Research On The Nearspace Distributed InSAR System Technology

Near space distributed InSAR altimeter system is a novel radar system which is formed as a result of the combination of airship formation and SAR technology. Altimetering will be made through the flying formation and collaboration of airship. It becomes a hotspot attractive to worldwide attention due to such advantages as high DEM(digital elevation model) accuracy, wide surveying band, long dwell time and less revisit cycle. Aiming at this leading subject, the interferometric principle and key technology (baseline metering, baseline optimization, time phase synchronization error and time phase synchronization method) of the new system as well as the overall parameter analysis and design methods of the system are studied in this paper.Based upon the space geometric relationship of near space distributed InSAR system, the interferometric principle is studied and the positioning and elevation equation is derived in Chapter 2. Following this equation, the error source at each level and the error transmission of InSAR system are analyzed to present a transmission model. Furthermore, the three operation modes of near space distributed InSAR system are analyzed and compared for the receiving/sending signal time sequence, formation size, baseline metering, radar synchronization and data capacity.The baseline metering error and baseline design optimization method are studied in chapter 3. In light of the baseline error transmission model mentioned in chapter 2, the requirements on baseline metering error index is analyzed and, in virtue of the baseline metering method of satellite-borne InSAR, employed in near space airship system. Two baseline metering methods are researched: radio-based metering method for relative relationship in airship formation and radio/laser-based metering method for relative relationship in airship formation. The solution of the best baseline in airship InSAR system is concluded as an optimization problem under restraint condition. A step-by-step design optimization method is put forward to make a rapid solution.In chapter 4 the time phase synchronization error and synchronization method are studied. The effects of time and frequency synchronization errors on imaging and height measurement are analyzed. In virtue of the time and phase synchronization method of satellite-borne InSAR which is employed in near space airship system, the 2-way frequency transmission phase synchronization method and 2-way transmission time synchronization method are studied.Overall system parameters analysis and design method is studied in chapter 5. Single baseline InSAR system overall parameter design flow is put forward. The simulation verification is made by taking X wave-band single platform double-antenna InSAR and P wave-band airship formation InSAR as two examples to obtain the overall system parameter scheme of two conceptual systems.