Satellite Remote Sensing LANDSAT
The first Landsat satellite was launched in July 1972. Of the sensors carried, the Multi-spectral Scanner (MSS) with 80-metre pixels and four spectral bands was found to provide information of unforeseen value. In July 1982, the launch of Landsat 4 saw the inclusion of the Thematic Mapper (TM) sensor with a 30-metre resolution and 7 spectral bands. Both sensors are on Landsat 5.
The latest in this series of remote sensing satellites is Landsat 7. Launched on 15 April 1999, Landsat 7 has the new Enhanced Thematic Mapper Plus (ETM+) sensor. This sensor has the same 7 spectral bands as its predecessor, TM, but has an added panchromatic band with 15-metre resolution and a higher resolution thermal band of 60 metres.
Today, Landsat 5 and Landsat 7 continue to scan the Earth’s surface and beam images back to Earth. Both satellites scan the entire globe every 16 days, and their orbits are 8 days a part, so that between them, the earth is scanned every 8 days.
Landsat 5 is suitable for mapping at scales up to 1:50 000, while Landsat 7 is suitable for mapping at up to 1:25 000 scale.
The main advantage of Landsat satellites include:
- An enormous archive of images dating back more than 30 years exists, which provides a valuable record of changes that have occurred during this period
- Landsat satellites are in continuous operation, rather than being programmed to acquire images as required.
- Landsat scenes are 180 km wide which make these satellites well suited to broad scale mapping and monitoring
- Landsat images consist of 7 spectral bands. In addition to the visible bands, red, green and blue, Landsat images include three infra-red and one thermal band. These bands provide valuable information about minerals, vegetation, climate, and atmosphere.
- Landsat is relatively inexpensive for large areas.
|Resolution:||25 metre multispectral (colour)
15 metre Panchromatic (black and white)
|Bands:||Landsat 5 seven bands – blue, green, red, near infra-red, middle
infra-red (x 2), thermal
Landsat 7 eight bands same as Landsat 5 plus 15 metre panchromatic band
|Revisit cycle:||8 days (16 days each for Landsat 5 and Landsat 7)|
|Image Size:||185 km wide|
Unfortunately, Landsat 7 malfunctioned on May 29, 2003, and since then, the images it produces have gaps that get wider, closer to the edge of the image. These images are called SLC-OFF images. In order to fill the gaps, multiple SLC-OFF images are combined to produce an SLC-OFF composite image.