GIS (geographic information system)

The first Landsat launched by the United Sates was on July 23, 1972.  They were used in an effort to collect data about the earth's resources from a satellite as stated by Arnoff.  The multi spectral scanner (MSS) provided digital images that could be used for computer analysis. It had four bands (4, 5, 6, and 7) in the visible and near infrared part of the spectrum. The sensor s spatial resolution was approximately 79m by 56m as stated by Arnoff. It also had a return orbit period of 18 days. The orbit was sun synchronous (in its orbital path, the satellite will always pass over a given location of the earth at the same local sun time).

Landsat TM   is more advanced multispectral scanner than the MSS system. The spectral resolution encompasses seven bands that range from visible blue to thermal infrared. Included is a Mid Infrared (MIR) band. Please note band seven is out of the spectral sequence because it was added after band 6 had been developed. Not only does TM cover more of the spectrum, but it has a higher spatial resolution of 30m x 30m. Images may have a "true" or "false" color. True reflects actual surface colors seen by the human eye.  False color results from selected band combinations being consecutively displayed on the color monitor through the red green blue (rgb) color guns.   The features will not look like they do to the naked eye.  In a Landsat 7 TM 4 (Infrared), 3 (red visible), 2 (green visible) color combination; the infrared band will be shown through the red gun, the red visible band will be shown through the green gun, and the green visible band will be shown through the blue gun.  In this combination, healthy vegetation will appear red (not green) in the image. 

Landsat 7 TM Sensor  

Systeme Pair l'Observation de la Terre (SPOT) started in France in 1978. It originated as a commercial program. SPOT has two HRV push broom scanners that can produce either a panchromatic (a single visible band black and white) with a 10 meter spatial resolution or a multi spectral 3 bands (2 visible, 1 infrared) with a 20 meter spatial resolution. The sensor orbit is sun synchronous with a 26 day nadir and 1-5 days off nadir temporal resolution. The sensor also has the capability to produce full scene stereo images which can be used to create topographic maps. SPOT 5,   launched in 2002 has improved spatial resolution for both panchromatic (2.5 and 5 meter) and multispectral images (10 meter visible, 10 meter Near IR).  Overall the Landsat TM has greater spectral resolution and SPOT has better spatial resolution.

The predecessor to QuickBird was the Early Bird Satellite system, developed by Earth Watch.  Earth Watch, former in 1993, was a pioneer company in the privatization of high resolution satellite based image sources. In 2001 Earth Watch changed its name to Digital Globe. 

The first EarlyBird satellite was launched by the Russians in December 1997.  Though the launch was a success, the satellite failed to achieve the proper orbit.  In April 1997, the satellite was declared a loss.  In November 2000, QuickBird  was launched at the Cosmodrome in Russian and failed to reach orbit.  In October 2001 QuickBird 2 was successfully placed into orbit with the capability of  .61 meter spatial resolution and 4 band (blue, green, red, NIR) spectral resolution.  Both spatial and spectral resolutions are much improved over the EarlyBird sensor. Temporal resolution of the QuickBird is 1-4 days, depending on latitude (poles = 1 day, equator = 4 days).  Data download locations include Norway, Alaska, and Colorado (company headquarters).

Ikonos was the first 1 meter spatial resolution commercial imaging satellite system to achive orbit.  Ikonos 1, Launched in 1998, failed to achieve orbit.  The 1999 launch of Ikonos 2 was a success.   Ikonos 2 provides customers world-wide with 1 meter panchromatic and 4 meter multispectral imagery spatial resolution.