Abstract
This paper introduces the theory of fire detection in moving vehicles by microwave radiometers. The system analysis is discussed and a feasibility study is illustrated on the basis of two implementation hypotheses. The basic idea is to have a fixed radiometer and to look inside the glass windows of the wagon when it passes in front of the instrument antenna. The proposed sensor uses a three-pixel multi-beam configuration that allows an image to be formed by the movement of the train itself. Each pixel is constituted by a direct amplification microwave receiver operating at 31.4 GHz. At this frequency, the antenna can be a 34 cm offset parabolic dish, whereas a 1 K brightness temperature resolution is achievable with an overall system noise figure of 6 dB, an observation bandwidth of 2 GHz and an integration time of 1 ms. The effect of the detector noise is also investigated and several implementation hypotheses are discussed. The presented study is important since it could be applied to the automatic fire alarm in trains and moving vehicles with dielectric wall/windows.
Highlights
The precise localization of fire spots is an operational aspect of great relevance to cope with fires
The instrument design should account for system parameters such as the observation frequency, angle and distance, the vehicle speed, the window size, the antenna beam-width and the temperature resolution
Each pixel is equipped with a direct amplification microwave receiver featuring a 2 GHz observation bandwidth, a 1 ms integration time and a 6 dB noise figure
Summary
The precise localization of fire spots is an operational aspect of great relevance to cope with fires. Lower performing in terms of spatial resolution than Infrared (IR) sensors, microwaves can penetrate layers of concrete material, vegetation and dense smoke, detecting a target even if it is invisible to an external observer [5,6,7]. This principle has been exploited by several mm-wave imaging systems [8,9,10,11]. Passenger trains have windows made of glass, the latter being quite a good dielectric from the point of view of microwave radiation. A system design, two implementation hypotheses are discussed, and the conclusions are drawn
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