Tapan Misra

We are learning SAR afresh, with Droneborne Ultra High Resolution L-band SAR from SISIR RADAR

All my understandings of SAR images in past 39 years, are turning upside down. We have grown up seeing SAR images where the variation of terrain height is very marginal to the altitude of SAR flight. Consider an airborne SAR, flying at altitude of 10 km over a city like Kolkata. The typical variation in heights of buildings will be 10 to 100 m. The layover, foreshortening and shadow effects of SAR image distortion will be predictable and definitive over an image, as these height variations are very negligible compared to the flight altitude. The effect will be more predictable for a satellite SAR images flying at altitudes of 500+ kms.

For the L band Drone SAR of SISIR RADAR, flying at altitude of 100 m over MAKAUT campus, with building heights varying over 10 to 40 m, the variation of radar imaging distortion is very much pronounced and not very easily predictable. The reason is very simple: the terrain height variation is very large in comparison to flying altitude. But the radar distortion effects are very complex. The high resolution of 20 cm along flight direction and 100 cm across flight direction, make the effect dramatic as none has ever encountered such SAR signatures, that too in L band.

Another interesting feature of this high resolution SAR: partial imaging of the shadow region. The azimuth beamwidth for imaging is 35 deg. During imaging process, the radar shadow also rotates by the same amount, making possible partial imaging of the shadow region.

Looks like our drone SAR images are revealing more than it hides. I am convinced that these drone SAR images will call for innovations in new analytical tools for better interpretation.

The author and founder of SISIR Radar, Tapan Misra, is recognised in knowledgeable circles across the world as the father of Indian SAR technology. He is a distinguished scientist, whose contribution to India’s Space Programme and Space Applications Centre, as it’s former Director, is immense.