Frequently Asked Questions

Mapping, Remote Sensing, and Geospatial Data

The USGS provides the mapping and digital geospatial foundation for the Nation.

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Cape Town, False Bay, South Africa
Landsat atmospheric correction and surface reflectance retrieval algorithms are not ideal for water bodies due to the inherently low surface reflectance of water. Similarly, surface reflectance values greater than 1.0 can be encountered over bright targets such as snow and playas. These are known computational artifacts in the Landsat surface...
Landsat TM No-Payload Correction Data Example
Payload Correction Data (PCD) provides critical information when correcting for geometric distortions inherent to the imaging system and temperature values used to estimate per-scan gains and biases necessary for the radiometric calibration of the instrument's thermal band data. Over 260,000 Landsat 5 Thematic Mapper (TM) scenes acquired between...
Earth at night.
Black browse images are night (ascending) scenes, which are occasionally acquired for WRS-2 rows 123 to 246. Ascending scenes are available to download. Learn more: How to search and download ascending Landsat scenes
Landsat image shows the marine stratus and stratocumulus cloud layer that moved into the San Francisco Bay-Delta
The C Function of Mask (CFMask) algorithm is used in Landsat Collection 1 Level-1 data processing. This algorithm provides a full-image “Scene Cloud Cover” estimation of the percentage of cloud cover calculated over an entire Landsat scene.   Land Cloud Cover, which is also included, is determined by calculating the percentage of clouds over land-...
SLC-Off showing showing satellite image with parallel bands of missing image; and SLC-On gap mask with correlating blue bands.
Band-specific gap mask files are included with every Landsat 7 Scan Line Corrector (SLC)-off Level-1 data product. These ancillary data identify the location of all pixels affected by the original data gaps in the primary SLC-off scene. The gap mask is provided as a series of individual band files, in compressed (GZIP) GeoTIFF format. Left:...
Example of striping in Landsat 7 ETM+ Band 6 high gain data, processed before Nov. 23, 1999.
Landsat 7 acquires thermal data in two bands from one detector in  both high (Band 6H) and low (Band 6L) gain. The difference in gain settings is important to different types of studies (i.e., clouds vs. deserts). Aside from the resolution differences and saturation on the high and low ends, the two bands provide the same Digital Numbers (DN) for...
World Reference System-2 (WRS-2) - Day/Descending
The Worldwide Reference System (WRS) is a global system that catalogs Landsat data by Path and Row numbers. Landsat satellites 1, 2 and 3 followed WRS-1, and Landsat satellites 4,5,7, and 8 follow WRS-2. Learn more: Landsat Path Row Shapefiles and KML Files The Worldwide Reference System (NASA)
Landsat Level-2 Surface Reflectance Example
There are several Landsat data products that are useful for science applications and land use/land change studies: Landsat Collections Level 1 - Ensures that the data in the Landsat Level-1 archive are consistent in processing and data quality to support time-series analyses and data stacking. Each Level-1 data product includes individual spectral...
Earth As Art 4 satellite image - geometric desert
Definitive Ephemeris is used for geometrically correcting Landsat 7 data and providing improved accuracy over predicted ephemeris. Learn more (and download DE files): Landsat Definitive Ephemeris
Aug 2013 Response Linearization Look Up Tables Update Close up - Band 6
Landsat Response Linearization Look Up Tables (RLUT) are additional files that accompany Calibration Parameter Files (CPFs) and contain a mapping lookup table to linearize the output of the Landsat 8 Operational Land Imager (OLI) detectors. Learn more (and download RLUT files): Landsat Response Linearization Look Up Tables
White Sands Radiometric Calibration Site
Landsat Bias Parameter Files (BPFs) supply radiometric correction parameters that are applied during Level-1 processing of Landsat data. Learn more (and search for BPF files): Landsat Bias Parameter 
Calibration/Validation Test Sites
Landsat Calibration Parameter Files (CPFs) provide radiometric and geometric coefficients needed for processing of raw, uncorrected Landsat image data into Level-1 data products. Over 15,000 coefficients are issued to span distinct timeframes and are updated with improved calibration coefficients. CPFs are often updated with improved coefficients...