Government Imagery Data, Free & Easy to Find!
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Aerial photography and satellite images provide state and local government officials with a bird’s eye view of the geography, assets, and infrastructure of their communities. These days, there are a lot of government imagery data formats that are freely available. Knowing what they are, how to access them, and what sorts of image analysis you can do with the data is very important.
Let’s start with going over some commonly used freely available data sources. I’ll start with ASTER imagery.
ASTER, (Advanced Spaceborne Thermal Emission and Reflection Radiometer) is a multispectral imaging instrument that launched in December 1999. ASTER data is used to create detailed maps of land surface temperature, reflectance, and it has two forward and backward looking bands of data, which can be used to generate digital elevation models, or DEMs. It also has a high spatial resolution, ranging from 15 -90 meters, so it can be used for a variety of image analysis applications, such as land cover analysis, vegetation mapping, change detection, and terrain analysis. You can access the imagery from the USGS GloVis Viewer, which is a quick and easy online search and order tool for selected satellite and aerial data.
Another type of data that you can access from the GloVIS site is MODIS data. MODIS (Moderate Resolution Imaging Spectro-radiometer) has a spatial resolution that ranges from 250 m – 1000m, and MODIS views the entire Earth's surface every 1 to 2 days, acquiring data in 36 spectral bands. These data products observe features of the land, oceans, and the atmosphere. MODIS Level 1 and atmosphere products are available through the LAADS web, Land Products are available through the Land Processes DAAC website at the U. S. Geological Survey EROS Data Center, and Cryosphere data products (snow and sea ice cover) are available from the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado.
Some other types of data that you may come across include ALI and Hyperion. ALI (Advanced Land Imager) provides image data over ten spectral bands, with spatial resolutions ranging from 30 meters for the multispectral bands and 10 meters for the panchromatic band. Hyperion collects 220 bands of data, with wavelengths ranging from 0.357 to 2.576 micrometers. It has a spatial resolution of 30 meters for all bands. Because it has this many bands, we refer to this type of data as hyperspectral data. Hyperspectral imaging has wide ranging applications for material identification in mining, geology, forestry, agriculture, and environmental management. These data products are also available for search and download through Earth Explorer or GloVis.
Landsat is one of the most popular of the freely available data sets. LANDSAT-7 is from the most recent Landsat mission, and is currently operated as a primary satellite with a spatial resolution of 30 meters. LANDSAT-5, from the previous Landsat mission, was equipped with a multispectral scanner (MSS) and thematic mapper (TM), which is a more advanced version of the observation equipment used in the MSS, and observes the Earth's surface in seven spectral bands that range from visible to thermal infrared regions. It has a spatial resolution of 30 meters, and all Landsat data is in now freely available in the USGS archive.
Another very popular freely available data type is NAIP data. The NAIP (National Agriculture Imagery Program) mission acquires multispectral aerial imagery during the agricultural growing seasons in the continental U.S. NAIP imagery products are available for free download through the USDA Geospatial Data Gateway.