Spectral testing of the Landsat-9 OLI-2 instrument using the Goddard Laser Absolute Measurement of Radiance (GLAMR)

The Landsat-9 Operational Land Imager 2 (OLI-2) instrument, currently under development for launch in late 2020, is a clone of the Landsat-8 OLI instrument, which was launched in 2013. Ball Aerospace built and rigorously characterized the Landsat-8 OLI and is repeating the process for the Landsat-9 OLI-2. A major difference between the testing for OLI and OLI-2 will be spectral test equipment. The instrument-level spectral test for OLI made use of a double monochromator; the OLI-2 test will use of Goddard Laser for the Absolute Measurement of Radiance (GLAMR). The GLAMR system is a set of lasers, which collectively cover the entire spectral range of the OLI-2 spectral bands. The laser outputs are fed to a 30” integrating sphere via fiber optic cables, which OLI-2 can view from its position inside the thermal vacuum chamber. The laser-based spectral characterization offers several major advantages over the monochromator-based methods: (1) higher signal levels as compared to the lamp in the double monochromator providing better signal to noise and capabilities to measure out of band response, (2) full aperture illumination and flood illumination of multiple focal plane modules so that all detectors are tested and crosstalk effects can be observed, as opposed to the approximately 60 detectors illuminated by the slit image of the monochromator (3) an absolute spectral response characterization as opposed to relative spectral response. OLI-2 spectral testing with GLAMR should begin in late 2018. This work describes the spectral-radiometric test plan, test requirements, and GLAMR performance demonstrated prior to OLI-2 characterization.