Active imaging can be used for surveillance or target identification at long range and low visibility conditions. Its principle is based on the illumination of a scene with a pulsed laser which is then backscattered to the sensor. The signal to noise ratio and contrast of the object over the background are increased in comparison with passive imaging. Even though, range and field of view (FOV) are limited for a given laser power. A new active imaging system presented here aims at overcoming this limitation. It acquires the entire scene with a high-speed scanning laser illumination focused on a limited region, whereas at each scan the full frame active image is acquired. The whole image is then reconstructed by mosaicking all these successive images. A first evaluation of the performance of this system is conducted by using a direct physical model. This end-to-end model, realistic in terms of turbulence effects (scintillation, beam wandering ...), gives us a sequence of images a synthetic scenes. After presenting this model, a reconstruction method of the total scene is described. And the performances of this new concept are compared to those of a conventional flash active camera by using usual metrics ( SNR, MTF ...). For various mean laser powers, we quantify the gains expected in terms of range and field of view of this new concept.
This paper describes a data collection on passive and active imaging and the preliminary analysis. It is part of an ongoing work on active and passive imaging for target identification using different wavelength bands. We focus on data collection at NIR-SWIR wavelengths but we also include the visible and the thermal region. Active imaging in NIRSWIR will support the passive imaging by eliminating shadows during day-time and allow night operation. Among the applications that are most likely for active multispectral imaging, we focus on long range human target identification. We also study the combination of active and passive sensing. The target scenarios of interest include persons carrying different objects and their associated activities. We investigated laser imaging for target detection and classification up to 1 km assuming that another cueing sensor – passive EO and/or radar – is available for target acquisition and detection. Broadband or multispectral operation will reduce the effects of target speckle and atmospheric turbulence. Longer wavelengths will improve performance in low visibility conditions due to haze, clouds and fog. We are currently performing indoor and outdoor tests to further investigate the target/background phenomena that are emphasized in these wavelengths. We also investigate how these effects can be used for target identification and image fusion. Performed field tests and the results of preliminary data analysis are reported.
The European Defence Agency (EDA) launched the Active Imaging (ACTIM) study to investigate the potential of active
imaging, especially that of spectral laser imaging. The work included a literature survey, the identification of promising
military applications, system analyses, a roadmap and recommendations.
Passive multi- and hyper-spectral imaging allows discriminating between materials. But the measured radiance in the
sensor is difficult to relate to spectral reflectance due to the dependence on e.g. solar angle, clouds, shadows... In turn,
active spectral imaging offers a complete control of the illumination, thus eliminating these effects. In addition it allows
observing details at long ranges, seeing through degraded atmospheric conditions, penetrating obscurants (foliage,
camouflage...) or retrieving polarization information. When 3D, it is suited to producing numerical terrain models and to
performing geometry-based identification. Hence fusing the knowledge of ladar and passive spectral imaging will result
in new capabilities.
We have identified three main application areas for active imaging, and for spectral active imaging in particular: (1) long
range observation for identification, (2) mid-range mapping for reconnaissance, (3) shorter range perception for threat
detection. We present the system analyses that have been performed for confirming the interests, limitations and
requirements of spectral active imaging in these three prioritized applications.
This paper will describe ongoing work from an EDA initiated study on Active Imaging with emphasis of using multi or
broadband spectral lasers and receivers. Present laser based imaging and mapping systems are mostly based on a fixed
frequency lasers. On the other hand great progress has recently occurred in passive multi- and hyperspectral imaging
with applications ranging from environmental monitoring and geology to mapping, military surveillance, and
reconnaissance. Data bases on spectral signatures allow the possibility to discriminate between different materials in the
scene. Present multi- and hyperspectral sensors mainly operate in the visible and short wavelength region (0.4-2.5 μm)
and rely on the solar radiation giving shortcoming due to shadows, clouds, illumination angles and lack of night
operation. Active spectral imaging however will largely overcome these difficulties by a complete control of the
illumination. Active illumination enables spectral night and low-light operation beside a robust way of obtaining
polarization and high resolution 2D/3D information.
Recent development of broadband lasers and advanced imaging 3D focal plane arrays has led to new opportunities for
advanced spectral and polarization imaging with high range resolution. Fusing the knowledge of ladar and passive
spectral imaging will result in new capabilities in the field of
EO-sensing to be shown in the study. We will present an
overview of technology, systems and applications for active spectral imaging and propose future activities in connection
with some prioritized applications.
Proc. SPIE. 7835, Electro-Optical Remote Sensing, Photonic Technologies, and Applications IV
KEYWORDS: Signal to noise ratio, 3D acquisition, Optical properties, Imaging systems, Clouds, 3D modeling, Laser scanners, Bidirectional reflectance transmission function, Optical simulations, 3D image processing
We compare results issued from a numerical model that simulates the point cloud obtained by 3D laser scanning of a
scene and measurements provided by a commercial laser scanner. The model takes into account the temporal and
transverse characteristics of the laser pulse, the propagation through turbulent and scattering atmosphere, the interaction
with the objects of the scene (which have special optical properties: BRDF...) and the characteristics of the opto-electric
detection system. The model derives 4D laser imaging information as temporal laser backscattered intensity (full wave
form) is considered here. Experiments and simulations are performed on targets and scenes in order to test the
performances of such imager under conditions that could be representative of future applications like Sense and Avoid,
Target Recognition and Mapping,...
Laser imaging offers potential for observation, for 3D
terrain-mapping and classification as well as for target
identification, including behind vegetation, camouflage or glass windows, at day and night, and under all-weather
conditions. First generation systems deliver 3D point clouds. The threshold detection is largely affected by the local
opto-geometric characteristics of the objects, leading to inaccuracies in the distances measured, and by partial
occultation, leading to multiple echos. Second generation systems circumvent these limitations by recording the temporal
waveforms received by the system, so that data processing can improve the telemetry and the point cloud better match
the reality. Future algorithms may exploit the full potential of the 4D full-waveform data. Hence, being able to simulate
point-cloud (3D) and full-waveform (4D) laser imaging is key.
We have developped a numerical model for predicting the output data of 3D or 4D laser imagers. The model does
account for the temporal and transverse characteristics of the laser pulse (i.e. of the "laser bullet") emitted by the system,
its propagation through turbulent and scattering atmosphere, its interaction with the objects present in the field of view,
and the characteristics of the optoelectronic reception path of the system.