Engineering topics

Wu, Sherman S. C.

Publications and source records attributed to Wu, Sherman S. C..

14 records

NASA NTRS1993

Chronology, eruption duration, and atmospheric contribution of the Martian volcano Apollinaris Patera

Results are presented of an investigation of the geology, physical properties, and topography of Apollinaris Patera which was performed on the basis of geologic mapping, thermal inertia measurements, and analysis of the color (visual wavelengths) of this Martian volcano. Initially, the main edifice was formed over a period of about 10 exp 7 yr, and then the volcano experienced a period of quiescence during which the basal scarp formed and the valleys were incised in the main flanks. Activity at the summit formed the present large outer caldera and floor materials. After, or during late stages of outer calder activity, the materials that formed the fan were erupted over 10,000 yr. After emplacement of the fan materials, the smaller, inner caldera and associated floor materials formed over an unconstrained time period. Morphologic analysis suggests that a significant portion of the main edifice is composed of poorly to nonwelded pyroclastic deposits, possibly including a phreatomagmatic component.

Robinson, Mark S.↗

NASA NTRS1992

Geodesy and cartography

An overview of geodesy and cartography of Mars over the past century is presented. The modern exploration began with the Mariner 4, 6, and 7 flyby missions, followed by the Mariner 9 and Viking missions that mapped the entire surface of Mars. The primary modern changes to the coordinate system have led to improved measurements of the rotational period, the direction of the spin axis, and the size and shape of Mars. Planimetric mapping based on Mariner 9 pictures began with a 1:25-M-scale sheet and 30 1:5-M-scale sheets that covered the entire Martian surface. The quality of the Viking Orbiter pictures was greatly improved over Mariner 9 and led to the publication of 140 controlled photomosaic sheets at a scale of 1:2 M. Two digital data bases have been compiled for Mars - the digital image model and the digital terrain model.

Davies, Merton E.↗

NASA NTRS1991

Triangulation using synthetic aperture radar images

For the extraction of topographic information about Venus from stereoradar images obtained from the Magellan Mission, a Synthetic Aperture Radar (SAR) compilation system was developed on analytical stereoplotters. The system software was extensively tested by using stereoradar images from various spacecraft and airborne radar systems, including Seasat, SIR-B, ERIM XCL, and STAR-1. Stereomodeling from radar images was proven feasible, and development is on a correct approach. During testing, the software was enhanced and modified to obtain more flexibility and better precision. Triangulation software for establishing control points by using SAR images was also developed through a joint effort with the Defense Mapping Agency. The SAR triangulation system comprises four main programs, TRIDATA, MODDATA, TRISAR, and SHEAR. The first two programs are used to sort and update the data; the third program, the main one, performs iterative statistical adjustment; and the fourth program analyzes the results. Also, input are flight data and data from the Global Positioning System and Inertial System (navigation information). The SAR triangulation system was tested with six strips of STAR-1 radar images on a VAX-750 computer. Each strip contains images of 10 minutes flight time (equivalent to a ground distance of 73.5 km); the images cover a ground width of 22.5 km. All images were collected from the same side. With an input of 44 primary control points, 441 ground control points were produced. The adjustment process converged after eight iterations. With a 6-m/pixel resolution of the radar images, the triangulation adjustment has an average standard elevation error of 81 m. Development of Magellan radargrammetry will be continued to convert both SAR compilation and triangulation systems into digital form.

Wu, Sherman S. C.↗

NASA NTRS1991

Publication of topographic atlas and control network of Mars

To aid planetary studies and the planning of future Mars missions, the Topographic Atlas and Control Network for Mars will be submitted by the end of fiscal year 1992 for publication as a NASA Special Publication. It will consist of reduced versions of 108 1:2 million-scale photomosaics that show contour lines from topographic maps at the same scale, as well as precisely located control points. The control points are from the planetwide network, which is not only instrumental in the compilation of maps at various scales, but is also widely used in other research such as studies of Mars' gravity and atmosphere. An example, a combination of MC 8-NW and -SW, of the photomosaics to be included in the atlas is presented. Contour lines in the figure are at 1-km intervals. The final adjusted ground coordinates and elevations of the 77 control points shown are given in table form. The last column in the table lists the topographic datum (zero elevation) that can be used to compute the solid radius of the control point from the center of mass of Mars. The atlas will also include information such as the adjusted C-matrices of each image, descriptions of the methods used, and their accuracy, and guidelines for users.

Wu, Sherman S. C.↗

NASA NTRS1991

Color-coded global topographic map of Mars

A Digital Terrain Model (DTM) was derived with both Mercator and Sinusoidal Equal-area projections from the global topographic map of Mars at a scale of 1:15 million and a contour interval of 1 km. Elevations on the map are referred to the Mars topographic datum that is defined by the gravity field at a 6.1-millibar pressure surface with respect to the center of mass of Mars. The DTM has a resolution at the equator of 1/59.226 degrees (exactly 1 km) per pixel. By using the DTM, color-coded global maps of Mars' topography were generated in both the Mercator projection and the Sinusoidal Equal-Area projection. On both maps, colors indicate 1 km increments of height. From the equal-are dataset, the positive and negative elevation distributions are calculated to be 67 and 33 percent, respectively.

Wu, Sherman S. C.↗

NASA NTRS1991

Mars elevation distribution

A Digital Terrain Model (DTM) of Mars was derived with both Mercator and Sinusoidal Equal-Area projections from the global topographic map of Mars (scale 1:15 million, contour interval 1 km). Elevations on the map are referred to Mars' topographic datum that is defined by the gravity field at a 6.1-millibar pressure surface with respect to the center of mass of Mars. The DTM has a resolution at the equator of 1/59.226 degrees (exactly 1 km) per pixel. By using the DTM, the volumetric distribution of Mars topography above and below the datum has previously been calculated. Three types of elevation distributions of Mars' topography were calculated from the same DTM: (1) the frequency distribution of elevations at the pixel resolution; (2) average elevations in increments of 6 degrees in both longitude and latitude; and (3) average elevations in 36 separate blocks, each covering 30 degrees of latitude and 60 degrees of longitude.

Wu, Sherman S. C.↗

NASA NTRS1991

Completion of compilation of the 1:2,000,000-scale topographic map series of Mars

Using special photogrammetric techniques, Mars' topography is being systematically mapped at a scale of 1:2,000,000 from high-altitude Viking Orbiter images. Of the 140 maps in the series, 120 have previously been compiled on the AS-11AM analytical stereoplotters. In fiscal year 1991, the remaining 20 maps will be compiled (most of these are between +/- 30 degrees latitude and the poles). Elevations on the maps are related to the Mars topographic datum. The Mars planetwide control net is used for the control of compilation. The maps have a contour interval of 1 km and a vertical precision of +/- 1 km; thus, they are more detailed than previous maps.

Wu, Sherman S. C.↗

NASA NTRS1991

A new edition of the Mars 1:5,000,000 map series

A new edition of the Mars 1:5,000,000 scale map series is in preparation. Two sheets will be made for each quadrangle. Sheet one will show shaded relief, contours, and nomenclature. Sheet 2 will be a full-color photomosaic prepared on the Mars digital image model (MDIM) base co-registered with the Mars low-resolution color database. The latter will have an abbreviated graticule (latitude/longitude ticks only) and no other line overprint. The four major databases used to assemble this series are now virtually complete. These are: (1) Viking-revised shaded relief maps at 1:5,000,000 scale; (2) contour maps at 1:2,000,000 scale; (3) the Mars digital image model; and (4) a color image mosaic of Mars. Together, these databases form the most complete planetwide cartographic definition of Mars that can be compiled with existing data. The new edition will supersede the published Mars 1:5,000,000 scale maps, including the original shaded relief and topographic maps made primarily with Mariner 9 data and the Viking-revised shaded relief and controlled photomosaic series. Publication of the new series will begin in late 1991 or early 1992, and it should be completed in two years.

Batson, R. M.↗

NASA NTRS1991

CD-ROM publication of the Mars digital cartographic data base

The recently completed Mars mosaicked digital image model (MDIM) and the soon-to-be-completed Mars digital terrain model (DTM) are being transcribed to optical disks to simplify distribution to planetary investigators. These models, completed in FY 1991, provide a cartographic base to which all existing Mars data can be registered. The digital image map of Mars is a cartographic extension of a set of compact disk read-only memory (CD-ROM) volumes containing individual Viking Orbiter images now being released. The data in these volumes are pristine in the sense that they were processed only to the extent required to view them as images. They contain the artifacts and the radiometric, geometric, and photometric characteristics of the raw data transmitted by the spacecraft. This new set of volumes, on the other hand, contains cartographic compilations made by processing the raw images to reduce radiometric and geometric distortions and to form geodetically controlled MDIM's. It also contains digitized versions of an airbrushed map of Mars as well as a listing of all feature names approved by the International Astronomical Union. In addition, special geodetic and photogrammetric processing has been performed to derive rasters of topographic data, or DTM's. The latter have a format similar to that of MDIM, except that elevation values are used in the array instead of image brightness values. The set consists of seven volumes: (1) Vastitas Borealis Region of Mars; (2) Xanthe Terra of Mars; (3) Amazonis Planitia Region of Mars; (4) Elysium Planitia Region of Mars; (5) Arabia Terra of Mars; (6) Planum Australe Region of Mars; and (7) a digital topographic map of Mars.

Batson, R. M.↗

NASA NTRS1987

Mapping experiment with space station

Mapping the earth from space stations can be approached in two areas. One is to collect gravity data for defining a new topographic datum using the earth's gravitational field in terms of spherical harmonics. The other, which should be considered as a very significant contribution of the Space Station, is to search and explore techniques of mapping the earth's topography using either optical or radar images with or without references to ground control points. Geodetic position of ground control points can be predetermined by the Global Positioning System (GPS) for the mapping experiment with the Space Station. It is proposed to establish four ground control points in North America or Africa (including the Sahara Desert). If this experiment should be successfully accomplished, it may also be applied to the defense charting service.

Wu, Sherman S. C.↗

NASA NTRS1987

A compilation system for Venus radar mission (Magellan)

A synthetic aperture radar (SAR) compilation system was developed for extraction of topographic information of Venus from stereoradar imagery to be obtained from the Magellan mission. The system was developed for an AS-11AM analytical stereoplotter. Extensive tests were made on this compilation software by using stereo images from various radar systems, both spaceborne and airborne. Maps were compiled and the precision of planimetry and contour measurement was evaluated. Digital data of some models were also collected for processing orthophoto or perspective views by using the original radar images.

Wu, Sherman S. C.↗

NASA NTRS1987

Aspects of Voyager photogrammetry

In January 1986, Voyager 2 took a series of pictures of Uranus and its satellites with the Imaging Science System (ISS) on board the spacecraft. Based on six stereo images from the ISS narrow-angle camera, a topographic map was compiled of the Southern Hemisphere of Miranda, one of Uranus' moons. Assuming a spherical figure, a 20-km surface relief is shown on the map. With three additional images from the ISS wide-angle camera, a control network of Miranda's Southern Hemisphere was established by analytical photogrammetry, producing 88 ground points for the control of multiple-model compilation on the AS-11AM analytical stereoplotter. Digital terrain data from the topographic map of Miranda have also been produced. By combining these data and the image data from the Voyager 2 mission, perspective views or even a movie of the mapped area can be made. The application of these newly developed techniques to Voyager 1 imagery, which includes a few overlapping pictures of Io and Ganymede, permits the compilation of contour maps or topographic profiles of these bodies on the analytical stereoplotters.

Wu, Sherman S. C.↗

NASA NTRS1987

Progress in compilation of the 1:2,000,000-scale topographic map

The application of special photogrammetric techniques has enabled the systematic mapping of Mars' topography at a scale of 1:2,000,000, using high-altitude Viking Orbiter pictures. In fiscal 86, compilation was completed of the 24 subquadrangles that make up the quadrangles MC-12, MC-13, MC-14, MC-15, MC-20, and MC-21. This work completes compilation of the 60 topographic maps covering the equatorial belt (lat. + or - 30 deg). The remaining 80 subquadrangles of Mars are planned to be completed within 3 years (27, 27 and 26 subquadrangles, in fiscal 87, 88, and 89, respectively). Elevations on all topographic maps are relative to the Mars topographic datum. The maps have a contour interval of 1 km and a precision of + or - 1 km. The equatorial-belt maps are Mercator projections having true scale at lat. + or - 27.476 deg. These maps provide more precise information than do those previously available and they will help in understanding the geologic processes that have shaped the Martian surface.

Wu, Sherman S. C.↗

NASA NTRS1987

Mars digital terrain model

The Mars Digital Terrain Model (DTM) is the result of a new project to: (1) digitize the series of 1:2,000,000-scale topographic maps of Mars, which are being derived photogrammetically under a separate project, and (2) reformat the digital contour information into rasters of elevation that can be readily registered with the Digital Image Model (DIM) of Mars. Derivation of DTM's involves interpolation of elevation values into 1/64-degree resolution and transformation of them to a sinusoidal equal-area projection. Digital data are produced in blocks corresponding with the coordinates of the original 1:2,000,000-scale maps, i.e., the dimensions of each block in the equatorial belt are 22.5 deg of longitude and 15 deg of latitude. This DTM is not only compatible with the DIM, but it can also be registered with other data such as geologic units or gravity. It will be the most comprehensive record of topographic information yet compiled for the Martian surface. Once the DTM's are established, any enhancement of Mars topographic information made with updated data, such as data from the planned Mars Observer Mission, will be by mathematical transformation of the DTM's, eliminating the need for recompilation.

Wu, Sherman S. C.↗