TerraShift: See how the land changes

See how the land changes

Compare Sentinel-2 satellite images of an area on two dates. How it works, limits and test results

Public 10 m satellite data: it can't identify people or vehicles. Don't use it to watch individuals or private property, and have a person check results before acting on them. Responsible use

1. Area

Search by Nominatim, data © OpenStreetMap contributors

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2. Dates

Before After

Before image: -

After image: -

Start by choosing an area.

Press Find images to look for changes between your two dates.

Changes found

Plants gained
Plants lost
New buildings or bare ground
Burned

Skipped because of cloud, shadow or missing data:

A hectare (ha) is 10,000 m²: a square 100 m long on each side, a bit bigger than a football pitch.

How are changes found?

Each 10 m square gets a plant greenness score (NDVI) and a built-up score (NDBI), both from −1 to +1. A square only counts as changed if its plant score moved by 0.15 or more, or its built-up score rose by 0.10 or more. Smaller shifts usually come from haze, the sun's angle or the season, not from real changes on the ground.

Bright new surfaces, like white fill on a building plot, can make the built-up score go down. So a square also counts as new buildings or bare ground if it became at least 30% brighter in visible light than the area as a whole did, ends up brighter than the area's usual ground, and is part of a patch of at least 2,500 m². Ground beside water or plants is left out, because drying out makes it brighter too. So is ground on slopes of 15° or more (from the Terrain tab): the sun lights steep slopes much more or less brightly as it gets higher or lower through the year, so brightening there is usually just the light.

Surfaces that were already dark, like solar panels, dark roofs and asphalt, aren't counted as new buildings if they only got darker. Dust, cleaning and shadows do that without anything new being built.

A square counts as burned if its burn ratio (NBR) fell by 0.27 or more, the level usually called a moderate burn, where there were some plants to burn. Burned ground goes dark in near-infrared light but not in short-wave infrared, so squares that went dark in both (shadows, water, new dark roofs) are not counted as burned. Nor are squares that got brighter in near-infrared, like wet mud drying out.

A changed square also needs at least 2 neighbours that changed the same way, because real changes cover a patch of ground. Water and shorelines, ground that was wet before, and ground that fell into a new shadow are left out, because tides and the sun make them look different without anything changing.

Lawns, crops and trees green up and dry out with the seasons. If your two images are from different seasons, a note says so, and Compare with a year earlier shows how much of the plant change is probably seasonal.

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