Preliminary Remediation of Scattered Light in NEAR MSI Images

During a failed Eros orbit insertion maneuver on 20 December 1998, more than 28 kg of hydrazine were expended by attitude control jets on the NEAR Shoemaker spacecraft. Deposition of burn products on the outer optic of the multispectral imager, or MSI, resulted in a wavelength-dependent degradation of the system point-spread function (PSF). The scattered light is progressively worse in the shortest and longest wavelength filters, especially at 450 and 1050 nm. The degraded PSF was characterized using numerous images of Canopus acquired subsequent to the anomaly. There is no evidence for temporal change in the PSF since the burn abort incident. A fast Fourier transform-based image restoration method using the optimal filter recovers most of the spatial resolution of the original images while preserving radiometric accuracy for the 550- to 1000-nm images. This procedure has enabled nearly unimpeded monochrome imaging of asteroid morphology and select 5-color measurements at a scale of ∼5 pixels.