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Henriksson M.,Swedish Defence Research Agency | Sjoqvist L.,Swedish Defence Research Agency | Seiffer D.,Fraunhofer Institute For Optronik
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

The hot exhaust gases from engines on helicopters are pushed down by the rotor in a turbulent flow. When the optical path of a laser beam or optical sensor passes through this region severe aberrations of the optical field may result. These perturbations will lead to beam wander and beam distortions that can limit the performance of optical countermeasure systems. To quantify these effects the Italian Air Force Flight Test Centre hosted a trial for the "Airborne platform effects on lasers and warning sensors" (ALWS) EDA-project. Laser beams were propagated from the airport control tower to a target screen in a slant path with the helicopter hovering over this path. Collimated laser beams at 1.55-, 2- and 4.6-μm wavelength were imaged with high speed cameras. Large increases in beam wander and beam divergence were found, with beam wander up to 200 μrad root-mean-square and increases in beam divergence up to 1 mrad. To allow scaling to other laser beam parameters and geometries formulas for propagation in atmospheric turbulence were used even though the turbulence may not follow Kolmogorov statistics. By assuming that the plume is short compared to the total propagation distance the integrated structure parameter through the plume could be calculated. Values in the range 10-10 to 10-8 m1/3 were found when the laser beams passed through the exhaust gases below the helicopter tail. The integrated structure parameter values calculated from beam wander were consistently lower than those calculated from long term spot size, indicating that the method is not perfect but provides information about order of magnitudes. The measured results show that the engine exhaust for worst case beam directions will dominate over atmospheric turbulence even for kilometer path lengths from a helicopter at low altitude. How severe the effect is on system performance will depend on beam and target parameters. © 2015 COPYRIGHT SPIE.

Milighetti G.,KUKA Laboratories GmbH | Bauer C.,Karlsruhe Institute of Technology | Mikut R.,Karlsruhe Institute of Technology | Kuntze H.-B.,Fraunhofer Institute For Optronik
At-Automatisierungstechnik | Year: 2013

Control of humanoid robots makes great demands not only on the development of cognitive functions and hardware components, but also on the design of planning, supervision and control methods, which establish the connecting element between cognition and hardware. Starting with an overview about current trends in the field of industrial and service robotics, we present in this contribution a general concept for a modular multisensory discrete-continuous supervisory control. We will analyze in particular the decomposition of complex robot actions in a sequence of primitive actions, each with integrated control and supervision solutions.

Schatz V.,Fraunhofer Institute For Optronik
Journal of Real-Time Image Processing | Year: 2013

This work describes a hardware implementation of the contrast-limited adaptive histogram equalization algorithm (CLAHE). The intended application is the processing of image sequences from high-dynamic-range infrared cameras. The variant of histogram equalization implemented is the one most commonly used today. It involves dividing the image into tiles, computing a transformation function on each of them, and interpolating between them. The contrast-limiting is modified to facilitate the hardware implementation, and it is shown that the error introduced by this modification is negligible. The latency of the design is minimized by performing its successive steps simultaneously on the same frame and by exploiting the vertical blank pause between frames. The resource usage of the histogram equalization module and how it depends on its parameters has been determined by synthesis. The design has been synthesized and tested on a Xilinx FPGA. The implementation supports substituting other dynamic range reduction modules for the histogram equalization component by partial dynamic reconfiguration. © 2011 Springer-Verlag.

Menze M.,Leibniz University of Hanover | Klinger T.,Leibniz University of Hanover | Muhle D.,Leibniz University of Hanover | Metzler J.,Fraunhofer Institute For Optronik | Heipke C.,Leibniz University of Hanover
Photogrammetrie, Fernerkundung, Geoinformation | Year: 2013

This article describes the application of stereoscopic analysis to typical image pairs from a surveillance camera network. An approach is presented that establishes correspondences between people detections across adjacent views and derives an estimation of body height for each person in the overlapping parts of the camera views. Dense image matching is applied to short stereoscopic sequences and the results are incorporated in a subsequent monocular tracking to improve the positioning accuracy. The method does not depend on a dedicated stereo setup of the camera network but is applicable to suitable image pairs in addition to monocular people detection and tracking. Based on realistic image sequences, the performance of the proposed approach is evaluated and compared to a current method for appearance-based data association. © 2013 E. Schweizerbart'sche Verlagsbuchhandlung.

Seiffer D.P.,Fraunhofer Institute For Optronik | Eisele C.,Fraunhofer Institute For Optronik | Henriksson M.,Swedish Defence Research Agency | Sjoqvist L.,Swedish Defence Research Agency | And 3 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

The performance of electro-optical platform protection systems can be degraded significantly by the propagation environment around the platform. This includes aero-optical effects and zones of severe turbulence generated by engine exhausts. For helicopters rotor tip vortices and engine exhaust gases that are pressed down by the rotor airflow form the so called downwash phenomena. The downwash is a source for perturbations. A wide range of spatial and temporal fluctuations in the refractive index of air can occur. The perturbations from the turbulent flow cause detrimental effects on energy delivery, angle of arrival fluctuations, jam-code transmission, tracking accuracy and imaging performance in general. Therefore the effects may especially have a severe impact on the performance of laser-based protection systems like directed infrared countermeasures (DIRCM). The chain from passive missile detection and warning to obtaining an optical break-lock by the use of an active laser system will be influenced. To anticipate the installed performance of an electro-optical defensive aids suite (DAS) for helicopter platforms it is necessary to develop models for the prediction of the perturbations. Modelled results have to be validated against experimental findings. However, the data available in open literature on the effects of rotor downwash from helicopters on optical propagation is very limited. To collect necessary data and to obtain a first impression about the magnitude of occurring effects the European defence agency group (EDA) on "airborne platform effects on lasers and warning sensors (ALWS)" decided to design and perform a field trial on the premises of the Italian Air Force Flight Test Center in Pratica di Mare, Italy. ALWS is a technical arrangement under the Europa MoU among France, Germany, Italy, Sweden and the United Kingdom. © 2015 COPYRIGHT SPIE.

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