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Application of Hapke photometric model to three geologic surfaces using PARABOLA bidirectional reflection data

The Geologic Remote Sensing Field Experiment (GRSFE) was conducted in July and September of 1989 to collect data with both ground and airborne instrumentation. A major objective of GRSFE was to collect data which could be used to test radiative transfer models for the extraction of composition and textural surface properties from remotely acquired data. Reported here are the initial results from an application of the Hapke photometric model, using data from the Portable Apparatus for Remote Acquisition of Bidirectional Observations of Land and Atmosphere (PARABOLA), a ground based radiometer with three spectral channels. PARABOLA data was collected in the Lunar Crater Volcanic Field in Nevada, specifically from the region of Lunar Lake, a playa. The Hapke model was found to be inadequate for three relatively common geologic surfaces (a clay-rich, hard packed surface with decimeter sized mudcracks; a cobble site, similar to a playa site, but strewn with basaltic cobbles and pebbles; and a surface mantled basalt lava flow). The model is not at fault; rather, the complexity of most geologic surfaces is not accounted for in the initial assumptions.

Shepard, Michael K.↗

Heat-Transfer Coefficients for a Full-Scale Pebble-Bed Heater

Large quantities of high-temperature air are needed for work with hypersonic flight problems. At temperatures above 2500 degrees Reamur, where conventional heat exchangers have exceeded their material limits, regenerative pebble-bed exchangers may be used with high-temperature refractories. The design of such a heat exchanger requires the use of reliable heat-transfer coefficients for a packed bed. Considerable data are available on the subject, but they spread over two orders of magnitude at any one Reynolds number value. The facility from which the present data were obtained is used at the Lewis Research Center (NASA) for testing air-breathing engine components. The purpose of this work was to obtain heat-transfer data during the initial operation of the bed as a guide to the design of similar equipment. The facility was designed with a conservative estimate of the heat-transfer coefficient, and is shown schematically. Temperatures throughout the packing were measured continuously so that point values of the coefficient might be obtained.

Lancashire, R. B.↗