HAPS: Potentials, Applications and Requirements for Radar Remote Sensing

Abstract

High Altitude Pseudo-Satellites (HAPS) are future platforms flying in the stratosphere. Owing to the expected long endurance, missions lasting for several weeks, months or even years are possible. This property makes HAPS very attractive as carrier platforms for remote sensing instruments. HAPS allow for short revisiting times or even for continuous observations, e.g., by performing circular flight tracks over the region of interest. Such an operating mode is not feasible with satellites and is also not realizable economically with state-of-the-art aircraft platforms over longer time frames. We focus on a synthetic aperture radar (SAR) as HAPS payload. The SAR principle ensures high resolution down to the sub-meter range independently from the flight altitude, weather conditions and sunlight illumination. Due to the side-looking radar imaging geometry also hazard areas can be monitored safely since the platform is not only separated in altitude, but additionally separated horizontally several kilometers far away from the scene center. In 2015 we have carried out a study for Airbus Defence and Space to investigate if it is feasible to bring and operate a SAR sensor on their solar-powered Zephyr HAPS platform. In the study we found that the two main platform restrictions, the limited payload weight and the limited available electrical power, can be overcome. For instance, a peak transmit power of 50 W at a duty cycle of 20 % is sufficient for obtaining high-quality SAR images with resolutions <1 m at X-band with a swath width of 25 km, acquired from a flight altitude of 20 km. In our talk we will give a detailed overview of the potentials and applications of HAPS-SAR. We will show the achievable SAR imaging and moving target detection performances of an exemplary radar designed for platforms like the Zephyr HAPS. One important point in the talk will be the requirements on the onboard navigation system, which are crucial for obtaining high-quality (circular) SAR images.