General Inversion Algorithm for Infrared Seeker with Reticles
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.
Advisor:Hung-Wen Chang; Nai-Hsiang Sun; Tsong-Sheng Lay
School:National Sun Yat-Sen University
School Location:China - Taiwan
Source Type:Master's Thesis
Keywords:ir seeker reticle
Date of Publication:07/31/2006