KEYWORDS: LIDAR, Sensors, Surveillance, Flame detectors, Signal to noise ratio, Signal detection, Semiconductor lasers, Detection and tracking algorithms, Transmitters, Receivers
Lidar (light detection and ranging) presents better sensitivity than fire surveillance based on imaging. However, the price of conventional lidar equipment is often too high as compared to passive fire detection instruments. We describe possibilities to downscale the technology. First, a conventional lidar, capable of smoke-plume detection up to ~10 km, may be replaced by an industrially manufactured solid-state laser rangefinder. This reduces the detection range to about 5 km, but decreases the purchase price by one order of magnitude. Further downscaling is possible by constructing the lidar smoke sensor on the basis of a low-cost laser diode.
We discuss the development of laser induced fluorescence sensors and their application in the evaluation of water pollution and physiological status of higher plants and algae. The sensors were built on the basis of reliable and robust solid-state Nd:YAG lasers. They demonstrated good efficiency in: i) detecting and characterizing oil spills and dissolved organic matter; ii) evaluating the impact of stress on higher plants (cork oak, maritime pine, and genetically modified Arabidopsis); iii) tracking biomass changes in intertidal microphytobenthos; and iv) mapping macroalgal communities in the Tagus Estuary.
A low cost modular system for automatic oil spill detection, based on laser induced fluorescence light detection and
ranging (LIF LIDAR) technology, which may be installed aboard watercraft and used for intensive surveillance of
harborages, rivers, channels, and coastal waters, is described. First experimental results obtained with the developed LIF
LIDAR detector prototype in the laboratory conditions are reported.
A method of automated early fire detection based on the light detection and ranging (lidar) technology is presented.
Specific lidar configurations and their application to forest and industrial-environment fire surveillance are discussed.
KEYWORDS: LIDAR, Signal to noise ratio, Signal detection, Flame detectors, 3D modeling, Wind energy, Surveillance, Mathematical modeling, Combustion, Particles
The possibility of early forest fire detection within a range up to ~2 km using a portable eye-safe 1540 nm lidar is
demonstrated in this paper, both on experimental and theoretical ground. An estimation of the detection efficiency using
a mathematical model based on the 3D system of Navier-Stokes equations describing the smoke plume evolution in the
presence of wind, agrees reasonably well with experimental results. Calculations made using the model show that a
detection range up to ~5.5 km can be achieved by accumulating lidar return signals.
KEYWORDS: LIDAR, Detection and tracking algorithms, Signal detection, Interference (communication), Received signal strength, Surveillance, Receivers, Backscatter, Nonlinear optics, Error analysis
A simple and robust algorithm for lidar-signal classification based on the fast extraction of sufficiently pronounced peaks
and their recognition with a perceptron, whose efficiency is enhanced by a fast nonlinear preprocessing that increases the
signal dimension, is reported. The method allows smoke-plume recognition with an error rate as small as 0.31% (19
misdetections and 4 false alarms in analyzing a test set of 7409 peaks).
Detection of fire smoke plume with a compact cheap rangefinder based on 905 nm laser diode (2 μJ pulse energy,
slashed oh 2 cm telescope and 720 m solid-target range) is demonstrated. Reliable detection of small experimental fires
(20×25 m2 fire plot, burning rate of ~3 kg/s) is achieved for the range of about 255 m. A theoretical model of the mixing
of burning products with air in the wind, based on three-dimensional system of Navier-Stokes equation and commercial
software PHOENICS, is developed. The model predicts 220 m range of smoke detection by the rangefinder, indicating
good agreement between the theoretical and experimental data. On the basis of this theoretical model an estimation of
the smoke detection efficiency for a longer range (20 km for solid targets) instrument, based on a 1540 nm laser with a
pulse energy of 8 mJ and a 4 cm telescope, is made. The obtained smoke-detection range estimation, 6 km, indicate that
more powerful rangefinders can be used not only in shot-range applications, such as fire detection in premises, tunnels
and storage yards, but in more demanding areas, such as wildland fire surveillance, as well.
It has recently been shown that lidar (LIght Detection And Ranging) can effectively detect smoke plumes from small bonfires up to distances of 6.5 km, so that the technique can be used for wildfire surveillance. The aim of the present work is to describe a method for calculating the optimal location and minimum number of lidar stations required for the surveillance of a given forest area, taking the hilly terrain of Sintra-Cascais Nature Park (Portugal) as an example. The placement and horizontal scanning of the lidar sensors must be such that the laser beam passes over the ground, while keeping sufficiently low to enable early smoke plume detection, before the smoke is dispersed by the wind. Simultaneously, the laser beam should not hit the ground at distances shorter than the instrument range. To solve the problem, a terrain rendering was created and the best laser-beam zenith angle for each azimuth and the effective range covered by each lidar were calculated. The computations showed that 95.2% of the 146 km2 of the Nature Park area can be covered by seven detectors with the laser beams scanning at a height of 50 m or less above ground.
Lidar is a promising tool for forest-fire monitoring because this active detection technique allows efficient location of tenuous smoke plumes resulting from forest fires at their early stages. For the technique to be generally usable instrumentation must be eye-safe, i.e. it must operate within the spectral range λ<0.4 or λ>1.4 micrometers . In this paper the lidar efficiency at the wavelengths 0.3472 micrometers (second harmonic of the ruby laser) and 1.54 micrometers (Er:glass laser) are compared using a theoretical model. The results of calculations show that the energy required for smoke-plume detection using 0.3472 micrometers becomes greater than the corresponding value for 1.54 micrometers when the distance exceeds some threshold, which ranges between 2 and 6 km depending on other parameters. Being caused by relatively higher absorption of the UV radiation in the atmosphere, this result is valid for any wavelength in the vicinity of 0.35 micrometers , for example, the third harmonic of Nd:YAG laser and the second harmonic of Ti:sapphire laser.
We demonstrate how to correct odd-order aberrations (tilt, coma, etc.) of the imaging system on the basis of information containing in the phase transfer function. For earth- observation systems this information can be obtained just by accumulation of the detected images, without source of the reference beam or wavefront detector. This technique is beneficial for elaborating robust equipment for long-term operation in autonomous conditions.
We produced a totally conservative finite-volume scheme for modeling of Al2O3-TiC ceramics processing with excimer laser radiation. Evolution of a cylindrical TiC grain at the surface of an alumina matrix is traced for a few nanaoseconds. Its melting causes a small surface swelling - a possible nucleator for the experimentally observed TiC globules.
In the report we consider a method of dynamic aberration measurement in the frameworks of the problem of minimization of difference between potential and operational resolution of the earth observation satellite systems. The method is based on statistical analysis of the current image at the output of the image receiver. The results of the measurement are recalculated into control signals of the actuators in the adaptive feedback loop.
The theoretical and experimental studies were carried out for statistical characteristics of photon paths in strongly scattering media dependently on type of inhomogeneities, boundary conditions and method of measurements. The possibility to represent the signal perturbations due to the macroinhomogeneities as an integral along the mean photon path is used to solve the tomography reconstruction problem in terms of volume quantization. The optimum quantization scale is chosen on the basis of area across which the macroinhomogeneity characteristics are averaged.
Peculiarities of constructing adaptive optical systems for forming and transportation of laser radiation through the atmosphere are considered. Results on elaboration and testing of the elements and the adaptive schemes on the special test-bench are given. The results on investigation of real-time compensation of the atmospheric phase disturbances using the adaptive optical train with the heterodyne wavefront analyzer, the electro-optical phase corrector, and the data-processing system based on the neural network are also reported. We analyze possible means of construction of adaptive optical trains to one-channel laser radiators and multi-channel phased systems.
This report is to call attention to a very simple class of neural networks (linear associative memories) that can be successfully adapted to data processing in linear adaptive optical trains for wavefront correction.
The possibility of application of a neural network to data processing in an adaptive optical system is investigated. In case of a linear input/output transformation, the simple two-layer feedforward neuron structure is shown to be a good choice for heteroassociative reconstruction of the driving signals from the current data on the phase distribution. Several learning algorithms for the neural net are presented and the opportunity to construct the training set with the help of experiment is discussed.
Inna Belousova, A. Bukanov, Vladimir Grigor'ev, Alexander Gorshkov, Sergei Leonov, A. Melkonyan, A. Skepko, M. Stolbov, Andrei Utkin, A. Shaposhnikov, A. Holodilov
The linear adaptive optical system with high-power CO2 laser, operating in the phase conjugation scheme and providing the wavefront correction for the laser system has been experimentally studied. Results of test of a typical loop adaptive optics system based on the multi-channel Hartmann wavefront sensor and multi-actuator flexible mirror are reported. We also report development of devices for linear adaptive optics and means for controlling its units during operation. Prospects of using the neural networks for corrections of radiation wavefront distortions in the linear adaptive optical systems with high-power CO2 lasers are analyzed.
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