Sustainability of Digital Formats: Planning for Library of Congress Collections

NLAPS Data Format (NDF) is a format designed and primarily used by the USGS (EROS Data Center) for distribution of radiometrically and geometrically corrected Landsat data (satellite imagery). NLAPS is one of the processing systems that has been used to generate U.S. Geological Survey (USGS) Landsat corrected Level 1 products from uncorrected Level 0 images. The newer system, LPGS, does not generate images in the NDF format. See Notes below for more on the history of Landsat imagery distribution.

NDF datasets consist of several files: a header file with the extension .H1 and one or more associated raw data files (often .I1, .I2, etc., for separate spectral bands). Files with supporting metadata may also be present using extensions .WO Work order report), HI (History and processing parameters ). Header and other supporting files are in ASCII. DEM (Digital Elevation Model) data may also be included, using extensions .HD and .DD. If more than one resolution is packaged together, the extensions, .H2, .H3, etc. will be used for the headers for each resolution.

Over the years, Landsat Level 1 imagery has been generated on demand from Level 0 images through different generations of processing systems of which NLAPS was the primary system from roughly 1995 to 2004. All orders for Landsat Level 1 imagery placed via EarthExplorer or GloVis (systems for online search and ordering of USGS data) prior to March 31, 2004 were processed by NLAPS and available in NDF format. All Landsat 4 Thematic Mapper scenes were processed through NLAPS prior to April 15, 2009. See Notes below for information about USGS transition from NLAPS to LPGS (Level 1 Product Generation System), which does not generate data in NDF format.

NLAPS NDF format is supported for import in several GIS, image processing, remote sensing analysis, and spatial modeling applications, including: ERDAS IMAGINE (see supported data formats), Envi, GDAL, PCI Geomatics and IDRISI. Several of these systems note limitations which may be limitations inherent in the format or in the software's ability to handle format variants. For example, GDAL documentation states, "The NDF driver only supports 8-bit data. The only supported projection is UTM. NDF version 1 (NDF_VERSION=0.00) and NDF version 2 are both supported."

Landsat satellites have been taking images of the earth since 1972. See Landsat Missions Timeline. Over this period, the systems for processing the imagery for distribution and the formats available have changed. In general, the procedure has been to store Level 0 (uncorrected images) and generate Level 1 images with various types of correction for distribution. See What are the descriptions of the levels of processing?

The National Landsat Archive Production System was one of the systems used for generation of Level 1 images from the Level 0R (raw, uncorrected) images based on user requests. Version 1 of the NLAPS Data Format (NDF) was published in 1995 and became the offical distribution format of the USGS EROS (Earth Resources Observation and Science Center. Prior to April 15, 2009, all Landsat 4 TM scenes were processed through NLAPS. Beginning in September 2010, LPGS (Level 1 Product Generation System) became the primary processing system for all Landsat standard data products. The LPGS system does not generate images in the NDF format, instead using more widely used formats, including GeoTIFF. As of January 2011, NLAPS was used only for processing a subset of Landsat 4 and Landsat 5 data.