Optical Space Domain Awareness (SDA) aims to provide high-quality angular (and possibly spectral/polarimetric) information on LEO and GEO satellites for object characterization and identification. In terms of spatial resolution, the goal is to achieve decimetric resolution for low-Earth orbit and decametric resolution for geostationary orbit (in order to monitor the satellites' immediate environment). This ambitious objective can only be achieved by combining a large telescope, a dedicated AO system optimized for the specific characteristics of SDA, differential imaging capabilities and post-processing techniques ranging from Point Spread Function estimation to data fusion, including multi-frame deconvolution. We will present an overview of the key ingredients required to achieve an efficient and operational system and the status of ONERA's new project called PROVIDENCE. It is based on a 2.5m adaptive optics telescope optimized for SDA activities. It will be installed at Observatoire de Haute Provence (in south of France) and should see its first light at the end of 2028.
To address the issues of maritime border surveillance or long range UAV identification, we develop two laser imagers (a 2D and a 3D system) with long range (LR) capacities to improve significantly the performances in terms of scope of monitoring and persistence of functions (e.g. H24, degraded visibility...). These systems are based on a new generation of focal plane arrays (FPA) with Avalanche PhotoDiode (APD) and are combined with high-performance image processing ("real-time") devoted to superresolution or tracking. In this paper, we first present the results of several maritime surveillance or Counter- Unmanned Aircraft System (C-UAS) demonstrations respectively conducted on a coastal site and a sensitive area. Comparisons between passive and active sensors are shown. The measurements obtained on various maritime targets are completed by end to end modelling in order to assess the systems performances in various atmospheric environments.
In this paper, we show the feasibility and the benefit to use a Geiger-mode Avalanche Photo-Diode (GmAPD) array for long range detection, up to several kilometers. A simulation of a Geiger detection sensor is described, which is a part of our end-to-end laser simulator, to generate simulated 3D laser images from synthetic scenes. Resulting 3D point clouds have been compared to experimental acquisitions, performed with our GmAPD 3D camera on similar scenarios. An operational case of long range detection is presented: a copper cable outstretched above the ground, 1 kilometer away the experimental system and with a horizontal line-of-sight (LOS). The detection of such a small object from long distance observation strongly suggests that GmAPD focal plane arrays could be easily used for real-time 3D mapping or surveillance applications from airborne platforms, with good spatial and temporal resolutions.
This paper addresses the problem of critical operations in Degraded Visual Environment (DVE). DVE usually refer when the perception of a pilot is degraded by environmental factors, including the presence of obscurants from bad weather (e.g. fog, rain, snow) or accidental events (e.g. brownout, whiteout, smoke). Critical operations in DVE are a growing field of research as it is a cause of numerous fatal accidents for operational forces. Due to the lack of efficient sources and sensors in the Terahertz (THz) region, this domain has remained an unexplored part of the electromagnetic spectrum. Recently, the potential use of sub-Terahertz waves has been proposed to see through dense clouds of obscurants (e.g. sand, smoke) in DVE conditions. In order to conduct a performance evaluation of sub-Terahertz systems, several sub-terahertz systems (e.g. bolometer-array cameras, liquid helium cooled bolometers) were operated in artificial controlled DVE conditions at ONERA facilities. The purpose of this paper is to report field experiments results in controlled DVE conditions: attenuation measurements from 400 GHz to 700 GHz with a performance evaluation of different sub-Terahertz systems are presented.
In the past few decades, laser imaging has demonstrated its potential in delivering accurate range images of objects or scenes, even at long range or under bad weather conditions (rain, fog, day and night vision). We note great improvements in the conception and development of single and multi infrared sensors, concerning embedability, circuitry reading capacity, or pixel resolution and sensitivity, allowing a wide diversity of applications (i.e. enhanced vision, long distance target detection and reconnaissance, 3D DSM generation). Unfortunately, it is often difficult to dispose of all the instruments to compare their performance for a given application. Laser imaging simulation has shown to be an interesting alternative to acquire real data, offering a higher flexibility to perform this sensors comparison, plus being time and cost efficient. In this paper, we present a 3D laser imaging end-to-end simulator using a focal plane array with Geiger mode detection, named LANGDOC. This work aims to highlight the interest and capability of this new generation of photo-diodes arrays, especially for airborne mapping and surveillance of high risk areas.
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.
A DIAL instrument on a moving platform is seen as a valuable remote sensing component in a sensor network for area monitoring, targeting sites involved in unauthorised explosive manufacturing. Such instrument will perform the area mapping of the vapour concentration of key substances, known to be used as precursors in explosive fabrication, such as acetone and nitromethane. The IR spectra of acetone and nitromethane vapours have been defined from available spectroscopy databases and from laboratory measurements as showing optimal spectral band for the DIAL operation in the spectral range of 3.0 μm - 3.5 μm. The DIAL operation has been numerically simulated, with inputs based on the HITRAN database, the U.S. Standard Atmosphere and aerosol simulation software package OPAC. A combination of OPO and OPA has been chosen as a transmitter, where the idler wavelength is used for probing, with wavelength tuning in sequence. A scanner mounted on top of the coaxially aligned laser and receiver, is capable of covering almost 360 degrees horizontally and ±30 degrees vertically. The detection is performed by a photovoltaic photodiode with 4-stage cooling, with a signal digitalisation having 14 bit amplitude resolution and 125 Ms/s sampling rate. Here we present the development and the first test of the DIAL instrument.
KEYWORDS: 3D modeling, Imaging systems, Fiber optic gyroscopes, Sensors, Atmospheric propagation, Air contamination, 3D image processing, Backscatter, Systems modeling, 3D acquisition
Onera, the French Aerospace Lab, develops and models 2D and 3D active imaging systems to understand the relevant
physical phenomena impacting on their performances. As a consequence, efforts have been done both on the propagation
of a pulse through the atmosphere (scintillation and turbulence effects) and, on target geometries and their surface
properties (radiometric and speckle effects). But these imaging systems must operate at night in all ambient illuminations
and weather conditions in order to perform the strategic surveillance of the environment for various worldwide
operations or to perform the enhanced navigation of an aircraft (A/C). Onera has implemented codes for 2D and 3D laser
imaging systems. As we aim to image a scene even in the presence of rain, snow, fog or haze, Onera introduces such
meteorological effects in these numerical models and compares simulated images with measurements provided by
commercial imaging systems.
Recent innovations in Supercontinuum or white laser sources provide a very useful tool to probe nanomaterials
physical and optical properties. Onera, The French Aerospace Lab, has developed a fast, in-line and
comprehensive optical characterization method. From the combination of hyperspectral, polarized and angular
measurements, physical properties of dense nanomaterials are to be retrieved. Based on achieved results, hyperspectral
polarized scattering properties are discussed depending on microphysical properties. This technique is
applied to a wide range of nanomaterials in suspensions: polymer, metal-oxide or metallic nanoparticles. It can
be applied in various fields as chemical control, defence, atmospheric studies or aeronautical industry.
Recent developments of active imaging and remote sensing systems in security and defence community require
comprehensive optical characterizations of man-made targets. Optical signature analysis of various targets
implies a better and comprehensive understanding of reflectance properties such as Bidirectional Reflectance
Distribution Function (BRDF) and Directional Hemispherical Reflectance (DHR). Measurements and modeling
of optical signatures are valuable for target classification and identification. Onera, the French Aerospace Lab,
has developed an original optical instrument to measure hyperspectral polarized BRDF. Measurements are
carried out on various targets to provide relevant data to simulate actual and future active imaging devices.
This paper reviews the design of the instrument and its hyperspectral calibration procedure in details. A
new specific tensorial hyperspectral reflectance framework is introduced. Experimental results for reference
Lambertian targets and airport targets are presented to illustrate the instrument capacities. A large optical
properties database is build from these measurements for defence, security and industrial needs.
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.
Using laser imaging systems to represent 3-D scene becomes a referent prospective technology in the areas of guidance and
navigation. Measurements with high spatial resolution for significant range can be achieved, even in degraded visibility
conditions such as the Brown-White Out, rain, fog, sandstorms... Moreover, this technology is well suited for assisted
perception tasks (access to 3D information) and obstacle detection (telemetry of small objects). For airborne applications, it is
very complementary to conventional enhanced vision systems such as Forward Looking Infrared (FLIR) and millimeter wave
radar to provide images of land in environments with limited visibility. It also offers a 3D mapping of land or a single location
in relation to the environment, which means alone or coupled with others, can realign and secure real-time database of
information used such in a synthetic vision system (SVS). The objective of the work is to assess the impact of degraded
visibility conditions on the laser radiometric propagation of a 3D laser scanner as they directly influence the performance of the
ladar system [1].
Onera, the French Aerospace Lab, develops and models active imaging systems to understand the relevant physical
phenomena impacting on their performances. As a consequence, efforts have been done both on the propagation of a
pulse through the atmosphere (scintillation and turbulence effects) and, on target geometries and their surface properties
(radiometric and speckle effects). But these imaging systems must operate at night in all ambient illuminations and
weather conditions in order to perform the strategic surveillance of the environment for various worldwide operations or
to perform the enhanced navigation of an aircraft. Onera has implemented codes for 2D and 3D laser imaging systems.
As we aim to image a scene even in the presence of rain, snow, fog or haze, Onera introduces such meteorological
effects in these numerical models and compares simulated images with measurements provided by commercial imaging
systems.
KEYWORDS: Imaging systems, Clouds, 3D acquisition, 3D modeling, Optical simulations, Signal to noise ratio, Laser scanners, 3D image processing, Optical properties, Bidirectional reflectance transmission function
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,...
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.
Onera, The French Aerospace Lab, has developed an active burst illumination imaging system with a short time gating.
This imaging device is used to obtain a passive or an active image of a small volume of the illuminated scene. To better
understand and evaluate the relevant physical phenomena (scintillation, speckle...) impacting on the performance on
burst illumination imaging system, Onera has implemented a code (PIAF). The aim of this paper is to describe the model
and to present some results. Efforts have done on 3D target geometries and surface properties. We analyze each
contribution like the incoherent solar field or the incident laser field. We adapt classical and physical models for light
reflection. Speckle contributions are also treated using data bases generated by an Onera tool.
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.
Laser Gated Imaging is a unique camera technology. It provides long-range night vision in complete darkness as well as
in degraded weather conditions, such as rain, fog and haze. Burst illumination laser (BIL) imaging combines an active
laser illumination with time gating (or range gating) camera. For these reasons, BIL imaging has become increasingly
important in Defense and security applications. In an associated paper [01], we present a model (PIAF) developed to
evaluate the relevant physical phenomena (scintillation, speckle...) impacting on the BIL imaging. This paper presents
preliminary experimental results and comparisons with PIAF simulations.
Optical density measurement is a very powerful tool to characterize particle size and physical property of scattering
media such as sprays and engine injection. The major difficulty of such a measurement is the tremendous amount of
scattered light: for such media, the optical density can be greater than 10. The goal of this work is to develop a new
experimental tool, based on femtosecond laser technology in order to isolate (spatially and temporally) a very limited
amount of non scattered transmitted light, and to measure the extinction of the media.
We collect the transmitted light and we use an optical Kerr gating. This technique is very powerful to determine the time
of flight of every photon in the scattering media. By fine-tuning the optical parameter of the setup, we have been able to
selectively increase the gating efficiency of the ballistic part vs the diffusive part of the collected light.
Furthermore, spectral tunability of amplified femtosecond laser system is straightforward. As a result, it has been
possible to measure the extinction spectra of a model diffused media (SiO2 particle in water), and to determine the
particle size distribution after inversion method.
The aim of this work is to contribute to a better determination of the optical parameters for dense scattering media. We
study the interaction of femtosecond polarized light pulse with a scattering medium considering Monte Carlo simulation.
The Monte Carlo scheme is based on temporal photon tracking, including a pseudo Monte Carlo approximation
associated to two small detectors in forward and backward directions. The statistical scattering properties are derived
from temporal phase matrices, which are evaluated through a scanning of frequency associated to the Lorenz-Mie theory.
We specially focused our attention on solid rocket motor modelling. In such scattering medium, large optical thickness,
various bimodal particle size distributions and concentration gradients could be observed. Moreover, such media consists
in a suspension of big particles (typically 100 &mgr;m diameter). The understanding of the scattering process of such particles
needs the introduction of Debye modes. We will explain the contribution of these modes and give an example with a
numerical application.
Several French research laboratories set up goniometers allowing BRDF measurements at different laser wavelengths in the infrared. On the effor of the Delegation Generale de l'Armement (DGA/STTC), a round robin set of painted targets BRDF measurements was undertaken, under the ONERA expertise. The laboratories participating in this round robin were the Aerospatiale Matra CCR Suresnes, The IPN SMA-Virgo Lyon, the Institut Fresnel Marseille, and the CEA DAM CESTA Le Barp. The goniometers of the four laboratories are firstly described. The targets studied are seven 5cm diameter painted disks of aluminum or steel, a spectralon reference sample, and a sandpaper sample. We have first demonstrated that the pollution of painted targets with dust has a very weak influence on the BRDF. Before and after each measurement series, the directional-hemispherical reflectance of the samples was measured at ONERA. The measurements have been achieved according to a protocol specifying the sample position and laser probe size. Chosen wavelengths for the inter-comparison are 1.064 micrometers . For both wavelengths, the characteristics of the different goniometers are compared in term of noise and repeatability. The difference between the painted targets BRDF measured with the various devices are relatively limited at 1.06 micrometers , and mainly induced by speckle. More important differences are obtained at 10.6 micrometers , particularly for a BRDF measurement device using an absolute calibration method. In order to explain these differences, few hypotheses are advanced. Information on the absolute accuracy is obtained by the comparison of the measured directional-hemispherical reflectance and the one computed from BRDF measurements.
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