Cross-Instrument Comparison of MapCam and OVIRS on OSIRIS-REx

Abstract

Two of the instruments onboard the OSIRIS-REx spacecraft, the MapCam color imager and the OVIRS visible and infrared spectrometer, observed the surface of asteroid (101955) Bennu in partially overlapping wavelengths. Significant scientific advances have been enabled by using data from these two instruments in tandem, but a robust statistical understanding of their relationship is needed for future analyses to cross-compare their data as accurately and sensitively as possible. Here we present a cross-instrument comparison of data acquired by MapCam and OVIRS, including methods and results for all global and site-specific observation campaigns in which both instruments were active. In our analysis, we consider both the absolute radiometric offset and the relative (normalized) variation between the two instruments; we find that both depend strongly on the photometric and instrumental conditions during the observation. The two instruments have a large absolute offset (>15%) due to their independent radiometric calibrations. However, they are very consistent (relative offset as low as 1%) when each instrument’s response is normalized at a single wavelength, particularly at low phase angles where shadows on Bennu’s rough surface are minimized. We recommend using the global datasets acquired at 12:30 pm local solar time for cross-comparisons; data acquired at higher phase angles have larger uncertainties.

Modeling optical roughness and first-order scattering processes from OSIRIS-REx color images of the rough surface of asteroid (101955) Bennu

“…MapCam is equipped with four band color filters (60-90 nm wide) centered at 473 (b ), 550 (v), 698 (w), and 847 (x) nm, in the visible range. The images are projected in 1024x1024 pixel CCD with a FOV of 4 • × 4 • (Rizk et al, 2018). The images are radiometrically calibrated into RADF and corrected for any optical distortion (Golish et al, 2020b).…”

“…The images are projected in 1024x1024 pixel CCD with a FOV of 4 • × 4 • (Rizk et al, 2018). The images are radiometrically calibrated into RADF and corrected for any optical distortion (Golish et al, 2020b).…”

“…In our study of Bennu, we model optical roughness and first-scattering processes following van Ginneken et al (1998) and using the four-band color images obtained by the OCAMS MapCam imager (Rizk et al, 2018;Golish et al, 2020b). Our goal is to reintroduce a consistent framework where rough surfaces can be mathematically treated without losing effectiveness to provide a photometric correction.…”

Modeling optical roughness and first-order scattering processes from OSIRIS-REx color images of the rough surface of asteroid (101955) Bennu

“…The images are projected in 1024x1024 pixel CCD with a FOV of 4 • × 4 • (Rizk et al, 2018). The images are radiometrically calibrated into RADF and corrected for any optical distortion (Golish et al, 2020b).…”

“…In our study of Bennu, we model optical roughness and firstscattering processes following van Ginneken et al (1998) and using the four-band color images obtained by the OCAMS MapCam imager (Rizk et al, 2018;Golish et al, 2020b). Our goal is to reintroduce a consistent framework where rough surfaces can be mathematically treated without losing effectiveness to provide a photometric correction.…”