Improvised Explosive Devices (IEDs) triggered by pressure-plates are a serious threat in current theatres of operation.
X-ray backscatter imaging (XBI) is a potential method for detecting buried pressure-plates. Monte-Carlo simulation code
was developed in-house and has been used to study the potential of XBI for pressure-plate detection. It is shown that
pressure-plates can be detected at depths up to 7 cm with high photon energies of 350 keV with reasonable speeds of 1 to
10 km/h. However, spatial resolution is relatively low due to multiple scattering.
KEYWORDS: LIDAR, Target detection, Receivers, Radar, Laser systems engineering, Surveillance, Optical parametric oscillators, Sensors, Visibility, Signal to noise ratio
Coastal surveillance and naval operations in the littoral both have to deal with the threat of small sea-surface targets.
These targets have a low radar cross-section and a low velocity that makes them hard to detect by radar. Typical threats
include jet skis, FIAC's, and speedboats. Previous lidar measurements at the coast of the Netherlands have shown a very
good signal to clutter ratio with respect to buoys located up to 10 km from the shore where the lidar system was situated.
The lidar clutter is much smaller than the radar clutter due to the smoothness of the sea surface for optical wavelengths,
thus almost all laser light is scattered away from the receiver. These results show that due to the low clutter a search lidar
is feasible that can detect small sea-surface targets. Based on these promising results a search-lidar demonstrator project
has started end of year 2008. The system set-up of the search lidar demonstrator is presented and experimental results
near the coast of Holland are presented. By using a high rep-rate laser the search time is limited in order to be useful in
the operational context of coastal surveillance and naval surface surveillance. The realization of a search lidar based on a
commercially available high power and high rep-rate laser is presented. This demonstrator is used to validate the system
modeling, determine the critical issues, and demonstrate the feasibility.
In recent years, much advance in the field of high-power femtosecond laser technology has been made. The high pulse
power of femtosecond laser systems leads to various interesting phenomena, such as a very high power density and the
formation of a plasma in the propagation medium, which is usually air. The possible application of femtosecond lasers
for infrared countermeasure (CM) applications, other than direct illumination of the detector, was suggested by several
authors. The goal of these countermeasures is to divert missiles from their interception course. We quantitatively
examined several suggested CM applications of femtosecond lasers from the literature. Our analyses show that
application of femtosecond laser beams for dazzling of missile seeker heads is not in any way promising, neither via
white-light generation in the ultra-short laser pulses nor via glowing plasma. In both these cases the generated light
intensity is too low to successfully compete with the signal of a typical target. Taking into account literature reports, we
conclude that the most promising application of femtosecond laser beams in the field of countermeasure applications
seems to be related to inducing damage of the optical components of the seeker system.
KEYWORDS: 3D modeling, Databases, Signal to noise ratio, Optical simulations, Lawrencium, Electro optical modeling, Receivers, Sensors, Systems modeling, 3D acquisition
Current coastal operations have to deal with threats at short range in complex environments with both neutral and
hostile targets. There is a need for fast identification, which is possible with a laser range profiler. A number of field
trials have been conducted to validate the concept of identification with a laser range profile. A laser range profiler with
a high bandwidth, fast laser receiver was used to perform tests on the capability of a laser range profiler for ship
identification. Typical rise and fall times are 2 ns corresponding to a range resolution of 0.6 meter. The experimental
profiles of the ships and simulated range profiles based on 3D target models show very good correspondence. It is
shown that laser range profiles match closely the geometric structure of the ship. Furthermore, the good match between
experimental and simulated laser range profiles means that a database of laser range signatures can be constructed from
3D-models, thus simplifying the database creation. Based on the experiments a system model was made for the range
profiling of air targets. The validated system model shows that air targets can be identified at ranges of several tens of
kilometers. An identification algorithm was used to distinguish three aircraft from their simulated range profile with
good results.
Naval operations in the littoral have to deal with the threat of small sea-surface targets. These targets have a low radar
cross-section and low velocity, which makes them hard to detect by radar in the presence of sea clutter. Search lidars
can provide an alternative detection capability for small sea-surface targets at ranges up to 10 km (using commercially
available parts). The lidar clutter is much smaller than the radar clutter due to the smoothness of the sea surface for
optical wavelengths, thus almost all laser light is scattered away from the receiver. By using a high rep-rate laser the
search time is limited in order to be useful in the operational context of coastal surveillance and naval surface
surveillance. In the same scenario, a laser range profiler with a high bandwidth, fast laser receiver can be used to for
identification of the various contacts. To this end, the experimental results have to be compared to a database with premeasured
or pre-calculated range profiles of possible targets. The good match between experimental and simulated laser
range profiles implies that such a database can be constructed from 3D-target models, thus simplifying the database
creation.
Coastal surveillance and naval operations in the littoral both have to deal with the threat of small sea-surface targets.
These targets have a low radar cross-section and a low velocity that makes them hard to detect by radar. Typical threats
include jet skis, FIAC's, and speedboats. Lidar measurements at the coast of the Netherlands have shown a very good
signal-to-clutter ratio with respect to buoys located up to 10 km from the shore where the lidar system was situated. The
lidar clutter is much smaller than the radar clutter due to the smoothness of the sea surface for optical wavelengths. Thus,
almost all laser light is scattered away from the receiver. These results show that due to the low clutter a search lidar is
feasible that can detect small sea-surface targets. A search-lidar demonstrator is presented and experimental results near
the coast of Holland are presented. By using a high rep-rate laser the search time is limited in order to be useful in the
operational context of coastal surveillance and naval surface surveillance. The realization of a search lidar based on a
commercially available high power and high rep-rate laser is presented. This demonstrator is used to validate the system
modeling, determine the critical issues, and demonstrate the feasibility.
Naval operations in the littoral have to deal with threats at short range in cluttered environments with both neutral and
hostile targets. There is a need for fast identification, which is possible with a laser range profiler. Additionally, in a
coastal-surveillance scenario a laser range profiler can be used for identification of small sea-surface targets
approaching the coast. A field trial in June 2007 at the coast of Norway was conducted to validate the concept of ship
identification with a laser range profile. A laser range profiler with a high bandwidth, fast laser receiver was used to
perform tests on the capability of a laser range profiler for identification. The ships in the field trial were of frigate size.
Good laser range profiles could be obtained up to a range of 10 km. The experimental results were compared with the
geometry of the ships and a simulated range profile based on a 3D target model. The good match between experimental
and simulated laser range profiles means that a database of laser range signatures can be constructed from 3D-models,
thus simplifying the database creation. It is shown that sea-surface targets can be distinguished by their laser range
profiles. A neural net approach could distinguish five ships with no false identification.
Laser countermeasures against infrared focal plane array cameras aim to saturate the full camera image. In this paper we
will discuss the results of dazzling experiments performed with MWIR lasers. In the "low energy" pulse regime we
observe an increasing saturated area with increasing power. The size of the saturated area can be explained by an
expression derived from the point spread function of the optics.
The experimental results for short "high energy" pulses show a strong non-linear response of the detector arrays.
Physical processes potentially responsible for these effects are described. Possible consequences of this non-linear
detector behaviour for the effectiveness of laser countermeasures applying short high energy pulses are discussed. A
better understanding of the response of infrared detectors to short high energy laser pulses, will allow changing the laser
design in order to mitigate these effects.
Maritime borders and coastal zones are susceptible to threats such as drug trafficking, piracy, undermining economical
activities. At TNO Defence, Security and Safety various studies aim at improving situational awareness in a coastal zone.
In this study we focus on multi-sensor surveillance of the coastal environment. We present a study on improving
classification results for small sea surface targets using an advanced sensor suite and a scenario in which a small boat is
approaching the coast.
A next generation sensor suite mounted on a tower has been defined consisting of a maritime surveillance and tracking
radar system, capable of producing range profiles and ISAR imagery of ships, an advanced infrared camera and a laser
range profiler. For this suite we have developed a multi-sensor classification procedure, which is used to evaluate the
capabilities for recognizing and identifying non-cooperative ships in coastal waters.
We have found that the different sensors give complementary information. Each sensor has its own specific distance
range in which it contributes most. A multi-sensor approach reduces the number of misclassifications and reliable
classification results are obtained earlier compared to a single sensor approach.
Naval operations in the littoral have to deal with threats at short range in cluttered environments with both neutral and
hostile targets. On board naval vessels there is a need for fast identification, which is possible with a laser range profiler.
Additionally, in a coast-surveillance scenario a laser range profiler can be used for identification of small sea-surface
targets approaching the coast. An eye-safe 1.5 μm laser range profiler has been used to validate these claims.
Experimental results show that range profiles of sea-surface targets can be obtained at ranges of several km's. Sea-surface
clutter is shown to be negligible. Simulation shows that sea-surface targets can be distinguished from their range
profiles. The influence on the identification performance of range resolution and a-priori knowledge of the aspect angle
is presented. Classification has been tested on simulated range profiles of a number of small boats. With a range
resolution of 0.3 meter (comparable to our experimental set-up), these small boats could be identified.
Naval operations in the littoral have to deal with the threat of small sea-surface targets. These targets have a low radar
cross-section and low velocity, which makes them hard to detect by radar in the presence of sea clutter. Typical threats
include periscopes, jet skies, FIAC's, and speedboats. Search lidars on board naval vessels can provide detection
capability for small sea-surface targets. Lidar measurements at the coast have shown a very good signal-to-clutter ratio
with respect to buoys located up to 10 km from the shore were the lidar system was situated. The lidar clutter is much
smaller than the radar clutter due to the smoothness of the sea surface for optical wavelengths, thus almost all laser light
is scattered away from the receiver. These results show that due to the low clutter a search lidar is feasible that can detect
small sea-surface targets. The concept of a search lidar is presented and its performance is derived from system models.
By using a high rep-rate laser and a variable beam divergence the search time can be limited. The design of a search lidar
based on a commercially available high power and high rep-rate laser is shown.
Laser countermeasures against infrared focal plane array cameras aim to saturate the full camera image. In this paper we
will discuss the results of three different dazzling experiments performed with MWIR lasers and show that the obtained
results are independent of the read-out mechanism of the camera and can be explained by an expression derived from the
point spread function of the optics. This expression also allows us to estimate the required laser power to saturate a
complete focal plane array in a camera system. Simulated Images with simulated dazzling effects based on this
expression will be shown.
Small maritime targets, e.g., periscope tubes, jet skies, swimmers and small boats, are potential threats for naval ships under many conditions, but are difficult to detect with current radar systems due to their limited radar cross section and the presence of sea clutter. On the other hand, applications of lidar systems have shown that the reflections from small targets are significantly stronger than reflections from the sea surface. As a result, dedicated lidar systems are potential tools for the detection of small maritime targets. A geometric approach is used to compare the diffuse reflection properties of cylinders and spheres with flat surfaces, which is used to estimate the maximum detectable range of such objects for a given lidar system. Experimental results using lasers operating at 1.06 μm and 1.57 μm confirm this theory and are discussed. Small buoys near Scheveningen harbor could be detected under adverse weather over more than 9 km. Extrapolation of these results indicates that small targets can be detected out to ranges of approximately 20 km.
Countermeasures against heat seeking missiles require access to efficient laser sources, which should emit wavelengths at band I, II and IV. Efficient diode pumped solid-state lasers, combined with efficient non-linear wavelength shifters, allow the development of practical tuneable mid-IR countermeasure sources. The paper describes the requirements and the development of a tabletop laser source for study of DIRCM techniques. Jamming laser systems must be able of creating pulse sequences in the frequency range between 100 Hz and 10,000 Hz, including the capability to mix and sweep the jam frequency. A Nd:YVO4 pump laser with maximum pump power of 3 Watt and pulse length of 10 ns, and a maximum modulation frequency of 100 kHz was selected. A linear single resonant OPO cavity with 30 mm long, 1mm thick PPLN crystals was build. With the tabletop laser system we were able to generate wavelengths from 1.5 to 4 micron. In band I, at 2 micron we can generate between 400-550 mW, and in band II, from 3-4 micron we can generate 130-160 mW laser jam power. The beam quality (M2) is approximately 2.5. The power efficiency for the idler was 8.8%, while the slope power efficiency was 15%. Jam patterns are generated by use of an acousto-optic modulator.
Acoustic landmine detection (ALD) is a technique for the detection of buried landmines including non-metal mines. Since it gives complementary results with GPR or metal detection, sensor fusion of these techniques with acoustic detection would give promising results. Two methods are used for the acoustic excitation of the soil: laser excitation and loudspeaker excitation. A promising concept is using lasers for excitation and monitoring for complete stand-off detection. Results from a field test and laboratory experiments show the feasibility of laser excitation for ALD. In these experiments buried landmine surrogates were measured with ALD using a Nd-YAG laser at 1.06 μm for the acoustic generation and a Laser Doppler Vibrometer (LDV) system at 1.54 μm for the detection of soil vibrations. An analysis is given of the experimental results showing the potential and the inherent limitations of the technique. We discuss the relative merits of LDV detection versus microphone detection of the laser-induced acoustic vibration. It was found that the LDV has limitations with respect to microphone detection due to the influence of surface effects that are prominent in LDV but absent in microphone detection.
KEYWORDS: Sensors, Cameras, Land mines, Motion estimation, Stereoscopic cameras, General packet radio service, Infrared cameras, Data fusion, Metals, Infrared radiation
Vehicles that serve in the role as landmine detection robots could be an important tool for demining former conflict areas. On the LOTUS platform for humanitarian demining, different sensors are used to detect a wide range of landmine types. Reliable and accurate detection depends on correctly combining the observations from the different sensors on the moving platform. Currently a method based on odometry is used to merge the readings from the sensors. In this paper a vision based approach is presented which can estimate the relative sensor pose and position together with the vehicle motion.
To estimate the relative position and orientation of sensors, techniques from camera calibration are used. The platform motion is estimated from tracked features on the ground. A new approach is presented which can reduce the influence of tracking errors or other outliers on the accuracy of the ego-motion estimate. Overall, the new vision based approach for sensor localization leads to better estimates then the current odometry based method.
Acoustic landmine detection (ALD) is a technique for the detection of buried landmines including non-metal mines. An important issue in ALD is the acoustic excitation of the soil. Laser excitation is promising for complete standoff detection using lasers for excitation and monitoring. Acoustic excitation is a more common technique that gives good results but requires an acoustic source close to the measured area. In a field test in 2002 both techniques were compared side by side. A number of buried landmines were measured using both types of excitation. Various types of landmines were used, both anti-tank and anti-personnel, which were buried at various depths in different soil types with varying humidity. Two Laser Doppler Vibrometer (LDV) systems of two different wavelengths for the different approaches were used, one based on a He-Ne laser at 0.633 μm with acoustic excitation and one on an erbium fiber laser at 1.54 μm in the case of laser excitation. The acoustic excitation gives a good contrast between the buried mine and the surrounding soil at certain frequencies. Laser excitation gives a pulse response that is more difficult to interpret but is potentially a faster technique. In both cases buried mines could be detected.
The conversion efficiency of a Raman cell at high pump energies has been increased with an astigmatic focus. Experimental and numerical results show that the increased conversion is due to the reduction of cascade second order Stokes. For our experimental setup, it is shown that other effects, namely Brillouin scattering, anti-Stokes generation, and ground-state depletion, are negligible. Another important advantage of an astigmatic focus is the reduced risk of optical breakdown due to the lower intensity at the focus with only a small gain reduction. Good agreement was found between experimental and numerical results. In particular, the pump energy where the conversion for an ordinary focus is identical to an astigmatic focus is reproduced by the calculations.
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