There is an increasingly important requirement for day and night, wide field of view imaging and tracking for both
imaging and sensing applications. Applications include military, security and remote sensing. We describe the
development of a proof of concept demonstrator of an adaptive coded-aperture imager operating in the mid-wave infrared
to address these requirements. This consists of a coded-aperture mask, a set of optics and a 4k x 4k focal plane array
(FPA). This system can produce images with a resolution better than that achieved by the detector pixel itself (i.e. superresolution)
by combining multiple frames of data recorded with different coded-aperture mask patterns. This superresolution
capability has been demonstrated both in the laboratory and in imaging of real-world scenes, the highest
resolution achieved being ½ the FPA pixel pitch. The resolution for this configuration is currently limited by vibration
and theoretically ¼ pixel pitch should be possible. Comparisons have been made between conventional and ACAI
solutions to these requirements and show significant advantages in size, weight and cost for the ACAI approach.
Coded Aperture Imaging (CAI) is a new approach to system design whereby the optics are simplified in a controlled way
so that system performance can be recovered using appropriate computer based algorithms. Adopting Coded Aperture
approaches to sensor designs opens up possibilities of increasing the system design trade-space thereby giving the system
designer greater degrees of freedom to optimise the system. A comparison has been made between a system adopting CA
in its optical train with systems based on conventional optics approaches. These comparisons show that CA based
systems can provide significant benefits to the user in some applications.
Pupil plane encoding has shown to be a useful technique to extend the depth of field of optical systems. Recently, further studies have demonstrated its potential in reducing the impact of other common focus-related aberrations (such as thermally induced defocus, field curvature, etc) which enables to employ simple and low-cost optical systems while maintaining good optical performance. In this paper, we present for the first time an experimental application where pupil plane encoding alleviates aberrations across the field of view of an uncooled LWIR optical system formed by F/1, 75mm focal length germanium singlet and a 320x240 detector array with 38-micron pixel. The singlet was corrected from coma and spherical aberration but exhibited large amounts of astigmatism and field curvature even for small fields of view. A manufactured asymmetrical germanium phase mask was placed at the front of the singlet, which in combination with digital image processing enabled to increase significantly the performance across the entire field of view. This improvement is subject to the exceptionally challenging manufacturing of the asymmetrical phase mask and noise amplification in the digitally restored image. Future research will consider manufacturing of the phase mask in the front surface of the singlet and a real-time implementation of the image processing algorithms.
There is strong evidence to suggest that polarimetric techniques offer significant improvements in the ability of electro-optic sensors to detect difficult targets in cluttered backgrounds. Many previous attempts to quantify the potential benefits have been hampered by an inability to gather all the polarimetric data simultaneously from a scene. Sequential data gathering can lead to artefacts in the polarimetric data which in turn lead to spurious and erroneous conclusions being drawn This paper describes work undertaken to build and test a pair of four camera, real time, polarimetric sensors that measure all four Stokes parameters simultaneously. One of the sensors operates in the visible waveband and the other in the near infrared. Example images obtained with both sensors are shown, together with measured target and background signal distributions for one of them. Preliminary results from this work show that the sensor can significantly improve target discrimination.
KEYWORDS: Cameras, Imaging systems, Sensors, Electronics, Calibration, Digital signal processing, Signal processing, Video, Video processing, Thermography
The Albion programme aims to develop high pixel count third generation infrared modules for medium, long and dual band infrared imager systems. The medium wave Albion detector having 1024x768 pixels on a 26μm pitch is the largest detector of its type in Europe. With a typical NETD of 12mK and capable of 50Hz frame rate output, this high performance detector has been encapsulated and combined with a high reliability cryogenic cooler to form a core module. To illustrate the high performance of the detector and to demonstrate the use of the core module a complete thermal imaging camera has been built. Although designed as an experimental system this camera, being only 300x420x180mm in size shows the relatively small step required to take the system to a fully productionised state. This paper describes the detector technology and other subsystems (e.g. optics, electronics and uniformity correction) which have been integrated into a high performance thermal imaging system.
There is a widespread requirement for wide area surveillance with target detection and recognition. To achieve the above aims with a single sensor is difficult and inevitably performance compromises have to be made. A system, designated Firefly, has been developed which splits the task of surveillance/target detection from that of recognition. Firefly uses separate sensors for both tasks, each sensor can then be optimized for the role it has to perform For surveillance and target detection, Firefly makes use of a previously developed scanned thermal imager operating in the 8 - 11 micrometer waveband. There was no suitable sensor available for the recognition role and so a 3 - 5 micrometer imager based on a 2D starring array was developed for this purpose. The Firefly system is described in this paper with emphasis being given to a description of the high resolution, recognition sensor where the development effort was concentrated. Results of performance also are given.
High resolution 400ns TEA carbon dioxide laser pulses with a 100ns rise time were used to observe the 10.6 micrometers radiation transmitted by polycrystalline vanadium oxide coatings deposited on germanium substrates. The variation in the transmission and reflection of the vanadium oxide coatings was simultaneously observed throughout the duration of the incident pulse over a range of incident fluences. The observation of fluence related changes in the behavior of both the transmitted and reflected pulses showed that the coatings exhibited a semiconductor-to-metallic phase transition that was power related and not energy dependent.
A coherent lidar system based on a 3W cw CO2 laser has been installed on an aircraft positioned to look forward and down. A monostatic optical geometry is employed and the optical system incorporates a scanning mechanism that generates a line scan in the horizontal plane perpendicular to the aircraft. This scan pattern, coupled with the aircraft motion, produces a 2D coverage of the ground. The laser reflections from terrain features are collected and 2D images of the ground generated based on the amplitude of the return signals. A flight program has been conducted and active images of a range of natural terrain and man made objects collected. This paper describes the coherent laser system, its aircraft installation, signal processing, and results obtained from the flight trial program.
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