Main applications in the Earth observation - SPOT
From INVESaTWIKI
Main applications in the Earth observation - SPOT satellites
The SPOT (Satellite Pour l'Observation de la Terre) satellite Earth Observation System was designed by the Centre National d'Etudes Spatiales (CNES), in France. The CNES, owns and operates the SPOT satellite system while worldwide commercial operations are anchored by private companies (i.e. SPOT IMAGE Corporation in the United States, SPOT IMAGE in France, SATIMAGE in Sweden, and distributors in over 40 countries). The SPOT Program supports commercial remote sensing on an international scale, establishing a global network of control centers, receiving stations, processing centres, and data distributors.
The SPOT satellites maintain a near-polar, near-circular, sun-synchronous orbit with a mean altitude of 832 km (at 45 degrees north latitude which corresponds to continental France), an inclination of 98.7 degrees, and a mean revolution period equaling 101.4 minutes. The SPOT satellites orbit the same ground track every 26 days with a nominal cycle of 369 revolutions. Crossing the equator from north to south at 10:30 a.m. mean local solar time, the satellites reference tracks are 108.6 km apart. The reference tracks draw closer at higher altitudes. The SPOT system provides global coverage between 87 degrees north latitude and 87 degrees south latitude. Each nominal scene covers a 60- by 60-km area.
Up to SPOT4 satellite have two viewing instruments (HRV and HRVIR for SPOT4) when operated simultaneously in the vertical viewing configuration are capable of imaging a 117 km wide strip on the Earth's surface. Both HRVS are fitted with programmable Strip Selection Mirrors giving access, off track, to areas within a 950 km wide corridor. This specific oblique viewing capability greatly increases the frequency at which the satellite can revisit a particular site (4 to 11 times within the 26 day cycle, according to latitude).
Consequently stereopairs, used for relief perception and elevation plotting (Digital Elevation Modelling) are formed from two SPOT images acquired at different viewing angles on successive satellite passes.
A single SPOT scene covers a geographical area of 60 x 60 km. Two alternative modes of imaging are possible :
- Panchromatic, black and white, with a ground resolution of 10 m which makes SPOT data the most advanced system in terms of image resolution as features as small as 10 m in size on the ground are detected. This complies with mapping at scale up to 1/50 000.
- Multispectral, colour, with 20 m ground resolution acquired simultaneously in 3 bands : green, red and near infrared.
SPOT key features such as ground resolution, repeat registration, acquisition programming and stereo capabilities makes the system the current most advanced programme to acquire up to date geographic information.
Many operational applications in a variety of domains ranging from Earth sciences to economic planning and decision making takes benefits of SPOT data : vegetation, agriculture, forestry, soils, geology, erosion, oil and mineral exploration, water resources, urban and rural planning, civil engineering, development projects, or environmental monitoring.
SPOT5 satellite is composed of two new HRG viewing instruments derived from SPOT4 HRVIR instruments which have a better resolution : 2.5 to 5 meters in panchromatic mode and 10 meters in multispectral mode. SPOT5 has a new HRS instrument operating in panchromatic mode that take images in front and behind the satellite at the same time which allow stereoscopy. [1]
