Physics – Optics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p13a0970m&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P13A-0970
Physics
Optics
5462 Polar Regions
Scientific paper
Laser Light Scattering (LLS) is a powerful, fast, and non-destructive way of optically interrogating embedded microparticles in solid ice. This is the basis for the design of the Laser Dust Detector (LDD) where laser light is directed via fiber optics into the ice surrounding the probe. If the ice is bubble and dust free the laser light will penetrate meters of ice before the light is attenuated completely. If, however, the laser light encounters dust particles the light will be scattered in all directions, according to the theory of Rayleigh and Mie scattering. Some of the scattered light will make its way into the aperture of the CCD camera and be detected in a digital image. A series of these images are taken as the Cryobot descends into the ice sheet. The images will be acquired in a way to ensure enough overlap between neighboring images to be able to fit them together to get a continuous in-situ mapping of the dust in this local environment of the ice sheet. In the laboratory, this method has been successful, in part, because the particle size distributions in archived ice cores have been very constant in time. Even during a change by a factor of 100 in concentration the size distribution is only slightly changed. Another reason the optical interrogation of dust has been successful is that the overall mineralogy of the dust particles appear to be more or less constant, i.e. the index of refraction of the particles doesn't change much with depth or particle size, an important factor when analyzing the experimental data. The key to obtaining suitable data on the properties of Mars ice caps is in the design of an exploratory polar cap in-situ mission and its instrumentation, of which the optical systems for the visible stratigraphy and dust character are significant. In taking steps to obtain the optical data we begin by noting that the polar cap ice may be clear in the fashion of deep ice sheet ice from Greenland or Antarctica, or it may have sufficient dust and bubbles to be opaque, or somewhere in between. A Cryobot instrumented with a Laser Dust Detector and an additional light source would be able to profile the ice column either by penetrating a rather clear ice sheet or by imaging the wall of the melt hole of an opaque ice sheet. Results from analysis of dust embedded in archived ice cores as well as `artificial ice' made in the laboratory will be shown. Applications for planetary in-situ dust detection will be discussed.
Carsey Frank
Hecht Michael H.
Lane Arthur L.
Mogensen C.
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