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This spreadsheet contains 99 Landsat 4 TM scenes and 10,138 Landsat 5 TM scenes processed by NLAPS: Download Landsat 4-5 TM NLAPS scene list. Future plans include adding these to EarthExplorer's Landsat Legacy dataset section and making them available to download.
LPGS vs NLAPS Processing Systems: Similarities and Differences
The data produced by NLAPS and LPGS have unique characteristics, and users need to be aware of when comparing data from each system:
Similarities
Pixel Alignment: For each scene, Landsat spectral bands are aligned to a common center 1,1 / X,Y location for each pixel. (The pixel centers are aligned but the edges are not.) The X,Y center location is noted in each scene's metadata file.
Differences
Resampling Methods: NLAPS and LPGS use different ephemeris files and different algorithms to process quaternion, gyro, and gyro drift data. This may cause some slight additional differences when comparing the data.
Data Format: while both NLAPS and LPGS have the 'BitsPerSample' tag set to 8 within the GeoTIFF file header, NLAPS has the SampleFormat tag set to unsigned integer format. LPGS does not use the SampleFormat tag in its GeoTIFF products, even though they are also unsigned integer format.
Gimbaled X-Band Antenna (GXA) Slewing Anomalies: GXA anomalies appear as scan line offsets or extensions and can occur when the GXA redirects itself from one ground station to another, and Level-1 processing may correct this problem in some instances. LPGS estimates an 'End-of-Line' (EOL) and processes the scans with that estimated number. NLAPS defines no EOL as 'no data,' and zero-fills the affected scans.
Metadata files: LPGS-processed Landsat Collection 1 Level-1 data products include a metadata (MTL.txt) file; data processed by NLAPS include a Work Order (WO.txt) file that contains the scene metadata.
NLAPS Specifications
NLAPS scene ID structure: Scenes processed by NLAPS retain the historical scene ID, as displayed below.
Example: LT50010651985144AAA02,
Structure: LLNppprrrYYYYDDDAAAXX, where:
LL= L = Landsat sensor (LT for TM scenes)
N= Satellite number (4 = Landsat 4 5 = Landsat 5)
ppp=Scene starting path
rrr= Scene starting row
YYYY= Last two digits of the acquisition year
DDD= Julian date of acquisition (DOY)
AAA= Ground station identifier
XX= Scene processing version (01, 02, etc.)
NLAPS Work Order (.WO.txt) File
The WO.txt file (titled Correction Processing Report) provides a record of the work executed into the product order. This file is in ASCII format and contains information relative to the processing performed and the parameters used (e.g., latitudes and longitudes specified in degrees, and heights specified in meters).
The following are included in the WO.txt file:
- Product order information (order number); processing levels, projection parameters and datum
- Radiometric correction coefficients used for each band, with gains and offsets displayed
- Radiometric quality assessment coefficients
- Product formatting
- Processing start and end times
Additional details about NLAPS data processing can be found in the National Land Archive Production System (NLAPS) Precision and Terrain Formats Description Document and the National Land Archive Production System (NLAPS) Systematic Format Description Document. Please contact custserv@usgs.gov for information on accessing these documents.
