Characterizing Spectral Response in Thermal Environments, the HYPSO-1 Hyperspectral Imager

Abstract

The ocean color mission, HYPerspectral Smallsat for ocean Observation (HYPSO-1), required an instrument built with spectral measurement capability. Anticipated spectral signatures needed to provide sufficient detail of the target ocean surface within a defined spectral range (visible, near-infrared). The resulting instrument for this mission is a custom-built hyperspectral imager composed of both machined parts and Commercial Off-The-Shelf (COTS) components. Many of the COTS components lacked details on material composition, re-quiring additional testing and assumptions about their thermal properties. The imager was characterized through spectral and radiometric calibration, analyzed for stray light, and sized to fit a 6U CubeSat bus. However, issues with spectral response stabil-ity were noted during thermal-vacuum testing of the integrated satellite. In this paper we characterize the thermally-influenced spectral response of the imager using a thermal chamber and fluorescent lamp setup. Through a comparison of response spectra, we measure bandwidth, calculated as Full Width at Half Maximum (FWHM) of the spectral lines, at temperatures ranging from − 20 to 50 degrees Celsius - the expected in-orbit operational range inside the CubeSat. It is apparent that bandwidth changes with rising imager temperature and peak spectral response shifts by a few nanometers depending on wavelength. This needed to be accounted for prior to launch as it will influence the results of planned ocean color analyses. In small satellites, passive thermal control systems can be con-strained by limited physical space and efficiency; active solutions often suffer from limited power budgets on-board. Al-though the chosen passive thermal control solution for HYPSO-1 will remain in place, this characterization procedure can be used to aid in thermally calibrating data received from the satellite throughout the mission.