Radar & SAR Imagery
It sees through cloud, and none of the numbers mean what they look like.
Radar is the instrument that keeps working when a flood arrives with a week of cloud, and the price is that nothing in the image is familiar: brightness is roughness and moisture, every pixel carries speckle, mountains lean towards the sensor, and the values are linear power with a nodata flag of −32768. These guides start with what backscatter is, what VV and VH each respond to, and why the grain is not noise; then find, read and mosaic Sentinel-1 scenes, convert and average them correctly, filter speckle, map a flood, detect change, build time series and composites — and fix the images that look noisy, distorted, misaligned or full of water that was never there.
The units guide at step nine is the quiet turn in this path. Backscatter is linear power, and almost every wrong number in radar work — a zonal mean two decibels off, a composite that darkens, a threshold that will not transfer — comes from arithmetic done in decibels. After it, the flood maps and change detections that follow are measuring what they claim to.
Start here
The cornerstone guide — the whole workflow end to end. Everything after it goes deeper into one part of it.
Step 1 SAR imagery explained: what radar measures and why it sees through cloud sar imagery explained Begin the path →The full path, in order
The concepts underneath the work, then each task, then the errors that task produces. Work down, or jump to the step you need.
- SAR polarisation explained: VV, VH and what each responds to vv vh polarisation sar 🧭 Concept
- Speckle explained: why radar images look grainy sar speckle explained 🧭 Concept
- SAR geometry explained: layover, foreshortening, shadow and look direction sar layover shadow foreshortening 🧭 Concept
- Sentinel-1 products explained: SLC, GRD and radiometrically terrain-corrected sentinel-1 slc grd rtc 🧭 Concept
- InSAR explained: measuring millimetres of ground motion from phase insar explained 🧭 Concept
- How to find Sentinel-1 scenes in Python find sentinel-1 scenes python ⚙️ How-To
- How to read Sentinel-1 RTC data in Python read sentinel-1 rtc python ⚙️ How-To
- How to convert SAR backscatter to decibels, and average it correctly sar backscatter decibels python ⚙️ How-To
- How to filter speckle in Sentinel-1 images speckle filter sentinel-1 python ⚙️ How-To
- How to map floods from Sentinel-1 in Python sentinel-1 flood mapping python ⚙️ How-To
- How to detect change between two Sentinel-1 images sar change detection log ratio ⚙️ How-To
- How to extract a Sentinel-1 time series for an area sentinel-1 time series polygon ⚙️ How-To
- How to make a Sentinel-1 composite over a period sentinel-1 composite python ⚙️ How-To
- How to monitor crops with Sentinel-1 in Python sentinel-1 crop monitoring python ⚙️ How-To
- A SAR image looks noisy after processing sar image noisy speckle 🔧 Fix
- SAR values come out negative, huge or averaged wrongly sentinel-1 values negative -32768 🔧 Fix
- SAR scenes from different dates do not line up sentinel-1 scenes do not align 🔧 Fix
- A SAR flood map shows water where there is none sar flood map false positives 🔧 Fix
- A SAR image looks stretched or smeared in mountains sar distortion mountains layover 🔧 Fix
Topics this path covers
A path is a route; a topic is everything the site has on a subject. Open a topic to see the guides this path skips.