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NASA NTRS1987

Solar object tracking for the Hubble Space Telescope

The Hubble Space Telescope (HST) is designed to carry five major scientific instruments to collect imagery, spectrographic, and photometric astronomical data. The Pointing Control System is to achieve pointing accuracies and line of sight jitter levels an order of magnitude less than can be achieved with ground mounted telescopes. In addition, the HST must be able to acquire and track solar system targets with apparent motion up to 0.21 arcsec/s. Such targets include planetary satellites, planetary surface features and comets. It is to perform this tracking with an accuracy under 0.03 arcsec at the maximum rate. Tracking of solar objects by the Space Telescope accounts for the effects of velocity aberration and parallax, as well as solar targeting a celestial object in a science instrument aperture. The design of the Pointing Control System solar object tracking features is discussed, with emphasis on the special timing and granulation problems inherent with a sampled-data, multirate digital control system.

Rodden, J. J.↗

NASA NTRS1988

DMSP-SSM/1 NASA algorithm validation using primarily LANDSAT and secondarily DMSP and/or AVHRR visible and thermal infrared satellite imagery

The approach to the DMSP SSMI (Defense Meteorological Satellite Program; Special Sensor Microwave Imager) sea-ice validation effort is to demonstrate a quantitative relationship between the SSMI-derived sea ice parameters and those same parameters derived from other data sets including visible and infrared satellite imagery, aerial photographic and high-resolution microwave aircraft imagery. The question to be addressed is to what accuracy (relative to these other observations) can the following ice parameters be determined: (1) position of the ice boundary; (2) total sea ice concentration; and (3) multiyear sea ice concentration. Specific tasks include: (1) a study of the interrelationship of surface information content and sensor spatial and spectral resolution in order to establish relationships between ice surface features and the manner in which they are expressed in the satellite observations; and (2) apply these relationships to map the sea ice features which can be used to evaluate NASA's proposed SSM/1 sea ice algorithms. Other key points to be addressed include the accuracy to which these parameters can be determined in different regions (marginal ice zone such as Bering Sea, Arctic ocean, such as Beaufort Sea); the accuracy of these parameters for different seasons; the accuracy of the algorithms weather filter under different weather conditions; and the effectiveness of the 85.5 GHz channels to locate the ice edge.

Steffen, K.↗

NASA NTRS1988

Small-scale volcanic landforms indicative of distributary tube systems

Surface features tens to hundreds of meters in size on Martian lava flows are revealed in high resolution Viking Orbiter images. Many of these morphological features form in response to certain flow emplacement mechanisms, eruptive styles, or rheological properties of the lava. Insight into the relationships between lava flow morphology and the emplacement and characteristics of magma is an ongoing areas of research and allows constraints to be placed on interpretation of Martian volcanism. This report focuses on pressure ridges, tumuli, and pressure plateaus which comprise a suite fo features characteristics of compound pahoehoe lava flows. Similar ridges and mounds were identified in the Tharsis region of Mars.

Theilig, E.↗

NASA NTRS1987

Polarized and non-polarized leaf reflectances of Coleus blumei

A polarization photometer has been used to measure the reflectance of three variegated portions of Coleus blumei, Benth. in five wavelength bands of the visible and near-infrared spectrum. The polarized component of the reflectance factor was found to be independent of wavelength, indicating that the polarized reflectance arises from the leaf surface. It is suggested that differences in the polarized component result from variations in surface features. The nonpolarized component of the reflectance factor is shown to be related to the internal leaf structure. The variation of the degree of polarization with wavelength was found to be greatest in the regions of the spectrum where absorption occurs.

Grant, Lois↗

NASA NTRS1987

Remote sensing from space; Proceedings of Symposium 3, Workshop V, and Topical Meeting A2 of the Twenty-sixth COSPAR Plenary Meeting, Toulouse, France, June 30-July 11, 1986

Various papers on remote sensing from space are presented. The use of such remote sensing to study terrestrial patterns and processes is examined, including the relevant processes and theories, observed vegetation and surface climate parameters, derived terrestrial processes, atmospheric effects, and new sensors. Quantitative radar remote sensing of land and oceanic surface features is addressed, including systems, calibration, simulation, data evaluation for vegetational studies, altimetry, sea ice monitoring, and oil slick detection. The use of satellite observations for weather prediction is discussed.

Goward, S. N.↗

NASA NTRS1988

High resolution images of Venus from ground-based radar

The Goldstone Deep Space Station ground-based synthetic aperture radar system has been used to obtain radar images of Venus with resolutions of close to 1.3 km. Observations were made at 12.5 cm wavelength using circular polarization. From 12 days of observations during the 1986 inferior conjunction, three images have been selected for initial processing. The images show remarkable surface features including craters, ridges, and regions of high Fresnel reflectivity in the plains region.

Jurgens, R. F.↗

NASA NTRS1988

Global albedo variations on Mars - Implications for active aeolian transport, deposition, and erosion

This paper describes the use of visible reflectance observations by the Viking IR thermal mapper for the construction of the time sequence of the Martian surface and atmospheric albedo throughout the Viking mission. The major variations in albedo were found to be associated with the two global dust storms of 1977. Visible albedo observations provided an excellent means for determining the onset and decay phases of the two storms, separating the surface and the atmospheric dust. Even at the height of the second storm some surface features were visible, particularly in the southern hemisphere. Significant differences were observed between the northern and the southern hemispheres in the dust load and the timing of the decay phase of the global storms. At the present time, there appears to be a net transport of dust from south to north, which is consistent with models of atmospheric circulation during the storm period.

Christensen, Philip R.↗

NASA NTRS1988

What should we look for when we return to Mars?

The current state of knowledge about Mars is examined, and the details of current planned missions (Phobos and the Mars Orbiter) are considered. Speculations on some of the major future avenues of Mars research are presented; particular attention is given to questions relating to the early geological processes that resulted in Martian surface features, the effect liquid water has had on the planet, the volatile dynamics and chemistry, the chemistry of the iron-rich clays, the organic-compound mystery, and the biological issue.

Soffen, G. A.↗

NASA NTRS1989

Phobos and Deimos control networks

Viking Orbiter images of Phobos and Deimos have been measured to establish global control networks for 98 surface features of the former and 53 of the latter; photogrammetric triangulation has yielded body-fixed coordinates of these control-points, as well as mean triaxial radii of 13.3 x 11.1 x 9.3 km for Phobos and 7.5 x 6.2 x 5.4 for Deimos. Expressions are also obtained for the inertial orientations of these bodies' spin axes and prime meridians. While these expressions should be accurate to a few tenths of a deg for the 1971-1980 period, their accuracy will degrade with time as the orbit accuracy degrades.

Duxbury, Thomas C.↗

NASA NTRS1989

Melting and solidification of acoustically levitated drops

A single axis acoustic levitator has been used to suspend a drop of commercial grade succinonitrile in air. The drop is subjected to thermal cycling in order to observe melting and solidification of the drop in the acoustically levitated state. Melting takes place over a temperature rise of a few degrees, which is typical for an impure material. Solidification initially progresses along the drop surface because of the temperature gradient developed in the drop. The resultant solid drop shows a dendritic surface feature with a cavity in some circumstances. An attempt is made to calculate the growth velocity of the dendrites.

Ohsaka, K.↗

NASA NTRS1990

Use of high-dimensional spectral data to evaluate organic matter, reflectance relationships in soils

Recent breakthroughs in remote sensing technology have led to the development of a spaceborne high spectral resolution imaging sensor, HIRIS, to be launched in the mid-1990s for observation of earth surface features. The effects of organic carbon content on soil reflectance over the spectral range of HIRIS, and to examine the contributions of humic and fulvic acid fractions to soil reflectance was evaluated. Organic matter from four Indiana agricultural soils was extracted, fractionated, and purified, and six individual components of each soil were isolated and prepared for spectral analysis. The four soils, ranging in organic carbon content from 0.99 percent, represented various combinations of genetic parameters such as parent material, age, drainage, and native vegetation. An experimental procedure was developed to measure reflectance of very small soil and organic component samples in the laboratory, simulating the spectral coverage and resolution of the HIRIS sensor. Reflectance in 210 narrow (10 nm) bands was measured using the CARY 17D spectrophotometer over the 400 to 2500 nm wavelength range. Reflectance data were analyzed statistically to determine the regions of the reflective spectrum which provided useful information about soil organic matter content and composition. Wavebands providing significant information about soil organic carbon content were located in all three major regions of the reflective spectrum: visible, near infrared, and middle infrared. The purified humic acid fractions of the four soils were separable in six bands in the 1600 to 2400 nm range, suggesting that longwave middle infrared reflectance may be useful as a non-destructive laboratory technique for humic acid characterization.

Henderson, T. L.↗

NASA NTRS1990

The Magellan Venus explorer's guide

The Magellan radar-mapping mission to the planet Venus is described. Scientific highlights include the history of U.S. and Soviet missions, as well as ground-based radar observations, that have provided the current knowledge about the surface of Venus. Descriptions of the major Venusian surface features include controversial theories about the origin of some of the features. The organization of the Magellan science investigators into discipline-related task groups for data-analysis purposes is presented. The design of the Magellan spacecraft and the ability of its radar sensor to conduct radar imaging, altimetry, and radiometry measurements are discussed. Other topics report on the May 1989 launch, the interplanetary cruise, the Venus orbit-insertion maneuver, and the in-orbit mapping strategy. The objectives of a possible extended mission emphasize the gravity experiment and explain why high-resolution gravity data cannot be acquired during the primary mission. A focus on the people of Magellan reveals how they fly the spacecraft and prepare for major mission events. Special items of interest associated with the Magellan mission are contained in windows interspersed throughout the text. Finally, short summaries describe the major objectives and schedules for several exciting space missions planned to take us into the 21st century.

Young, Carolynn↗

NASA NTRS1990

Satellite sensor estimates of Northern Hemisphere snow volume

In the Northern Hemisphere the mean monthly snow-covered area ranges from about 7 percent of the land area in summer to over 40 percent in winter, thus making snow one of the most rapidly varying natural surface features. The mean monthly snow volume ranges from about 1.5 x 10 to the 16th g in summer to about 3.0 x 10 to the 18th g in winter. Currently several algorithms utilizing passive microwave brightness temperatures are available to estimate snow cover and depth. The algorithm presented here uses the difference between the 37-GHz channel and the 18-GHz channel of the SMMR on the Nimbus-7 satellite to derive estimates of snow volume. Even though satellite sensor snow records are currently too short to reveal trends, continued monitoring over about the next 10 years should make it possible to establish whether incipient or current trends are significant in the context of global climate change.

Chang, A. T. C.↗

NASA NTRS1989

Speckle interferometry of asteroids

Steward Observatory's two-dimensional power spectrum signature analysis of speckle interferometry observations is summarized. Results for six asteroids are presented. The poles and triaxial ellipsoid dimensions of 4 Vesta, 433 Eros, 511 Davida, and 532 Herculina have been previously reported. New results for 2 Pallas and 29 Amphitrite are given, as well as further results for Vesta. Image reconstruction is ultimately required to minimize biasing effects of asteroid surface features on the simpler power spectrum analysis. Preliminary imaging results have been achieved for Vesta and Eros, and images for these two are displayed. Speckle interferometry and radiometry diameters are compared, and diameters from the two occultations of Pallas are addressed.

Drummond, Jack D.↗

NASA NTRS1990

The role of secondary resonances in the orbital history of Miranda

A simple 'perturbed pendulum' model is developed in order to ascertain the origin and dynamics of the secondary resonances in the tidal evolution of Miranda and Umbriel through the 1:3 mean motion commensurability. Long-term evolution is addressed on the basis of the computation-accelerating method of algebraic mappings. It is found that the present 4.34-deg value of Miranda's orbital inclination is probably a result of capture into the primary resonance, as well as subsequent capture into the 3/1 secondary resonance. The damping of an eccentricity as high as 0.035 by tidal dissipation in the satellite may account for the surface features of Miranda.

Malhotra, Renu↗

NASA NTRS1990

Ridge belts - Evidence for regional- and local-scale deformation on the surface of Venus

Models for the formation of the ridge belt fan assemblage on Venus are evaluated through consideration of the orientation, spatial distribution, topographic expression, and wavelengths of observed tectonic surface features. A compressional mechanism is favored for long wavelength deformation corresponding to the spacing of ridge belts (300 - 400 km). However, short wavelength ridges and grooves (10 - 20 km) that are contained within belts and trend parallel to them are likely to be compressional and extensional, and to reflect both regional and local stress fields. It is hypothesized that large-scale (much greater than ridge spacing) early-stage mantle downwelling is the source of regional compression responsible for the establishment of the long wavelength of deformation.

Zuber, M. T.↗

NASA NTRS1990

Discontinuities in the shallow Martian crust at Lunae, Syria, and Sinai Plana

Detailed photoclinometric data are presented for a variety of surface features (pits, troughs, wall valleys, and grabens) within three study areas in the western equatorial regions of Mars (Lunae, Syria, and Sinai Plana) that provide evidence for mechanical discontinuities within the shallow Martian crust in these regions. The data's relation to some of the previously proposed mechanical discontinuities within the Martian crust is discussed, and the geologic significance of these features is speculated upon.

Davis, Philip A.↗

NASA NTRS1991

Stereoscopic Video Weld-Seam Tracker

Stereoscopic video camera and laser illuminator operates in conjunction with image-data-processing computer to locate weld seam and to map surface features in vicinity of seam. Intended to track seams to guide placement of welding torch in automatic welding system and to yield information on qualities of welds. More sensitive than prior optical seam trackers and suitable for use in production environment. Tracks nearly invisible gap between butted machined edges of two plates.

Kennedy, Larry Z.↗