Abstract
We report on the ground and on-orbit radiometric calibration of the SWIR sensors on the Rogue Alpha/Beta CubeSats. Also known as AeroCube 15 A and B, this rapid prototype constellation comprised of two 30x10x10-cm CubeSats flying commercially available InGaAs cameras, was boosted into low Earth orbit on 14 January 2020. The sensor optics are outfitted with a narrowband filter centered within the atmospheric H2O overtone absorption band near 1.4 microns. Pre-flight calibration activities in the lab at the Aerospace Corporation included characterization of sensor linearity and pixel-to-pixel uniformity through the filtered optical system, and radiometric response was derived using measurements of Lambertian scattering surfaces illuminated by incandescent sources. In-flight radiometric calibration of both the SWIR sensors and visible-wavelength context cameras were performed via observations of stars Betelgeuse, Antares, Sirius, and Vega; these stars are frequently observed by our Astronomy Field Observations team at Aerospace and their modeled spectral energy distributions are utilized for radiometric calibration of various visible and infrared sensors. A dithered pointing strategy was used for imaging, enabling timely subtraction of the dark signal. The SWIR radiometric responses derived from each star are in excellent agreement with each other, and also with the pre-flight lab radiometry. We discuss our methodology, results, application to a sample Earth image, and lessons learned for future programs.
Radiometric Calibration of Aerocube 15 (Rogue-Alpha/Beta)
We report on the ground and on-orbit radiometric calibration of the SWIR sensors on the Rogue Alpha/Beta CubeSats. Also known as AeroCube 15 A and B, this rapid prototype constellation comprised of two 30x10x10-cm CubeSats flying commercially available InGaAs cameras, was boosted into low Earth orbit on 14 January 2020. The sensor optics are outfitted with a narrowband filter centered within the atmospheric H2O overtone absorption band near 1.4 microns. Pre-flight calibration activities in the lab at the Aerospace Corporation included characterization of sensor linearity and pixel-to-pixel uniformity through the filtered optical system, and radiometric response was derived using measurements of Lambertian scattering surfaces illuminated by incandescent sources. In-flight radiometric calibration of both the SWIR sensors and visible-wavelength context cameras were performed via observations of stars Betelgeuse, Antares, Sirius, and Vega; these stars are frequently observed by our Astronomy Field Observations team at Aerospace and their modeled spectral energy distributions are utilized for radiometric calibration of various visible and infrared sensors. A dithered pointing strategy was used for imaging, enabling timely subtraction of the dark signal. The SWIR radiometric responses derived from each star are in excellent agreement with each other, and also with the pre-flight lab radiometry. We discuss our methodology, results, application to a sample Earth image, and lessons learned for future programs.