Modeling and Precise Processing for Spaceborne Transmitter/Missile-Borne Receiver SAR Signals

Abstract

The spaceborne transmitter/missile-borne receiver (ST/MR) synthetic aperture radar (SAR) could provide several unique advantages, such as wide coverage, unrestricted geography, a small detection probability of the missile, and forward-looking imaging. However, it is also accompanied by problems in imaging, including geometric model establishment and focusing algorithm design. In this paper, an ST/MR SAR model is first presented and then the flight-path constraint, characterized by geometric configurations, is derived. Considering the impacts brought about by the maneuvers of the missile, a non-'Stop-Go' mathematical model is devised and it can avoid the large errors introduced by the acceleration, which is neglected in the traditional model. Finally, a two-dimensional (2-D) scaling algorithm is developed to focus the ST/MR data. Without introducing any extra operations, it can greatly remove the spatial variations of the range, azimuth, and cross-coupling phases simultaneously and entirely in the 2-D hybrid domain. Simulation results verify the effectiveness of the proposed model and focusing approach. missile-borne SAR will inevitably bring some limitations, such as the large power antenna and high probability of being detected. Moreover, the monostatic SAR is incapable of forward-looking imaging, which seriously limits its applicability in the military field because information in the movement direction cannot be obtained directly. Compared with the monostatic missile-borne SAR, the ST/MR SAR has many advantages and they are:(1) The large-maneuver and receiving-only features of the missile-borne receiver reduce the detection probability. The corresponding anti-interference and anti-interception are greatly improved in the ST/MR SAR system. (2) The radar antenna, installed on the missile-borne platform, is used to receive the echo signals without a transmitting function, which indicates that a large power device can be avoided in the missile system to greatly save space and costs.(3) Spaceborne transmitter has the characteristics of wide coverage, unrestricted geography, net flexibility, and a high revisiting-frequency, which could provide some degrees of freedom (DOFs) in target area selection, flight trajectories, and number of missile-borne receivers. (4) By setting the transmitter and receiver on different platforms with a special style, the non-complete coupling areas between iso-range and iso-Doppler lines could be formed in front of missile, which means that the missile has the capability of forwarding-looking imaging.Note that these advantages for the ST/MR SAR also hold for other BiSAR systems, such as the spaceborne/airborne SAR and the airborne BiSAR, which are of special significance for the missiles mainly applied in the military fields. Generally, these common features of the BiSAR can avoid disadvantages inherent in the monostatic missile-borne SAR and make the ST/MR SAR a flexible and effective tool for information retrieval [11][12][13][14][15]. However, there are also a number of problems broug...

Imaging Algorithm for Multireceiver Synthetic Aperture Sonar

“…After the decoupling operation, the azimuth compression is usually performed in the range Doppler domain. It is easily concluded that the filtering function related to the azimuth compression is only a function of the range r and Doppler frequency f t [8,9]. In other words, the azimuth modulation is independent of the instantaneous frequency f τ [8,9].…”

“…It is easily concluded that the filtering function related to the azimuth compression is only a function of the range r and Doppler frequency f t [8,9]. In other words, the azimuth modulation is independent of the instantaneous frequency f τ [8,9]. If the azimuth modulation were obtained, the phase difference between the PTRS and azimuth modulation denotes the coupling term.…”

“…Since Remote Sens. 2019, 11, 672 5 of 22 the azimuth modulation is independent of the instantaneous frequency [8,9], we obtain the azimuth modulation by setting f τ = 0 in (7). This is given by:…”

“…ϕ ac_i ( f t ; r) = Ψ i ( f τ , 0;t i ) = −2π f c τ i (t i ) − 2π f tti (8) In (8),t i ∈ [−T s /2, T s /2] represents the PSP used by the azimuth modulation. At this point, we call it the azimuth PSP.…”

“…For the multireceiver SAS, the point target reference spectrum (PTRS) [8] is a prerequisite of fast imaging algorithms. The two-way slant range of the multireceiver SAS consists of two hyperbolic range histories, which include the instantaneous range between the moving transmitter and target and that between the target and moving receiver.…”