Two-dimensional spectrum for MEO SAR processing using a modified advanced hyperbolic range equation

Abstract

To improve further the accuracy in the approximation of the range history for a synthetic aperture radar (SAR) onboard a mediumearth-orbit (MEO) satellite a fourth power term has been added to the advanced hyperbolic range equation (AHRE), and the new one is called a modified AHRE (MAHRE). Then, a two-dimensional spectrum using the MAHRE was derived, and the accuracy of the spectrum analysed. Promising results were obtained. Introduction:The integration time of one synthetic aperture of a medium-earth-orbit (MEO) synthetic aperture radar (SAR) can be long or a fine spatial resolution can be achieved. However, the long integration time means that the approximation in range history with a straight flight path within one synthetic aperture could become invalid. Thus, the use of a typical hyperbolic range equation can be questionable. An accurate but potentially complicated equation is needed for the processing of the MEO SAR data. Eldhuset [1] approximated the relative earth and satellite motion using a fourth-order Taylor expansion of the equation in azimuth time. Although Eldhuset achieved accurate range approximation, one drawback was the complicated algebraic operations involved in the development of imaging algorithms for data processing with the approximation. Then, Huang et al. [2] studied an advanced hyperbolic range equation (AHRE) consisting of terms up to the third order of the range equation in [1] and a linear term. They simplified the range equation of [1]. Using the AHRE, Huang et al. derived the 2D spectrum and then developed an advanced nonlinear chirp scaling (ANLCS) algorithm [3]. Closely examining the AHRE, one notices that the AHRE only compensates for the range history up to the cubic term. Under some circumstances, the compensation might not be enough or the level of accuracy might be inadequate. To increase the accuracy level, we modify the AHRE with an addition of a fourthorder term or modified AHRE (MAHRE). This addition is not simply a roll-back to the original range equation in [1]. Instead, the addition is directly applied to the AHRE. Thus, the MAHRE is still concise in expression.

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

“…In this paper, 't' and 'r' denote the transmitter and receiver, respectively. After reviewing the studies in the available literature [9,10,16,[38][39][40][41][42][43], we integrate the important results and then show that the flight path of spaceborne SAR can be equivalent to a curved path, which is mainly caused by the curved orbit and the rotating planetary surface and the flight path of the missile can be described by using the motion parameters, including the velocity, acceleration, and higher-order parameters, obtained from the information provided by the inertial navigation system (INS). According to the imaging geometry, the instantaneous slant range |r(η, A)| of the point A is expressed as:…”

Equivalent hyperbolic range model for synthetic aperture radar with curved track

“…To analyse the precision of EHRM, MAHRE [5] and MESRM [6] are taken as reference. Besides, a point target located on the edge of azimuth dimension 3 km away from the centre is selected and the detail parameters are the same as listed in, but the range resolution is changed into 0.5 m. Fig.…”

“…To guarantee the imaging quality of SAR with curved track, not only the range model, but also the imaging algorithms of high precision should be sought after. As similar with spaceborne SAR in terms of curved orbit, some referenced methods can be used [1][2][3][4][5][6]. For the problem of range model accuracy, Eldhuset [1], Luo et al [2] and Wu et al [3] achieved accurate range approximation using a fourth-order range model (FORM4 or DRM4), but the complicated algebraic equations limited the development of imaging algorithms.…”

Study of Ionospheric Effects on Azimuth Imaging for Medium-Earth-Orbit Sar

“…Many researchers have studied MEOSAR for synchronization technology, orbit design, performance analysis, imaging process, moving target detection, etc. [5][6][7][8][9]. Therefore, we can see that MEOSAR has become one of the most popular spaceborne SAR sensors.…”