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This paper investigates active and passive short-wave infrared (SWIR) imaging for slant paths close to ground. The main sensor, a gated SWIR camera, was collecting both passive and active images along a 2 km long path over an airfield and also from our rooftop laboratory looking over open fields. For some investigations we also used a gated system working in the near-infrared region and thermal as well as color CCD cameras. The sensor was elevated by a lift in steps from 1.6–13.5 m or placed in a rooftop laboratory 13 m above ground. Targets were resolution charts and man targets. The turbulence was measured along the path with anemometers and scintillometers. The image performance was evaluated by measurement of the image blur and also by performing observer perception tests. The results reveal a strong dependence on the sensor height especially during daytime.

The identification of human targets including their activities and handheld objects at range is a prime military and security capability. We have investigated this capability using active and passive imaging for video cameras, and sensors operating in the NIR and SWIR regions. For a limited data set we also compare sensor imagery from visible, NIR and SWIR sensors with that from a thermal imaging camera. The target recognition performance is studied vs. the gate position relative to the target, target range, turbulence conditions and target movement. A resolution chart is also included in the scene. The performance results from observer tests are compared with models and discussed from a system perspective.

The detection and classification of small surface targets at long ranges is a growing need for naval security. Laser range profiling offers a new capability for detecting and classifying such targets even if they appear as point (transversally unresolved) targets in radar or passive/active imaging EO sensors. Modifying a conventional laser range finder to have a higher range resolution can this increase it’s value as a sensor. Laser range profiles will reveal basic reflecting structures on the ship. The best information is obtained for profiles along the ship. Several range profiles from different aspects will increase the classification performance. If many aspects angles are possible a tomographic reconstruction of the ship may be done. We have used high resolution (sub cm) laser radar based on time correlated single photon counting (TCSPC) to acquire range profiles from different small model ships. The collected waveforms are compared with simulated wave forms based on 3 D models of the ships. A discussion of the classification accuracy based on the number of waveforms from different aspect angles is done as well as the influence of the reflectivity from different parts of the ship is made. The results are discussed with respect to the potential performance of modified laser range finder measuring on real ships and the combination with active imaging.

This paper will report experiments and analysis of slant path imaging using 1.5 μm and 0.8 μm gated imaging. The investigation is a follow up on the measurement reported last year at the laser radar conference at SPIE Orlando. The sensor, a SWIR camera was collecting both passive and active images along a 2 km long path over an airfield. The sensor was elevated by a lift in steps from 1.6-13.5 meters. Targets were resolution charts and also human targets. The human target was holding various items and also performing certain tasks some of high of relevance in defence and security. One of the main purposes with this investigation was to compare the recognition of these human targets and their activities with the resolution information obtained from conventional resolution charts. The data collection of human targets was also made from out roof top laboratory at about 13 m height above ground. The turbulence was measured along the path with anemometers and scintillometers. The camera was collecting both passive and active images in the SWIR region. We also included the Obzerv camera working at 0.8 μm in some tests. The paper will present images for both passive and active modes obtained at different elevations and discuss the results from both technical and system perspectives.

The paper describes work done by FOI to develop cost-effective methods for the detection and classification of small surface vessels at sea or in littoral waters. We report on the architecture, current realization, and initial tests of a prototype system consisting of a coherent pulse-Doppler radar operating at S-band and an optical sensor module consisting of a gated active laser imaging sensor for classification of candidate targets. The two sensor modules have complementary capabilities and can be used to realize an integrated system with both good area coverage and high angular resolution. Improved clutter-reduction methods using coherent 2D-filtering are also discussed. (6 pages)

This paper investigates the prospects of "seeing around the corner" using active imaging. A monostatic active imaging system offers interesting capabilities in the presence of glossy reflecting objects. Examples of such surfaces are windows in buildings and cars, calm water, signs and vehicle surfaces. During daylight it might well be possible to use mirrorlike reflection by the naked eye or a CCD camera for non-line of sight imaging. However the advantage with active imaging is that one controls the illumination. This will not only allow for low light and night utilization but also for use in cases where the sun or other interfering lights limit the non-line of sight imaging possibility. The range resolution obtained by time gating will reduce disturbing direct reflections and allow simultaneous view in several directions using range discrimination. Measurements and theoretical considerations in this report support the idea of using laser to "see around the corner". Examples of images and reflectivity measurements will be presented together with examples of potential system applications.

This paper will report experiments, analysis and simulations of slant path imaging using 1.5 μm gated imaging. The measurements were taking place at a former airfield along a 2 km path. The sensor was elevated by a lift in steps from 2-12.5 meters. Targets were resolution charts. The turbulence was measured along the path with a scintillometer. Turbulence information was also obtained at various path positions including the elevated cage using anemometers. The camera was collecting both passive and active images in the SWIR region. In the passive mode (using solar illumination) the noise due to speckles are eliminated and the influence by scintillation limited. In the active mode on the other hand these noise sources are present to a varying degree depending on stabilized frame averaging and on the sensor elevation. A trend is that the image quality is improved for elevated sensor positions. Two light sources in the camera FOV (head lights from a car) gave independent turbulence level estimates. The paper will present evaluated images for both passive and active modes obtained at different elevations and the result will be compared with theory including image simulation.

The development of new asymmetric threats to civilian and naval ships has been a relatively recent occurrence. The bombing of the USS Cole is one example and the pirate activities outside Somalia another. There is a need to recognize targets at long ranges and possibly also their intentions to prepare for counteractions. Eye safe laser imaging at 1.5 μm offers target recognition at long ranges during day and night. The 1.5 μm wavelength is suitable for observing small targets at the sea surface such as boats and swimmers due to the low reflectivity of water compared to potential targets. Turbulence and haze limits the sensor performance and their influence is estimated for some cases of operational interest. For comparison, passive EO images have been recorded with the same camera to investigate the difference between sun illuminated and laser illuminated images. Examples of laser images will be given for a variety of targets and external conditions.Image segmentation for future automated recognition development is described and examplified. Examples of relevant 1.5 μm laser reflectivities of small naval targets are also presented. Finally a discussion of system aspects is made.

Some advanced concepts for gated viewing are presented, including spectral diversity illumination techniques, non-line-of-sight imaging, indirect scene illumination, and in particular setups in bistatic configurations. By using a multiple-wavelength illumination source target speckles could be substantially reduced, leading to an improved image quality and enhanced range accuracy. In non-line-of-sight imaging experiments we observed the scenery through the reflections in a window plane. The scene was illuminated indirectly as well by a diffuse reflection of the laser beam at different nearby objects. In this setup several targets could be spotted, which, e. g., offers the capability to look around the corner in urban situations. In the presented measuring campaigns the advantages of bistatic setups in comparison with common monostatic configurations are discussed. The appearance of shadows or local contrast enhancements as well as the mitigation of retroreflections supports the human observer in interpreting the scene. Furthermore a bistatic configuration contributes to a reduced dazzling risk and to observer convertness.

We have performed a field trial to evaluate technologies for stand-off detection of biological aerosols, both in daytime and at night. Several lidar (light detection and ranging) systems were tested in parallel. We present the results from three different lidar systems; one system for detection and localization of aerosol clouds using elastic backscattering at 1.57 μm, and two systems for detection and classification of aerosol using spectral detection of ultraviolet laser-induced fluorescence (UV LIF) excited at 355 nm. The UV lidar systems were utilizing different technologies for the spectral detection, a photomultiplier tube (PMT) array and an intensified charge-coupled device (ICCD), respectively. During the first week of the field trial, the lidar systems were measuring towards a semi-closed chamber at a distance of 230 m. The chamber was built from two docked standard 20-feet containers with air curtains in the short sides to contain the aerosol inside the chamber. Aerosol was generated inside the semi-closed chamber and monitored by reference equipments, e.g. slit sampler and particle counters. Signatures from several biological warfare agent simulants and interferents were measured at different aerosol concentrations. During the second week the aerosol was released in the air and the reference equipments were located in the centre of the test site. The lidar systems were measuring towards the test site centre at distances of either 230 m or approximately 1 km. In this paper we are presenting results and some preliminary signal processing for discrimination between different types of simulants and interference aerosols.

FOI (Sweden) and FGAN-FOM (Germany) have carried out common field trials using range gating imaging at 1.5 μm. Some examples showing the potential of bi-static vs. the common mono-static configurations are given. In addition the experiments include a comparison between active SWIR and passive EO-IR imaging. The paper discusses the results with respect to suitability for defence and security applications.

This presentation will review some of the work on range gated imaging undertaken at the Swedish Defence Research Agency (FOI). Different kind of systems covering the visible to 1.5 μm region have been studied and image examples from various field campaigns will be given. Example of potential applications will be discussed.

Range-gated or burst illumination systems have recently drawn a great deal of attention concerning the use for target classification. The development of eye-safe lasers and detectors will make these systems ideal to be combined with thermal imagers for long range targeting at night but also for short range security applications. This presentation will describe performance modelling and simulation of range-gated systems and discuss these together with experimental data.

Detailed 3D environment models for visualization and computer based analyses are important in many defence and homeland security applications, e.g. crisis management, mission planning and rehearsal, damage assessment, etc. The high resolution data from airborne laser radar systems for 3D sensing provide an excellent source of data for obtaining the information needed for many of these models. To utilise the 3D data provided by the laser radar systems however, efficient methods for data processing and environment model construction needs to be developed. In this paper we will present some results on the development of laser data processing methods, including methods for data classification, bare earth extraction, 3D-reconstruction of buildings, and identification of single trees and estimation of their position, height, canopy size and species. We will also show how the results can be used for the construction of detailed 3D environment models for military modelling and simulation applications. The methods use data from discrete return airborne laser radar systems and digital cameras.

Over the years imaging laser radar systems have been developed for both military and civilian (topographic) applications. Among the applications, 3D data is used for environment modeling and object reconstruction and recognition. The data processing methods are mainly developed separately for military or topographic applications, seldom both application areas are in mind. In this paper, an overview of methods from both areas is presented. First, some of the work on ground surface estimation and classification of natural objects, for example trees, is described. Once natural objects have been detected and classified, we review some of the extensive work on reconstruction and recognition of man-made objects. Primarily we address the reconstruction of buildings and recognition of vehicles. Further, some methods for evaluation of measurement systems and algorithms are described. Models of some types of laser radar systems are reviewed, based on both physical and statistical approaches, for analysis and evaluation of measurement systems and algorithms. The combination of methods for reconstruction of natural and man-made objects is also discussed. By combining methods originating from civilian and military applications, we believe that the tools to analyze a whole scene become available. In this paper we show examples where methods from both application fields are used to analyze a scene.

The main purpose of the work presented here is to study the potential for an active imaging system for target recognition at long distances. This work is motivated by the fact that there are a number of outdoor imaging needs where conventional passive electro optical (EO) and infrared (IR) imaging systems are limited due to lack of photons, disturbing background, obscurants or bad weather. With a pulsed illuminating source, several of these problems are overcome. Using a laser for target illumination, target recognition at 10's of km can be achieved. Powerful diode pumped lasers and camera tubes with high spatial and time resolution will make this technique an interesting complement to passive EO imaging. Beside military applications, civilian applications of gated viewing for search and rescue, vehicle enhanced vision and other applications are in progress. To study the performance limitations of gated viewing systems due to camera, optics and the atmosphere an experimental system was developed. Measurements up to 10 km were made. The measurements were taken at the wavelength 532 nm. To extrapolate the results to future system performance at an eye safe wavelength, 1.5 micrometers nm, a theoretical performance model was developed. This model takes into account the camera and atmospheric influence on resolution and image quality, measured as a signal-to-noise-ratio, SNR. The result indicates turbulence influence, in agreement with the modeling. Different techniques were tested for image quality improvement and the best results were obtained by applying several processing techniques to the images. Moreover, the tests showed that turbulence seriously limits the resolution for horizontal paths close to the ground. A tactical system at 1.5 micrometers should have better performance than the used 532 nm in atmospheric-limited applications close to ground level. The potential to use existing laser range finders and the eye safety issue motivates the future use of 1.5 micrometers for gated viewing.