European Remote Sensing Satellite
The European Remote Sensing Satellites ERS- 1 and ERS -2 are two satellites of the European Space Agency ( ESA), which served to remote sensing of the earth's surface. Both satellites are no longer in operation. ERS- 1 was the first Earth observation satellite, the ESA, and one of its main satellites developments of the 1980s.
- 3.1 Innovation by combination
- 3.2 Additional benefits
Development and construction
First project studies began in 1978. DASA was the prime contractor for both missions and supplied both the platform and some key instruments. Equipped were the satellites, each with multiple ( "multi -disciplinary " ) measurement techniques for different spectral ranges (UV / VIS range, the IR range, microwave ). Built were ERS- 1 and ERS -2 by a consortium of companies under the leadership system of the Dornier System GmbH in Friedrichshafen. This company has also developed the SAR sensor. Similarly, the ERS ground station in Antarctica was built by Dornier.
Satellite orbits and video tracks
The two satellites were put in orbit on 17 July 1991, to April 21, 1995 with Ariane 4 rocket. The ERS satellites orbited the Earth in about 100 minutes and run on nearly polar orbits, so they could be interpreted in sun-synchronous. This means that the sheet layers are always at the same angle to the sun and which have picked up image strips at different times as the same conditions with lighting and contrast.
Strip -like scanning the earth
The satellite orbits were designed so that they painted over in 35 days almost every place on the earth at least once with their sensors.
This strip-shaped flying over comes about by two effects: the Earth's rotation and the precession of the orbital planes. The orbits of satellites represent ellipses or circles and extend approached by the Kepler laws. Your planes remain in the surrounding space ( reference system of stars) largely fixed in space, so that our home planet rotates away from these pathways. As a result, similar satellites ERS and the surface can be scanned in consecutive image strips by one.
Would a polar satellite near (north-south flying) now exactly 14 times around the Earth every day, he would come back after every day almost the same strip. If so, for example, ERS- 2, this orbital period of 102.57 minutes, he could indeed daily observe the Earth's surface along certain meridians, but the areas between them not. It changes and therefore stabilizes the tracks so that it runs every day at a certain distance to the previous meridian.
Satellite orbit
The ERS satellites circling the Earth in a sun-synchronous orbit at 800 km at first an inclination of 98.5 °. The railway track leads about 900 km at the poles over. The satellite rastered the earth from strip-wise and reach the exit point after 35 days. The orbit was designed as a frozen orbit.
Instruments of the ERS satellites
The main instrument was a C-band Synthetic Aperture Radar with a ground resolution of 30 x 30 meters. It was pivoted by 12 ° to the left and right and captured a 100- km wide strip on the earth. Due to the sun-synchronous path she saw the surface at about the same local time.
ERS -2 also contributes to the instruments of the ERS- 1, the GOME spectrometer. Other devices are:
Innovation by combining
After the launch of ERS -2 SAR sensors ERS- 1 and ERS -2 were in very short time intervals ( a day in the rule) capture the same surface of the earth and these data are used for interferometry. Here, (a few 100 meters usually ) the slightly different orbits of the two satellites lead to slightly different " angles " of the same area of the Earth's surface. By mathematical combination of the two recordings thus either digital elevation models of the earth's surface could be created or even small movements of the Earth's surface between the two recordings to about a centimeter recorded and visualized (differential radar interferometry, DInSAR ).
Thus, the satellite provided data on changes in the Earth's surface before or after a volcanic eruption or displacement of the earth's surface by earthquakes. The expansion of a Lavakammer of Etna or the prediction of the mudslide of a volcano in Iceland were more examples.
A similar combination of two SAR sensors is performed with the satellite TerraSAR -X. From the end of 2010, this will launch together with the almost identical satellite TanDEM- X is a multi-year joint interferometric mission.
Additional benefits
The satellite is not only the achievement of research objectives for the International Charter for Space and Major Disasters.
Health of satellite
ERS -1 is since 10 March 2000 is not longer active, but surpassed the planned useful life doubled.
In June 2003 the band memory of ERS -2 failed. The satellite could not cache more, he registered at a circumnavigation of the earth in 100 minutes, the signals. He only sent the data it just took up when he was in contact with a ground station for 10 minutes. Through an extensive international network of ground stations, this disadvantage was compensated as much as possible.
Since February 2001, resulted in problems with the gyro sensors to certain limitations in the usability of some sensors. These problems could be in 2003, partially offset by a new software control. Otherwise, ERS -2 works to 2011 properly.
Late 2007 and early 2008, a tandem mission with ESA's Envisat satellite was carried out in which the overflying staggered in time (about 30 minutes difference) important new data have been obtained, such as about rapidly changing glaciers in the Arctic.
On 5 July 2011, the ESA announced the end of the mission of ERS -2. From the 6th July, the orbital altitude of the satellite was lowered by several brake ignitions from 800 km to 550 km, where the risk of collision is lower. Furthermore, all tanks were emptied and the batteries are discharged, to prevent explosions on board create more space debris. The last command on ERS -2 was sent on September 5, 2011 at 13:16 UTC. Within the next 25 years, ERS -2 will then burn up in the Earth's atmosphere.