Measuring emissivity in the field and the lab with an emulator of the VERITAS Venus Emissivity Mapper (VEM)

Abstract

Both NASA’s VERITAS and ESA’s EnVision missions to Venus carry a Venus Emissivity Mapper (VEM/VenSpec-M) to characterize the surface mineralogy, with the main goal of distinguishing basaltic from more felsic rock types. Though Venus’ optically dense atmosphere makes direct observations of the surface challenging, five spectral windows in the CO2 transmission spectrum near 1 μm will be exploited by the VEM instrument. In preparation for these missions, an analog of the VEM instrument (VEMulator2.0) was constructed for both field and laboratory measurements. It was used at Venus-analog sites in Iceland in August 2023 as part of a two-week VERITAS Science Team field campaign. The instrument has also proven useful for emissivity laboratory investigations, allowing two-dimensional information of hot samples in the near infrared. This paper describes the design and calibration of the VEMulator2.0, its integration into the emissivity chamber of the Planetary Spectroscopy Laboratory at DLR in Berlin, and the results of a measurement campaign looking into the effects of spatial surface and composition variations on the measured emissivity.