Research On Image Formation For Sliding Spotlight Bistatic Forward-looking SAR

Sliding Spotlight bistatic forward-looking SAR is a special kind of bistatic SAR system.The traditional bistatic forward-looking SAR has someadvantages, such asstrong concealment, high anti-interference ability, more flexible space configuration, front direction can be imaged, etc. However, due to the transmitterand receiver are mounted on difference platforms, the velocity of the transmitter and receiver usually have bigger difference, so that beam overlap time and azimuth mapping width was severely affected, thus limiting the azimuth resolution and azimuth mapping width. This paper introduced Sliding Spotlight mode to Spaceborne/Airborne bistatic forward-looking SAR system, compared with traditional Spaceborne/Airborne bistatic forward-looking SARazimuth resolution and azimuth width mappinghas greatly improved, and then the applicability and the flexibility of traditional Spaceborne/Airborne bistatic forward-looking SAR has been improved.This paper established a slide Spotlight Spaceborne/Airbornebistatic forward-looking SAR system model to analyze the performance of this model, proposed appropriate imaging algorithms.The specific content and innovation are as follows:1. Studiedtraditional bistatic forward-looking SAR echo model,introduce the spatial resolution, synthetic aperture time, azimuth mapping width and other properties of traditional bistatic SAR.Analyze the existing two-dimensional spectral and applicability.Introducethe single base slide spotlight principles and characteristics.2.Establishedthe sliding spotlight bistatic forward-looking SAR model, detailed analysis of the performance of this mode, including spatial resolution, synthetic aperture time, azimuth width mapping, doppler bandwidth.Extends the expressions of synthetic aperture time and azimuth width mapping of traditional Spaceborne/Airborne bistatic forward-looking SAR, make it suitable for sliding spotlight bistatic forward-looking SAR.And through this expressions theoretically explainedtheazimuth width mapping increasedfrom tens of meters to several kilometers, theazimuth resolution increasedalmost ten times compared with stripe pattern. At the same time the beam speed of transmitter and receiver can be changed according to different system requirements, and then changeazimuth resolution and azimuth width mapping, finally, greatly improve the flexibility and applicability of Spaceborne/Airborne bistatic forward-looking SAR.In addition, deduced the doppler bandwidth under this pattern, explained the doppler bandwidth is higher than stripe pattern, use the traditional stripe pattern imaging algorithm can lead to bearing to blur. So this paper introduces a processing method to solve the problem, and make it easier to full aperture imaging processing.3.Proposeda two-dimensional spectral and imaging algorithm based on Chebyshevapproximation. Firstly, proposeda two-dimensional spectral model based on Chebyshev approximation, by use this theory reduce the forth-order slant range to third-order, then get the stationary phase point by series reversion.andfinally get the two-dimensional spectral model.Compared this model with the traditional order Taylor approximation,the accuracy of slant distance approximation increase by about one order of magnitude. Then proposedfull apertureRange-Doppler imaging algorithm and full apertureOmega-K imaging algorithm base on the two-dimensional spectral this paper proposed. The effectiveness of this two imaging algorithm is verified by simulation.4. Proposedtheimaging algorithm based on two-dimensional spectrum which solved by use geometry model. The expression of this model is more concise and clear. First, proved the spectrum model is suitable for the sliding spotlight bistatic forward-looking SAR modelby simulation, and then proposed thefull apertureimaging algorithmbased onthis spectrum. This algorithm makes full use of the transmitter and receiver geometric relationships between the platform and the target point. Through the geometric relationships the receive platform position relationship expression can be rewrite to transmit platform position relationship, and the expression can be used to Omega-K imaging processing. The algorithm idea is straightforward, a new equivalent distance’s the physical meaning is clear.Finally comparing the algorithm with two imaging algorithms which have mentioned, illustrates the advantages of each algorithm by simulation.