Transponder-Aided Joint Calibration and Synchronization Compensation for Distributed Radar Systems

PLOS ONE, Dec 2019

High-precision radiometric calibration and synchronization compensation must be provided for distributed radar system due to separate transmitters and receivers. This paper proposes a transponder-aided joint radiometric calibration, motion compensation and synchronization for distributed radar remote sensing. As the transponder signal can be separated from the normal radar returns, it is used to calibrate the distributed radar for radiometry. Meanwhile, the distributed radar motion compensation and synchronization compensation algorithms are presented by utilizing the transponder signals. This method requires no hardware modifications to both the normal radar transmitter and receiver and no change to the operating pulse repetition frequency (PRF). The distributed radar radiometric calibration and synchronization compensation require only one transponder, but the motion compensation requires six transponders because there are six independent variables in the distributed radar geometry. Furthermore, a maximum likelihood method is used to estimate the transponder signal parameters. The proposed methods are verified by simulation results.

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Transponder-Aided Joint Calibration and Synchronization Compensation for Distributed Radar Systems

March Transponder-Aided Joint Calibration and Synchronization Compensation for Distributed Radar Systems Wen-Qin Wang 0 1 2 0 School of Communication and Information Engineering, University of Electronic Science and Technology of China , Chengdu , P. R. China 1 Funding: The work described in this study was supported by the National Natural Science Foundation of China under grant 41101317 and the Program for New Century Excellent Talents in University under grant NCET-12-0095. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript 2 Academic Editor: Ke Lu, University of Chinese Academy of Sciences , CHINA High-precision radiometric calibration and synchronization compensation must be provided for distributed radar system due to separate transmitters and receivers. This paper proposes a transponder-aided joint radiometric calibration, motion compensation and synchronization for distributed radar remote sensing. As the transponder signal can be separated from the normal radar returns, it is used to calibrate the distributed radar for radiometry. Meanwhile, the distributed radar motion compensation and synchronization compensation algorithms are presented by utilizing the transponder signals. This method requires no hardware modifications to both the normal radar transmitter and receiver and no change to the operating pulse repetition frequency (PRF). The distributed radar radiometric calibration and synchronization compensation require only one transponder, but the motion compensation requires six transponders because there are six independent variables in the distributed radar geometry. Furthermore, a maximum likelihood method is used to estimate the transponder signal parameters. The proposed methods are verified by simulation results. - Competing Interests: The authors have declared that no competing interests exist. Distributed radar system operating with separated transmitters and receivers offers many operational advantages [14] to conventional monostatic and multi-frequency or multi-polarized radars [58], like the exploitation of additional information contained in bistatic reflectivity of targets [9], reduced vulnerability [10], and forward-looking imaging [11]. Distributed radar may offer reduced vulnerability to countermeasures such as jamming, as well as increased slow-moving target detection and identification capability via clutter tuning, in which the receiver maneuvers so that its motion compensates for the motion of the illuminator to create a zero Doppler shift for the area being searched. This could be worthwhile, e.g., for topographic features and drainage, to show the relationships that occur between forest, vegetation, and soils. This also provides important information for land classification and land-use management such as agriculture monitoring, soil mapping, and archaeological investigation. Attracted by these special advantages, various spaceborne and airborne distributed radar missions have been suggested or developed [12]. However, in a distributed radar the receiver uses an oscillator that is spatially displaced from that of the transmitter; hence, the phase noise of two independent oscillators cannot be canceled out. This superposed phase noise corrupts the received radar signal over the whole coherent integration time, and may significantly degrade subsequent imaging performance. Even when low-frequency or quadratic phase errors as large as 45 degree in a coherent processing interval can be tolerated, the requirement of frequency stability is only achieved by using ultra high-quality oscillators [13]. In the example of the bistatic spaceborne radar system TanDEMX [2, 14], the relative phase has to be measured with at least 1 Hz sampling frequency in order to follow, unwrap and compensate the oscillator phase drifts within the acquisition [15, 16]. Furthermore, aggravating circumstances are often accompanied for airborne platforms due to different platform motions, the frequency stability will be further degraded. Thus, frequency synchronization compensation is required for distributed radar systems. There is relative lack of practical synchronization technique for distributed radar systems. Since distributed radar is of great scientific and technological interest, several potential synchronization techniques have been suggested. The use of duplex links for oscillator frequency drift compensation was proposed in [14]. This concept is similar to the microwave ranging technique. However, this two-way operation is too complex to be applied for multistatic radar systems. We have investigated a direct-path signal-based phase synchronization technique in [17]. To receive the direct-path signal, the receiver must fly with a sufficient altitude and position to maintain line-of-sight contact with the transmitter/illuminator. In [18], we propose a time and phase synchronization method via global positioning systems (...truncated)


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Wen-Qin Wang. Transponder-Aided Joint Calibration and Synchronization Compensation for Distributed Radar Systems, PLOS ONE, 2015, 3, DOI: 10.1371/journal.pone.0119174