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Data Set ID:

SMAPVEX12 Vegetation Water Content Map, Version 1

The Vegetation Water Content (VWC) Map for the Soil Moisture Active Passive Validation Experiment 2012 (SMAPVEX12) was derived by calculating Normalized Difference Water Index (NDWI) from SPOT and RapidEye satellite overpasses. In addition, samples from a range of vegetation types were used to compare VWC and NDVI to the satellite imagery.

Geographic Coverage

  • Vegetation > Plant Characteristics > Vegetation Water Content
Spatial Coverage:
  • N: 50.17, S: 49.31, E: -97.36, W: -98.74

Spatial Resolution:
  • 5 m x 5 m
Temporal Coverage:
  • 14 May 2012 to 19 July 2012
Temporal Resolution: 1 day
Data Format(s):
  • TWF
  • GeoTIFF
Platform(s) RAPIDEYE, SPOT-4
Sensor(s): HRVIR, REIS
Version: V1
Data Contributor(s): Michael Cosh
Data Citation

As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Cosh, M. 2014. SMAPVEX12 Vegetation Water Content Map, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: [Date Accessed].

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The documentation for this data set was provided solely by the Principal Investigator(s), and was not further developed, thoroughly reviewed, or edited by NSIDC. Thus, support for this data set may be limited.

Detailed Data Description

The Vegetation Water Content (VWC) Map for the Soil Moisture Active Passive Validation Experiment 2012 (SMAPVEX12) was derived by calculating Normalized Difference Water Index (NDWI) from SPOT and RapidEye satellite overpasses. In addition, samples from a range of vegetation types were used to compare VWC and NDVI to the satellite imagery.


Data are provided as Georeferenced Tagged Image File Format (GeoTIFF) image files with associated TIFF world files (TFW) containing georeferencing information. Extensible Markup Language (XML) metadata files are also provided.

Pixel size in east-west direction: 5 m
Pixel size in north-south direction: 5 m
Upper left corner in the projection file.
Universal Transverse Mercator (UTM) Zone 14 U, World Geodetic System 1984 (WGS84)

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File and Directory Structure

Data files are available on the HTTPS site in the directory. Within this directory are both GeoTIFF image files and TIFF world files (TFW) with associated XML metadata files for each day.

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File Naming Convention

Data files are named according to the following convention, and as described in Table 1:



Table 1. Description of File Naming Convention
Variable Description
SV12VWC Short Name
YYYYMMDD 4-digit year, 2-digit month, 2-digit day
SMAPVEX12 Soil Moisture Active Passive Validation Experiment 2012
VWC Vegetation Water Content (VWC); VWC = 0.5328 (a constant)

Indicates platform (RE: RapidEye; SP: SPOT). 

Files without XX in the name indicate data are interpolated between the observations made with either Rapideye or SPOT. 

Files named RE_SP indicate data are directly from Rapid Eye scene, and that there was a SPOT measurement on this day as well.

.tif Indicates this is a GeoTIFF file
.tfw Indicates this is a TIFF World file
.MET.xml Indicates this is an XML metadata file
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File Size

The data files range in size from approximately 2 to 19 GB.

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Spatial Coverage

Southernmost Latitude: 49.31°N
Northernmost Latitude: 50.17°N
Westernmost Longitude: 98.74°W
Easternmost Longitude: 97.36°W

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Spatial Resolution

Data are at 5 m resolution.

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Grid Description

Data are provided as a GeoTIFF image file with associated TIFF World file (TFW) containing georeferencing information. GeoTIFF defines a set of publicly available TIFF tags that describe cartographic and geodetic information associated with TIFF images. GeoTIFF enables referencing a raster image to a known geodetic model or map projection. The initial tags are followed by image data, that in turn may be interrupted by more descriptive tags. By using the GeoTIFF format, both metadata and image data can be encoded into the same file.

The TFW file provides georeference information for the image with the same file name and is a text file with six numbers. Refer to Table 2 for a description of the TFW file contents.

Table 2. TFW File Rows
Row Description
the dimension of a pixel in map units in the x direction
rotation term for row
rotation term for column
the dimension of a pixel in map units in the y direction
x coordinate for upper left corner
y coordinate for upper left corner
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Temporal Coverage and Resolution

In situ samples and measurements were collected on thirteen days from 14 May through 19 July 2012. Refer to SMAPVEX12 In Situ Vegetation Data for Agricultural Area for more information regarding in situ sampling.

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Parameter or Variable

The parameter for this data set is Vegetation Water Content (VWC) [kg/m2].

Parameter Range

Valid parameter values are: 0 - 40 kg/m2

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Software and Tools

Various software packages can be used to read the GeoTIFF data file, such as ArcGIS and MATLAB.

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Data Acquisition and Processing

There were four satellite scenes from RapidEye and four scenes from SPOT, which provided near wall-to-wall coverage of the SMAPVEX12 Intensive Observation Period.
Available Cloud-Free Scenes

RapidEye: 5/14, 5/20, 6/4, 7/5
SPOT: 6/23, 6/28, 7/5, 7/14

To compensate for the difference in sensors between RapidEye and SPOT, the SPOT NDVI was regressed to a RapidEye NDVI standard for this exercise. There is a very good relation between the NDVI values for the concurrent date of 7/5 and this conversion is applied to all of the SPOT scenes. For 7/5, the original RapidEye scene is used.

RapidEye NDVI=1/1.0541 * SPOT NDVI

SPOT-RapidEye Comparison Image
Figure 1. Differences in NDVI between RapidEye and SPOT

The field averages of each of the physically sampled fields are collected for each day of the satellite overpasses and a linear interpolation is used to compare the physical vegetation samples to satellite based NDVI values. For each major crop in the study, a relationship was developed to compute Vegetation Water Content (VWC) in kg/m2.


VWC=162.24*NDVI-121.26, except after 7/14; all forest VWC values after 7/14 use the 7/14 value.

VWC=.028207 * exp(5.7649*NDVI)



Spring Wheat

Winter Wheat


Table 3 shows the RMS difference between the VWC retrieved with equation and VWC obtained from the physical ground measurements.

Table 3. RMS Differences between Satellite and In Situ Measurements
Crop Type VWC [kg/m2]
Beans/Soybeans 0.250
Canola 0.800
Corn 0.760
Forage/Pasture 0.164/0.130
Spring Wheat 0.620
Winter Wheat 0.660

The scenes for VWC are calculated for each day of satellite overpass. The images are then linearly interpolated between the scenes. The last scene is 7/14, so the VWC values are extrapolated out to 7/19 for all crops on the same trend as prior to 7/14, with the exception of forest which is held static to the 7/14 values.

Error Sources

The interpolation of the Normalized Vegetation Index (NDVI) between satellite acquisitions causes some uncertainty in both regression with the field observations and estimation of the value for a particular campaign day.

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Quality Assessment

The quality of the VWC estimation from the NDVI images is in accordance with the expected fidelity of such estimations, with the exception of the uncertainty caused by the interpolation of NDVI between the satellite acquisitions. Table 2 lists the RMS difference between the retrieved VWC and the VWC obtained from the physical ground measurements.

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References and Related Publications

Contacts and Acknowledgments

Michael Cosh
USDA ARS Hydrology and Remote Sensing Laboratory
Beltsville, Maryland USA 20705
phone: +1 301.504.6461

Document Information


March 2014



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