Experimental results are presented indicating a causal effect between exposure time of the detection system and variations in measured differential stellar image motion. The variability is also dependent on atmospheric winds encountered along the entire propagation path at the precise time of measurement, making explicit comparison of experimental results with theory impractical. Earlier theoretical development is recast in terms of Fried's seeing parameter, r 0 , and collected data are tested for conformance to stationarity criteria. It is recommended that atmospheric turbulence seeing monitors based on differential image motion measurements be restricted to exposure times of not more than 2 ms.

No abstract

Optical correlators employing magnetooptic spatial light modulators (MOSLMs) can process binary phase-only filter (BPOF) responses at kilohertz frame rates,1 making real-time recognition possible. However, aspect invariant recognition is difficult since simple BPOFs are highly sensitive to geometric distortions. Aspect invariant composite BPOFs have been developed; unfortunately, filters that achieve aspect invariance over wide distortion ranges produce reduced correlation peak values, rendering simple threshold decision rules ineffective. A statistical correlation plane filter (CPF) based on analysis of variance has been shown to improve recognition system performance.2 This paper examines a multiclass quadratic CPF based on a Bayes likelihood ratio test. The quadratic CPF allows the correlation system to be calibrated by repeatedly analyzing correlation peaks for all object–filter combinations. This off-line calibration process yields a vector of expected correlation peak values and an associated covariance matrix for each unique object with each filter in the filter bank. Once gathered, these data are used on-line to calculate the Mahalanobis distance between an observation vector of peak values obtained with an unknown object and each mean vector. Recognition based on the shortest Mahalanobis distance delivers robust performance, even when composite BPOFs are used in the optical correlator.

No abstract

With the advent of high speed spatial light modulators, it is possible to write binary phase-only filters (BPOFs) faster than standard video rates. However, an optical correlation system which uses a camera operating at standard video rates to capture output correlation responses is limited to a maximum filter rate of 60 Hertz. This paper examines the use of a charge injection device (CID) camera to speed up the processing time of a BPOF-based rotationinvariant optical correlation system. Having integrating capabilities, the CID camera can integrate several output correlation plane responses during the frame time of the camera. In this paper, the performance of an integrating correlator is presented. The influence of factors such as the input image noise density, the number of integrated correlation responses, and the size of ternary low-frequency blocks on correlation responses are explored.