By far the majority of users of Geocento’s EarthImages platform search for optical imagery. Very few consider using radar imagery. Given its undoubted advantages in terms of being able to see the Earth’s surface through cloud, why is it not used more? First, a bit of background. Radar imagery from satellites has been around for a long time, since the days of NASA’s Seasat satellite way back in 1978, but a technical fault resulted in early failure of the mission after just 3 months and it was the European Space Agency who started things up again in 1991. Since that year, there has been continuous radar imaging from space from institutional and commercial satellites and radar imaging now covers about 20% of the market for image sales.
Sentinel-1 radar imagery of Indonesia from the European Space Agency.
In some ways, it is odd that radar imagery does not cover more of the global imagery market, given its strengths. First it can see through cloud, almost all weather conditions and through day and night. This alone represents a massive benefit over visible imagery. The “lottery” aspect of visible imaging is removed, at least in terms of the impact of cloud conditions. This is very useful at sea, for example, where radar makes it possible to check for oil spills, icebergs, and illegal activities without having to worry too much about the weather.
Second, some of the unique properties of radar have resulted in some intriguing capabilities. Take “radar interferometry”, which is the specialism of our intern Serena Moretto from the University of Roma and Geohazards assessment company Nhazca in Italy. It turns out that if you create patterns of interference fringes from slightly displaced radar images collected from satellites (which many of us will remember from Physics lessons at high school), you can estimate the height of the surface. If you repeat this for the same area, you can estimate the displacement of the surface to just a few millimetres. This has created all sorts of applications such as mapping of mining subsidence, changes in elevation associated with building projects, volcanic and earthquake-induced movements in the ground, etc. But there is more. Some radars penetrate beneath the surface in dry regions enabling you to see ancient buried river beds and archaeological features, or ancient layers underneath the surface of the ice cap in Antarctica
Surface displacement rate in millimeter/year from radar imagery, with each coloured point representing a time series of displacement. The colour of the point indicates the displacement rate (blue ~+10mm/yr; red ~-10mm/yr), courtesy Nhazca.
So why is radar not more popular? Well, as hinted in our last blog, it can be a real headache to interpret. It is nothing like a visible image. Visually, it is quite possible to interpret a radar image in completely the wrong way. Show a radar image to an expert and even they like to get some context before they will hazard an interpretation, so the price of a radar image also comes with the price of an expert and/or the need for some highly specialist analysis that enables the results of the imagery to be used with confidence.
However, watch this space. There has been steady growth in radar imaging over the last decade. The European Space Agency is now providing radar imagery from two satellites, Sentinel-1A and 1B and this is now available on our platform EarthImages. Our partners S I Imaging, Airbus and MDA offer the ability to access radar imagery and there are plenty of organisations that provide the ability to make good use of it, while there are plans to develop radar imaging constellations that have the ability to view the planet almost continuously. For example Capella Space are looking towards a capability of imaging the surface every 3-6 hours by launching a constellation of radar imaging satellites. It may be challenging to use, but technology aids are improving all the time and the value of being able to reliably see the surface of the planet is difficult to ignore.
Contact us to find out whether radar can help you.