SMEX02 Iowa Satellite Vegetation and Water Index (NDVI and NDWI) Data

Summary

This data set is part of the Soil Moisture Experiment 2002 (SMEX02) project, which is associated with the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) validation project. It consists of Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) data, derived from Landsat 5 Thematic Mapper (TM) and Landsat 7 Enhanced Thematic Mapper plus (ETM+) imagery. The satellite data were acquired during select dates in June and July 2002. These data cover the SMEX02 Walnut Creek watershed and the regional Iowa study areas in south-central Iowa, USA.

Data are provided as flat binary files and are available via FTP.

These data were collected as part of a validation study for the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E). AMSR-E is a mission instrument launched aboard NASA's Aqua Satellite on 04 May 2002. AMSR-E validation studies linked to SMEX are designed to evaluate the accuracy of AMSR-E soil moisture data. Specific validation objectives include assessing and refining soil moisture algorithm performance; verifying soil moisture estimation accuracy; investigating the effects of vegetation, surface temperature, topography, and soil texture on soil moisture accuracy; and determining the regions that are useful for AMSR-E soil moisture measurements.

Citing These Data:

Thomas Jackson, and Michael Cosh. 2003. SMEX02 Iowa Satellite Vegetation and Water Index (NDVI and NDWI) Data. Boulder, CO: National Snow and Ice Data Center. Digital media.

Overview Table

Category	Description
Data format	Files are in flat binary format with no header. Regional files for NDVI and NDWI are 1851 columns by 3831 rows. Watershed files for NDVI and NDWI are 1216 columns by 611 rows. Data are in PC byte order (little endian). SGI and Sun users will need to byte-swap these data before using them.
Spatial coverage	42° N, 93° W 30 m resolution
Temporal coverage and resolution	Daily coverage for the dates 6 June, 23 June, 1 July, 8 July, 16 July, and 17 July 2002.
Tools for accessing data	Open these files in an appropriate image processing or image viewing application.
File naming convention	File names begin with a six-digit date, followed by the data type, NDVI or NDWI. Watershed files include "WC" after the data type.
File size	File sizes range from 725 KB to 6.76 MB.
Parameter(s)	Normalized Difference Vegetation Index (NDVI) Normalized Difference Water Index (NDWI)
Procedures for obtaining data	Data are available via FTP.

Table of Contents

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments:

Investigator(s) Name and Title:

Thomas J. Jackson, Hydrologist and Michael H. Cosh, General Physical Scientist, USDA ARS Hydrology Lab.

Technical Contact:

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org

2. Detailed Data Description:

Format:

Files are in flat binary format with no header. Data are in PC byte order (little endian). SGI and Sun users will need to byte-swap these data before using them

Regional files for NDVI and NDWI are 1851 columns by 3831 rows.

Watershed files for NDVI and NDWI are 1216 columns by 611 rows.

The data are eight-bit binary or byte data. To maximize the dynamic range, the following scaling was performed:

File and Directory Structure:

There are two main directories, NDVI and NDWI. The two subdirectories under each of these are Regional and Watershed, named for the different coverage areas.

File Naming Convention:

File names begin with a six-digit date, followed by the data type, NDVI or NDWI. Regional files have no other designation, for example, "071702_NDVI.bil." Watershed files include "WC" after the data type, for example, "071702_NDVI_WC.bil."

File Size:

File sizes range from 725 KB and 6.76 MB.

Spatial Coverage:

Regional area:

Location	Latitude	Longitude	Easting	Northing
Upper Left	42.729 N	93.416 W	431100.000 E	4731100.000 N
Upper Right	42.732 N	93.163 W	486600.000 E	4731100.000 N
Lower Left	41.694 N	93.827 W	431100.000 E	4616200.000 N
Lower Right	41.697 N	93.161 W	486600.000	4616200.000 N

Watershed area:

Location	Latitude	Longitude	Easting	Northing
Upper Left	42.037 N	93.832 W	431100.000 E	4654300.000 N
Upper Right	42.040 N	93.392 W	467550.000 E	4654300.000 N
Lower Left	41.872 N	93.830 W	431100.000 E	4636000.000 N
Lower Right	41.875 N	93.391 W	467550.000 E	4636000.000 N

Spatial Resolution:

The Landsat TM and ETM+ data were used to produce high resolution (30 m) NDVI and NDWI data sets.

Projection:

Universal Transverse Mercator (UTM) Zone 15

Temporal Coverage:

Select dates during June and July 2002 were covered.

Temporal Resolution:

Daily coverage for the dates 6 June, 23 June, 1 July, 8 July, 16 July, and 17 July 2002.

Parameter or Variable:

Parameter Description:

Parameters are NDVI and NDWI. NDVI is the difference between the visible (red) and near-infrared (nir) bands, over their sum. The NDVI is a measure of vegetation amount and condition. It is associated with vegetation canopy characteristics such as biomass, leaf area index and percentage of vegetation cover. NDWI divides the difference between reflected green-light and reflected near-infrared by the sum of those two bands. NDVI helps researchers determine the density of vegetation in an area, and NDWI gives a measurement of the soil moisture.

Parameter Source:

Two TM scenes from Landsat 5 and four ETM+ from Landsat 7 were acquired during the primary study period. These data were used to produce high resolution (30 m) NDVI and NDWI data sets. The following table details the Landsat coverage for the dates of the study.

Date	Landsat number	Path	Row
June 6	7	27	31
June 23	5	26	31
July 1	7	26	31
July 8	7	27	31
July 16	5	27	31
July 17	7	26	31

Sample Data Record:

The following image is a screen shot of a portion of the image file "060602_NDVI.bil."

The next image is a screen shot of a portion of the image file "071702_NDWI.bil."

3. Data Access and Tools:

Data Access:

Data are available via FTP.

Volume:

Total volume of all images is 27 MB.

Software and Tools:

Open these files in an appropriate image processing or image viewing application.

Related Data Collections:

See Soil Moisture Experiment (SMEX) for more information.

4. Data Acquisition and Processing:

Sensor or Instrument Description:

TM is a multispectral scanning radiometer carried on Landsat 4 and 5. The TM has seven spectral band, with a spatial resolution of 30 meters for most bands.

ETM+, an improved version of TM, is carried on Landsat 7. The ETM+ has eight spectral bands with a spatial resolution of 30 meters for most bands. ETM+ calibration is good to within five percent.

Derivation Techniques and Algorithms:

Radiance from a satellite platform is strongly affected by the presence of the atmosphere. Atmospheric correction is needed to convert satellite-based radiance to an estimate of ground reflectance.

The atmospheric correction for the visible and near infrared channels was conducted using the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) code during the SMEX02 experiment (Vermote et al., 1997a). The input data for the 6S included Cimel sun photometer data obtained through the AERONET network.

The sun photometer is designed to view the sun and sky at preprogrammed intervals for aerosol optical thickness, water vapor amounts, particle size distribution, aerosol scattering, phase function, and single scattering albedo. It measures the intensity of sunlight arriving directly from the sun. These measurements are used to radiometrically correct satellite imagery in the visible and infrared bands using the interpreted information about atmospheric aerosols. The instrument was installed at a central location (41.963 N, 93.661 W) to provide data appropriate for the intensive site and for the regional area studies.

If the area surrounding a target is assumed to be the same as the target and we assume the target is Lambertian and uniform, the reflectance at the target can be expressed conveniently as (Vermote, et al., 1997b; Vermote and Vermeulen,1999; Adler-Golden et al., 1999):

where:
Lt is the satellite based radiance
S is the reflectance of the atmosphere
Lp is the atmospheric path radiance
Edir is the direct irradiance at the surface
Ediff is the diffuse irradiance at the surface
T is the total diffuse transmittance from the ground to the top of the atmosphere in the view direction of the satellite.

Formulae:

The NDVI and NDWI were computed for each pixel using the following equations (Gao, 1996):

Values of NDVI and NDWI are in the range between -1 and +1. Values less than 0 were filtered out to maximize the NDVI values of interest (0 to 1). These values composed less than 1% of the imagery.

5. References and Related Publications:

Gao, B.C., 1996: NDWI - A normalized difference water index for remote sensing of vegetation liquid water from space. Remote Sensing of Environment, Vol. 58: 257-266

Richtsmeier, P.K. Acharya, G.P. Anderson, G. Felde, J. Gardner, M. Hoke, L.S. Jeong, B.Pukall, J. Mello, A. Ratkowski and H.H. Burke, 1999. Atmospheric correction for short-wave spectral imagery based on MODTRAN4. SPIE Proc. Imaging Spectrometry V, 3753: 61-91

Vermote, E.F., D.Tanre, J.L. Deuze, M. Herman and J.J. Morcrette, 1997a. Second Simulation of the Satellite Signal in the Solar Spectrum, 6S: An Overview. IEEE Transactions on Geoscience and Remote Sensing, Vol. 35: 675-686.

Vermote, E.F., N.E. Saleous, C.O. Justice, Y.J. Kaufman, J.L. Prevette, L. Remer, J.C. Roger and D. Tanre, 1997b. Atmospheric correction of visible to middle-infrared EOS-MODIS data over land surface: Background, operational algorithm and validation. Journal of Geophysical Research, Vol. 102: 17131-17141.

Vermote, E.F. and A.Vermeulen, 1999. Atmospheric correction algorithm: spectral reflectances (MOD09). Algorithm Technical Background Document.

Global Land Biosphere Data and Resources

Landsat Project information

Thematic Mapper (TM)

6. Document Information:

Acronyms and Abbreviations

The following acronyms and abbreviations are used in this document.

AMSR-E	Advanced Microwave Scanning Radiometer - Earth Observing System
NDVI	Normalized Difference Vegetation Index
NDWI	Normalized Difference Water Index
SMEX	Soil Moisture Experiment
UTM	Universal Transverse Mercator

Document Creation Date:

August 2003

Document URL:

http://nsidc.org/data/docs/daac/nsidc0184_smex_ndvi_ndwi.gd.html