KRAS - A Danish High Resolution Airborne SAR 
Sgren Ngrvang Madsen, Erik Lintz Christensen and Niels Skou 
Electromagnetics Institute, Technical University of Denmark 
Building 348, DK-2800 Lyngby, Denmark 
ABSTRACT 
The Electromagnetics Institute, the Technical University of Denmark, is presently 
constructing a C-band high resolution airborne SAR. The main purpose of the project, which 
is called KRAS, is to develop the knowledge base required to build advanced coherent 
radars. The paper will present the design rationale. The design of the radar is based on digital 
technology to the largest possible degree. This results in a very flexible radar system, with 
most of the system parameters being software controlled. Variable waveforms of bandwidths 
uarger than100 MHz and durations up to 20 us can be generated. Calibration of the system 
has also been given much consideration, and design principles usually applied in radiometers 
have been implemented. The significant flexibility and the calibration is of major importance 
since the system is intended for applications ranging from medium resolution wide swath 
mapping, i.e. sea ice mapping or oil pollution surveillance, to high resolution narrow swath 
mapping for cartography or reconnaissance . 
I INTRODUCTION 
The Electromagnetics Institute has been involved in the development of specialized radar 
systems for nearly 30 years. It all started when the Institute undertook the development of a 
60/300 MHz radar sounder for measuring the thickness of the inland ice of Greenland and 
Antarctica [Gudmandsen, 1980]. In cooperation with a number of foreign institutes such as 
the Scott Polar Research Institute, U.K. and with the support from the National Science 
Foundation, U.S.A., the ice sounder has surveyed more than 200,000 km. of bed-rock un- 
der the two major ice caps of the world, and a thickness of up to 3.2 km was measured in 
Greenland and 4.8 km was measured in Antarctica. 
Since then, a number of special purpose radars have been developed at the Electromagnetics 
Institute e.g. a number of weather radars for measuring both horizontal and vertical 
distribution of rain. Other studies have involved marine radar systems and sea clutter studies 
[Maalge, 1982], a coherent 1.5 GHz earth penetrating radar system, and design studies for 
the European Space Agency of planetary radars. Simultaneously passive microwave 
radiometers were developed. 
Ten years ago the Institute modified a conventional incoherent marine radar so that it could 
be used as an X-band SideLooking Airborne Radar ( SLAR). This system was improved a 
number of times and it was successfully used in a number of field experiments. In one of 
these experiments the system was modified to acquire HH and VV polarized images si- 
multaneously. The system is today commercially available. 
The Electromagnetics Institute's activities within the Synthetic Aperture Radar field started in 
1977, where the breadbording of a real-time digital processor for a medium resolution 
airborne SAR was initiated [Sgndergaard,1977]. In 1982 a study of the basic properties of 
SAR images was initiated. This study involved speckle theory, procedures for estimating the 
power transfer function of the SAR system as well as postprocessing algorithms for edge 
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