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About the WELD Project

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 ten years 2003, 2004, ... 2012. These products will be reprocessed as improved versions of the algorithms are developed.


WELD Team

Principal Investigator: David Roy
Scientist (algorithms and processing): Valeriy Kovalskyy
Scientist (algorithms): Hankui Zhang
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


Version 1.5 Product Documentation

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.


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.

 

7 percent alaska tilemap 7 percent conus tilemap

 

 

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).

 

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.


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.


WELD V1.5 5 year Land Cover Land Cover Change Product Documentation

A 30m Land Cover Land Cover Change WELD tiled HDF product has been developed for the conterminous United States (CONUS).

The product has the following file name convention, based on the standard WELD product HDF tile filename convention:

WELD LCLUC HDF Product Filename Convention
<Region>.<Period>.<StartYear>to<EndYear>.h<xx>v<yy>.lcluc.v<WELD Version Number>.hdf
e.g. CONUS.5year.2006to2010.h29v01.lcluc.v1.5.hdf
  Valid Range Notes
<Region> CONUS Only conterminous United States products are available currently.
<Period> 5 year Product made from 5 years of consecutive WELD inputs.
<Start Year> 2006 Start Year generated from growing season 2006 inputs.
<End Year> 2010 End year generated from growing season 2010 inputs.
<xx> 00, 01, ..., 32 Horizontal WELD tile coordinate.
<yy> 00, 01, ..., 21 vertical WELD tile coordinate.
<WELD Version Number> 1.5, 1.6,...., 2.0, 2.1,... Product version number. Major and minor algorithm version changes reflected in the first and second digits respectively.

The contents of each HDF product tile are described below:
WELD LCLUC Version 1.5 Product Contents
Band Name Data Type Valid Range Scale factor Units Fill Value Notes
LCLUC_TREE_COVER uint8 0 - 100 1 percent 255 Peak growing season Tree Canopy cover per 30m pixel (0-100%) estimated over 5 annual growing seasons.
LCLUC_TREE_COVER_DQAPRO uint8 0 - 4 - level of confidence 255 The Data Quality Assessment layer for tree cover, estimating the level of confidence for tree/no-tree classification where 0 = high confidence trees or no trees, 1 = medium confidence trees, 2 = low confidence trees or no trees, 3 = medium confidence no trees, and 4 = no confidence / no decision.
LCLUC_TREE_COVER_DQASTD uint8 0 - 100 1 percent 255 The Data Quality Assessment layer for Tree Canopy cover: For 25 regression trees applied per pixel, the mean of the per node standard deviations.
LCLUC_BARE_GROUND uint8 0 - 100 1 percent 255 Peak growing season Bare Ground cover per 30m pixel (0-100%) estimated over 5 annual growing seasons.
LCLUC_BARE_GROUND_DQASTD uint8 0 - 100 1 percent 255 The Data Quality Assessment layer for Bare Ground cover: For 25 regression trees applied per pixel, the mean of the per node standard deviations.
LCLUC_WATER_SURFACE uint8 0 - 100 1 percent 255 Growing season Water Surface cover per 30m pixel (0-100%) estimated over 5 annual growing seasons.
LCLUC_WATER_SURFACE_DQAPRO uint8 0 - 4 - level of confidence 255 The Data Quality Assessment layer for water surface, estimating the level of confidence for water/land classification where 0 = high confidence water or land, 1 = medium confidence water 2 = low confidence water or land, 3 = medium confidence land, and 4 = no confidence / no decision.
LCLUC_SNOW_AND_ICE uint8 0 - 100 1 percent 255 Growing season Snow and Ice cover per 30m pixel (0-100%) estimated over 5 annual growing seasons.
LCLUC_SNOW_AND_ICE_DQAPRO uint8 0 - 4 - level of confidence 255 The Data Quality Assessment layer for snow and ice, estimating the level of confidence for snow and ice / no snow and ice classification where 0 = high confidence snow and ice or no snow and ice, 1 = medium confidence snow and ice 2 = low confidence snow and ice and no snow and ice, 3 = medium confidence no snow and ice, and 4 = no confidence / no decision.
LCLUC_NUMBER_OF_GOOD_ACQUISITIONS uint8 0 - 254 1 number of acquisitions 255 Number of good (not cloudy) acquisitions over 5 annual growing seasons
LCLUC_TREE_COVER_LOSS int16 0,6017 - 10046 - coded date -32768 Forest loss (yes or no) and bare ground gain (yes or no) over the 5-year period. 0 represents no forest loss and no bare ground gain over the 5 year period. Positive values store the week of the detected forest loss or bare ground gain where the thousands place represents the year of the 2000 decade and tens represents the week within the given year. e.g., 8034 represents year 2008, week 34.
LCLUC_BARE_GROUND_GAIN int16 0,6017 - 10046 - coded date -32768

Citation for this 30m land cover product:
Hansen, M.C., Egorov, A., Potapov, P.V., Stehman, S.V., Tyukavina, A., Turubanova, S.A., Roy, D.P., Goetz, S.J., Loveland, T.R., Ju, J., Kommareddy, A., Kovalskyy, V., Forsythe, C., Bents, T., 2014, Monitoring conterminous United States (CONUS) land cover change with Web-Enabled Landsat Data (WELD), Remote sensing of Environment, 140, 466-484.


Version 1.5 Product Quality

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. 


Missing June 2003 data

The Landsat 7 ETM+ Scan Line Corrector failed May 31st 2003 http://landsat.usgs.gov/products_slcoffbackground.php and reduced the amount of available data in each ETM+ acquisition by about 22%. For operational reasons after this failure no Landsat 7 ETM+ L1T data were generated for nearly a 5 week period. Consequently the June 2003 monthly product and the weekly 2003 products for Week 23, 24, 25, 26 and 27 are all Fill values (i.e, no data).


2007 and 2010 product mixed 30m thermal band resolution issue

Since February 26th 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 26th 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.


New version GDAL utilities are unable to read HDF tile information for certain WELD product years

GDAL Version 1.8.1 is unable to read certain 2007-2009 CONUS and Alaska products and unable to read all years of the weekly Alaska products. Note, earlier versions, such as GDAL 1.4.2, do not have this problem.


GDAL utilities in Ubuntu Operating System are unable to read HDF tile information for certain WELD product years

This issue is currently under investigation, it occurs for product years 2006-2009 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.

The WELD V1.5 5 year Land Cover Land Cover Change Product has had a minor update to fix incorrect population of global HDF attributes "UL corner of UL pixel Albers" and "UR corner of UR pixel Albers" in a subset of the 5 year product tiles. The filename LCLUC Version Number has been updated from 1.0 to 1.1, e.g., filenames have been changed from CONUS.5year.2006to2010.h29v01.v1.5.lcluc.v1.0.beta.hdf to CONUS.5year.2006to2010.h29v01.v1.5.lcluc.v1.1.beta.hdf.

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.



How To Obtain WELD Products

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 HTTP at http://e4ftl01.cr.usgs.gov/WELD/


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



WELD Product Distribution Metrics

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
2012 May 2428 321.95
2012 June 1580 143.21
2012 July 4715 250.03
2012 August 989 123.48
2012 September 26964 3152.84
2012 October 14685 2526.29
2012 November 2149 285.46
2012 December 35111 3245.85
2013 January 11797 1241.62
2013 February 9410 1160.98
2013 March 5980 683.16
2013 April 2932 324.68
2013 May 755 154.66
2013 June 157285 15244.62
2013 July 205437 19451.88
2013 August 233980 22008.8
2013 September 87148 6475.37
2013 October 473 51.14
2013 November 1320 115.282
2013 December 17275 253.43
2014 January 233913 10887
2014 February 162752 5927
2014 March 39445 3293.52
2014 April 81309 6766.35
2014 May 59121 5817.01
2014 June 6166 552.95
2014 July 26125 3812.89
2014 August 119346 10982.44
2014 September 10571 1263.57
2014 October 3358 530.96
2014 November 268 7.51
2014 December 1924 390.21
2015 January 5600 1,046.42
TOTAL 1,975,792 172.047TB

Software Tools

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.


How to access and visualize WELD products in MATLAB, IDL, NCL

Code to help access and visualize WELD products in MATLAB, IDL and NCL at http://www.hdfeos.org/zoo/index_openLPDAAC_Examples.php#WELD


Online Open Source WELD Product Training

Training


Algorithm Theoretical Basis Document

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

Publications

Ju, J., Roy, D.P., Vermote, E., Masek, J., Kovalskyy, V., 2012, Continental-scale validation of MODIS-based and LEDAPS Landsat ETM+ atmospheric correction methods, Remote Sensing of Environment,122, 175-184.

 

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.


Recent Presentations

"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): Demonstration of MODIS-Landsat Data Fusion to Provide a Consistent, Long-term, Large-area Data Record for the Terrestrial User Community", Roy, D.P., Ju, J., Vermote, E., Zhang, C., Egorov,A., Kovalskyy, V., Loveland, T., Hansen, M., Scaramuzza, P., Kline, K., Yoem, J.M., Kommadreddy, I., Eos Trans. AGU, 90(52), December 2009, San Francisco, Fall Meet. Suppl., Abstract IN43C-1166. 


Example WELD Browse Images

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

Links


Global WELD


WELD Citation

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. 


Frequently Asked Questions (FAQ)

  • 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 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.

  • Why are there sometimes large gaps in the monthly, seasonal and annual WELD products?

This occurs because when the WELD product was generated the US Landsat Project had not L1T processed the Landsat images at the gap location/time because they were considered too cloudy.
At the start of the U.S. free Landsat data policy only Landsat images with cloud cover <20% were L1T processed, this threshold was subsequently changed to <40%, then <80%, and in 2011 nearly all the data are L1T processed regardless of cloud cover (although certain images may not be L1T processed because clouds preclude the collection of sufficient ground control).
The WELD CONUS and Alaska products are made with L1T data only. The large gaps in the monthly, seasonal and annual WELD products correspond to regions/times with missing input Landsat L1T data.
Usually the next WELD reprocessing version will be more complete with fewer large gaps as more input L1T data will have become available to the WELD processing system through user orders.

  • Why are there large gaps in the weekly WELD products?

These gaps occur systematically because the Landsat ETM+ orbit and view geometry is such that the same location is only sensed once every 16 days and over the CONUS adjacent paths are 7 days apart, so the weekly composited mosaics never contain more than one Landsat acquisition per 7 day period. At higher latitudes, including Alaska, this is not the case due to the poleward convergence of the Landsat orbits. Large gaps are also caused by missing cloudy input L1T data (see previous FAQ).

  • 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.

  • 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 see a blank screen when I click the "Bulk Order Pixel Time Series" button in the What You See Is What You Get (WYSIWYG) WELD Internet distribution interface at http://weld.cr.usgs.gov

Please clear your bowser "recent history" and try again, for example, in the Firefox browser do a Firefox tab-> History - >Clear Recent History.

  • 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.

  • Will WELD products ever be made available over <country outside of the CONUS and Alaska> ?

Yes, new NASA MEaSUREs funding will make annual and monthly global WELD products for six epochs (1985, 1990, 1995, 2000, 2005, 2010), 36 monthly products per epoch. Please visit http://globalmonitoring.sdstate.edu/projects/weldglobal/gweld.html

 


Training: Introduction to the Web-enabled Landsat Data (WELD) products using open source software


WELD Help Email


 

This web site is hosted at the Geospatial Sciences Center of Excellence (GSCE), South Dakota State University.
The contents of this web site were written by the GSCE WELD staff. This site was last updated February 9th 2015.