Synthetic Aperture Radar (SAR)
Definition
An active microwave sensor that generates its own energy pulse and measures the return from the surface. Cloud-penetrating and day/night capable. Backscatter intensity responds to surface roughness and dielectric constant, the latter driven largely by soil moisture.
- Sensor type
- Active microwave (self-illuminating)
- Weather capability
- Cloud-penetrating, day and night
- Key signal
- Backscatter intensity
- Driven by
- Surface roughness and dielectric constant (soil moisture)
- Field
- Remote sensing for forensic/geospatial investigation
Common questions
Why is SAR preferred over optical satellite imagery for time-sensitive forensic search?+
Because SAR generates its own microwave energy and measures the return, it can image through cloud cover and darkness, letting investigators acquire usable data on a fixed schedule regardless of weather, while optical sensors depend on sunlit, cloud-free conditions that can delay coverage for days.
How does SAR backscatter help detect ground disturbance such as a buried grave or recent digging?+
Disturbed soil changes surface roughness and moisture content compared to undisturbed ground, which alters the dielectric constant and therefore the backscatter intensity returned to the sensor, producing a detectable anomaly in the SAR image even when no visible surface trace remains.
What limits SAR's usefulness compared to optical imagery for a forensic analyst?+
SAR imagery is harder to interpret visually because it records radar backscatter rather than reflected light, requires specialist processing to correct for terrain and speckle noise, and does not directly show colour or fine surface texture the way optical imagery does.
Related terms
- Ground Sampling Distance (GSD)
- The dimension on the ground represented by one pixel in an image. A 10 m GSD means each pixel covers a 10...
- 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...
- NDWI
- Normalised Difference Water Index. Computed from green and near-infrared or shortwave-infrared bands. Sensitive to water content in vegetation canopy and surface soil....
- Temporal Change Detection
- The comparison of multi-date images of the same area to identify pixels or features that have changed between acquisition dates. A disturbed...
- Thermal Infrared (TIR)
- Sensor bands measuring emitted heat radiation (approximately 8-14 micrometres). Decomposing organic matter generates heat; soil with high moisture retains heat longer than...