In this thesis, we focus on the position inversion algorithm for infrared (IR) seekers with reticles. The IR seeker system is composed of a reticle, an IR sensor and the optical/electronic systems. The pattern on a reticle is specially designed and is made of both transparent and opaque materials. It is placed right in front of the focal plane of the IR optical imaging system. The area of the IR seeker is comparable to that of an IR sensor. The instantaneous received power is proportional to the overlap integral of infrared image and the reticle¡¦s transmittance function. The target is assumed to be quasi-stationary. When the target is idle in space the infrared detector will receive a one-dimension periodical signal. It is a quite difficult problem to obtain the desired target location in 2-D space from the 1-D infrared seeker waveform. We propose a general inversion algorithm that will handle both amplitude/frequency modulation (AM/FM) modulated as well as other more complicated IR reticles. An IR target in space can be of any location (X, Y coordinate) and of any size (or intensity). Our idea is to perform a search in the 3-D parametric space. After calculating all possible situations, we compare the simulated waveforms with the measured one and find the best fit. We are able to reduce to just search the 2-D positional space by applying a low-pass filter to the measured waveform before processing. We further speed up the convolution calculation by using the fast Fourier transform (FFT). We are able to complete our search in less time for the reticle to rotate half a cycle. Thus, the inversion algorithm is done in real time and is suitable for the field installation. We also can apply this method to help design the reticles for IR seekers based on success rate of identical targets under various situations. Normally it is highly impossible to obtain the original 2-D image from its modulated 1-D signal. In our case, IR images made of just a few bright spots are relatively simple. It allows us to perform the 2-D inversion when only the positional parameters of the targets are needed.

Infrared target tracking devices (called IR seeker) are important part of the heat seeking missiles. They are based on a simply principle that heat produced by the operation of each machine emits strong infrared radiation. Take an aircraft for an example, an exhaust of the combustion engines produce much heat. The IR radiation is then detected and processed by the IR seeker which then guides the missile to the desired target. There are many kinds of IR seeker. In this thesis we focus on ¡§reticle¡¨ and ¡§image¡¨ types of IR seekers. In the early 1950s, the IR technology is limited to a single detector. To be able to locate the target, a rotating reticle was placed before the detector. The pattern on the reticle introduces a specific modulation onto the output signals of the IR seeker thus giving the missile the equivalent of an IR eye. This is the built-in feature of the familiar sidewinder heat seeking missiles. In recent years, technology has greatly improved. The so called ¡§image¡¨ IR seeker uses a focal plane arrays (FPA), similar to the charge coupled device (CCD) of digital camera, to capture the IR image generated from the target. These high definition images are then processed by the computer and help the missile to track its targets. We studied both types of IR seekers and developed approximation methods to generate IR signatures as well as algorithms to locate and identify the target. The ¡§image seeker¡¨ is technologically more advanced and can detect and track several targets simultaneously. Its inversion methods are however, simpler and easier to implement. From the simulation results, we can correctly locate of the target position. Due to the limited input information, more elaborate efforts are needed for the ¡§reticle seekers¡¨ because different reticle have different characteristics and need to be handled differently. To speed up the calculation, we use 2-D Fast Fourier transform of the reticle pattern and IR images of the target for both generation of detector waveforms and for target location. The overall results are satisfactory and meet the IR seeker simulator¡¦s requirements.