Pre-Launch Calibration of the HYPSO-1 Cubesat Hyperspectral Imager

This paper describes the pre-launch optical calibration and characterization of the hyperspectral imager for the HYPerspectral Smallsat for ocean Observation (HYPSO-1) cubesat. The aim of the mission is to observe algal blooms and other ocean color phenomena from a cubesat platform using a pushbroom HyperSpectral Imager (HSI) design based on Commercial Off-The-Shelf (COTS) components. A thorough prelaunch characterization is necessary to study the expected quality of the hyperspectral data, and to identify any potential deficiencies and weaknesses in the design. The calibration work was focused on spectral and radiometric calibration, characterizing smile and keystone, and measuring the polarization sensitivity. Smile and keystone effects were noticeable during preliminary tests, and were therefore characterized to provide necessary corrections. From spectral calibration data the average bandwidth was found to be 3.93 nm, which is close to the theoretical value of 3.3 nm. The full spectral range of the instrument was found to be 224 to 962 nm. The radiometric calibration data was also used to characterize the sensor performance, which was shown to be as expected. Smile was measured to be 3.58 pixels and 0.38 pixels before and after correction, respectively, while keystone was found to be 1.72 pixels before correction and 0.56 pixels after correction. The polarization sensitivity was within the required value of 5% for wavelengths above 410 nm. Finally, a spatial focus test was performed indicating best spatial focus at the center wavelength of 600 nm. Future work for the HYPSO-1 mission includes developing methods for in-orbit calibration, and for future HYPSO missions a more thorough characterization and correction for varying temperature is suggested.