Robin B. Jenkin

The simulation of laser-based guided weapon engagements

The laser is an integrated part of many weapon systems, such as laser guided bombs, laser guided missiles and laser beam-riding missiles. These systems pose a significant threat to military assets on the modern battlefield. The lasers used in beam-riding missiles are particularly hard to detect as they typically use relatively low power lasers. Beamriders are also particularly difficult to defeat as current countermeasure systems have not been optimized against this threat. Some recent field trails conducted in the United Arab Emirates desert have demonstrated poor performance of both laser beam-riding systems and the LWRs designed to detect them. The aim of this research is to build a complete evaluation tool capable of assessing all the phases of an engagement of a main battle tank or armoured fighting vehicle with a laser based guided weapon. To this end a software model has been produced using Matlab & Simulink. This complete model has been verified using lab based experimentation and by comparison to the result of the mentioned field trials. This project will enable both the evaluation and design of any generic laser warning receiver or missile seeker and specific systems if various parameters are known. Moreover, this model will be used as a guide to the development of reliable countermeasures for laser beam-riding missiles.

Errors due to quantization in MTF determination using sinusoidal targets

Abstract A theoretical treatment of the effect of quantization upon the determination of modulation transfer functions (MTF) of digital acquisition devices is initially developed for a noiseless system, when using sinusoidal targets. The analytical work shows that a component due to quantization exists in the measured MTF which increases as the bitdepth of the quantization and the amplitude of the input signal decrease. An expression to estimate this component from parameters describing the input signal and quantizer is derived. Modifications are made to account for quantization and input signal noise, yielding new estimates of the component for single measurements. The estimates were experimentally tested using an analogue-to-digital converter (ADC).

Use of the first-order Wiener kernel transform in the evaluation of SQRIn and PIC quality metrics for JPEG compression

JPEG compression is highly non-linear and non-stationary. This renders the system scene dependent and thus calculation of its MTF is challenging. Evaluation using differing methodologies yields vastly contradictory results. Further, local MTF can vary significantly with respect to position within sub-image blocks for a given measurement technique. Estimation of the first order Wiener kernel transform has been shown to provide a consistent and intuitive alternative to calculation of the MTF. The lack of reliable MTF curves for such a non-linear system may lead to poor performance of image quality metrics calculated using them. This work examines the use of first order Wiener kernel transform curves in the calculation of SQRIn and PIC metrics for JPEG compression compared to those previously calculated using a traditional edge and sine wave technique. New analysis of previous psychometric experimentation is presented. Results are discussed and conclusions drawn.

Extension of the ISO 12233 SFR measurement technique to provide MTF bounds for critical imaging arrays

The ISO 12233 SFR measurement technique provides a quick and reliable method to evaluate the SFR and, with slight modification, the MTF of digital imaging systems. This work demonstrates that the MTF provided by the technique approaches the theoretical result for a single imaging element once all other factors, such as image forming optics, have been accounted for. Digital imaging is being increasingly accepted as a solution for critical systems as issues regarding security and provenience are being resolved. The evidential need for recording fingerprints is just one example. Jenkin et al. previously showed that a lower bound of array MTF could be derived taking account of the sampling pitch, aperture and phase differences between the signal and imaging elements. This is a pessimistic estimate of array performance and, as such, holds advantages for design of critical systems. This work shows simple extension of the ISO 12233 SFR measurement technique to provide an estimate of the lower bound and compares it to known exposures of a simple Monte-Carlo model and a commercial digital camera.