What is SAR (radar imagery)?

Optical satellites need daylight and clear skies. Radar satellites carry their own signal: they send microwave pulses and measure what bounces back, so clouds, smoke and darkness don’t block the view.

The European Sentinel-1 satellites carry C-band SAR. Large changes in the land surface — new buildings, earthworks, flooding — change the radar echo, so researchers and governments use it for flood mapping and change detection when optical images are clouded out.

Radar images look nothing like photos: they are grainy, black-and-white and distorted on slopes, and they need specialist processing to read reliably at the scale of a single small plot.

PlotPehra does not use radar. We use free Sentinel-2 optical images, tell you plainly when monsoon cloud has blocked the view, and keep checking the official land record every week in 19 states, which weather doesn’t affect.

Why it matters if you live abroad

If someone offers to watch your land “through the clouds”, it helps to know what radar can and can’t show for a small plot — and that paper changes in the land record matter just as much in the monsoon.