Data Preprocessing Circuit Designs and Analyses for Subsonic Cruise Mis- sile Infrared Image Seeker

In this literature, a data pre-processing circuit designs and analyses for an infrared image seeker of a subsonic cruise missile are proposed. The flight speed of the missile is 250m/s. Therefore, automatic contrast control and automatic brightness control are usually needed to keep wanted contrast and brightness for best image properties in target recognition and tracking; especially for the missile at the terminal approaching phase to prevent signal saturation. Signal saturation implies target lost. The major parameters of imaging systems for contrast and brightness controls include average, maximum and minimum of gray level of the whole picture in the sampling interval. Therefore, the overall system is a complicated nonlinear sampled-data control system. It is difficult to describe, analyze and design the system. In this literature, the overall system is first decomposed into two linearized sampled-data control systems to get needed loop compensations, and verified by a special range-dependent testing signal to the overall system secondly. The controlled system is further verified by a thermal plate and real flight testing. Testing results give the proposed method can provide effective way to analyze and design the considered system. INTRODUCTIONS Multiple sensors for ECCM are generally expected for missile homing systems. The first dual seeker application of the world for subsonic antiship missile is the HF-2 developed in Taiwan. It includes a Radar seeker and an IR image seeker with data fusing algorithm. This application prompts the capability for ECCM from chaff jamming to RF seeker and thermal jamming to IR Image seeker. The problem for IR image seeker for the missile application is the thermal energy to the charge-coupled device (CCD) [1-3] is the fourth power of the reciprocal the distance between image seeker and thermal source; i.e.; missile and target. It needs faster automatic gain control (AGC) for contrast and automatic pedestal control (APC) for brightness [4-7] to keep best imaging properties for target recognition and tracking; especially for the missile at terminal approaching phase. Slower response for coping with thermal energy increasing will make the signal output be saturated; i.e., all white of full frame and will lost tracking centre point for missile guidance. It this literature, models for contrast, brightness and dynamic signals are proposed to analyses and designs of the AGC and APC circuit loops. The AGC and APC are the preprocessing systems of the video signal. The block diagram considered is shown in Fig. (1). It includes thermal sensors, analog circuits, and microprocessor. The output of the processed signal satisfies RS-170 video standard. The sensor elements for thermal imaging is 256 256 focal plane CCD[1-3], the gray level of each element is digitalized to be 256 states with 8bit A/D converter. Fig. (2) shows typical minimal and maximal gray level of a thermal picture. Analog circuit gives faster signal amplification in forward-loop. It needs 256 256 60 10Hz at least for 60Hz picture Address correspondence to this author at the Department of Aeronautical Engineering, National Formosa University, 64, Wen Hua Road, Huwei, Yunlin, 63208, Taiwan; Tel: +886-5-631-5537; Fax: +886-5-631-2415; Email: tstsay@ nfu.edu.tw updating frequency ; i.e., greater than 39.32MHz. Microprocessor providing thermal cell addressing for sampling and storing CCD sensing data, maximal, minimal, and average values calculations of the whole picture and digital filters for AGC and APC loops. Fig. (1a). Block diagram of the data pre-processing. Fig. (1b). The minimal and maximal Brightness of a thermal picture. Fig. (2) shows the analog circuit component of the overall system. The input is “Signal” form CCD and output is digitalized with AD converter ADC208, the “Gain” is the connection for AGC with 60Hz updating rate. The “Offset” is the connection for APC with 60Hz updating rate, the “Extern” is the selection for APC/AGC and manual adjustment ! "