SPOT: build a repeatable record of changing landscapes

France initiated the SPOT program in the 1970s, and SPOT 1 launched in February 1986. CNES developed the first five satellites with industrial partners and international ground support. The family supplied optical views for mapping vegetation, settlements and other features of Earth’s surface. Its value included returning to places as they changed, rather than producing a single definitive portrait.

SPOT 6 and SPOT 7 continued the family through a different industrial funding and development arrangement, without CNES participation in those missions. A family label therefore does not mean every generation had identical ownership or institutional responsibilities. The 1985 SPOT 1 test photograph belongs to the earlier national program and cannot document later spacecraft simply because they share its name.

SPOT could acquire views of the same terrain from different directions. Corresponding features appear in different positions within those views; with the imaging geometry known, a stereoscopic pair can support an elevation model. This is a relationship between images and geometry, not an automatic height reading from the brightness of one pixel.

In a fictional mapping exercise, a bright roof and a pale field may have similar image values while standing at different elevations. Matching their positions across suitable views helps address height; brightness alone does not. Clouds, shadows and changes between acquisitions can complicate matching. A useful terrain product needs the processing assumptions and quality information that explain where its estimates are reliable.

SPOT World Heritage preserves imagery from SPOT 1 through SPOT 5 for later use. Archive availability does not mean every downloaded scene already has every correction needed for comparison. CNES distinguishes radiometrically corrected Level 1A imagery from geometrically corrected products. Users must check the actual processing level before measuring changes between maps.

The later Take Five experiments altered SPOT 4 and SPOT 5 observing patterns to prepare methods for Sentinel-2. They tested repeated acquisitions and processing approaches using existing spacecraft. This connects an older satellite family to a newer operational system without making the vehicles identical. It also shows why a mission’s final useful work can involve testing how future users will interpret and combine its successors’ data.