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Welch, R.

Publications and source records attributed to Welch, R..

26 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

SIR-B cartography and stereo topographic mapping

The SIR-B mapping experiment which will evaluate the utility of SAR images taken singularly, in pairs, and in combination with other data sets for cartographic, topographic, and thematic mapping, and determine the optimum configuration of a SAR system for future mapping mission is outlined. SIR-B is the first orbital imaging radar mission which will incorporate maintenance of geometric image fidelity along with careful calibration and documentation of internal timing and frequency parameters. This along and and the multiple incidence angle images of the same target which are necessary for stereoscopy and topographic mapping, make it the ideal opportunity for cartographic experimentation. It is emphasized that comprises a significant part of the overall experiment objectives.

Kobrick, M.↗
NASA NTRS1984

Cartographic accuracy of Landsat-4 MSS and TM image data

Investigations of the cartographic quality of Landsat-4 MSS and TM image data in CCT-p formats have produced rectification accuracies (rmse/xy/ values) of + or - 2/3 to + or - 1 data pixel for both whole and subscene areas using polynomials of the first through third degree. In order to achieve these accuracies with MSS data, 15 or more Ground Control Points (GCPs) are required, whereas with the TM data sets as few as 5-10 GCPs will suffice. Factors which limit the cartographic rectification accuracies of the Landsat-4 data include: (1) spatial resolution of the data; (2) map and digitizing errors; and (3) terrain relief. Of these factors, data resolution is the most significant, limiting the location of GCPs to about + or - 0.5 pixel. Horizontal displacements due to terrain relief can be minimized by selecting GCPs at or near midrange elevations. Overall, the representative rmse(xy) values of + or - 25 and + or - 55 m for TM and MSS data sets are within U.S. National Map Accuracy Standards for cartographic products of 1:100,000 and 1:200,000 scale, respectively.

Welch, R.↗
NASA NTRS1983

Comparative assessment of LANDSAT-4 MSS and TM data quality for mapping applications in the southeast

The initial objectives of analyses of the MSS data are two-fold: (1) to evaluate the geodetic accuracy of CCT-P data of the test sites; and (2) to improve the geodetic accuracy by additional processing if the original data either do not meet pre-launch specifications or mapping requirements. The location of 45 ground control points (GCP) digitized from 35 U.S. Geological Survey 1:24,000 scale quadrangles (UTM coordinates) were identified in terms of pixel and scan line values. These 46 points are used to establish UTM position error vector distributions in the scene. As an initial check on the geometric reliability of the MSS data, 28 well-distributed GCPs were input to a program which compares the scaled image distances between all possible point pairs with the corresponding map distances and computes the distance differences; that is, the relative positional errors. The relative errors obtained from initial computations averaged about +/- 200 m. These errors could result from a number of sources, including misidentification of GCP locations, UTM coordinate errors introduced by the map digitizing process or errors resulting from data acquisition and geometric processing.

Welch, R.↗
NASA NTRS1983

Geometric accuracy of LANDSAT-4 MSS image data

Analyses of the LANDSAT-4 MSS image data of North Georgia provided by the EDC in CCT-p formats reveal that errors of approximately + or - 30 m in the raw data can be reduced to about + or - 55 m based on rectification procedures involving the use of 20 to 30 well-distributed GCPs and 2nd or 3rd degree polynomial equations. Higher order polynomials do not appear to improve the rectification accuracy. A subscene area of 256 x 256 pixels was rectified with a 1st degree polynomial to yield an RMSE sub xy value of + or - 40 m, indicating that USGS 1:24,000 scale quadrangle-sized areas of LANDSAT-4 data can be fitted to a map base with relatively few control points and simple equations. The errors in the rectification process are caused by the spatial resolution of the MSS data, by errors in the maps and GCP digitizing process, and by displacements caused by terrain relief. Overall, due to the improved pointing and attitude control of the spacecraft, the geometric quality of the LANDSAT-4 MSS data appears much improved over that of LANDSATS -1, -2 and -3.

Welch, R.↗
NASA NTRS1982

Map accuracy requirements: The cartographic potential of satellite image data

Cartographic products fall into a variety of classes: topographic maps that are concerned with planimetric information and elevations or heights; thematic maps, which might be used for geology, vegetation, water, or to display these subjects; digital elevation maps that would be produced from digital terrain data; and finally image maps. In terms of satellite applications, thematic maps and image maps are emphasized. The objectives are to consider, first, if resolution will be adequate for the identification of control and for the compilation of map products. Then, second, to define map accuracy standards and to determine the potential for meeting these standards with image data from the film camera, scanner and linear array systems of the 1980s.

Welch, R.↗
NASA NTRS1981

Cartographic potential of a spacecraft line-array camera system - Stereosat

A study of the Stereosat mission, which may acquire analog/digital stereo image data of cartographic quality with linear array camera systems, is presented, with attention given to the Stereosat system and the mission parameters, the utilization of the Stereosat studies in order to indicate the nature and scope of the problems associated with recording image data of high geometric fidelity from spacecraft equipped with line array sensors, and the assessing of the possibilities of meeting the completeness and accuracy requirements of cartographic products. A 713-km circular, sun-synchronous, near polar orbit, with an inclination of 98.24 deg and a repeat cycle of 48 days is designed to insure global coverage of the earth's land masses during the three-year lifetime of the mission. Three cameras (fore, vertical, and aft looking), mounted so as to record stereotriplets for a 61.4 km wide swath at a nominal focal plane scale of 1:1,000,000, are considered. The IFOV of 15 m should be adequate for producing thematic and image maps at scales of 1:50,000 to 1:250,000. The value of the coverage to cartographers will be dictated by the accuracy of the digital image data, which is largely a function of satellite control.

Welch, R.↗
NASA NTRS1981

Remote sensing education for the Earth sciences: The University of Georgia experience

A prospectus is presented of the following courses offered by the Department of Geography: (1) use and interpretation of aerial photographs; (2) advanced photogrammetry; (3) remote sensing of environment; (4) geographic information systems; and (5) directed problems in the remote sensing of the environment. In addition to the course content and objectives, the various equipments available for student training and use are listed.

Welch, R.↗