The BABAR-ERI Instrument: An Innovative Solution for Imaging Broadband Radiation at High Spatial Resolution

Broadband radiation measurements are essential for detecting climate change signals and attributing them to their underlying sources. Technological advances made to measure the broadband radiation at cloud-resolving, 1-km, spatial resolution and at high radiometric accuracy will increase the information content of the broadband observations relative to current sensors and enhance and accelerate process-level understanding of climate drivers, such as clouds and aerosols.

In this presentation, we will give the instrument development status of the Black Array of Broadband Absolute Radiometers (BABAR) Earth Radiation Imager (ERI) and briefly outline its utility to process-level and Earth radiation budget missions. BABAR-ERI is an absolute radiometer to image high-accuracy broadband radiances at 1-km spatial footprint from a 12U CubeSat form factor supported by the NASA Earth Science Technology Office (ESTO) Instrument Incubator Program (IIP). It is a suite of 3 instruments that is currently at Technology Readiness Level (TRL) 5 and will be at TRL 6 by the end of the IIP program. The primary technology being advanced is the 32-element, ambient temperature, microbolometer linear array detectors with vertically aligned carbon nanotubes (VACNT) as the optical absorber. The BABAR arrays are designed to measure the total (0.2 to 100 μm) and shortwave (0.2 to 4.5 μm) broadband radiation using 32 pixels with 1-km x 1-km spatial resolution from two co-registered telescopes. The longwave broadband radiation (4.5 to 100 μm) will be derived from the subtraction of the shortwave radiation from the total channel. Closed-loop electrical substitution techniques at each detector pixel provide fast and precise radiometry, and eliminate the need for on-orbit radiometric calibration. Absolute radiometry will be verified during ground calibrations using blackbody sources and an absolute detector standard also being developed under the IIP program. The absolute detector standard, the Planar Bolometric Radiometer for Radiance (PBR-R), has heritage from the Compact Total Irradiance Monitor (CTIM) In-Space Validation of Earth Science Technologies (InVEST) program. The BABAR-ERI instrument suite also incorporates two PBR-Rs as on-board calibrators designed to operate at different exposure duty-cycles for tracking on-orbit degradation of the science channels to maintain stability. Finally, BABAR-ERI has a single-channel camera for providing scene context, sub-pixel variability at 100-m resolution, and for ensuring pointing accuracy. The BABAR-ERI has been fabricated and characterization studies and instrument-level vibration and thermal/vacuum testing are underway. BABAR-ERI completion is scheduled for May, 2024.