Engineering topics

Blumberg, Dan G.

Publications and source records attributed to Blumberg, Dan G..

6 records

NASA NTRS1995

Preliminary study of Kelso Dunes using AVIRIS, TM, and AIRSAR

Remote sensing of sand dunes helps in the understanding of aeolian process and provides important information about the regional geologic history, environmental change, and desertification. Remotely sensed data combined with field studies are valuable in studying dune morphology, regional aeolian dynamics, and aeolian depositional history. In particular, active and inactive sands of the Kelso Dunes have been studied using landsat TM and AIRSAR. In this report, we describe the use of AVIRIS data to study the Kelso dunes and to compare the AVIRIS information with that from TM and AIRSAR.

Xu, Pung↗

NASA NTRS1995

New observations of Bolivian wind streaks by JPL Airborne SAR: Preliminary results

In 1993 NASA's Jet Propulsion Laboratory Airborne Synthetic Aperture Radar system (AIRSAR) was deployed to South America to collect multi-parameter radar data over pre-selected targets. Among the sites targeted was a series of wind streaks located in the Altiplano of Bolivia. The objective of this investigation is to study the effect of wavelength, polarization, and incidence angle on the visibility of wind streaks in radar data. Because this is a preliminary evaluation of the recently acquired data we will focus on one scene and, thus, only on the effects of wavelength and polarization. Wind streaks provide information on the near-surface prevailing winds and on the abundance of winderodible material, such as sand. The potential for a free-flyer radar system that could provide global radar images in multiple wavelengths, polarizations, and incidence angles requires definition of system parameters for mission planning. Furthermore, thousands of wind streaks were mapped from Magellan radar images of Venus; their interpretation requires an understanding of the interaction of radar with wind streaks and the surrounding terrain. Our experiment was conducted on wind streaks in the Altiplano of Bolivia to address these issues.

Blumberg, Dan G.↗

NASA NTRS1994

Stars and linear dunes on Mars

A field containing 11 star and incipient star dunes occurs on Mars at 8.8 deg S, 270.9 deg W. Examples of linear dunes are found in a crater at 59.4 deg S, 343 deg W. While rare, dune varieties that form in bi- and multidirectional wind regimes are not absent from the surface of Mars. The occurence of both of these dune fields offers new insight into the nature of martian wind conditions and sand supply. The linear dunes appears to have formed through modification of a formerly transverse aeolian deposit, suggesting a relatively recent change in local wind direction. The 11 dunes in the star dune locality show a progressive change from barchan to star form as each successive dune has traveled up into a valley, into a more complex wind regime. The star dunes corroborate the model of N. Lancaster (1989), for the formation of star dunes by projection of transverse dunes into a complex, topographically influenced wind regime. The star dunes have dark streaks emanating from them, providing evidence that the dunes were active at or near the time the relevant image was obtained by the Viking 1 orbiter in 1978. The star and linear dunes described here are located in different regions on the martian surface. Unlike most star and linear dunes on Earth, both martian examples are isolated occurrences; neither is part of a major sand sea. Previously published Mars general circulation model results suggest that the region in which the linear dune field occurs should be a bimodal wind regime, while the region in which the star dunes occur should be unimodal. The star dunes are probably the result of localized complication of the wind regime owing to topographic confinement of the dunes. Local topographic influence on wind regime is also evident in the linear dune field, as there are transverse dunes in close proximity to the linear dunes, and their occurrence is best explained by funneling of wind through a topographic gap in the upwind crater wall.

Edgett, Kenneth S.↗

NASA NTRS1993

AIRSAR views of aerolian terrain

The Stovepipe Wells Dune Field provides a unique opportunity to observe several dune forms in one scene. These forms include reverse dunes, star dunes, transverse, and linear dunes. A sand mantle surrounds the dune field and can also be observed in the radar image. Dune types were discriminated best in co-polarized channels. Three major wind directions are responsible for the various dune forms. Winds from the north and south are responsible for the reverse dunes, winds from north for the transverse dunes, and the north - south and westerly winds for the star dunes. The winds also reflect the topographic configuration of this part of Death Valley. Vegetation over the dunes was most pronounced in the cross-polarized images. Lancaster et al. (1992) find that cross-polarized images are most useful in differentiating active from inactive dunes. This is because the vegetation backscatter signature is present over inactive dunes. Future studies should include multiple look and incidence angles to determine if the dune forms can still be seen at other angles.

Blumberg, Dan G.↗

NASA NTRS1992

Detecting surface roughness effects on the atmospheric boundary layer via AIRSAR data: A field experiment in Death Valley, California

The part of the troposphere influenced by the surface of the earth is termed the atmospheric boundary layer. Flow within this layer is influenced by the roughness of the surface; rougher surfaces induce more turbulence than smoother surfaces and, hence, higher atmospheric transfer rates across the surface. Roughness elements also shield erodible particles, thus decreasing the transport of windblown particles. Therefore, the aerodynamic roughness length (z(sub 0)) is an important parameter in aeolian and atmospheric boundary layer processes as it describes the aerodynamic properties of the underlying surface. z(sub 0) is assumed to be independent of wind velocity or height, and dependent only on the surface topography. It is determined using in situ measurements of the wind speed distribution as a function of height. For dry, unvegetated soils the intensity of the radar backscatter (sigma(sup 0)) is affected primarily by surface roughness at a scale comparable with the radar wavelength. Thus, both wind and radar respond to surface roughness variations on a scale of a few meters or less. Greeley showed the existence of a correlation between z(sub 0) and sigma(sup 0). This correlation was based on measurements over lava flows, alluvial fans, and playas in the southwest deserts of the United States. It is shown that the two parameters behave similarly also when there are small changes over a relatively homogeneous surface.

Blumberg, Dan G.↗

NASA NTRS1992

Influence of aerodynamic roughness length on aeolian processes: Earth, Mars, Venus

The aerodynamic roughness length (z sub 0) is the height at which a wind profile assumes a zero velocity. The lower part of the atmospheric boundary layer will be impeded by friction with the surface. An increase in surface roughness will also increase the shear stress required to initiate particle entrainment by the wind. Bagnold (1941) estimated z sub 0 as being 1/30 of the mean particle size. In Nature, surface roughness is composed of nonerodible elements as well as sand-size erodible particles. To assess z sub 0 values as a function of terrain, field experiments were conducted to obtain wind profiles monitored over natural surfaces at 15 sites in the Mojave Desert, Death Valley, and Nye County, Nevada. These sites span a variety of arid-land terrains, including smooth playas, alluvial fans, and lava flows; z sub 0 values ranged from 0.0001 cm to 1 cm. These values were incorporated in a threshold model and a flux model to assess transport efficiency over such terrains in three planetary environments (Venus, Earth, and Mars), and for particle sizes ranging from 60-500 micron. Threshold and flux are a function of planetary environment, particle density and size (Dp), and z sub 0, and the shear velocity of 1.2 x U sub *t (for Dp = 250 micron and z sub 0 = 0.84). Results show that flux on Mars is approximately 14 g/(cm x s), on Earth it is approximately 3 g/(cm x s), and on Venus 0.5 g/(cm x s). Under all planetary environments, the results also show a dramatic decrease in the flux for particles greater than 200 microns when z sub 0 increases above 0.0085 cm (corresponding to sites consisting of alluvium). When z sub 0 approaches 0.03 cm (corresponding to a mantled pahoehoe lava), the flux diminishes.

Blumberg, Dan G.↗