About OhioLINK's Landsat7 Data Server

About OhioLINK's LANDSAT 7 Satellite Data Server

Contents:
Background
Image Views Available on the Web
Images Available via FTP
Technical Specifications
Useful Links

Background

The Landsat 7 satellite was launched in April of 1999. This satellite orbits the earth and captures digital snapshots from space. OhioLINK has purchased all Ohio based data captured by Landsat 7 since the first data sets were available, and maintains a standing order for new data as it is captured.

A new 'snapshot' of the state is captured every 16 days. A complete 'snapshot' of Ohio is represented by nine Landsat 7 scenes that each represent ground cover approximately 115 miles wide by 106 miles long. Within each scene, nine different 'layers' are captured. (These 'layers' are actually different bands of the electromagnetic spectrum). These are available via FTP for expert users. Additionally these are processed at OhioLINK to create a variety of meaningful products viewable on the web for other academic users and the public.

Currently OhioLINK only purchases scenes which have less than 30% cloud cover.

Image Views Available on the Web

OhioLINK processes the satellite data into formats that are accessible through the web. This involves combining some of the layers captured by LandSat 7 and applying color information to them. The resulting images can be used to analyze various properties of the built and natural environment. Currently OhioLINK produces the following views: True-Color Composite, High-Resolution Monochrome, NDVI, and Near-Infrared Composite.

True-Color Composite
True-color composite images approximate a normal color photograph. The atmosphere affects certain wavelengths more than others, and may alter the images slightly. Landcover analysis such as urban expansion is a common application of true-color composite images. Each pixel in this composite represents 30 meters on the earth.
Near Infrared Composite
Near Infrared Composite images are created by adding the near infrared band (band 5) and dropping the visible blue band (band 1). Vegetation appears as various shades of red in this composite and water appears dark. This is due to the near infrared band's sensitivity to chlorophyll. Each pixel in this composite represents 30 meters on the earth.
NDVI (Normalized Differential Vegetation Index)
NDVI calculations are based on the principle that growing plants strongly absorb radiation in the visible region of the spectrum while strongly reflecting radiation in the near infrared (NIR) region. This composite is similar to a near infrared composite.
In this view Green represents vegetation - the lighter the green the more vegetation. Pink represents cloud cover, Blue represents water, and Yellow represents areas of the ground with no detectable vegetation.
Each pixel in this composite represents 30 meters on the earth.
High Resolution Monochrome
The High Resolution Monochrome image, in effect, a black and white photograph of the earth. The data in it represents all the visible and near-infrared bands of the electromagnetic spectrum. Each pixel in the panchromatic image represents 15 meters on the earth.

Images Available via FTP

Expert users may wish to download the 'Raw' satellite data. This is the data that is used to create the web viewable images and is available via FTP. These files, in GeoTIFF format, are intended for remote sensing experts, geologists, and other researchers familiar with these data formats and applications needed to manipulate and view them.

For each scene there are 9 files that may be downloaded. The smallest of these files, the two infrared bands, are 15 MegaBytes each. The largest of these files, the panchromatic band, is 219 MegaBytes. Other files are 55 MegaBytes.

Important Notice: OhioLINK cannot offer assistance for the use of GeoTIFF images. Issues or problems with our FTP server will be addressed promptly.

Technical Specification of Satellite Data

The LANDSAT 7 satellite captures 9 different pieces of information. The following table describes this data.

Band
Number Band
Name Spectral Range
(micrometers) Ground
Resolution
(meters) File Size
(Megabyes) File
(Uncompressed
GeoTIFF)

1 (Blue) 0.450-0.515 30 55 b10.tif

2 (Green) 0.525-0.605 30 55 b20.tif

3 (Red) 0.630-0.690 30 55 b30.tif

4
0.750-0.900 30 55 b40.tif

5
1.550-1.750 30 55 b50.tif

6 Thermal infared, HIGH GAIN 10.40-12.50 60 20 b61.tif

6 Thermal infared, LOW GAIN 10.40-12.50 60 20 b62.tif

7
2.090-2.350 30 55 b70.tif

8 Panchromatic 0.520-0.900 15 220 b80.tif

Band Number	Band Name	Spectral Range (micrometers)	Ground Resolution (meters)	File Size (Megabyes)	File (Uncompressed GeoTIFF)
1	(Blue)	0.450-0.515	30	55	b10.tif
2	(Green)	0.525-0.605	30	55	b20.tif
3	(Red)	0.630-0.690	30	55	b30.tif
4		0.750-0.900	30	55	b40.tif
5		1.550-1.750	30	55	b50.tif
6	Thermal infared, HIGH GAIN	10.40-12.50	60	20	b61.tif
6	Thermal infared, LOW GAIN	10.40-12.50	60	20	b62.tif
7		2.090-2.350	30	55	b70.tif
8	Panchromatic	0.520-0.900	15	220	b80.tif

Useful Links:

The following web sites contain useful background information, tutorials, and other highly relevant information:
USGS LANDSAT 7 Page
NASA LANDSAT 7 Page
The OhioView Consortium
A Global View of the Earth (K-12 Teacher's Kit from Ohio State University)
Three federal agencies responsible for LandSat7:
NOAA National Oceanic & Atmospheric Administration
NASA National Aeronautics and Space Administration
USGS U.S. Geological Survey

For more information about OhioLINK's LandSat 7 Satellite Data Server, please send e-mail to info@ohiolink.edu.