A distant point – such as from a satellite orbiting our planet – provides a particularly good vantage point from which to view the earth. Whereas optical satellites require cloudless conditions, satellites with a synthetic aperture radar (SAR) collect high-precision images day and night and in any weather - even when the terrain in question is shrouded in clouds.
What is OHB’s SAR-Lupe system capable of?
SAR-Lupe is Germany’s first satellite-based reconnaissance system and was developed by OHB on behalf of the German Federal Armed Forces. SAR satellites use a synthetic aperture radar (SAR), which scans the surface of the earth with electromagnetic waves, using the data obtained to generate a two-dimensional representation of a section of the earth. SAR images have a very high resolution and resemble photographs. They can be readily interpreted with the necessary background information. However, a number of factors have to be taken into account: Images of objects on the sea may produce duplicate structures as the signal is reflected by the object itself but partially also bounced onto the water surface, where it is picked up again by the satellite.
Radar can be used at any time and in any weather
The great advantage of SAR is that it can be used regardless of the time or weather conditions. This is because the electromagnetic waves used by the radar penetrate clouds and fog, supplying detailed images even in the dark. The satellite emits electromagnetic radar signals which are bounced off the earth. The satellite then picks up the reflected satellite signal.
Reconnaissance is normally a national mission. However, reconnaissance programs are used on a cooperative basis by several countries that share the data on a reciprocal basis. For example, the ground segments of SAR-Lupe and the French optical reconnaissance system Helios II have been combined to form a single system.
Satellite reconnaissance has many benefits beyond military applications
“Reconnaissance programs help to detect developments anywhere in the world at an early stage and to prevent potential crises before they occur. The images can help to identify and react to a given situation before any problems arise,” says Tino Zehetbauer, Director of Satellite-Based Reconnaissance Programs at OHB System AG. “If a national government has its own reconnaissance system, it is able to make an independent assessment and is not dependent on third-party information.”
Some countries adopt a dual-use approach to satellite data, using it for public and also commercial applications. Although this has economic advantages, it may take longer for the information sought to be received due to the restricted utilization times. For this reason, it may make more sense for a country to have its own satellite reconnaissance system.
The information collected depends on the circumstances of the specific case. In the event of a catastrophe, for example, it is important for the satellite images to show what roads are still intact. However, as radar images are not photos, it is necessary to take a step back and to analyze what is actually going on. Precise evaluation and reference points play a crucial role in the interpretation of the image.
Working together, the five SAR-Lupe satellites provide a very consistent image, something that facilitates evaluation enormously.
10 years of error-free operation
Satellites are tested on the ground before being placed in orbit to make sure that they are operating properly. In addition to the compulsory ESA testing, SAR-Lupe underwent a separate procedure known as inverted testing. This involved aligning the satellites on the earth to International Space Station ISS to capture images of the station. As all the details of the ISS are known, it was possible to assess the precision and reliability of the system by reference to the quality of the radar images.
Careful design planning, construction, testing and quality control helped to ensure that by November 2017 the five SAR-Lupe satellites had been operating free of any faults for ten years.
Now the system has to be replaced
The SAR-Lupe satellite are designed for a service life of at least ten years.
This size of the satellite tank is not the sole determinant for this. In addition, all satellites are exposed to harsh conditions in space, causing the materials to age and performance to decline. This is why satellites must be replaced when they reach the end of their lives.
The SAR-Lupe satellites will be receiving a successor after they are decommissioned to ensure that there are no interruptions in coverage for the operator. The follow-up SARah project has been configured for a life span of a further ten years.
What makes the SAR systems from OHB so special?
The SAR-Lupe project was executed on time and in budget and has been operating perfectly throughout its entire service life. Generally speaking, the satellite is handed over to the buyer when construction has been completed. This was not the case with SAR-Lupe. As Zehetbauer explains: “OHB executed SAR-Lupe as an integrated system from the preliminary design phase and construction, to the start-up in space, control and beyond to end-of-life disposal.” This will also be case with the follow-up project SARah.
Using as a basis the experience gained from the development of SAR-Lupe, OHB System has amassed expertise in this area and is offering systems for commercial and institutional high-resolution earth observation systems in the visible, infrared and radar ranges. Potential applications include catastrophe management, security applications and humanitarian aid, all areas in which it is important to have a precise view of the “big picture”.