µm region at 0.84 µm spectral resolution, operating for one seasonal cycle (a year) with diurnal subsampling.
The threshold mission would consist of one 6U CubeSat spacecraft (470-650 km altitude) in near-polar orbit (82° - 98° inclination), operating for a half seasonal cycle (6 months).
The PREFIRE satellites are due to be launched in August 2023.
Orbit: The two 6U cubesats will be in distinct 470-650 km, near-polar orbits with an orbital inclination of 82°-98°.
- Early 2018: PREFIRE was one of two selections made in the fourth NASA Earth Venture Instrument (EVI-4) opportunity which will, for the first time, measure the variability in spectral fluxes from 5-45 microns on hourly to seasonal timescales and will reveal fluctuations in Earth’s thermostat by capturing the full spectrum of Arctic radiant energy. The other selected mission, EMIT, to be hosted on the ISS, will map the surface mineralogy of arid dust source regions via imaging spectroscopy in the visible and short-wave infrared (VSWIR). The mission is cost-capped with a budget of $US 32.78 M.
- Early 2018: The University of Wisconsin (UW) Department of Atmospheric and Oceanic Sciences and Space Science and Engineering Centre (SSEC) collaborates with NASA to take the lead on the PREFIRE mission with Tristan L’Ecuyer as the Principal Investigator.
- 16 June 2020: The official PREFIRE mission website, hosted by UW SSEC, was launched.
- January 2023: The PREFIRE satellites are due to be launched in August 2023.
TIRS (Thermal IR Spectrometer)
Each PREFIRE CubeSat will carry its own Thermal InfraRed Spectrometer (TIRS), a pushbroom spectrometer with 64 channels that measure mid and far-infrared radiation from 5 to 54 µm at 0.86 µm resolution. The dimensions and a rough schematic of the TIRS are shown in Figure 2. TIRS continuously records eight cross-track pixels with a ground spacing of approximately 7 km. In order to meet the mass, power and cost constraints imposed by a CubeSat platform, an uncooled focal plane is required. TIRS is thermally isolated from the spacecraft and regulated through controlled dissipation of its steady-state power. It is calibrated by rotating a calibration mirror to provide space and internal calibration views, eight or more times per orbit. The intentional calibration includes a radiometric measure of all light using the zeroth-order reflection off the grating. TIRS will provide measurements of spectral fluxes, column-water vapour, surface emissivity and broadband radiances over the majority of thermal wavelengths.
The expected radiometric performance of TIRS is better than 1.5 K (at 300K) for all individual MIR and FIR channels from 5 to 54 µm.
Performing the required accurate and sensitive radiometric measurements across infrared and far-infrared wavelengths in a miniaturised satellite is achieved with the help of JPL MDL’s Focal Plane Module (FPM). The FPM will use a thermophile detector array designed and fabricated at MDL with a pixel and format size customised for PREFIRE. The array operates uncooled, which is critical to fitting it in a small CubeSat. The thermopile chip has “gold black” deposited on the pixels to make the pixels sensitive to infrared and far-infrared light. The FPM will utilise custom readout integrated circuits built by Black Forest Engineering that show no measurable low frequency noise enabling the entire FPM to observe the Earth over long integration times to enhance the signal-to-noise ratio of the instrument. 4)
64 x 8 pixels
0.84 µm from 0-54 µm
8 cross-track pixels with 1.3º footprints
10 m resolution over a 10-15 km sampling range
Nadir pushbroom scanning, perpendicular to orbit track with maximums swath of 300 km.
Measurement noise less than 0.33 K for a 300 K unit emissivity scene in each channel between 6 and 11 microns.
Measurement noise less than 1.1 K for a 300K unit emissivity scene, in each channel between 12 and 24 microns.
1) PREFIRE, https://prefire.ssec.wisc.edu. Accessed 16 January 2023.
2) Kahn, Brian H., et al. “Assessment of Sampling Sufficiency for Low-Cost Satellite Missions: Application to PREFIRE.” Journal of Atmospheric and Oceanic Technology, vol. 37, no. 12, 2020, pp. 2283-2298. https://journals.ametsoc.org/view/journals/atot/37/12/jtech-d-20-0023.1.xml. Accessed 16 01 2023.
3) L'Ecuyer, Tristan S., et al. “The Polar Radiant Energy in the Far Infrared Experiment: A New Perspective on Polar Longwave energy Exchanges.” Bulletin of the American Meteorological Society, vol. 102, no. 7, 2021, pp. E1431-E1449. https://journals.ametsoc.org/view/journals/bams/102/7/BAMS-D-20-0155.1.xml?tab_body=fulltext-display. Accessed 16 01 2023.
4) Kenyon, Matt. “PREFIRE.” Microdevices Laboratory, https://microdevices.jpl.nasa.gov/capabilities/broadband-thermal-detectors/prefire/. Accessed 16 January 2023.
5) “New NASA Space Sensors to Address Key Earth Science Questions.” NASA, 5 February 2018, https://www.nasa.gov/press-release/new-nasa-space-sensors-to-address-key-earth-science-questions. Accessed 16 January 2023.
6) Drouin, Brian, et al. “JPL Science: PREFIRE (Polar Radiant Energy in the Far-InfraRed Experiment).” JPL Science, https://science.jpl.nasa.gov/projects/prefire/. Accessed 16 January 2023.
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. Comments and corrections to this article are always welcome for further updates (email@example.com).