Producing Maps and Images
| GPS data collected during field work were draped
onto topography from published maps and image data from satellites and
aircraft. Click here to see these products. Landsat Thematic Mapper (TM) data were used to provide multispectral information in visible and infrared wavelengths. A 1984 TM image was acquired from INPE, the Brazilian space agency. This image was georeferenced using control points collected during field work. The image of the Lloqueta area shows the main tributaries of the river, the Cordillera de Chilca, and the Colca Valley. |
3D view with Nevado Mismi in the background
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Maps of this area were produced at 1:100,000 scale by Peru's Instituto Geografico Militar (IGM). These map sheets were also used to provide topography for this project. These sheets were digitized and combined using Arc/Info software. Airphotos taken in 1955 were used to identify features of interest and for navigation during field work. These photos were taken by the U.S. Air Force and are part of the collection at the Servicio Aerofotografico Nacional in Lima. The photos were digitally scanned and then georeferenced using coordinates collected during field work. |
The two types of image data were combined by using the hue and saturation from Landsat and intensity from the scanned airphotos. The resulting image contained color information from Landsat at the resolution of the airphoto. Stereo airphotos were used to create a digital elevation model (DEM) of the area. Topography was extracted using airphoto stereo-matching software. This software matches common points and attempts to define elevation values across the image. While consistent results were obtained for most of the drainage channels, the method failed for almost 40% of the total area. This was due to the extensive snow cover and the lack of GPS points in much of the northern part of the river basin. The digitized maps were used to provide topographic information in areas where the use of airphotos failed. A raster DEM interpolated from contours. This was combined with the results from the stereo airphotos, producing a DEM of the entire area suitable for the purposes here. The combined image data were draped onto topography, creating three dimensional views of the area. |
Landsat Image
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For more information, please contact:
Andrew K. Johnston
Smithsonian Institution
National Air and Space Museum
Center for Earth and Planetary Studies