Due to the growing threat of a wide range of unmanned aerial vehicles (UAVs), including consumer micro-drones that are increasingly used for defense purposes, the need to develop active and passive countermeasures against armed and intelligence gathering UAVs has been identified in order to increase force protection, critical infrastructure resilience, and information security. Several counter-drone solutions have been reported. To accomplish the task of UAV localization, in addition to electro-optical detection and tracking, we consider the distance determination as a fundamental task for stand-alone observation stations. Laser Ranging is one of the promising tools and currently widely used in determination of distance to large objects or slow-moving targets. Within the scope of this paper we are going to evaluate the features and limitations, when applying it for performing laser ranging on UAV. As a target, we are using a typical representative of commercial micro UAV. In this paper, we will present theoretical analysis and experimental results of UAV laser range measurements under realistic environmental conditions. Investigations about the laser transmitter signal are included. We are going to describe qualitative results of laser ranging at different operational modes. Research is based on ranging micro UAV from different directions and various distances. To estimate the maximum ranging distance on the limits of our system, we are going to apply an artificial scaled reference target. This target creates the same optical reflectance cross section as our commercial micro UAV with a given distance.
We present a new approach to an optical UAS detection system that confirms several requirements specified by the authorities. Our UAS detection system consists of a ground unit and a folding mirror located in the air. The ground based unit contains high resolution camera system mounted on a pan tilt unit. Therefore, the lens of the camera system can be actively aligned to a convex mirror which is located in vertical distance over the ground unit on the lower side of a raised captive balloon. The focal length of the ground based lens, the altitude of the balloon and the curvature of the mirror define the field of view towards the ground. The recorded video streams are processed in a vision system using change detection and other algorithms to alert a UAS intrusion. We will outline the design parameters of the optical system, the requirements and the implementation of the mechanical system as well as the active alignment system and show first results of outdoor operation
Lasers arouse an increasing interest in remote sensing applications. In order to deliver as much as possible of the available laser power onto a flying object the subsystems of a beam control system have to operate precisely together. One important subsystem is responsible for determination of the target’s angular position.
Here, we focus on an optical system for measuring precisely the angular position of flying objects. We designed this subunit of a beam control system exclusively from readily available commercial-off-the-shelf components. Two industrial cameras were used for angle measuring and for guiding the system to the position of the flying object. Both cameras are mounted on a modified astronomical mount with high-precision angle encoders. To achieve a high accuracy we temporally synchronize the acquisition of the angle from the pan tilt unit with the exposure of the camera. Therefore, a FPGA-based readout device for the rotary encoders was designed and implemented. Additionally, we determined and evaluated the influence of the distortion of the lenses to the measurement.
We investigated various scenarios to determine the accuracy and the limitations of our system for angular position determination of flying targets. Performance tests were taken indoor and outdoor at our test sites. A target can be mounted on a fast moving linear stage. The position of this linear stage is continuously read out by a high resolution encoder so we know the target’s position with a dynamic accuracy in the range of a few μm. With this setup we evaluated the spatial resolution of our tracking system. We showed that the presented system can determine the angular position of fast flying objects with an uncertainty of only 2 μrad RMS. With this mobile tracking system for angular position determination of flying targets we designed an accurate cost-efficient opportunity for further developments.
Different types of high power or high energy lasers in the multi kW class are currently available or are under development with promising progress reports. A major challenge is to deliver as much as possible of the available power onto a small and fast moving target over a long distance through a disturbing atmosphere.
High resolution imaging is a common way to identify the category of targets dedication and to determine the spatial position relative to the observer. By illuminating the target with a laser the imaging system becomes more resilient towards ambient light and the exposure time can be reduced drastically. Fast and deterministic control loops are demanding for the moving parts in order to maintain a high accuracy for the pointing of the turret and aiming of the laser countermeasure system.
Here, we report on the progress of such a beam control system developed at the Institute of Technical Physics of DLR. In an overview we present the beam control system and explain different sub-systems. Performance tests were taken at our test. At a distance we simulated various scenarios for probing the limits of the tracking and pointing accuracy with a target on a fast moving linear stage. We present first results of the beam control system performance.
High Energy Laser weapons (HEL) have unique attributes which distinguish them from limitations of kinetic energy
weapons. HEL weapons engagement process typical starts with identifying the target and selecting the aim point on the
target through a high magnification telescope. One scenario for such a HEL system is the countermeasure against
rockets, artillery or mortar (RAM) objects to protect ships, camps or other infrastructure from terrorist attacks.
For target identification and especially to resolve the aim point it is significant to ensure high resolution imaging of
RAM objects. During the whole ballistic flight phase the knowledge about the expectable imaging quality is important to
estimate and evaluate the countermeasure system performance. Hereby image quality is mainly influenced by
unavoidable atmospheric turbulence.
Analytical calculations have been taken to analyze and evaluate image quality parameters during an approaching RAM
object. In general, Kolmogorov turbulence theory was implemented to determine atmospheric coherence length and
isoplanatic angle. The image acquisition is distinguishing between long and short exposure times to characterize tip/tilt
image shift and the impact of high order turbulence fluctuations. Two different observer positions are considered to show
the influence of the selected sensor site. Furthermore two different turbulence strengths are investigated to point out the
effect of climate or weather condition.
It is well known that atmospheric turbulence degenerates image sharpness and creates blurred images. Investigations are
done to estimate the effectiveness of simple tip/tilt systems or low order adaptive optics for laser based C-RAM systems.
Large and lightweight primary mirrors of high optical quality are considered to be a key element of next generation
deployable space telescopes. In this paper we present a membrane mirror demonstrator and show experimental results of
the associated mechanical and optical characteristics. The mounting conditions of such a membrane mirror cause static
optical aberrations which are compensated as a proof of principle using an adaptive mirror and a metric optimizationbased
control system. The feasibility of the complete system for receiving and transmitting applications will be
We present a rugged and reliable real-time beam stabilization system which is adapted on a mobile 10" amateur
Schmidt-Cassegrain telescope (SCT) to demonstrate the functionality on different ground locations. Recently, the tip/tilt
system was tested in horizontal direction on a 130 m free space propagation range. Tip/tilt compensation with a rootmean-
squared accuracy better than 0.5 μrad has been confirmed. All system characteristics were measured in relation to
metrological conditions and turbulence strength.
High-resolution telescope systems used for observational tasks require sufficiently large apertures to enhance the spatial resolution. Due to the propagation through turbulent layers of the atmosphere the distorted wavefront implicates a broadening of the imaged spot and hence a loss in optical resolution.
The improvement in visual resolution by applying adaptive optics has been successfully demonstrated in a mobile telescope platform. To compensate for the effects of atmospheric turbulence, a closed-loop system was developed with a bandwidth of up to 600 Hz capable to achieve a wavefront correction with a residual wavefront deformation of <50 nm RMS. A reference signal which is probing the wavefront distortion is realized with the help of a coherent laser beam emanating from the object. The developed adaptive optical system is capable of compensating phase distortions in a conjugated plane with time constants of 30 ms. Turbulence was artificially induced along the optical path by a turbulence generator. Measurements of MTF values and Strehl ratio will be presented.
We present a rugged and reliable real-time laser beam tracking system operating with a high speed, high resolution
piezo-electric tip/tilt mirror. Characteristics of the piezo mirror and position sensor are investigated. An industrial
programmable automation controller is used to develop a real-time digital PID controller. The controller provides a
one million field programmable gate array (FPGA) to realize a high closed-loop frequency of 50 kHz. Beam tracking
with a root-mean-squared accuracy better than 0.15 μrad has been laboratory confirmed. The system is intended as an
add-on module for established mechanical mrad tracking systems.
We compare active optical elements based on different technologies to accomplish the requirements of a 2-dim. fine tracking control system. A cascaded optically and electrically addressable spatial light modulator (OASLM) based on liquid crystals (LC) is used for refractive beam steering. Spatial light modulators provide a controllable phase wedge to generate a beam deflection. Additionally, a tip/tilt mirror approach operating with piezo-electric actuators is investigated. A digital PID controller is implemented for closed-loop control. Beam tracking with a root-mean-squared accuracy of Δα=30 nrad has been laboratory-confirmed.
We present experimental and theoretical results on aberration control in solid state laser amplifiers and resonators. In lasers with diffraction-limited beam quality, aberrations cause diffraction losses that reduce the output power. In laser amplifiers, aberrations in the active medium degrade the beam quality of the amplified beam. Adaptive optics can be used to correct for the aberrations and thus increase output power and beam quality, respectively.
The required precision of the adaptive aberration correction can be estimated with a simple mode expansion model in which an aberrated TEM00 mode is expanded into Gauss-Hermite modes. Apart from these theoretical results we will present experimental results for a MOPA (Master-Oscillator-Power-Amplifier) laser system consisting of a Nd:YVO4 master oscillator and two Nd:YAG power amplifiers. A micromachined deformable mirror was used in a closed-loop system to correct for the thermo-optic aberrations of the amplifiers. A beam with a beam quality of M2= 2.5 at an out power of 80 W was obtained. The deformable mirror was controlled by a genetic algorithm.