Missile geo-location using missile-borne SAR

Abstract

ABSTRACT Missile borne Synthetic Aperture Radar can effectively impr ove the guidance accuracy of th e Inertial Guidance System of long-range missile. The basic principle of the missile geo-location is described at first. According to the range equations and Doppler equations, the analytical mathematical expressions of the missile’s position are deduced without complicated and unstable iterations, and the detailed flow of the missile position solving is described. Based on simulation, the effects of digital image matching, altitude an d velocity errors on the geo-location accuracy are compared. Keywords: missile borne SAR, missile geo-location 1. INTRODUCTION The Inertial Navigation System (INS) is a kind of self-depen dent navigation system, with the advantages such as good stealth and all-weather working ability[1]. It has been widely used in medium and long range missiles. However, with the navigational errors accumulated over time, INS will suffer from considerable accumulative er rors[2]. For the missile with terminal guidance system, the errors above will degrade the probability of handover from midcourse guidance to terminal guidance, while they will augment the miss distan ce for the missile without terminal guidance system. Synthetic aperture radar (SAR) has been successfully applied to airborne integrated navigation systems. The real-time image containing typical objects measured by SAR is matched with the reference image pres orted in the electronic map database, yielding the positions of objects in the scenario. Fed to the navigation system as measurements, the positions combined with the range difference, rang e rate difference due to SAR and INS, azi muth and elevation angle, are used to compensate INS errors through filtering[1], and the resulting ho rizontal error can be of the same order as the accuracy of GPS P-code[3]. In contrast with the airborne condition, missile-borne SAR c onfronts not only the problem of nonlinear track due to the missile’s vertical velocity[4] and its tactical flight to avoid enemy air defense bastions[5], but also the limitations of missile borne computing and storage devices. Hence, the dada rate according to which missile-borne SAR image matching is performed can not meet the requirement of integrated navigation filtering, and consequently INS errors can only be corrected once or twice in the terminal of midcourse guidance or in the beginning of terminal guidance. Therefore in this case, it is necessary to locate the missile directly via measurements, and then the resulting missile position is utilized to compensate INS errors. [6] presents a method for extracting ballistic parameters using nonlinear least squares estimation, which employs the coordinates of all pixels in the matched image and the dist ance between the pixels and the radar calculated according to fast time. While making full use of spatial information, the method has considerable iteratively optimizing computation load and doesn’t utilize the Doppler history. It’s also difficult to correct the geometric distortion of each pixel in the scenario before geo-location. For side-l ooking SAR, [7] gives a geo-location method using the positions of three points at the same range, which solves the problem of irregularl y flying missile geo-location by introducing Doppler equations. While free of complicated solving or tremendous computation load, it’s difficult for the method to find the three points above to obtain their real positions by accurate correlation in the imag e domain or range profile domain. This paper focuses on the missile geo-location with an altim eter aiding for the medium-long range missile application. Section II provides an instruction to the basic principle of mi ssile geo-location. In Section III, by introducing the sphere hypothesis and local coordinate, the model for missile geo-location is established according to the range equations and