The Danube Delta Looks Gorgeous Through Radar Eyes From Space

Illustration for article titled The Danube Delta Looks Gorgeous Through Radar Eyes From Space

This so called interferogram was created by combining two Sentinel-1A radar scenes from over the Danube River Delta, which covers more than 4,180 square kilometers in Romania.

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European Space Agency’s Hydro-SAR project monitors wetlands, such as Danube Delta, playing an important role in sustainable water management with the help of satellite radar data. ESA explains how:

With many areas within the delta virtually inaccessible, satellites provide the means to map and monitor this biologically diverse wetland. In particular, radars – such as the one on the Sentinel-1 mission – can provide information on the present state of a wetland, hydrological interactions between the different types of reservoirs, and can help to refine current hydrological models dedicated to wetland management.

To do this, multiple images from synthetic aperture radars – or SARs – are combined to create ‘interferograms’ showing changes between the radar scans. The measurements are then analysed to show various hydrological parameters such as water surface extent, water level changes and the direction and gradients of water flow.

Here is the full image of this UNESCO World Heritage Site. Click on the top left corner to see the full size.

Illustration for article titled The Danube Delta Looks Gorgeous Through Radar Eyes From Space

[Copernicus data (2015)/Terrasigna via ESA]

DISCUSSION

For those who don’t know what SAR interferometry is, here’s a quick primer. The fundamental premise of radar is that you actively emit RF pulses and then receive the echos of those pulses. Traditional radar only really measures the timing of the echos, which gives you a measurement of the range to the object that caused the echo. Modern SAR receivers measure the phase of the received pulses. When you take two images of the same area from the same place and overlap them comparing the received phase differences, you get an interferogram like this. The “rainbow” colors show phase difference, so the more rainbow you see (like the area at the right) the more height change has occurred in the time between when the images were taken.