Landsat processing standards in brief
There are two type of processing system to shape the standard products,
Level 1 Product Generation System (LPGS) – currently, all Landsat data is processed through LPGS. LPGS metadata is contained in a MTL.txt file and have these parameters,
- GeoTIFF output format
- Cubic Convolution (CC) resampling method
- 30-meter (TM, ETM+) and 60-meter (MSS) pixel size (reflective bands)
- Universal Transverse Mercator (UTM) map projection (Polar Stereographic projection for scenes with a center latitude greater than or equal to -63.0 degrees)
- World Geodetic System (WGS) 84 datum
- MAP (North-up) image orientation
There are three types of Level 1 processing
- Standard Terrain Correction (Level 1T) – provides systematic radiometric and geometric accuracy by incorporating ground control points while employing a Digital Elevation Model (DEM) for topographic accuracy.
- Systematic Terrain Correction (Level 1Gt) – provides systematic, radiometric, and geometric accuracy, while employing a Digital Elevation Model (DEM) for topographic accuracy.
- Systematic Correction (Level 1G) – provides systematic radiometric and geometric accuracy, which is derived from data collected by the sensor and spacecraft.
Another processing standard is the National Land Archive Production System (NLAPS). There are some available Landsat 4 and Landsat 5 data were processed through NLAPS. NLAPS metadata is contained in a .WO file, which accompanies all data files.
While the products generated by the LPGS and NLAPS systems are similar, there are geometric, radiometric and data format differences.
- Geometric differences, where both systems align the bands to the center of each pixel. Before December 2008, LPGS aligned the bands to the center of each pixel, and NLAPS aligned bands to the edge of each pixel.
- Radiometric Differences, where both system scale Level 1 products to a range of 1-254. DN values of 0 are reserved for scan gap and flag fill. DN values of 255 are reserved for saturation.
- Data Format Differences, where both system uses GeoTIFF format. But The 60 meter and 15 meter NLAPS and LPGS products may have different image sizes.
A very small number of Landsat TM scenes are processed using the National Land Archive Production System (NLAPS).
Some Landsat TM scenes include a Work Order (.WO) file that contains the metadata information about scenes processed on the National Land Archive Production System (NLAPS), common for Landsat 5 archives.
A file containing the ground control points (GCP) used during image processing is also included with Landsat MSS and TM data for controlled georeferencing.
Landsat 8 scenes include a Quality Assessment (QA) band file. Used effectively, the bits of the Quality Band improve the integrity of science investigations by indicating which pixels might be affected by instrument artifacts or subject to cloud contamination.
Landsat MSS and TM scenes also include a Verify Image File (VER.jpg), which displays a grid of verification points in various colors that represent the accuracy of geometric correction. Cross-correlation techniques based on the GLS 2000 dataset are used as reference. This graphic representation of the Geometric Verify Report (VER.txt) assists users in determining the geometric accuracy of each MSS and TM scene.
Landsat ETM+ SLC-off scenes also include Gap Mask files for each band. These ancillary data allow users identify the location of all pixels affected by the original data gaps in the primary SLC-off scene. Gap mask is a set of flat binary scan gap mask file which comes one per band.
The README file contains a summary and brief description of the file contents and naming convention. This file contains further clarification of files and metadata of the archive contents, a general documentation and contact information.
Need some more?
- determine the processing level of the Landsat scene from metadata
- FAQ for Landsat, band designation of each band
- Landsat Data Dictionary with more Landsat-related terms and thoughts