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ESA’s 9th Earth Explorer, the Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission aims to record the emission spectrum of the Earth’s atmosphere in the spectral range of 100 cm-1 to 1600 cm-1 (between 6.25 μm and 100 μm). The payload is composed of the FORUM Sounding Instrument (FSI), a Fourier Transform Spectrometer scanning the Earth atmosphere in a step-and-stare acquisition mode, sounding a 15 km diameter Field Of View (FOV) with a ground sampling distance of 100 km and providing a spectral resolution of 0.5 cm-1. Additionally, a thermal infrared imager called FORUM Embedded Imager (FEI) is co-located with the footprint of FSI providing a FOV of 36 km x 36 km, covering a spectral band centered at 10.5 μm with a bandwidth of 1.5 μm. While previous satellite missions provide observations of either the total integrated outgoing longwave radiation, or the outgoing spectrum across the mid-infrared, none provides the spectral detail necessary to test the understanding of key physical processes in the energetically significant far-infrared. FORUM will provide these observations for the first time. Theory predicts that such measurements are key for understanding exactly how Earth currently cools to space, and, critically, how it responds to both natural and anthropogenic change. Therefore, the overarching science objective of the FORUM mission is the evaluation of the role of the far-infrared in shaping the current climate and thus reducing uncertainty in predictions of future climate change. Key to FORUM science objectives is the capability to provide a highly accurate (0.1 K at 3σ) global dataset of FIR radiances, traceable to SI in orbit, to validate present-day climate in climate models and to validate Numerical Weather Prediction models. The authors will develop a blackbody source to provide in-flight radiometric calibrations throughout the FORUM mission lifetime. The blackbody is based on an emissive plate and a baffle, both black-coated to provide the specified emissivity performance. The emissive plate is highly decoupled to minimize thermal gradients and is based on a concentric V-groove geometry with integrated high accuracy Platinum Resistance Thermometers (PRTs). Traceability to SI for the T will be established on ground and kept in orbit during the mission life-time by allocating appropriate budgets for performance degradation in-flight during mission lifetime, relying in on-ground calibration and in line with the required radiometric accuracy for the FORUM mission.
Topic : Theme 1: Earth Energy Balance.
Reference : T1-C17
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