DOWNLOADING DATA VIA HTTPS
To learn more about Earthdata Login and register for an account, please see How to Register with Earthdata Login. Once you have logged in, data can be downloaded via a Web browser, command line, or client. For help with downloading data, please see Options Available for Bulk Downloading Data from HTTPS with Earthdata Login.
DOWNLOADING DATA VIA FTP
Data can be downloaded through a Web browser or command line via FTP. When using a Web browser, the FTP link first directs you to an Optional Registration Form that if filled out, will allow you to receive notifications about updates or processing changes related to that specific data set. After completing the Optional Registration Form, the FTP directory becomes available. For additional help downloading data through an FTP client, go to the How to access data using an FTP client support page.
SMEX02 Iowa Satellite Vegetation and Water Index (NDVI and NDWI) Data, Version 1
This data set 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.
|Spatial Resolution:||Not Specified|
|Temporal Resolution:||Not specified|
|Data Contributor(s):||Thomas Jackson, Michael Cosh|
|Metadata XML:||View Metadata Record|
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.Jackson, T. and M. Cosh. 2003. SMEX02 Iowa Satellite Vegetation and Water Index (NDVI and NDWI) Data, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/2R7KUXDQ3S44. [Date Accessed].
Detailed Data Description
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:
NDWI = DN / 255-0.5
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 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, "
File sizes range from 725 KB and 6.76 MB.
Total volume of all images is 27 MB.
|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|
|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|
The Landsat TM and ETM+ data were used to produce high resolution (30 m) NDVI and NDWI data sets.
Universal Transverse Mercator (UTM) Zone 15
Select dates during June and July 2002 were covered.
Daily coverage for the dates 6 June, 23 June, 1 July, 8 July, 16 July, and 17 July 2002.
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.
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.
Sample Data Record:
The following image is a screen shot of a portion of the image file "
The next image is a screen shot of a portion of the image file "
Software and Tools
Open these files in an appropriate image processing or image viewing application.
Data Acquisition and Processing
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):
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.
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.
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.
References and Related Publications
Contacts and Acknowledgments
Thomas J. Jackson, Hydrologist and Michael H. Cosh, General Physical Scientist, USDA ARS Hydrology Lab.
DOCUMENT CREATION DATE