This paper presents recent progress in the development of a scanning time-of-flight imaging system employing time-correlated single-photon counting (TCSPC) designed for the acquisition of depth information at kilometre ranges. The device is capable of acquiring information on non-cooperative target surfaces at eye-safe average optical power levels in the near-IR regime (<1 mW at 842 nm illumination wavelength). Target illumination is periodic or non-periodic at typical repetition frequencies in the MHz domain, utilising a sub-ns pulse-width laser diode. The system output is steered over the optical field of interest, and return photons from the target are routed towards a single-photon detector. Measurements are performed with a silicon single-photon avalanche diode (SPAD). Effective optical spatial and spectral filtering techniques permit operation in bright daylight conditions. Results in the form of depth images from a variety of targets, taken under various environmental conditions, are presented. Achieved improvements of this first-generation system are discussed in terms of parametric enhancement of quantities such as spatial and spectral filtering, internal optical attenuation and beam size. We detail progress in the design process both based on theoretical assumptions and actual measurements at distances between few 100's of metres and several km. The trade-offs between acquisition time, maximum range and excitation laser power levels are discussed and projections made for this and future depth imaging systems. State-of-the-art TCSPC hardware solutions facilitate the rapid transfer and storage of large quantities of raw data. This renders possible real-time analysis with speed-optimised algorithms such as fast Fourier transform-supported cross-correlation methods, as well as gathering additional information about the scene in post-processing steps, based on approaches such as reversible-jump Markov-chain Monte Carlo (RJMCMC). This algorithm dynamically adapts the number of degrees of freedom of a range measurement, resulting in multi-surface resolution and the possible identification of targets obscured by objects such as foliage.

Elbit Systems is a developer of time-resolved laser-gated Active Night Vision systems. The active systems are developed for a variety of configurations and applications. Part of the applications are non-covert and covert night driving, perimeter security, tunnels and maritime applications. In every application different requirements and limitations are being considered. In this paper we will discuss the basics of active imaging and its components. We will describe few applications for this technology.

Electronically steered antenna quality mainly relies on the accurate periodicity of the radiating element positions. Very thin antenna with non-rigid structures will permit the implementation of disruptive mechanical designs and provide better tactical deployment and permit implementation on non-dedicated platforms. To maintain planar antenna performances, we propose to dynamically cope with distortions with an innovative method. In this presentation, we will report on an innovative real-time and embedded measurement technique in harsh environment based on an optical polarization sensor coupled with an adapted mechanical model, designed in order to maintain a sufficient calibration of the antenna during its operational use.

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.

Laser radars have the unique capability to give both intensity and full 3-D images of an object or a scene. The latest addition to these capabilities is the possibility to acquire motion. These systems have many civilian and military applications such as terrain modeling, depth sounding, object detection, classification and positioning as well as object tracking. In order to fully understand the performance of laser radars vs experimental data a computer simulation model is of high value. We have developed a modularized computer model capable of modeling performance of a variety of laser radar systems. In order to derive the returned signal waveform from the object one has to account for the laser pulse time characteristics, media effects such as the atmospheric attenuation and scattering as well as object characteristics like shape, BRDF, surface roughness and others. The noise from target speckle and scintillations has to be coupled with detector noise generated by the inherent noise in the detectors and subsequent amplifiers and read out circuitry as well as the noise induced from the optical background. The result can be of help when designing and using new laser radar systems, as well as extending real system parameters and evaluate performance. We will give examples of simulated sensor data in different applications/scenarios together with some real measured data.

As a part of the project agreement between the Swedish Defence Research Agency (FOI) and the United States of American's Air Force Research Laboratory (AFRL), a joint field trial was performed in Sweden during two weeks in January 2009. The main purpose for this trial was to characterize AFRL's latest version of the ASC (Advanced Scientific Concepts [1]) FLASH 3D LADAR sensor. The measurements were performed essentially in FOI´s optical hall whose 100 m indoor range offers measurements under controlled conditions minimizing effects such as atmospheric turbulence. Data were also acquired outdoor in both forest and urban scenarios, using vehicles and humans as targets, with the purpose of acquiring data from more dynamic platforms to assist in further algorithm development. This paper shows examples of the acquired data and presents initial results.

The purpose of this study is to explore novel monostatic ladar detection principles utilizing polarimetric Bidirectional Reflectance Distribution Function (BRDF) and single-pixel detection parameters. The depolarization of backscattered elliptical polarized light beams, from extended area space materials, was studied at different sample orientations. Specifically, the depolarization ratio for both linearly and circularly polarized light waves was estimated under quasimonostatic transceiver geometry. The experimental results indicate that space object materials exhibit distinct depolarization signatures, which provide enhanced discrimination capabilities. The outcome of this study would enhance the monostatic-ladar detection and discrimination capabilities.

For naval surveillance, automatic detection of surface objects, like vessels, in a maritime environment is an important contribution of the Electro-Optical (EO) sensor systems on board. Based on previous research using single images, a background estimation approach using low-order polynomials is proposed for the automatic detection of objects in a maritime environment. The polynomials are fitted to the intensity values in the image after which the deviation between the fitted intensity values and the measured intensity values are used for detection. The research presented in this paper, includes the time information by using video streams instead of single images. Hereby, the level of fusing time information and the number of frames necessary for stable detection and tracking behaviour are analysed and discussed. The performance of the detection approach is tested on a, during the fall of 2007, collected extensive dataset of maritime pictures in the Mediterranean Sea and in the North Sea on board of an Air Defence Command frigate, HNLMS Tromp.

We describe progress in the third year of the EMRS DTC TEP theme project entitled "Temporal Resolution Enhancement from Motion". The aim is to develop algorithms that combine evidence over time from a sequence of images in order to improve spatial resolution and reduce unwanted artefacts. Years one and two of this project developed and demonstrated an efficient algorithm that provided good resolution enhancement of a scene viewed in the far field (approximately flat) [1]. This paper reports a new algorithm which is applicable to a three dimensional scene where substantial depth variation causes parallax within the imagery. The new algorithm is demonstrated using airborne infra-red imagery.

In this work, Spectral Signature-Based Target Detection (SSBTD) as applied to airborne monitoring for surveillance and reconnaissance of ground targets is addressed, and techniques that can help to approach in-flight processing are analyzed from this perspective. In fact, SSBTD is a challenging task from an operating viewpoint, mainly due to the crucial atmospheric compensation step, which is required to make the target measured reflectance comparable to the sensoracquired radiance. Both physics-based radiative transfer modeling techniques and empirical scene-based methods are considered for atmospheric compensation, and their applicability and adaptability to in-flight processing are discussed. Experimental data acquired by a hyperspectral sensor operating in the Visible Near-InfraRed range are employed for analysis. The data consist in multiple images collected during subsequent flights performed over the same scene. Such a situation well reproduces the typical scenario of regularly monitoring an area of interest, and can, therefore, be adopted for examining the aforementioned approaches from an in-flight applicability perspective. Target detection results are analyzed and discussed by examining objective performance measures such as the Receiver Operating Characteristic (ROC) curves.

Optical measurements and tests of optical instruments are often performed through an opened window or from the roof of an elevated building. This can also be a common situation for free-space optical (FSO) communication systems. Wind friction in combination with solar heating of the wall and the ground will create increased turbulence in a boundary layer close to the wall. For an outgoing laser beam this thin region of strong turbulence causes beam wander, beam broadening and beam break-up. For imaging and detection systems angle of arrival fluctuations and image blurring may result. In an attempt to estimate the strength of the atmospheric turbulence in the layer at the wall the refractive index structure constant (C_n²) was measured with an ultra sonic anemometer as a function of distance from the wall. The measurements were performed at the lower part of a window that was open just enough to give space for the anemometer. The window was placed 10 m above ground in a 12 m high building, with brick wall below the window and wooden panel above the window. Measurements of the turbulence as a function of distance from the wall were performed during different times of the day to study the influence of sun heating of the wall. The measured average C_n² shows an exponentially decreasing function of distance from the wall. The exponential decay of C_n² depends on the time of the day. The highest measured value of C_n² was approximately 3x10^-11 m^-2/3 near the wall. The influence of wall turbulence is discussed with respect to its influence on laser beam propagation.

We report on recent results obtained with a fiber optic hydrophone based on the intensity modulation of the laser light in a FBG (Fiber Bragg Grating) under the influence of the sound pressure. In order to control the behavior of the hydrophone in terms of sensitivity and bandwidth, FBGs have been coated with proper materials, characterized by different elastic modulus and shapes. In particular, new experiments have been carried out using a cylindrical geometry with two different coating, showing that the sensitivity is not influenced by the shape but by the transversal dimension and the material characteristics of the coating.

A public-private research collaboration has demonstrated a promising three-dimensional volumetric display system with the capability of satisfying the performance criteria of: ease of viewing, high-resolution, scalability, and reliability. The system utilizes commercial off-the-shelf micro-electro-mechanical systems (MEMS) based mirror arrays to direct infrared light beams into an image space. To date, monochromatic images have been demonstrated in an image space material that exhibits two-photon upconversion. The prototype display requires no special viewing aids, produces a volumetric image that is viewable from 360 degrees, and as presently designed is capable of producing 800 million volumetric pixels of image content.

This paper proposes a color mixing control system that provides adjustable color mixing using pulse-modulation light brightness period control while driving red-green-blue (RGB) light-emitting diodes (LED). The proposed control system includes a clock unit that provides a first clock signal and a second clock signal with a frequency lower than that of the first clock signal. Three control units are coupled to three LEDs emitting three different colors, respectively. Each control unit is operated based on the clock signals and a corresponding set of first and second reference values output to a driving pulse signal to the corresponding LED. Using four bit digital signal control, 4096 different colors and 16 gray levels can be provided by the digital pulse width modulator (DPWM) system. The system works using a single 5V power supply with a maximum clock frequency of 1MHz.

A temperature insensitive silicon photoconductor has been designed and produced, which significantly improves the detector performance over a wide operational temperature range. The detector Responsivity in conventional silicon photodetectors is a function of temperature. The Responsivity and the associated detector sensitivity can vary by as much as 600% over the normal operating temperature ranges of many commercial and military products. The temperature controlled photoconductor described in this paper incorporates a sheet resistance heater that is integrated into the silicon wafer structure. A closed loop control circuit operates the detector at an optimized temperature. This is done in a way so as to maximize the system signal-to-noise ratio, regardless of the temperature and background illumination level of the environment. The measured detector sensitivity improvement is approximately 6 times higher at the low end of the operational temperature range of an electro-optical sensor employing the heated detector and 1.7 to 2.0 times higher for an electro-optic sensor operating at 20 degrees C, compared to a sensor employing a standard silicon photo-conductor. An electro-optical system incorporating the new device can realize a significant performance increase and/or realize a significant reduction in the system aperture size (and related packaging parameters like weight, volume, etc.) while maintaining parity performance with similar systems that do not use the new detector. The paper describes the device and presents laboratory and field test results that testify as to the performance improvement that was achieved. These test results, for devices operating between -54 deg C and +100 deg C show that the heated detectors have significantly higher performance than conventional silicon detectors operating in the same environments. The advantages of using these devices in place of conventional detectors are also covered.

Sensitive and broadband detection of MWIR and LWIR radiation with any wavelength within the 2 to 16 μm spectral range and bandwidth from DC to GHz range is reported. Recent efforts have been concentrated on the extension of useful spectrum range above 13 micrometers. This was achieved with improved architecture of the active element, use of monolithic optical immersion technology, enhanced absorption of radiation, dedicated electronics, series connection of small cells and applying more efficient Peltier coolers.

One promising approach to target detection in hyperspectral imagery exploits a statistical mixture model to represent scene content at a pixel level. The process then goes on to look for pixels which are rare, when judged against the model, and marks them as anomalies. It is assumed that military targets will themselves be rare and therefore likely to be detected amongst these anomalies. For the typical assumption of multivariate Gaussianity for the mixture components, the presence of the anomalous pixels within the training data will have a deleterious effect on the quality of the model. In particular, the derivation process itself is adversely affected by the attempt to accommodate the anomalies within the mixture components. This will bias the statistics of at least some of the components away from their true values and towards the anomalies. In many cases this will result in a reduction in the detection performance and an increased false alarm rate. This paper considers the use of heavy-tailed statistical distributions within the mixture model. Such distributions are better able to account for anomalies in the training data within the tails of their distributions, and the balance of the pixels within their central masses. This means that an improved model of the majority of the pixels in the scene may be produced, ultimately leading to a better anomaly detection result. The anomaly detection techniques are examined using both synthetic data and hyperspectral imagery with injected anomalous pixels. A range of results is presented for the baseline Gaussian mixture model and for models accommodating heavy-tailed distributions, for different parameterizations of the algorithms. These include scene understanding results, anomalous pixel maps at given significance levels and Receiver Operating Characteristic curves.

Between the wavelengths of the visible and the Short Wave Infrared (SWIR), the glow of the sky from chemical radiance and absorption changes dramatically. Thus too, the structure and appearance of clouds change. By directly and simultaneously examining clouds in an urban and a rural setting, we investigate the correlation between the appearance of clouds present in the SWIR, NIR, and visible. The experimental setup consists of two sensors, one a NIR to SWIR sensitive InGaAs array, and the other a visible CCD, both co-located on an AZ-EL mount, and both co-boresighted so that different viewing angles of the sky are possible. The SWIR sensor is sensitive from 0.9 μm to 1.7 μm. The CCD sensor collects cloud images in the visible region. By making corrections for focal length and pixel size, the visible and SWIR data can be compared. After taking several nights of data in the urban environment of Albuquerque, NM, the entire system was then re-located to a rural location in southern New Mexico.

Hyperspectral ground mapping is being used in an ever-increasing extent for numerous applications in the military, geology and environmental fields. The different regions of the electromagnetic spectrum help produce information of differing nature. The visible, near-infrared and short-wave infrared radiation (400 nm to 2.5 μm) has been mostly used to analyze reflected solar light, while the mid-wave (3 to 5 μm) and long-wave (8 to 12 μm or thermal) infrared senses the self-emission of molecules directly, enabling the acquisition of data during night time. Push-broom dispersive sensors have been typically used for airborne hyperspectral mapping. However, extending the spectral range towards the mid-wave and long-wave infrared brings performance limitations due to the self emission of the sensor itself. The Fourier-transform spectrometer technology has been extensively used in the infrared spectral range due to its high transmittance as well as throughput and multiplex advantages, thereby reducing the sensor self-emission problem. Telops has developed the Hyper-Cam, a rugged and compact infrared hyperspectral imager. The Hyper-Cam is based on the Fourier-transform technology yielding high spectral resolution and enabling high accuracy radiometric calibration. It provides passive signature measurement capability, with up to 320x256 pixels at spectral resolutions of up to 0.25 cm-1. The Hyper-Cam has been used on the ground in several field campaigns, including the demonstration of standoff chemical agent detection. More recently, the Hyper-Cam has been integrated into an airplane to provide airborne measurement capabilities. A special pointing module was designed to compensate for airplane attitude and forward motion. To our knowledge, the Hyper-Cam is the first commercial airborne hyperspectral imaging sensor based on Fourier-transform infrared technology. The first airborne measurements and some preliminary performance criteria for the Hyper-Cam are presented in this paper.

Advanced multispectral, or hyperspectral, camera systems are being used to identify objects of interest on the basis of spectral characteristics. In previous papers we have described the development of a hyperspectral real time tracking system using matched filtering. This paper will discuss alternative methods of gathering hyperspectral imagery and consider how they should be adapted to suit the various applications. It will also present some recent improvements made to the design and operation of our fast visible hyperspectral imaging system. These improvements are allowing objects of interest to be successfully tracked in lower light levels with reduced false alarm levels. Aerial applications of hyperspectral imagers will also be discussed.

Ship-based automatic detection of small floating objects on an agitated sea surface remains a hard problem. Our main concern is the detection of floating mines, which proved a real threat to shipping in confined waterways during the first Gulf War, but applications include salvaging,search-and-rescue and perimeter or harbour defense. IR video was chosen for its day-and-night imaging capability, and its availability on military vessels. Detection is difficult because a rough sea is seen as a dynamic background of moving objects with size order, shape and temperature similar to those of the floating mine. We do find a determinant characteristic in the target's periodic motion, which differs from that of the propagating surface waves composing the background. The classical detection and tracking approaches give bad results when applied to this problem. While background detection algorithms assume a quasi-static background, the sea surface is actually very dynamic, causing this category of algorithms to fail. Kalman or particle filter algorithms on the other hand, which stress temporal coherence, suffer from tracking loss due to occlusions and the great noise level of the image. We propose an innovative approach. This approach uses the periodicity of the objects movement and thus its temporal coherence. The principle is to consider the video data as a spacetime volume similar to a hyperspectral data cube by replacing the spectral axis with a temporal axis. We can then apply algorithms developed for hyperspectral detection problems to the detection of small floating objects. We treat the detection problem using multilinear algebra, designing a number of finite impulse response filters (FIR) maximizing the target response. The algorithm was applied to test footage of practice mines in the infrared.

The purpose of this paper is to establish an evaluation method of the observability performance for equipment that enables day and night vision (using thermal cameras, gated image intensification and CCD cameras using L3V based on e2v technology). This is done by modelling of experimental results of simulation setup in the lab. Starting from the predictive evaluation procedures of the observation, the paper analyses the relevance of method to establish the limits in the utilization of the above- mentioned equipment, from the point of view of the observation probability, in difficult ambient conditions, such as reduced illumination level or aerosol curtains. Moreover, the present work compares subjective factors that can influence the prediction by the participants on the experiments (age, training, decision time) and objective factors (contrast between background and image, resolution of the observation system and image noise).