WELD Product Information

Overview

Since January 2008, the U.S. Geological Survey has been providing free terrain-corrected and radiometrically calibrated Landsat data via the Internet. This revolutionary data policy provides the opportunity to use all the data in the U.S. Landsat archive and to consider the systematic utility of Landsat data for long-term large-area monitoring. The NASA funded Web-enabled Landsat Data (WELD) project is systematically generating 30m composited Landsat Enhanced Thematic Mapper Plus (ETM+) mosaics of the conterminous United States and Alaska from 2002 to 2012. The WELD products are developed specifically to provide consistent data that can be used to derive land cover as well as geophysical and biophysical products for regional assessment of surface dynamics and to study Earth system functioning. The WELD products are free and are available via the internet. The WELD products are processed so that users do not need to apply the equations and spectral calibration coefficients and solar information to convert the ETM+ digital numbers to reflectance and brightness temperature, and successive products are defined in the same coordinate system and align precisely, making them simple to use for multi-temporal applications. They provide the first instance of continental-scale science-quality Landsat data with a level of pre-processing comparable to the NASA MODIS land products.

Data Policy

The WELD products are freely available for educational, research, or commercial applications. If you use the WELD products please cite them following the WELD Citation guidelines.

Funding

The WELD project is funded by the National Aeronautics and Space Administration (NASA) Making Earth System Data Records for Use in Research Environments (MEaSUREs) program under Cooperative Agreement NNX08AL93A. The free Landsat data access and the WELD product distribution is funded by the USGS.

Product Years Available and Planned Availability

Version 1.5 products are currently available for 2005, 2006, 2007, 2008, 2009, 2010 and 2011. Years 2002, 2003, 2004, and 2012 will be added as the input data become available. All years will be reprocessed as improved versions of the algorithms are developed.

WELD Team

Principal Investigator: David Roy

Scientist (algorithms and processing): Yuchu Qin

Scientist (algorithms and processing): Valeriy Kovalskyy

Distribution System Software & Web Developer: Indrani Kommareddy

Distribution System Hardware Architect: Anil Kommareddy

Senior Scientist (land cover mapping): Matthew Hansen

Scientist (land cover mapping): Alexey Egorov

Senior Scientists (Atmospheric Correction): Eric Vermote and Jeff Masek

EROS Distribution System Program Manager: John Dwyer

EROS Distribution System Integration and Maintenance: Tom Maiersperger, Jason Werpy, David Hill, Adam Dosch

Product Types

The WELD products are available for the conterminous United States (CONUS) and Alaska as weekly, monthly, seasonal (3 month) and annual products.

The monthly, seasonal and annual products are defined in a temporally nested manner following climate modeling conventions; the weekly products are defined more simply with respect to each calendar year.

The annual products are defined with each year as the preceding year's December through the current year's November.
The seasonal products are defined as Winter: December, January, February; Spring: March, April, May; Summer: June, July, August; Autumn: September, October, November.
The monthly products are defined by the days in each month.
The weekly products are defined as consecutive 7-day products with Week01: January 1 to January 7, Week02: January 8 to January 14, , Week 52: December 24 to December 30 (non-leap years) or December 23 to December 29 (leap years), Week 53: December 30th to December 31st (leap years) or December 31st (non-leap years).

The WELD products are available in GeoTIFF and HDF formats; the contents are the same, but the product distribution interfaces and product spatial dimensions are different.

Data Policy

The WELD products are freely available for educational, research, or commercial applications. If you use the WELD products please cite them following the WELD Citation guidelines.

Product Contents

Each pixel has 14 bands storing the information described below.

WELD Version 1.5 Product Contents
Band Name	Data Type	Valid Range	Scale factor	Units	Fill Value	Notes
Band1_TOA_REF	int16	-32767 -- 32767	0.0001	unitless	-32768	Top of atmosphere (TOA) reflectance and brightness temperature (BT) are computed using standard formulae and calibration coefficients associated with each ETM+ acquisition. Band 6 brightness temperature data are resampled to 30 m. The conventional ETM+ band numbering scheme is used.
Band2_TOA_REF	int16	-32767 -- 32767	0.0001	unitless	-32768
Band3_TOA_REF	int16	-32767 -- 32767	0.0001	unitless	-32768
Band4_TOA_REF	int16	-32767 -- 32767	0.0001	unitless	-32768
Band5_TOA_REF	int16	-32767 -- 32767	0.0001	unitless	-32768
Band61_TOA_BT	int16	-32767 -- 32767	0.01	Degrees Celsius	-32768
Band62_TOA_BT	int16	-32767 -- 32767	0.01	Degrees Celsius	-32768
Band7_TOA_REF	int16	-32767 -- 32767	0.0001	unitless	-32768
NDVI_TOA	int16	-10000 -- 10000	0.0001	unitless	-32768	Normalized Difference Vegetation Index (NDVI) value generated from Band3_TOA_REF and Band4_TOA_REF.
Day_Of_Year	int16	1 -- 366	1	Day	0	Day of year the selected ETM+ pixel was sensed on. Note (a) days 1-334 (or 1-335) were sensed in January-November of the nonleap (or leap) current year; (b) days 335-365 (or 336-366) were sensed in December of the nonleap (or leap) previous year; (c) in the annual composite of a leap year, day 335 always means November 30.
Saturation_Flag	uint8	0 -- 255	1	unitless	None	The least significant bit to the most significant bit corresponds to bands 1, 2, 3, 4, 5, 61, 62, 7; with a bit set to 1 signifying saturation in that band and 0 not saturated.
DT_Cloud_State	uint8	0, 1, 2, 200	1	unitless	255	Decision Tree Cloud Classification, 0 = not cloudy, 1 = cloudy, 2 = not cloudy but adjacent to a cloudy pixel, 200 = could not be classified reliably.
ACCA_State	uint8	0, 1	1	unitless	255	ACCA Cloud Classification, 0 = not cloudy, 1 = cloudy.
Num_Of_Obs	uint8	0 -- 255	1	unitless	None	Number of ETM+ observations considered over the compositing period.

Product Map Projections

The conterminous United States (CONUS) and Alaskan products are defined with the following map projection parameters.

WELD Product Projection Parameters
Projection: Albers Equal Area
Datum: World Geodetic System 84 (WGS84)
	CONUS	Alaska
First standard parallel	29.5˚	55.0˚
Second standard parallel	45.5˚	65.0˚
Longitude of central meridian	-96.0˚	-154.0˚
Latitude of projection origin	23.0˚	50.0˚
False Easting	0.0	0.0
False Northing	0.0	0.0

Note: The latitude of the CONUS and Alaskan projection origins fall outside the WELD product regions so that the Albers Northing value is always positive.

HDF Format Products

The products are generated in Hierarchical Data Format (HDF4) in separate 5000 x 5000 30-m pixel tiles defined in the Albers Equal Area projection. The HDF tiled products are available from EROS via simple anonymous FTP access.

There are a total of 501 CONUS and 162 Alaskan tiles referenced using a two digit horizontal and vertical tile coordinate system that is reflected in the HDF product filename. The images below illustrate the HDF product tile coordinate systems, please click on them to see higher resolution versions.

The HDF product filename is descriptive, simple, and amenable to scripting.

HDF Product Filename Convention
*<Region>.<Period>.<Year>.h<xx>v<yy>.doy<min DOY>to<max DOY>.v<Version Number>.hdf*
	Valid Range	Notes
<Region>	CONUS / Alaska
<Period>	annual, spring/summer/autumn/winter, month01/month02/, …,/month12, week01/week02/, …, /week52/week53	Annual products are generated from a year of data sensed from December 1st of the previous Year to November 30th of the current year. The standard seasonal definition adopted by the climate modeling community is used where winter is defined by the months: December, January and February. Week01 = January 1st to January 7th, Week53 = December 30th to December 31st (leap years) or December 31st (non-leap years).
<Year>	2005, 2006, 2007, ..., 2012
<xx>	00, 01, ..., 32 (CONUS) or 00, 01, ..., 16 (Alaska)	horizontal WELD tile coordinate.
<yy>	00, 01, ..., 21 (CONUS) or 00, 01, ..., 13 (Alaska)	vertical WELD tile coordinate.
<min DOY>	001, 002, …, 366	minimum non-fill Day_Of_Year pixel value present in the tile.
<max DOY>	001, 002, …, 366	maximum non-fill Day_Of_Year pixel value present in the tile.
<Version Number>	1.1, 1.3, …, 2.0, 2.1, 2.2, …	Major and minor algorithm version changes reflected in the first and second digits respectively.

In addition, for each WELD tile there is a corresponding static Alaska.latlon.h<xx>v<yy>.v<Version Number>.hdf or CONUS.latlon.h<xx>v<yy>.v<Version Number>.hdf file that contains the geographic latitude and longitude for the center of each 30m pixel (decimal degrees, scale factor 1, data type double, datum WGS84).

GeoTIFF Format Products

The products are also available in the GeoTIFF format. The GeoTIFF format data are only available via the What You See Is What You Get WELD Internet distribution interface. This interface supports interactive ordering of any arbitrary rectangular area that has a data volume of no more than 2GB. The products are defined in the Albers Equal Area projection.

Due to the filename length constraint of the Microsoft Windows operating system, each of the 14 bands are saved as separate GeoTIFF files in a sub-directory. The sub-directory name conforms to the HDF filename convention and also includes the bounding longitude and latitude of the ordered data area.

GeoTIFF Product Filename Convention
*sub-directory name: <Region>.<Period>.<Year> .lon<min lon>to<max lon> .lat<min lat>to<max lat>. doy<min doy>to<max doy>. v<Version Number>* band name: <band name>.TIF
	Valid Range	Notes
<Region>	CONUS / Alaska
<Period>	annual, spring/summer/autumn/winter, month01/month02/, …,/month12, week01/week02/, …, /week52/week53	Annual products are generated from a year of data sensed from December 1st of the previous Year to November 30th of the current year. The standard seasonal definition adopted by the climate modeling community is used where winter is defined by the months: December, January and February. Week01 = January 1st to January 7th, Week53 = December 30th to December 31st (leap years) or December 31st (non-leap years).
<Year>	2005, 2006, 2007,..., 2012
<min lon>	-127.000000 to -65.000000 (CONUS) -175.000000 to -125.000000 (Alaska)	the minimum pixel center longitude of the ordered data area; specified to 6 decimal places.
<max lon>	-127.000000 to -65.000000 (CONUS) -175.000000 to -125.000000 (Alaska)	the maximum pixel center longitude of the ordered data area; specified to 6 decimal places.
<min lat>	23.000000 to 52.000000 (CONUS) 50.000000 to 72.000000 (Alaska)	the minimum pixel center latitude of the ordered data area; specified to 6 decimal places.
<max lat>	23.000000 to 52.000000 (CONUS) 50.000000 to 72.000000 (Alaska)	the maximum pixel center latitude of the ordered data area; specified to 6 decimal places.
<min DOY>	001, 002, …, 366	minimum non-fill Day_Of_Year pixel value in the data.
<max DOY>	001, 002, …, 366	maximum non-fill Day_Of_Year pixel value in the data.
<Version Number>	1.1, 1.3, …, 2.0, 2.1, 2.2, …	Major and minor algorithm version changes reflected in the first and second digits respectively.
<band name>	Band1_TOA_REF, Band2_TOA_REF,…, Num_Of_Obs	Name of the band, see HDF Product Filename Convention.

Known Version 1.5 Product Issues

Pixel alignment

The Albers coordinates of the WELD pixels have a sub-pixel misalignment with the Albers coordinates defining the U.S. National Land Cover Data dataset. The WELD Albers projection origin does not fall perfectly at a WELD product pixel center. For example, the CONUS projection origin is in horizontal tile 17, vertical tile 22 at column 520.000, row 493.333, and the Alaska projection origin is in horizontal tile 5, vertical tile 16 at column 3390.000, row 2478.333 (where column 0.5, row 0.5 refers to the center of the NW pixel of a tile). This issue will be rectified in the next WELD product version.

2007 and 2010 product mixed 30m thermal band resolution issue

Since February 26^th 2010 the Landsat L1T data have been produced at USGS EROS with the 60m thermal bands resampled to 30m (resampling applied in the L0 to L1T processing at USGS). Prior to February 26^th 2010 the WELD product thermal bands were generated at 30m as part of the WELD processing using a different nearest neighbor resampling methodology. As a consequence the 2007 and 2010 WELD product 30m thermal bands were generated from L1T data processed with both methodologies. The impact of this mixed thermal band resolution issue is thought to be minimal.

2010 Summer and Annual Composite (central Iowa, SE Minnesota, Wisconsin)

There were unusually cloudy conditions at the time of Landsat ETM+ overpass for a single Landsat path over central Iowa, SE Minnesota, and west central Wisconsin in the summer months of 2010; consequently, the 2010 Summer WELD product is cloudy and the Annual WELD product does not include summer observations in this locality.

Extent of Alaska

Because of the scarcity of Landsat acquisitions over the islands off the Alaskan west coast, many western islands are not included in the Version 1.5 Alaska WELD products. More of these Aleutian islands are being considered for inclusion in the next WELD product version.

gdalinfo utility in Ubuntu Operating System is unable to read hdf tile information for certain WELD product years

This issue is currently under investigation, it occurs for product years 2006 to 2009 only; we suspect that it is caused by a production system library incompatibility.

Product Improvements on Previous Versions

Version 1.5

Fix the tile bounding box coordinates in the HDF global attributes. Although the global attributes of tile bounding box coordinates are not required by remote sensing software packages, they are provided so that users can access the coordinates using command line software such as the HDF "ncdump" utility.

Version 1.4

Accommodate improved incoming solar radiation and sun-earth distance astronomical model data published in Chander, G., Markham, B.L., Helder, D.L. (2009). Summary current radiometric calibration coefficients for Landsat MSS, TM, ETM+, and EO-1 ALI sensors, Remote Sensing of Environment 113 (2009) 893 903.

Compute top of atmosphere reflectance using per-pixel solar zenith angle rather than the fixed acquisition center solar zenith angle.

Add the GridStructure data model of the HDF-EOS format to support all major proprietary remote sensing software packages (ENVI, ERDAS Imagine, PCI Geomatica, etc) to enable them to directly access the map projection information.

Version 1.3

Fix the compositing algorithm so that it selects smoke-free rather than smoke contaminated observations.

Version 1.2

First publicly available WELD product version.

Product Accuracy/Consistency

No formal assessment of the WELD product accuracy/consistency has been undertaken. This is planned for the Version 2.0 products.

Planned Version 2.0 Product Improvements

(1) improved compositing algorithm

(2) atmospheric correction of the top of atmosphere reflectance bands.

(3) radiometric normalization of the reflectance to nadir view and fixed solar zenith angle.

(4) gap filling of the Landsat ETM+ SLC-off gaps in the reflectance and thermal bands.

(5) CONUS 30m land cover: weekly snow/ice, water and bare ground; annual peak greenness tree cover, bare ground and other vegetation.

GeoTIFF

The GeoTIFF format products are available for all or select bands and in user defined regions via the What You See Is What You Get (WYSIWYG) WELD Internet distribution interface at http://weld.cr.usgs.gov

HDF

The HDF tiled products are available via anonymous FTP at ftp://weldftp.cr.usgs.gov/

Single Pixel Time Series

Users may extract WELD product pixel values for any 30m pixel location, selected either interactively or by entering the pixel latitude and longitude coordinates, via the What You See Is What You Get (WYSIWYG) WELD Internet distribution interface at http://weld.cr.usgs.gov. The ordered pixel values for all years of available product are emailed to the user in a simple comma separated text format with the relevant band scale factors and offsets applied.

Open Geospatial Consortium (OGC) compliant browse imagery

Select OGC compliant WELD browse images are available at http://webmap.ornl.gov/wcsdown/dataset.jsp?ds_id=111112

Distribution metrics for the What You See Is What You Get WELD Internet distribution interface are available at http://weld.cr.usgs.gov/WYSIWYG/request_metrics.php
The FTP distribution metrics are tabulated below:

	Number of WELD tiles	Download Volume (GB)
2010 October	2330	457.53
2010 November	3226	497.92
2010 December	876	165.21
2011 January	123	24.59
2011 February	121091	12664.72
2011 March	2	0.48
2011 April	1913	360.05
2011 May	60819	5841.55
2011 June	715	154.22
2011 July	520	114.67
2011 August	592	164.76
2011 September	2094	301.91
2011 October	325	39.15
2011 November	65288	6741.32
2011 December	2506	312.6
2012 January	105638	15229.35
2012 February	11097	1757.57
2012 March	19017	1933.58
2012 April	5309	924.91
TOTAL	403,481	47,686.09GB

WELD HDF tile coordinate calculator

This tool allows one to find the WELD tile and pixel coordinates, or the Albers map coordinates of a specified geographic coordinate (Forward Mapping), or to find the geographic coordinates of a specified WELD pixel location (Inverse Mapping). There are two ways to access the tool. An online version is available. A standalone version is available for computers running Unix/Linux operating systems; the C source code and installation instructions can be downloaded.

WELD Tile to GeoTIFF

This tool converts WELD tile products from HDF format to GeoTIFF format. This standalone code runs on Linux/Unix operating systems and the C source code and installation instructions can be downloaded.

This format conversion can also be accomplished using the gdal support library (we recommend that you use gdal support library version 1.8.1 or higher), for example as:
>gdal_translate -a_srs WeldConusTiles.prj HDF4_EOS:EOS_GRID:"input.hdf":WELD_GRID:Band1_TOA_REF output.tif
where the file "WeldConusTiles.prj" is available at http://globalmonitoring.sdstate.edu/projects/weld/weld_arc.php

Please note that due to a past software library issue WELD V1.5 HDF products for years 2007, 2008, and 2009 data cannot be converted using gdal command tools and for these years we recommend that you use the above C code as a workaround. This issue will be resolved in the next WELD product version.

How to import and visualize WELD HDF tile products in Arc-GIS

This package contains notes, shape files, projection files, and an Excel spreadsheet World File generator, that can be used to import and visualize WELD HDF tile products in Arc-GIS. This package can be downloaded.

How to attach projection information to WELD HDF tile products in ENVI

This package contains notes and an Excel spreadsheet that can be used to attach projection information to WELD HDF tile products in ENVI. This package can be downloaded.

The Algorithm Theoretical Basis Document is now available (2.2MB).

Kovalskyy, V., Roy, D. P., Zhang, X., Ju, J., 2011, The suitability of multi-temporal Web-Enabled Landsat Data (WELD) NDVI for phenological monitoring – a comparison with flux tower and MODIS NDVI, Remote Sensing Letters, 3:4, 325-334.

Hansen, M.C., Egorov, A, Roy, D.P., Potapov, P., Ju, J., Turubanova, S., Kommareddy, I., Loveland, T. , 2011, Continuous fields of land cover for the conterminous United States using Landsat data: First results from the Web-Enabled Landsat Data (WELD) project. Remote Sensing Letters, 2, 4:279-288.

Wulder, M.A., White, J.C., Masek, J.G., Dwyer, J., Roy, D.P., 2011, Continuity of Landsat observations: Short term considerations, Remote Sensing of Environment, 115: 747-751.

Roy, D.P., Ju, J., Kline, K., Scaramuzza, P.L., Kovalskyy, V., Hansen, M.C., Loveland, T.R., Vermote, E.F., Zhang, C., 2010, Web-enabled Landsat Data (WELD): Landsat ETM+ Composited Mosaics of the Conterminous United States, Remote Sensing of Environment, 114: 35-49.

Roy, D.P., Ju, J., Mbow, C., Frost, P., Loveland, T.R., 2010, Accessing Free Landsat Data via the Internet: Africa’s Challenge, Remote Sensing Letters, 1:111-117.

Roy, D.P., Ju, J., Lewis, P., Schaaf, C., Gao, F., Hansen, M., Lindquist, E., 2008, Multi-temporal MODIS-Landsat data fusion for relative radiometric normalization, gap filling, and prediction of Landsat data, Remote Sensing of Environment, 112:3112-3130.

Ju, J. and Roy, D.P., 2008, The Availability of Cloud-free Landsat ETM+ data over the Conterminous United States and Globally, Remote Sensing of Environment, 112:1196-1211.

"The Web Enabled Landsat Data (WELD) Products and Global Product Prototyping",Roy, D.P., Kovalskyy, V., Kommareddy, I., Qin, Y., Votava, P., Nemani, R., Hansen, M., Vermote, E.F., Boschetti, L., Baraldi, A. , Ju, J., Dwyer, J. , Loveland, T., Center for Earth Observation and Digital Earth (CEODE), Beijing, China, January 18 2012.

"The Web Enabled Landsat Data (WELD) Products and Global Product Prototyping",Roy, D.P., Kovalskyy, V., Kommareddy, I., Qin, Y., Votava, P., Nemani, R., Hansen, M., Vermote, E.F., Boschetti, L., Baraldi, A. , Ju, J., Dwyer, J. , Loveland, T., International Workshop on Finer Resolution Global Land Cover Mapping, Tshingua University, Beijing, China, January 16-17 2012.

"An improved multi-temporal Landsat ETM+ compositing approach for the generation of Web-enabled Landsat data (WELD) mosaics",Qin, Y. and Roy, D.P., 2011, B51M. Remote Sensing of Long-Term Ecological Trends III session, Fall Meeting, AGU, San Francisco, Calif., 5-9 Dec. 2011.

"Web-enabled Landsat data (WELD) Project Status and Some Lessons Learned From Bulk Landsat Science Data Processing",Roy, D.P., Kommareddy, I., Ju, J., Hansen, M., Vermote, E., Qin, Y., Kovalskyy, V., Landsat Science Team, USGS EROS Center, Sioux Falls, August 16-18 2011.

"Overview of WELD status, early product utility, and planned WELD developments",Roy, D.P., Ju, J., Kommadreddy, I., South African National Space Agency (SANSA), Earth Observation Centre, Hartebeesthoek, South Africa, May 12th 2011.

"Web-Enabled Landsat Data (WELD): A Consistent, Long-Term, Large-Area, 30m Data Record For The Terrestrial User Community", Roy, D.P., Ju, J., Kommadreddy, I., 34th International Symposium on Remote Sensing of Environment, April 10-15, 2011, Sydney, Australia.

"Continental-scale validation of MODIS-based and LEDAPS Landsat ETM+ atmospheric correction methods", Ju, J., Vermote,E., Roy, D.P., Masek, J., 34th International Symposium on Remote Sensing of Environment, April 10-15, 2011, Sydney, Australia.

"Demonstration of MODIS-Landsat data fusion to provide a consistent, long-term, large-area data record for the terrestrial user community - The Web-enabled Landsat data (WELD) Project - a 5 year NASA MEASURES funded project", Roy, D.P., Ju, J., Kommadreddy, I., American Geophysical Meeting, Fall Meeting, San Francisco, CA, 13-17 December 2010, Eos Transactions, Suppl., v. 91: Washington, D.C., American Geophysical Union, ID IN31C-04, IN31C.

"Web-enabled Landsat data (WELD) Project a NASA Making Earth System data records for Use in Research Environments (MEASURES) funded project, Quick Overview of WELD Project & WELD Product Distribution Metrics", Kommareddy, I., Roy, D.P., Ju , J., 9th Earth Science Data System Working Group (ESDSWG), New Orleans, October 20-22, 2010.

"Web-enabled Landsat data (WELD) Project, a NASA Making Earth System data records for Use in Research Environments (MEASURES) funded project, Quick Overview of WELD Project Status & Recent WELD Reflectance Domain Research", Roy, D.P., Ju, J., Kommadreddy, I., Landsat Data Products Workshop II, Boston University, November 1-3, 2010.

"NASA Web-enabled Landsat Data (WELD) project status", Ju, J. and Roy, D.P., Workshop on Earth Observation for Sensitive Factors of Global Change: Mechanisms and Methodologies, June 16-17, 2010, Beijing, China.

"Web-enabled Landsat data (WELD) Project Status", Roy, D.P., Ju, J., Kommareddy, I., NASA Land Cover Land Use Spring Science Team Meeting, April 20-22, 2010, Bethesda, Maryland.

"Web-enabled Landsat data (WELD) Project Status", Roy, D.P., Ju, J., Kommareddy, I., Landsat Science Team Meeting, January 19-21, 2010, Computer History Museum, 1401 N Shoreline Boulevard, Mountain View, CA.

"Web-enabled Landsat data (WELD): a consistent seamless near real time MODIS-Landsat data fusion for the terrestrial user community a NASA Making Earth System data records for Use in Research Environments (MEASURES) funded project", Roy, D.P. and Ju, J., Landsat Data Products Workshop, October 27-29, 2009, Boston University, Boston, MA.

"Web-enabled Landsat data (WELD): a consistent seamless near real time MODIS-Landsat data fusion for the terrestrial user community", Roy D.P. and Ju, J., Landsat Science Team Meeting, January 6-8, 2009, U.S. Forest Service, NRRC Building E - Fort Collins, Colorado.

"Web-enabled Landsat data (WELD): a consistent, long-term, large-area, data record for the terrestrial user community", Roy, D.P., Ju, J., Vermote, E., Egorov, A., Kovalskyy, V., Zhang, C., Loveland, T., Hansen, M., Scaramuzza , P., Kline, K., Yoem, J.M., Kommadreddy, I., Eos Trans. AGU, 90(52), December 2008, San Francisco, Fall Meet. Suppl., Abstract IN43C-1166.

Example true color CONUS and Alaska WELD product browse JPG images are available.

The Landsat Program

Landsat Image Mosaic Of Antarctica (LIMA)

Landsat Image Mosaic of Canada

Landsat Image Mosaic of Australia

Landsat Data Continuity Mission (LDCM)

NASA Earth Exchange (NEX) Web Portal

If you wish to cite the WELD products in a report or publication please cite:

Roy, D.P., Ju, J., Kline, K., Scaramuzza, P.L., Kovalskyy, V., Hansen, M.C., Loveland, T.R., Vermote, E.F., Zhang, C., 2010, Web-enabled Landsat Data (WELD): Landsat ETM+ Composited Mosaics of the Conterminous United States, Remote Sensing of Environment, 114: 35-49.

If you use a WELD product generated graphic or browse image please insert the text "WELD" somewhere that is clearly visible.

I cannot open HDF files downloaded from the WELD FTP site using gdal command line tools.

Please note that due to a past software library issue WELD V1.5 HDF products for years 2007, 2008, and 2009 cannot be opened reliably using gdal command line tools. To read these products using gdal please see the Software Tools section of this site and click on "WELD Tile to GeoTIFF link" and download the C code. Follow the instructions in the Readme. This software converts any WELD tile from HDF format to GeoTIFF format and will circumvent this issue.

Please note that WELD V1.5 HDF products for years 2005, 2006, 2010 and 2011 do not have this issue. This issue will be resolved in the next WELD product version.

Should I use the HDF or the GeoTIFF format WELD products ?

If your application requires large-area and long-term WELD data then the HDF products are recommended because the HDF internal compression greatly reduces the file size and because the anonymous ftp access allows simple bulk data ordering.

If you wish to select the WELD products interactively by examination of browse imagery and/or your application requires WELD data for a small region then the GeoTIFF format available via the What You See Is What You Get (WYSIWYG) WELD Internet distribution interface is recommended.

Why are there sometimes gaps in the WELD products?

The gaps are caused by (i) the failure of the Landsat 7 ETM+ Scan Line Corrector which since May 2003 has reduced the amount of available data in each ETM+ acquisition by about 22% , (ii) the Landsat ETM+ orbit and view geometry such that the same location is only sensed once every 16 days, (iii) cloud cover - only Landsat acquisitions with a cloud cover less than 80% are used to make the WELD products.

I have an older version of the WELD products, do I need the more recent version ?

Major and minor version changes are reflected in the first and second digits respectively of the version number. In general it is preferable to use the latest WELD product version which reflects improvements to the WELD processing algorithms and input data. Please consult the Version Product Quality/Product Improvements on Previous Version information posted on this web site.

How can I calculate the geographic longitude and latitude coordinates of a pixel in an HDF tile?

There are two ways: (1) a WELD tile calculator software tool is provided, or (2) for each WELD tile there is a corresponding static Alaska.latlon.h<xx>v<yy>.hdf or CONUS.latlon.h<xx>v<yy>.hdf file that contains the geographic latitude and longitude for the center of each 30m pixel available via the HDF anonymous ftp access.

Why are the pixel values so high ?

The Product Documentation / Product Contents information on this web site explains that the data are stored with a scale factor; multiply the pixel value by the scale factor to get the true pixel value; for example, reflectance is stored in the WELD products with a scale factor of 0.0001, so a pixel value of 500 corresponds to a reflectance of 500 x 0.0001 = 0.05.

What is a fill value ?

Pixels that have no data in them are denoted with a fill value; see The Product Documentation / Product Contents information on this web site for the fill values for each WELD band.

Why do the monthly, seasonal and annual WELD products for 2003 onwards sometimes look stripey ?

This is because of the failure of the Landsat 7 ETM+ Scan Line Corrector which since May 2003 reduced the amount of available data in each ETM+ acquisition by about 22% in a regular striped pattern - the compositing algorithm is sensitive to the number of observations in the compositing period. If you really hate the stripes, try the gaps, please use the weekly WELD products, for example, see http://globalmonitoring.sdstate.edu/projects/weld/browses.html.

I order data from the What You See Is What You Get (WYSIWYG) WELD Internet distribution interface at http://weld.cr.usgs.gov but do not receive any notification emails.

This may be because your Spam filter is not accepting the WELD notification emails from weld@usgs.gov or because the notification emails have been placed in your junk email folder. Please check.

I have forgotten my password for the What You See Is What You Get (WYSIWYG) WELD Internet distribution interface at http://weld.cr.usgs.gov

No problem, do the following: 1) Enter your email only (do not enter a password as you have forgotten it), 2) Click on Reset Password, 3) You will be emailed a temporary password, 4) Enter your email and the temporary password you were emailed, 5) Follow the instructions to reset your password to a different one.