Remediation of scattered light in NEAR-Shoemaker MSI imager; study of Martian debris aprons.

摘要

Asteroids contain the most pristine record of our solar nebular. NEAR-Shoemaker, the first mission to orbit an asteroid, 433 Eros, provided important information on the physical and spectral properties of near-Earth asteroids. Because part of the burn products condensed on the outer optics of the instrument Multispectral Imager (MSI), images were severely degraded. In this thesis I present a digital image processing technique for remediation of the scattered light problem in the MSI and show results, by implementation of an optimal filter algorithm. This procedure resulted in scientifically useful images of the asteroid Eros.; Debris aprons are thick, lobate-shaped deposits within 30-60° latitude of both the martian northern and southern hemispheres. Thought to be a geomorphological indicator of ground ice, they indicate on-going terrain erosion at the martian crustal dichotomy boundary and at mid- to high latitude regions on the highlands. I employed images from Mars Global Surveyor (MGS) and Odyssey, altimetry from MGS, and developed idealized rheological models to study 36 debris aprons in the northern hemisphere. I estimated the lower limit of ice concentration (40% by volume) in debris aprons by comparing observed topography with predictions of simple plastic and power law models. With the northern typical apron measuring 400x12,000x60,000 meters, the volume of ice could reach 5.6x10 10 m3 for 40% concentration. The abundant ice preserved in aprons represents potentially exploitable reservoirs to sustain future operations on Mars. Abundant ice and the young surface ages (100 Ma) of debris aprons derived from crater density suggest that the climate of Mars in the late Amazonian differed from that today, and at that time it likely resembled the current terrestrial periglacial climate. For comparison, I analyzed the formation and evolution of 50 debris aprons in the southern hemisphere, characterized by higher elevations and more diverse topographic shape. These deposits exist as large debris apron complexes composed of multiple flows, but each flow is volumetrically smaller than the northern counterpart. Aprons in the southern hemisphere display profiles more convex than both northern ones and simple plastic models. This may indicate southern deposits are still evolving through solid-state ice deformation.