In its initial design as well as in its long-term outlook, the Spot programme concept is predicated on assuring continuity of service to users worldwide.
Up to Spot 4 the satellites had two viewing instruments (HRV and HRVIR for Spot 4) which, when operated simultaneously in the vertical viewing configuration, are capable of imaging a 117-km swath of the Earth's surface. Both HRVs are fitted with programmable strip selection mirrors able to view off track areas within a 950-km corridor. This specific oblique viewing capability greatly increases how often the satellite can revisit a specific 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 is suitable for mapping at scale up to 1/50 000.
- Multispectral, colour, with 20-m ground resolution acquired simultaneously in three bands: green, red and near-infrared.
Spot key features such as ground resolution, repeat registration, acquisition tasking and stereo capabilities make the system the currently most advanced programme for acquiring up-to-date geographic information.
Many operational applications in a variety of domains ranging from Earth sciences to economic planning and decision making benefit from Spot data, including vegetation monitoring, agriculture, forestry, soils, geology, erosion, oil and mineral exploration, water resource management, urban and rural planning, civil engineering, development projects and environmental monitoring.
The Spot 5 satellite is composed of two new HRG viewing instruments derived from Spot 4's HRVIR instruments, only with better resolution: 2.5 to 5 metres in panchromatic mode and 10 metres in multispectral mode. Spot 5 also has a new HRS instrument operating in panchromatic mode that take images in front of and aft of the satellite at the same time for stereoviewing .