Published in IET Radar, Sonar and Navigation Received on 23rd July 2008 Revised on 15th May 2009 doi: 10.1049/iet-rsn.2008.0121 ISSN 1751-8784 Problem of signal synchronisation in space-surface bistatic synthetic aperture radar based on global navigation satellite emissions – experimental results R. Saini R. Zuo M. Cherniakov School of Electronic, Electrical & Computer Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK E-mail: rxz311@bham.ac.uk Abstract: This study presents the synchronisation problem in ‘space-surface bistatic synthetic aperture radar (SS- BSAR)’ system. Global Navigation Satellite Systems (GNSS) are considered as transmitters of opportunity. It highlights various important issues of synchronisation, specifically related to SS-BSAR utilising GLONASS as the transmitter. Experimental testing of the synchronisation algorithm is described and verified using the GLONASS satellite. Also, experimental images obtained from GLONASS are presented and briefly analysed. 1 Introduction Synthetic aperture radar (SAR) is a type of radar used for imaging terrain. It utilises the relative motion between the radar antenna and a ground patch to generate high- resolution images. In a monostatic SAR the transmitter and receiver are on the same platform whereas in a bisatic SAR (BSAR) the transmitter and receiver are separated by a distance [1–5]. There is one subclass of BSAR known as: space-surface bistatic SAR (SS-BSAR) [6]. It consists of a spaceborne transmitter (dedicated or non-cooperative) and a receiver mounted on or near the earth’s surface. Its general topology is shown in Fig. 1a. The core of such system is its essentially asymmetric topology. This is in contrast to a more usual BSAR configuration where the transmitter and receiver are moving along nearly collinear trajectories. In this paper, we consider a non-cooperative SS-BSAR using GNSS as transmitters of opportunity and receiver mounted on an aircraft. The GNSS transmitters are: GPS (USA), GLONASS (Russia) and Galileo (European Union). One of the key advantages of using GNSS transmitters compared to other satellite systems (e.g. Geostationary DTV satellite) is that the user can choose the desired bistatic topology (optimal transmitter position, no or less restrictions on the receiver path, hence to achieve best possible range resolution). This is due to the fact that 4–10 GNSS satellites are simultaneously visible at any point on the earth’s surface (without shadowing) at anytime. As a result, a particular satellite in the best (or at least suitable) position can be selected and there is no need for a very specific aircraft path to allow the observation of a particular area. On the other hand, geostationary satellites are fundamentally positioned above the equator and this requires a specific aircraft path for mapping a particular area and, in many or even most situations, a vital loss in ground resolution may take place. The most promising GNSS for the considered purpose are the EU Galileo satellites and the new GPS III satellites [7]. These satellites can potentially provide a range resolution of about 8 m against 30 m for GLONASS [8]. The Galileo E5 and new GPS L5 signals also provide at least 6 dB more received power compared to GLONASS L1 channel. In addition, the GPS satellites after modernisation will transmit signals using a spot beam. It will cover a ground area of about 1200 km  1200 km (significantly large considering the typical operational range of 5–10 km for SS-BSAR) and generate 20 dB more power budget than using GLONASS satellite. 110 IET Radar Sonar Navig., 2010, Vol. 4, Iss. 1, pp. 110–125 & The Institution of Engineering and Technology 2010 doi: 10.1049/iet-rsn.2008.0121 www.ietdl.org