Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p52b0579j&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P52B-0579
Physics
5415 Erosion And Weathering, 5460 Physical Properties Of Materials, 5464 Remote Sensing, 6213 Dust, 6225 Mars
Scientific paper
Knowledge of Martian atmospheric dust deposition rates is important for understanding aeolian and climate dynamics and the degree to which dust can affect landed spacecraft operability. Observations of temporal changes in albedo or visible/near-infrared spectra of surface features and lander components can help constrain dust deposition rates. We are using calibrated Imager for Mars Pathfinder multispectral images to document spectral changes associated with dust deposition on the radiometric calibration targets (RCTs). RCT images from Sol 3 were assumed to be least contaminated with dust and used to calibrate RCT images acquired on later Sols under similar illumination conditions. We constructed simulated RCTs using a radiative transfer model of sky illumination for a specific opacity, wavelength, and sun position. Differences in spectra from the target models and the calibrated RCT images reveal increasing dust deposited on the RCTs with time. Such spectra will be used in two-layer radiative transfer scattering models to estimate changes in dust coating thickness on the RCTs, thereby providing estimates of dust deposition rates at the Pathfinder site. We are also investigating albedo changes associated with slope streaks observed in narrow-angle (NA) MOC images as a means of constraining dust deposition rates. In particular, upper limits on some streak ages are provided by repeat NA images that reveal the occurrence of new streaks. Algorithms developed to calibrate NA images to I/F help quantify albedo differences among streaks of variable image tone and nearby "standard" terrains (assumed to be completely dust-covered). Simple shadow subtraction and ratioing techniques between streak and standard regions reveal differences consistent with those observed for ratios computed from laboratory spectra of basaltic rocks coated with different thicknesses of palagonite dust. Although this preliminary method suggests dust deposition rates of 20-200 microns/year, uncertainties in atmospheric compensation from shadow subtraction limit its accuracy. We are investigating combined use of MOLA topography and photoclinometric methods to provide better estimates of atmospheric haze in MOC images, which will allow better retrieval of surface albedoes and dust thickness estimates.
Grundy Will M.
Herkenhoff Ken
Johnson Jay Robert
Lemmon Mark
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