TerraSAR-X image of the month – stage clear for the salt flats

TerraSAR-X radar satellite image of salt flats
19 October 2012

Clouds, darkness, rain – the radar 'vision' of TerraSAR-X is unaffected by these conditions. Dark and light areas contrast clearly in this image, acquired by the German Aerospace Center's (Deutsches Zentrum für Luft- und Raumfahrt; DLR) TerraSAR-X satellite. The black areas represent water, where radar signals transmitted by the satellite are not returned, as they are reflected away by the smooth surface of the water. The city of Wendover is conspicuous in the upper half of this space radar image. "These are not lights shining. The radar is detecting a strong increase in the local variance of the return signal," explains DLR researcher Daniel Schulze. The reason for this is that the colouring of the image is based on a statistical assessment of the data set, where the variance in the roughness of the surface is colour-coded. Hence, built-up areas appear rough to the radar and appear orange, as there is a high probability that the radar signal will find its way back to the satellite following direct or multiple reflections off the buildings and streets.

The Bonneville Salt Flats is the largest salt pan lying to the west of the Great Salt Lake, in the northern part of the US state of Utah. The salt pan arose towards the end of the last ice age as a consequence of Lake Bonneville drying up. This was a prehistoric lake that stretched across a large section of the major basin to the west of the Rocky Mountains, and of which only the Great Salt Lake now remains. The former Bonneville Lake is history; today the salt flats stretch out over an area of some 10,360 square kilometres.

Full speed across the desert

TerraSAR-X circles the Earth in a polar orbit at an altitude of 514 kilometres. Its active array antenna enables it to provide radar data with a resolution of down to one metre, regardless of weather conditions, cloud coverage and availability of daylight. It acquired this unique image at 13:40 local time on 23 June 2009. The scene measures 50 by 30 kilometres. TerraSAR-X also cast a penetrating eye on the around 2000-metre-high mountains and the salt lake, which lies at an altitude of some 1270 metres. The image shows rough surfaces in orange and smooth ones in grey/black.

The salty desert is also known for the Bonneville Speed Races, which have been held here since 1912, and for each of which new tracks are created. The extensive, 1.5-metre-thick, hard, smooth salt surface offers the perfect surface for high-speed driving. Because of its size, the salt flat is often used for world speed record attempts.

The large, black surface bordering the industrial area in the middle of the image is the Wendover Facility. Large-scale industrial extraction of brine takes place here, which is needed for manufacturing potash. Next to the city of Wendover is the airport, which was an air force base until 1965. Even from an altitude of over 500 kilometres, TerraSAR-X can detect the fine, parallel orange lines extending from the airport, which are other transportation routes such as Highway I-80 and the railway running from east to west.

Famous from film and television

The Great Salt Lake has been used as a backdrop in a number of films, such as 'Pirates of the Caribbean: At World's End' with Johnny Depp and 'Independence Day', directed by Roland Emmerich and featuring Will Smith. Wendover Airport, to the left of centre in the image, is known from numerous cinema productions, such as 'Con Air', directed by Simon West and starring Nicholas Cage.

The TerraSAR-X mission

TerraSAR-X is the first German satellite manufactured under what is known as a Public-Private Partnership between the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and Astrium GmbH in Friedrichshafen. The satellite travels around the Earth in a polar orbit and records unique, high-quality X-band radar data about the entire planet using its active antenna. TerraSAR-X works regardless of weather conditions, cloud cover or the absence of daylight and is able to provide radar data with a resolution down to one metre.

DLR is responsible for using TerraSAR-X data for scientific purposes. It is also responsible for planning and implementing the mission as well as controlling the satellite. Astrium built the satellite and shares the costs of developing and using it. Infoterra GmbH, a subsidiary company founded specifically for this purpose by Astrium, is responsible for marketing the data commercially.