Multi-Temporal Analysis
Definition
Comparison of imagery acquired at different dates to detect change. A soil disturbance present in a 2009 image but absent in 2005 constrains when the disturbance occurred.
- Method
- Compare imagery from different acquisition dates
- Purpose
- Detect ground or vegetation change
- Field
- Aerial and satellite remote sensing
- Output
- Time window constraining when a disturbance occurred
Common questions
What limits the precision of the time window it produces?+
The window is only as narrow as the gap between available image dates, so a change detected between a 2005 and a 2009 image could have occurred at any point in that four-year span, not on a specific day.
Why is image consistency between dates important for this method?+
Differences in season, sun angle, sensor, or resolution between the compared images can themselves look like ground change, so analysts try to match acquisition conditions as closely as possible before attributing a difference to real disturbance.
Related terms
- Crop Mark
- A differential growth or colour pattern in surface vegetation caused by a sub-surface soil change, including disturbance from digging, which alters moisture...
- NDVI
- Normalised Difference Vegetation Index. Computed as (NIR-Red)/(NIR+Red) from multispectral imagery. Values near 1 indicate dense healthy vegetation; values near 0 indicate bare...
- Orthomosaic
- A geometrically corrected image assembled from many overlapping photographs, with a consistent scale across its extent. UAV-derived orthomosaics can be georeferenced to...
- SfM (Structure from Motion)
- A photogrammetric method that builds a 3D point cloud and orthomosaic from overlapping images by computing camera positions and feature matches. Standard...
- UNOSAT
- The UNODC Satellite Centre, a UN programme that provides satellite-derived analysis in support of humanitarian and legal investigations, including imagery used for...