Date of Award:

1976

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Advisor/Chair:

Inge Dirmhirn

Abstract

The main objectives of this study were to develop the indicatri es of reflected solar radiation from different natural surfaces and to show comparisons between values sensed in space of emergent radiation to ground values obtained from accounting for anisotropic reflection and estimating the effect of the intervening atmosphere. Thus, this study demonstrated that a prior knowledge of the angular distribution of reflected radiation allows determining the true hemispherical reflected radiation from a narrow field of view instrument such as found on a flying platform. Measurements for determining the indicatrices were made from a tower-mounted Nimbus MRIR and, in one case, with a hand-held TIROS five-channel radiometer.

Anisotropy of reflected radiation was found for all surfaces examined and increased with decreasing solar angle. Different surfaces showed different degrees and patterns of fonvard and backscatter. A clearly defined anti-solar point was found for plowed field, various agricultural crops and vegetated desert surfaces, while snow, the Alkali Flats, and Bonneville Salt Flats showed a broad pattern of backscatter. As a consequence of surfaces exhibiting well-defined antisolar points the anisotropic correction factors relating normal reflectances to 2π reflected values were less than 100 percent for solar angles greater than approximately 60°. All surfaces examined showed anisotropic correction factors increasing with decreasing solar angles.

The albedo over the White Sands dune field decreased with decreasing solar angles due to large shadow patterns which are produced at low solar angles. The sand dunes values were derived from aircraft measurements.

Comparisons were made between estimated emergent radiation from the top of the earth 's atmosphere accounting for anisotropy of the ground reflection pattern and estimates of atmospheric attenuation to values of reflected radiation obtained from the MSS subsystem of the ERTS program for the lava beds region and White Sands area in New Mexico. Also comparisons were shown between the estimated emergent radiation from the earth's surface for the same features and spectral bands to the values sensed in space. Under high albedo conditions as found in the White Sands area there was a decrease in emergent radiation to space while with low surface albedo, such as the lava beds region, the extra-terrestrial radiation increased from the ground values.

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