Earth Explorer Data Sets
National Atlas of United States
The national atlas of United States provides several types of maps and information. Some of the maps include topographic maps, forestation, climatic maps, historical maps, transportation, environmental maps, mineral wealth, etc. moreover it also has articles, graphs, etc. The information that they provide is very useful.
Digital elevation models (DEMS)
The digital elevation models are raster grids of uniformly spaced values of elevation. They are primarily derived from USGS topographic series of maps.
However from November 14 2006 Digital Elevation Models are not offered by USGS. Therefore if you want to view the most recent elevation coverage you can view National Elevation Dataset.
Satellite imagery: USGS sites
The Advanced Very High Resolution Radiometer: It provides multispectral data from the NOAA polar-orbiting satellites. This data is four to six band.
It has quite a continuous global coverage from June 1979. The data is generally acquired during morning or afternoon. On screen the images have a resolution of 1.1 kilometer at nadir.
The number of bands available is based on the satellite.
From EROS archive :
Georegistered Single-Scene AVHRR is a radiometrically as well as geometrically corrected single screen AVHRR data. It is processed depending on the parameters desired by the user. Therefore the user can decide the parameters like projection, pixel size, resembling method. The data is distributed on DVD and it is available in binary format which is 8- or 10-bit.
Apart from the AVHRR data mentioned above the USGS also prepares a series of derived AVHRR NDVI composites and Global Land Cover Characterization GLCC data.
Raw (level 1b) is a single scene and was collected from just one AVHRR satellite on a certain date and time. Roughly the size of this scene is about 2400X6400 kilometers. This is approximately 1491 X 4000 miles. NOAA Satellite Active Archive is used for public distribution.
The price of DVD or FTP of Georegistered(Level 1b) is $190.00.
AVHRR Normalized Difference Vegetation Index Composites
They are produced from the daily observations of multiple AVHRR. These daily observations have been composite together for creating an image that is almost cloud free. Thus these images feature maximum greenness. Bands one and two of AVHRR are used to create an NDVI ratio. This ratio produces a derived NDVI band composite.
The NDVI products available are given below.
Conterminous US and Alaska weekly and biweekly NDVI composites are available from January 1989 to date.
Lambert Azimuthally Equal-Area projection is used for casting US composites, while composites for Alaska are cast for Albers Equal-Area Conic projection. The data generally would consist of a composite for every AVHRR brands acquired as well as the derived NDVI bands. Binary 8-bit format is used for the files and you can get the them in the form of file download, CD, or DVD.
Global 10-day composites: these compose of AVHRR data which is 10 day composed. Moreover it also has a derived NDVI band for the period from April 1992 to may 1996. The data is cast to the interrupted Goode's Homolosine projection. Geographic subsets and resolution which is subsampled also are available.
Binary 8-bit format is used for these files and you can get them through File Download on a band-by-band basis.
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