Earth Explorer Data Sets 2
National Aerial Photography Program(NAPP):This is a set of aerial photographs covering conterminous US. These images are free from clouds and they are over five to seven year cycles. This program was started in the year 1987 and from then onwards it has been providing images to earth explorer. Earth explorer regards it as the most recent as well as consistent source of high quality aerial photography.
These photographs are obtained from an altitude of 20,000 feet. They are available as black and white or colored infrared. This depends on the location and date when they were taken. Each of the photos is centered on a 1/4th section of a 7.5 minute USGS quadrangle. An mile area of 5.5 X5.5 is covered by each of the photos.
The price for a high resolution scanned is $ 30.00 for each frame and for a medium resolution digitized frame is $ 3.00 for each.
National high altitude photography
The national high altitude photography program was functional between the years 1980-89. During these years its aim was to obtain aerial photography of the 48 conterminous states of united states on a repeat cycle of 5-7 years.
This photography has been taken from an altitude of 40,000 feet. It was acquired with the help of two different camera systems. The aim of doing so was acquiring coverage with two different scales. The black and white images were obtained by a lens having 6-inch focal length. The approximate scale for these images is 1:80,000. These photos cover an area of 11X11 miles.
While the colored images were obtained by a 8.35 inch lens. The approximate scale for these images is: 58,000. these images cover a 8 X 8 miles area.
The prices for these images are as usual, $30.00 for high resolution scanned and $3.00 for a medium resolution digitized scan.
Digital Line Graphs(DLGs):
In these images cartographic information is represented in digital vector form. The information derived from USGS maps and other related sources. The layers, categories or features available will depend on the scale.
Three primary types of DLG data sets are produced by USGS. They are large-scale DLGs (7.5 minutes), intermediate-scale DLGs (1:1000,000-scale), and small-scale DLGs( 1,2,000,000-scale). You will have to pay for these images only if you want them on CD or DVD. There are no charges for an FTP download.
Maps
There are two types of maps viz Digital Raster Graphics and National Atlas of the United States.
Digital raster graphic DRG is an image from USGSs standard series of topographic maps which include all collar information as well. It is actually scanned from the standard series of topographic maps.
The image within the neatline of the map is georeferenced towards the earths surface. It fits into the Universal Transverse Mercator projection. The DRH has the same horizontal positional accuracy and datum as the source map. The minimum resolution with which the maps is scanned is 250 dots per inch.
All quadrangles from the USGSs standard topographic map series for US, all its trusts as well as territories, have been covered in the DRGs.
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