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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Landsat Collections Fact Sheet
In 2016, the USGS reorganized the Landsat archive into a tiered collection. This structure ensures that Landsat Level-1 products provide a consistent archive of known data quality to support time-series analyses and data “stacking”, while controlling continuous improvement of the archive and access to all data as they are acquired. Learn more:...
Landsat Geometric Verify Image
The Verify Image (_VER.jpg) and Geometric Verify Report (_VER.txt) files are included with Landsat MSS and TM Collection 1  Level-1 scenes that have processed into Tier 1. The Verify Image File displays a colored grid of verification points to represent the accuracy of geometric correction, using cross-correlation techniques to compare the product...
Land of Terror - Earth As Art image of Algeria
The sensors aboard each of the Landsat satellites were designed to acquire data in different ranges of frequencies along the electromagnetic spectrum (View Bandpass Wavelengths for all Landsat Sensors). The Multispectral Scanner (MSS) carried on Landsat 1,2,3,4 and 5 collected data in four ranges (bands); the Thematic Mapper (TM) sensor on Landsat...
color photo of South Dakota state mosaic puzzle
In order to obtain a "seamless" mosaic, radiance (and preferably reflectance) might need to be calculated before performing the mosaic because gain changes might occur in one or more of the scenes. When two scenes have different gain states, they have different dynamic ranges and there will be a shift in Digital Number (DN) values from one scene...
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; see this FAQ for more information on searching and downloading ascending 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...