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Data Formats

GeoTIFF: Imagery in this format use the industry-wide TIFF image specification from Adobe and include a special header for storing georeferencing information. Scenes in GeoTIFF format can easily be read into any image software package that recognizes TIFFs and those that can understand the GeoTIFF-specific header can also automatically georeference the image. More information about GeoTIFF can be found at the GeoTIFF site at remotesensing.org.
 
Orthorectified: Primarily Landsat imagery, and then primarily Landsat GeoCover Site. Orthorectification is the process by which the geometric distortions of the image are modeled and accounted for, resulting in a planimetricly correct image. To put it another way, our 3D world is imaged by most sensors in 2D and orthorectification corrects for many of the anomalies resultant from this conversion. Orthorectified imagery is particularly useful in areas of the world with exacerbated terrain features such as mountains, plateaus, etc. The orthorectification process for Landsat GeoCover yields map-accurate images which can be highly useful as base maps and may be easily incorporated into a GIS. The success of the orthorectification process depends on the accuracy of the DEM and the correction formulae. In the case of the data provided by GLCF, the most accurate publicly available DEM was used and an RMS error of 50 meters or better can be expected.
 
Terrain Corrected: Primarily Landsat imagery, the term is used at the USGS EROS Data Center. Terrain Correction (Level 1T) includes radiometric, geometric, and precision correction, as well as the use of a digital elevation model (DEM) to correct parallax error due to local topographic relief. For locations outside the U.S., the accuracy of the terrain-corrected product will depend upon the availability of local ground control points (GCPs), as well as the resolution of the best available DEM. All Level 1T products are processed by the National Land Archive Production System (NLAPS). See the USGS for further information.
 
Not Validated: Indicates that the data set has not been checked for calibration errors, processing errors, or excessive cloud cover. This refers to the data set itself and not necessarily the browse or preview images.
 
SLC-Off: The Scan Line Corrector (SLC) on the Landsat 7 ETM+ sensor malfunctioned in May of 2003. Since then, the only imagery the sensor is capable of acquiring is termed .SLC-off.. This type of Landsat 7 scene includes considerable striping on the sides of the WRS-2, though the center is still intact. See the USGS for a detailed explanation of this format. Also, the USGS and NASA created a solution to the striping issue by providing a .Gap-Filled. edition of .SLC-off.. This format fills the striped areas with imagery from a simultaneous acquisition. It is not perfect, but provides an entire scene.s worth of imagery. See the USGS for further discussion of this process. Note that the Gap-Filled solution sometimes results in stripes still, but mainly among clouds. The GLCF provides these two formats to its users to help continue the long-term record of Landsat imagery.
 
Level 1G: This is a format created by NASA to indicate imagery that is basically ready to use. .L1G" is indicative of "Level 1G", meaning the data has been processed to level 1 and is radiometrically and geometrically corrected. Note this is a systematic (automated correction) and does not mean that the pixels in the image are georeferenced. However, NASA claims that the Landsat 7 data is accurate to within 3-4 pixels. This is usually the case, if not better. In order to indicate processing level - not format - we have added the "L1G" extension. The format of the L1G data is "Unwrapped HDF". This means that in some image processing packages, you may easily download the _HDF.L1G file and load that, gaining access to all the HDF metadata, from corner point locations to sun zenith angle. This can be very helpful, particularly if you would rather not enter the specifications of each and every band by hand. Other users may prefer to load each band individually or their software may lack support for HDF. In this case, you need to load each band separately as a generic binary file. Most image processing packages will query for spatial data information for the file, and this can be found in the *.MTL.L1G file. See our Unwrapped HDF (L1G) File Format Guide. See the USGS website for further information.
 
BSQ: These data are stored as a flat binary file with header information stored in a separate file. A wide variety of header files exist; software packages may or may not be able to read the header files to get the image dimensions or georeferencing information. If the software package cannot understand the header file, this information must be entered in manually.
 
Mr.SID: This is a format developed by LizardTech Software, recently acquired by Celartem. Using wavelet technologies, images can be compressed at a fraction of the actual size. If your software does not support this image format, a free viewer, GeoExpress View can be downloaded from LizardTech's web site.



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