Black Array of Broadband Absolute Radiometers for Imaging Earth Radiation

We propose to develop and demonstrate a novel instrument utilizing a linear array of electrical substitution microbolometers for imaging outgoing Earth radiation with low uncertainty. Our instrument will measure in several broad bands spanning the electromagnetic spectrum from 0.2 µm to 100 µm with a 1 km spatial footprint from a low Earth orbit vantage point. Accurate measurements of outgoing broadband radiation are critical for understanding Earth's climate. Our focus on beginning with an instrument of reduced volume, mass, and power, while enhancing spatial resolution and providing high accuracy supports key measurement objectives for use in the next generation of science missions. These objectives include broadened applicability to small satellite platforms and reduced risk from potential data record gaps. Our instrument, the Black Array of Broadband Absolute Radiometers (BABAR) Earth Radiation Imager (BABAR-ERI), capitalizes on linear detector array technology in development under an Advanced Component Technology (ACT) award (#ACT-17-0025). BABAR is an uncooled microbolometer electrical-substitution radiometer array with Vertically Aligned Carbon Nanotubes (VACNT) as the optical absorber. Electrical-substitution radiometers are used extensively in precision radiometry, but have never been used for imaging despite their many advantages. Relative to traditional microbolometer arrays, the BABAR detector allows for faster response, higher linearity, higher accuracy, and higher long-term stability. This is achieved by using closed-loop electrical substitution techniques in conjunction with electrical substitution radiometry. The VACNTs provide spectrally flat absorptance greater than 99.8% over the range from 0.2 µm to 100 µm. The combination of electrical substitution and broadband VACNT absorption provides a path to a compact, high resolution, and high accuracy instrument because on-board calibration hardware is not required. Absolute radiometry will be verified against the Planar Bolometric Radiometer for Irradiance (PBR-I) reference standard. These properties make BABAR-ERI ideal for space-based Earth energy budget and remote sensing applications. In order to accommodate the broad wavelength range desired for energy budget applications, an all-reflective imaging system will be implemented. A key aspect of this IIP will be generating a compact design which can fit onto a 6U CubeSat bus. This will enable a future, straightforward on-orbit demonstration as well as facilitate potential future deployment of multiple BABAR-ERI instruments on a constellation of small spacecraft. The proposing team has a long history of instrument development and deployment of radiometers in space-based and suborbital platforms. The proposed sensors draw heritage from: the Compact Solar Spectral Irradiance Monitor (CSIM), developed under a 2013 IIP award, that has been making daily solar irradiance measurements from a 6U CubeSat platform since early 2019; the Compact Total Irradiance Monitor (CTIM), in development for the In-Space Validation of Earth Science Technologies (InVEST) program with a planned launch in 2021; and the BABAR ACT project. The BABAR linear array detector is currently at a Technology Readiness Level (TRL) of 3. We are proposing an exit TRL of 6 at the end of this three-year project. More »