Pierre Andersson

Long-range three-dimensional imaging using range-gated laser radar images

An approach to long-range 3-D imaging using laser illuminated range-gated viewing is presented. The basis for 3-D scene reconstruction is an image sequence acquired using a sliding gate delay time. Two different methods are suggested, and algorithm performance is investigated through Monte Carlo simulations using a simplified system and imaging model. Assumptions are justified by comparison with real measurements at range of 0.8 to 7.2 km. It is shown that range resolution and precision become significantly better than system design parameters such as gate length, gate transition length, and gate step length. The presented reconstruction methods thus enable high-precision range imaging using available long-range gated imaging systems.

Overview of range gated imaging at FOI

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.

Performance of 3D laser radar through vegetation and camouflage

One of the more exciting capabilities foreseen for future 3-D imaging laser radars is to see through vegetation and camouflage nettings. We have used ground based and airborne scanning laser radars to collect data of various types of terrain and vegetation. On some occasions reference targets were used to collect data on reflectivity and to evaluate penetration. The data contains reflectivity and range distributions and were collected at 1.5 and 1.06 μm wavelength with range accuracies in the 1-10 cm range. The seasonal variations for different types of vegetation have been studied. A preliminary evaluation of part of the data set was recently presented at another SPIE conference. Since then the data have been analyzed in more detail with emphasis on testing algorithms and future system performance by simulation of different sensors and scenarios. Evaluation methods will be discussed and some examples of data sets will be presented.

Image quality for range-gated systems during different ranges atmospheric conditions

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 like reading of signs and licence plates, looking into cars and buildings etc. Examples of imagery collected for different range and atmospheric conditions will be presented and discussed with respect to image quality and processing techniques.

Methods for recognition of natural and man-made objects using laser radar data

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.

Registration and change detection techniques using 3D laser radar data from natural environments

In this paper, we present techniques related to registration and change detection using 3D laser radar data. First, an experimental evaluation of a number of registration techniques based on the Iterative Closest Point algorithm is presented. As an extension, an approach for removing noisy points prior to the registration process by keypoint detection is also proposed. Since the success of accurate registration is typically dependent on a satisfactorily accurate starting estimate, coarse registration is an important functionality. We address this problem by proposing an approach for coarse 2D registration, which is based on detecting vertical structures (e.g. trees) in the point sets and then finding the transformation that gives the best alignment. Furthermore, a change detection approach based on voxelization of the registered data sets is presented. The 3D space is partitioned into a cell grid and a number of features for each cell are computed. Cells for which features have changed significantly (statistical outliers) then correspond to significant changes.

Performance modeling and simulation of range-gated imaging systems

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.

Aided target recognition from 3D laser radar data

This paper presents our ongoing research activities on target recognition from data generated by 3-D imaging laser radar. In particular, we focus on future full flash imaging 3-D sensors. Several techniques for laser range imaging are applied for modelling and simulation of data from this kind of 3-D sensor systems. Firstly, data from an experimental gated viewing system is used. Processed data from this system is useful in assisting an operator in the target recognition task. Our recent work on target identification at long ranges, using range data from the gated viewing system, provides techniques to handle turbulence, platform motion and illumination variances from scintillation and speckle noise. Moreover, the range data is expanded into 3-D by using a gating technique that provides reconstruction of the target surface structure. This is shown at distances out to 7 km. Secondly, 3-D target data is achieved at short ranges by using different scanning laser radar systems. This provides high-resolution 3-D data from scanning a target from one single view. However, several scans from multiple viewing angles can also quite easily be merged for more detailed target representations. This is, for example, very useful for recognizing targets in vegetation. Hereby, we achieve simulated 3-D sensor data from both short and long ranges (100 meters out to 7 km) at various spatial resolutions. Thirdly, real data from the 3-D flash imaging system by US Air Force Research Lab (AFRL/SNJM), Wright Patterson Air Force Base, has recently been made available to FOI and also used as input in the development of aided target recognition methods. High-resolution 3-D target models are used in the identification process and compared to the 3-D target data (point cloud) from the various laser radar systems. Finally, we give some examples from our work that clearly show that future 3-D laser radar systems in cooperation with signal- and image analysis techniques have a great potential in the non-cooperative target recognition task and will provide several new and interesting capabilities, for example, to reveal targets hidden in vegetation.

Coordinated multi-wavelength laser system propagation experiments

Atmospheric propagation degradation effects including attenuation, aerosol scattering and turbulence have a great impact on the performance of optical systems. Relevant military optical systems include active and passive imaging for target recognition, free-space optical communication and DIRCM/EOCM. This paper will report on experimental work including measurement of retro signals at 1.5 and in the 3-5 μm wavelength regions for evaluation of retro communication links and DIRCM performance. Imaging experiments using a range-gated system both in the active and passive mode at 1.5 μm, will also be carried along the same paths. A dedicated target box and test targets have been fabricated for mounting on a mast at 8 km from our laboratory. The box contains reflectors and receivers in different slots each of which can be opened by a telephone call. A heated target on top simulates a point target in the IR region. The test targets are aimed for the range-gated imaging system. Preliminary experimental data will be presented and discussed.

Multi-optical mine detection: results from a field trial

As a part of the Swedish mine detection project MOMS, an initial field trial was conducted at the Swedish EOD and Demining Centre (SWEDEC). The purpose was to collect data on surface-laid mines, UXO, submunitions, IEDs, and background with a variety of optical sensors, for further use in the project. Three terrain types were covered: forest, gravel road, and an area which had recovered after total removal of all vegetation some years before. The sensors used in the field trial included UV, VIS, and NIR sensors as well as thermal, multi-spectral, and hyper-spectral sensors, 3-D laser radar and polarization sensors. Some of the sensors were mounted on an aerial work platform, while others were placed on tripods on the ground. This paper describes the field trial and the presents some initial results obtained from the subsequent analysis.