The CLARREO Absolute Radiance Interferometer (ARI) to Provide a New On-orbit IR Transfer Standard for Operations and Climate Benchmarking

The accuracy of operational satellite systems and their utility for decadal climate trending can be greatly enhanced by implementing on-orbit transfer standards. This concept of establishing on-orbit standards is an important part of the Climate Absolute Radiance and Reflectivity Observatory (CLARREO) mission, originally recommended as a Tier 1 mission in the 2007 Decadal Survey.

The Absolute Radiance Interferometer (ARI) was designed to measure absolute spectrally resolved infrared radiance (200 - 2700 cm^-1 at 0.5 cm^-1) with ultra-high accuracy (<0.1 K, k = 3 brightness temperature). A key feature of the ARI instrument is the On-orbit Verification and Test System (OVTS), which provides end-to-end calibration verification of the ARI measurements with direct on-orbit traceability to international standards (SI). The SI standard On-orbit Absolute Radiance Standard (OARS) is a high emissivity cavity blackbody with fundamental temperature scale established by three miniature phase change cells and emissivity measured on-orbit using a "heated halo" source. The ARI instrument has demonstrated the required radiometric accuracy and has achieved NASA Technology Readiness Level 6.

The International Space Station (ISS) would provide an affordable opportunity to demonstrate this new capability. The ISS orbit gives good time of day coverage for latitudes below 52 degrees, and the natural precession of the ISS offers many orbit crossings for radiance intercomparisons with operational satellites in sun-synchronous orbits (CrIS at 1330 from JPSS, IASI at 0930 from Metop-B and Metop-C, and HIRAS at 0530 from China's FY3E). Thus, the ARI could serve as an on-orbit reference calibration standard for the operational infrared sounders, and these sounders could in turn be used to create climate benchmark products at all latitudes. In this approach, an ARI mission on the ISS would leverage operational instruments to provide a demonstration of the new climate decadal trending capability offered by spectrally resolved radiances with high accuracy proven on-orbit.