Scattered Light Remediation and Recalibration of NEAR Shoemaker’s NIS Global Dataset at 433 Eros

The original calibration of NEAR Shoemaker’s Near Infrared Spectrometer (NIS), while complete, omitted a critical correction for internal scattered light of the spectrometer grating. This kind of scatter is a natural feature of grating spectrometers, but it was initially discounted as a significant factor in NIS calibration. After a re-analysis of the ground calibrations, determined the scattered light contribution to be significant enough to warrant correction, and generated a correction factor for the instrument’s raw data-to-radiance conversion coefficients. The NIS+MSI in used calibrated and photometrically corrected Eros spectra, and a post-processing scattered light correction applied to those spectra directly. Ideally the scattered light, and other post-mission calibration corrections should be applied as part of the calibration pipeline, before any post-processing (including photometric correction). Future analysis using calibrated NIS data is better served by propagating corrections through the complete (over 200,000 spectrum) dataset from the raw original.