We describe a high performance optomechanically scanned millimeter-wave imager intended to monitor the ground movement of aircraft in adverse weather conditions. It employs two counter-rotating mirrors that are tilted about their axes of rotation. They simulate the linear scan of a single high speed, large aperture flapping mirror. When used with a linear receiver array, they can produce a 2-D scan of the scene at TV rates. In the present application, they were used with a single receiver and a large flapping mirror to produce a 2-D scan of the scene ±10 deg vertically and 60 deg horizontally. One of the rotating mirrors has a concave surface and acts as the focusing element in the imager. The two mirrors are driven from a single servo motor using timing belts and toothed pulleys. The flapping mirror is slaved to the motion of the rotating disks using an electronic cam. The single channel 94-GHz receiver consisted of an InP LNA followed by a down converter and a detector. The video output passes to an A/D converter and is displayed on a conventional PC. This system has virtually 100% transmission and can be used at any waveband.
The ability of millimetre-waves (mm-wave) to penetrate obscurants, be they clothing, fog etc., enables unique imaging applications in areas such as security screening of personnel and landing aids for aircraft. When used in an outdoor application, the natural thermal contrast provided by cold sky reflections off of objects allow for direct imaging of a scene. Imaging at mm-wave frequencies in an indoor situation requires that a thermal contrast be generated in order to illuminate and detect objects of interest. In the case of a portal screening application the illumination needs to be provided over the imaged area in a uniform, omni-directional manner and at a sufficient level of contrast to achieve the desired signal to noise ratio at the sensor. The primary options are to generate this contrast by using active noise sources or to develop a passive thermally induced source of mm-wave energy.
This paper describes the approaches taken to developing and implementing an indoor imaging configuration for a mm-wave camera that is to be used in people screening applications. The camera uses a patented mechanical scanning method to directly generate a raster frame image of portal dimensions. Imaging has been conducted at a range of frequencies with the main focus being on 94GHz operation. Experiences with both active and passive illumination schemes are described with conclusions on the merits or otherwise of each. The results of imaging trials demonstrate the potential for using mm-wave imaging in an indoor situation and example images illustrate the capability of the camera and the illumination methods when used for personnel screening.
The use of millimetre-wave imaging to identify threat objects such as guns and bomb material concealed on the person is well documented. However, the technology has been hindered by the performance and cost barriers typically associated with imaging at mm-wave frequencies. A novel scanning technique that minimises the receiver count while operating at very high efficiency levels has made it possible to build a cost-effective and high-performance mm-wave imager that can make security screening a commercial reality. The imager design allows for either passive or active operation and its compact form factor is suitable for practical installation in security channel situations. The uses of this technology include portal screening of personnel for high-resolution imaging of concealed threat objects or longer distance surveillance type monitoring of checkpoints and crowds. This presentation details the use of the imager in an active configuration to observe a checkpoint or crowd scene at stand-off distances of up to 50 metres. Target objects to be detected are the hidden metal components associated with suicide bomb constructions. A typical bomb consists of several explosive filled pipes strapped to the body or clusterings of small metallic objects embedded in explosives. Trials at 94GHz have yielded positive results by showing the presence of concealed metallic objects on people at distances of 25 metres. Objects detected have included simulated bomb constructions such as groups of metal pipes and clusters of nuts and bolts. These tests have been conducted using a Gunn based CW source and direct detect receiver unit. Further enhancement of the system includes the use of an FMCW front-end configuration.
This paper describes a high performance opto-mechanically scanned mm-wave imager intended to monitor the ground movement of aircraft in adverse weather conditions. It employs two counter-rotating mirrors that are tilted about their axes of rotation. They simulate the linear scan of a single high speed, large aperture flapping mirror. When used with a linear receiver array they can produce a two-dimensional scan of the scene at TV rates. In the present application they were used with a single receiver and a large flapping mirror to produce a two-dimensional scan of the scene of ±10° vertically and 60deg; horizontally. One of the rotating mirrors had a concave surface and acted as the focusing element in the imager. The two mirrors were driven from a single servo motor using timing belts and toothed pulleys. The flapping mirror was slaved to the motion of the rotating discs using an electronic cam. The single channel 94GHz receiver consisted of an InP LNA followed by a down-converter and a detector. The video output passed to an A/D converter and was displayed on a conventional PC. This system has virtually 100% transmission and can be used at any waveband.
KEYWORDS: Fuzzy logic, Process modeling, Sensors, Data fusion, Neural networks, Detection and tracking algorithms, Associative arrays, Filtering (signal processing), Data modeling, Control systems
The problem addressed in this paper is that of estimating the tracks of dynamic obstacles in the environment of a helicopter operating in hazardous conditions. Fuzzy logic and neural networks have shown their strength in recent years in the solutions to non-linear problems. The aim of this paper is to present neuro-fuzzy data fusion algorithms which can be used to fuse information provided by multiple spatially separate sensors engaged in the tracking of obstacles whose dynamics are a priori unknown.
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