This PDF file contains the front matter associated with SPIE Proceedings Volume 11160, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.

We investigate a novel quantum based active imaging system for remote sensing that has inherent resistance to hostile detection and jamming. It is an advanced quantum ghost imaging setup, which does not rely on preliminary information on the distances of objects. The photon source of the setup will be suited for standoff detection with illumination of remote objects in the infrared, while retrieving the spatial information in the visible regime with matured silicon technology. Due to inherent randomness of illumination patterns in space and time only the observer is able to distinguish illumination photons from ambient background noise by position- and time-correlation of entangled partner photons.

A laser gated-viewing system primarily provides range-gated 2D images without any range resolution within the range gate. However, it is possible to extract 3D information by the combination of two images with appropriately overlapping range gates. This approach uses the fact that the range-intensity profile can be basically described by the convolution of the temporal functions of the reflected laser pulse and the detector sensitivity. Thus, this profile consists of a rising and falling edge with a plateau region in between. We have previously shown ([1]) how to generate these two required images from only one laser pulse by correlated double sampling realized in the read-out integrated circuit of the gated-viewing camera. Because there is a marginal temporal difference between the capturing times of the reset and signal level images this approach is notably suited for 3D imaging in dynamic scenarios with fast moving objects. The length of the slope of the range-intensity profile limits the distance range in which 3D reconstruction is possible. In another previous work ([2]), we have extended this 3D distance range by refining the original reconstruction algorithm and using an illumination laser with significantly longer pulse duration. The gated-viewing camera that we use for the experiments is sensitive in the short-wave infrared spectral band and has a focal plane array with 640 x 512 avalanche photodiodes with a pixel pitch of 15 μm. In this paper, we experimentally investigate the influence of the temporal detector behavior on the 3D distance range. Increasing the detector response time by reducing the current of the in-pixel capacitive transimpedance amplifier gives a further important extension of the mean slope length of the range-intensity profile by a factor of approximately 3. As an unexpected outcome, the length of the slope depends linearly on signal strength. This dependency has been finally taken into account in an exemplary 3D reconstruction showing reasonable range results with respect to the signal strength.

A novel gated-viewing instrument is presented for vision enhancement in maritime search and rescue applications predominantly under limited visibility conditions at night. The compact device consists of a camera and an eye-safe NIR (near-infrared) illuminator and has a field of view of ≈7° x 6°, which is similar to field glasses. The detection range is 250 m for Lambertian reflectors, but is much larger if clothes with retro-reflectors are worn. A key challenge is the cost effectiveness of the instrument as potential users in the field of maritime search and rescue applications usually suffer from financial limitations. As a result, no image intensifier, but an off-the-shelf CMOS camera in accumulation mode with a reasonable quantum efficiency in the NIR region is used. The active illumination is based on a self-developed illuminator consisting of 7 pulsed vertical-cavity surface-emitting laser (VCSEL) arrays. The mean optical power is 7 W, the center wavelength is λ≈804 nm, and the light pulse width is ≈100 ns at a repetition rate of 345 kHz. Detailed simulations leading to the system design are presented together with respective characterization measurements of the camera and illuminator as well as first test measurements of the complete system.

Small high-resolution lidar systems can be used in a broad range of applications such as object detection, foliage penetration, and positioning. In this study, a scanning lidar was used together with two visual cameras and a low-cost inertial measurement unit to obtain precise positioning in forest environments. Position accuracy better than 0.05 % of the traversed path was obtained with the system. The visual cameras and the inertial measurement unit were used to estimate an approximate trajectory and the lidar data were applied to refine the positioning using high level and low level features extracted from the lidar data. Low level features were characterized by planes and sections of the tree stems, and high level features by whole trees. The system was able to operate without support from satellite navigation data or other positioning support. The results can be applied for navigation in forest environments e.g. for small unmanned aerial vehicles or ground vehicles.

In 2019, the French-German Research Institute of Saint-Louis (ISL) is celebrating its 60th anniversary, but the roots of the institute are going back to the early end of the WWII when a team of German scientists led by Prof. Schardin from the Air Force Technical Academy (Technische Akademie der Luftwaffe) in Berlin-Gatow came in the Upper Rhine to work for the French Army. There, the Prof. Schardin was working in the field of ballistics and was world-wide renowned for his works in high-speed physics. In his early years, as a permanent assistant to the eminent German ballistics Professor Carl Cranz, he developed the famous Cranz-Schardin camera, a revolutionary electro-optical high-speed cinematography method using electric sparks or flash x-rays for illumination and able to work at frame rates over 10⁶ images/second. This technique brought huge improvements in the comprehension of ballistic phenomenon and moreover in high-speed physics.

Since 1945, the LRSL, renamed ISL in 1959, maintained a leading position in the domain of high-speed phenomenon. In the beginning of the 60's, the invention of the laser was a true revolution that permits the emergence of new techniques like holography and interferometric holography. With the introduction of semiconductor lasers, ISL has a leading position on range-gated active imaging and deploys a significant research effort in a new emerging domain: computational imaging which includes scientific thematic such as see around the corner, compressed sensing or imaging with multiple scattered photons.

In this paper the improved Background Oriented Schlieren technique called CBOS (Colored Background Oriented Schlieren) is described and used to reconstruct density fields of three-dimensional flows. The Background Oriented Schlieren technique allows to measure the light deflection caused by density gradients in a compressible flow. For this purpose the distortion of the image of a background pattern observed through the flow is used. In order to increase the performance of the conventional Background Oriented Schlieren technique, the monochromatic background is replaced by a colored dot pattern. The different colors are treated separately using suitable correlation algorithms. Therefore, the precision and the spatial resolution can be highly increased. The CBOS technique is explained and applied to the measurement of the flow field around a free-flight space model. These flow conditions lead to very strong shocks in the front region of the model. Therefore a special arrangement of the different colored dot patterns in the background allows astigmatism in the region with high density gradients to be overcome. An algebraic reconstruction technique (ART), taking into account forward and backward projections, is then used to reconstruct the density field of such flows from CBOS measurements. It could be shown that the accuracy and the spatial resolution of the CBOS technique allows us to obtain a reliable reconstruction of the density field. Especially for complex flows the distribution of the density helps considerably to understand the flow phenomena.

Micro unmanned aerial vehicles (MUAV) have become increasingly popular during the last decade due to their access to a wide consumer market. With the increasing number of MUAV, the unintended and intended misuse by flying close to sensitive areas has risen as a potentially increasing risk. To counter this threat, surveillance systems are under development which will monitor the MUAV flight behavior. In this context, the reliable tracking and prediction of the MUAV flight behavior is crucial to increase the performance of countermeasures. In this paper, we discuss electro-optical computational imaging methods with a focus on the ability to perform a tracking of the three dimensional (3D) flight path. We evaluate the analysis of different imaging methods performed with active laser detection as well as with passive imaging using advanced scenario analysis. In first experimental investigation, we recorded and analyzed image sequences of a MUAV quad-copter flying at low altitude in laboratory and in outdoor scenario. Our results show, that we are able to track the three dimensional flight path with high accuracy and we are able to give a reliable prediction of the MUAV flight behavior within the near future.

The detection of potential threats such as IEDs is essential for the security of military vehicle convoys. We present an image change detection approach that estimates change probabilities in outdoor routes, using a monocular optical camera system. The camera system is part of a multi-sensor system mounted on the lead vehicle of a vehicle convoy, and the estimated change probabilities of each sensor are exploited by a data fusion algorithm. Our change detection approach is based on illumination-invariant image representations and is thus insensitive to illumination differences (e.g., due to shadows), and detects potential changes of multiple sizes. We introduce a temporal weighting scheme based on intra-sequence homography coherence to reduce false detections due to the parallax effect. For the experimental evaluation we have used image sequences acquired on outdoor routes which include different types of changes, strong illumination differences, and scenes with parallax.

Atmospheric turbulence degrades focal-plane-array (FPA) camera images because of intensity fluctuation, distortion, and blur, notably for long-range applications. Compressive sensing (CS) imaging techniques use series of measurements whose temporal and spatial characteristics differ from those of conventional FPA systems. The paper discusses how turbulence affects the SWIR image quality using both CS techniques and a conventional InGaAs FPA camera.

Until the nineties, the domain of terahertz waves (THz), which extends between 100 GHz and a few tens of THz in the electromagnetic spectrum, was difficult to access. This situation radically changed with the advent of the THz time domain spectroscopy. Terahertz spectroscopy has indeed become an important tool for studying molecules in the condensed phase. In particular, many chemical, biological, radiological, nuclear and explosive agents exhibit characteristic spectral features in this frequency region, which has thus a strong potential for security applications. However, because a current challenge for atmospheric THz spectroscopy is to overcome the high absorption of ambient humidity that can extinguish a THz signal over 1-m-long distances, there is a growing demand for intense THz sources. Also an important constraint is to be able to cover large spectral bandwidths, in order to collect many molecular signatures. Whereas conventional THz systems usually offer a narrow bandwidth limited to a few THz only, a terahertz emitter based on an air plasma created by femtosecond laser pulses can supply broad bandwidths above 20 THz. Exploiting this technique is the core of the project named ALTESSE (“Air Laser-based TErahertz SpectroScopy of Explosives”), the main objective of which is to test a THz spectroscopy using a plasma source created by means of optical pulses coupling a fundamental and its second harmonic in the air. Initially, the scientific tasks of the ALTESSE project aimed at: (i) Optimizing THz emission in a spectral window extending up to 50 THz using femtosecond pulses in either focused or filamentary propagation, (ii) Carrying out THz spectroscopy of materials by the Air-Biased Coherent Detection (ABCD) method, (iii) Examining the amplification of the detected THz signal at long laser wavelengths (1.5 - 2 µm) compared to that delivered by fundamental 800-nm pulses, (iv) Performing the THz/ABCD spectroscopy of explosives, in transmission then in reflection, over distances far away from the laser source, (v) Modeling numerically the nonlinear propagation of intense laser pulses in the air together with the emitted THz radiation, in support to the experiments. After three years of intensive work, the major highlights of ALTESSE which will be presented during the talk are: (i) The acquisition of spectra extending up to 60 THz and exploited to directly identify solid powders. Systematic comparisons between the measured THz spectra and ab-initio simulations allowed us to countercheck the molecular absorption coefficients and distinguish between the inter- and intra-molecular motions of the probed samples. (ii) The strong increase, by a factor close to 10, in the THz energy yield measured for laser fundamental wavelengths operating in the mid-infrared, (iii) The first spectral measurements of explosives capturing molecular fingerprints up to 20-THz bandwidths and obtained at long distances (15 m) from the laser source, (iv) The first compelling comparisons of absorption spectra both in transmission or reflection geometries, (v) The optimization of a unidirectional propagation code in terms of computational performance, completed by the incorporation of the HITRAN database to describe absorption of air in a broad spectral range > 10 µm.

The Laser Doppler Vibrometry (LDV) can continuously measure the speed, acceleration and other parameters of the micro-vibration target. However, with the increase of the surface roughness and the decrease of the diffuse reflectance of the measured object, or the increase of the measurement distance, the laser echo energy will decrease rapidly according to the basic theory of optical propagation. The typical laser doppler vibration measurement technology is based on the principle of two-beam heterodyne interference. However, due to the limitation of the optical device, the third beam, namely the system stray light, from multiple optical devices in the optical path, is inevitable, and has a certain intensity and phase distribution. The system stray light will seriously nonlinear suppress the vibration phase signal of the micro-vibration target. To reduce the system stray light, methods like surface coating, tilt design and curved lens design are employed, but it greatly affects the detection signal-to-noise ratio and micro-vibration detection capability of the system. In this paper, a method based on four-wave hybrid interference to eliminate stray light is proposed. A calibration laser beam is added to the original interference optical path. With measurement on the system stray light, the laser external modulation is used to make the intensity, frequency and phase of the calibration beam vary with the parameters of the system stray light. The influence of stray light in the system can be theoretically eliminated if the intensity and frequency of the calibration beam is consistent with the stray light, and the initial phase difference is π.

Laser Emission of a blue ECDL at a single transverse mode (TEM₀₀) was confirmed and Raman spectra of O₂ and N₂ in the atmosphere were acquired using the intra-cavity beam of the ECDL. The center wavelength of the diode laser is 416 nm in the blue region of the visible spectrum. A Fabry-Perot resonator composed of two high reflectivity mirrors was used as an external cavity and a fraction of the intra-cavity beam was feedbacked to the anti-reflection coated facet of the diode laser. The optical feedback makes it possible that the diode laser oscillates stably at a specific frequency in the gain band of the laser diode chip. This configuration includes only four optics and has potential to be utilized as a compact Raman gas sensor that can be mounted on drones or the other machines. The detection limits in 1 second integration time were estimated to be lower than 100 ppm in the case of N₂ gas and 200 ppm in O₂, respectively.

Learning an object category from only a few samples is generally not adequate for correct classification. One needs many training samples to obtain a classifier that generalizes well and that has sufficient success rates. However, in several applications, including target detection from Ground Penetrated Radar (GPR) data, collecting many annotated data is not always possible. In a GPR data collection, the images formed show a nonlinear dependence on the soil properties such as the permeability and permittivity. Therefore, even if enough training data were available to train a good classifier for one soil type (such as dry sand); the success of this classifier does not translate well if the soil type is changed (say, to wet sand).

In this work, we propose a multi-model knowledge transfer (KT) framework to detect a picnic tube buried in different media using GPR. In the proposed method, scale invariant feature transform (SIFT) features are extracted from GPR data. Then, least-square support vector machine (LS-SVM) classifiers are trained for three soil types (i.e. dry sand, dry sandstone, and wet sandstone) where there is ample data available. Then, adaptive LS-SVM is used to train a classifier that detects the target picnic tube in wet sand from where there is only scarcely available training data. We show that (i) knowledge transfer from multiple sources (i.e. multiple types of sand) generates better results than single source transfer; and (ii) as little as 3 training data from the unknown source increases the detection rates by 10% for single KT, and 4% for multiple KT.

We are developing the remote measurement system for detecting harmful substances such as nitrogen dioxide and chemical materials using the resonance Raman scattering effect. Although the most remote measurement systems were designed to use the light from ultraviolet to visible wavelengths region, the characteristic Raman spectra of complex materials were observed in deep-ultraviolet (DUV) wavelengths region. The development of the standoff detection system by measuring the DUV light contributes to identify the various materials remotely. In this study, the design results of the Raman scattering light receiving equipment (light receiving system) consisting of telescope, relay optical system and spectrometer were considered. The optical design of the light receiving system was performed based on the estimation model of the signal-to-noise ratio (SNR) and the ray tracing method. The important parameters (the attenuation of the laser pulse and Raman light in the atmosphere, the amplification factor of the scattering cross section in DUV wavelength region etc.) are included in the model, and SNR of the Raman spectrum can be evaluated by changing each parameter. The estimation results suggest that SNR depends strongly on the reflectance of mirror and the amplification factor of the scattering cross section in DUV wavelength region. The durability test of the mirror has been performed to evaluate the use in outdoor. The results show that the mirrors with high reflectance in DUV wavelength region have enough tolerance to the temperature change and the scratch.

This paper presents the Time-Correlated Single-Photon Counting (TCSPC) technique applied to underwater environments in order to reconstruct three-dimensional scenes. Two different transceiver systems approaches are described. The first transceiver comprised a single-pixel monostatic scanning unit, which used a fiber-coupled silicon single-photon avalanche diode (SPAD) detector, and a fiber-coupled supercontinuum laser source used in conjunction with an acousto-optic tunable filter (AOTF) for wavelength selection. The experiments were performed using the supercontinuum pulsed laser source operating at a repetition rate of 19.5 MHz, fiber coupled to the AOTF in order to select one operational wavelength, tuned for best performance for the level of scattering of the particular underwater environment. Laboratory-based experiments were performed using average optical powers of less than 1 mW and depth profiles were acquired at up to 8 attenuation lengths between the transceiver and target. The second transceiver system was based on a complementary metal-oxide semiconductor (CMOS) SPAD detector array in a bistatic configuration. It comprised an array of 192 × 128 SPAD detectors, with each detector having an integrated time to digital converter, and a laser diode operating at a wavelength of 670 nm, a repetition rate of 40 MHz, and average optical power up to 9 mW. The experiments demonstrated the recovery of intensity and depth profiles associated with moving targets at up to 4 attenuation lengths. Using data from both systems, various image processing techniques were investigated to reconstruct target depth and intensity profiles in highly scattering underwater environments.

This paper investigates optical camera performance in natural atmospheres with low visibility including fog, mist, haze, and precipitation. Cameras that operated in most optical wavelengths windows were tested: VIS, NIR (active GV), SWIR, MWIR, and LWIR. An eye safe lidar was also included to estimate transmission in the SWIR region. The measurements were made against contrast board targets placed at 0.5, 1, and 2 km from the sensors. The targets were heated during parts of the campaign to create a thermal contrast, which was relevant for the infrared images. For each image, the contrast, PSF, and MTF were calculated with an in-house developed analysis tool. The parameters were plotted against visibility for various weather conditions. Long wavelengths have better transmittance through haze and small particle fog. In rain, snow or dense fog, where the particles are large, the transmittance is rather independent of the wavelength as is well documented elsewhere. In haze a SWIR camera can be expected to perform better than a visual (at least as good) but since the performance of the cameras was partly masked by different updates (and quality) this does not appear quite clear in the measurement data. The active GV-camera, operating in NIR gave the best results during low daylight conditions. However, the daylight background dominated over the laser illumination during day operation. In addition to the cameras, LIDAR measurements were made to investigate how the atmospheric attenuation is estimated using a single ended measurement sensor. The LIDAR data was used to calculate the atmospheric backscatter maximum and integrated backscatter and backscatter slope. These parameters in general correlated well with the visibility readings from the weather station.

Satellite remote sensing, which has the ability of searching large areas, plays an important role in the emergency rescue of natural disasters. In this paper, based on the spectral characteristics of different substances, a multi-color and multi feature target identification measurement for target detection is proposed. Firstly, the optimized selection is carried out the spectral section selection, which reduces the data volume of the system and improves the signal-to-noise ratio of the system. Secondly, in terms of information acquisition, multi-dimensional information (space, spectrum, motion, radiation and background) of spatial moving targets can be detected comprehensively through satellite motion, and the recognition probability of detection can be improved through multi-color and multi-feature comparison. At the same time, using the bifocal length imaging system, using imaging system, using the long focal length and short focal length two optical channel common aperture technology, through the reasonable choice of system structure and optimization design method, reduce the system volume, reduce the weight of the system, so as to achieve based on spectrum- space multiplexing bifocal length imaging system miniaturization design. Finally, the new combined detection mode is combined with parallel processing algorithm to realize fast search and recognition.

The main aim of this research is to examine the interpretation possibilities of images from the constellation of Sentinel satellites, i.e. Sentinel-1, and Sentinel-2, and to assess their suitability for the analysis of objects from category 01 Airfields according to the standardization document STANAG 3596. In the presented research analysis of chosen airbases in Europe was presented. In the course of the research, image data, both electro-optical and microwave data, were pre-processed appropriately, i.e. radiometric and geometric corrections, and filtrations were applied, in order to finally analyze and evaluate interpretations. In the research radar images in the C band, which are recorded by sensors placed on the satellites of the Sentinel-1 constellation, as well as electro-optical images acquired by multispectral sensors placed on the satellites of the Sentinel-2 constellation, were used. In addition, the fusion of microwave and electro-optical data was made to verify the usefulness of data integration for reconnaissance purposes. Then the Sentinel data was combined with high-spatial-resolution data from Google Earth, in order to improve the quality and to verify the usefulness of the integration of multitemporal data in the process of imagery interpretation and object detection. The analysis consisted of assessing the interpretability of images by the possibility of distinguishing specific objects on it. The results were next evaluated using high- spatial resolution open-source imagery data from Google Earth, and open source GIS data. The conducted analyses showed that the use of Sentinel image data in recognizing objects at airports seems to be justified due to their availability, although these should be objects of considerable size. In order to detect smaller objects, multi-resolution data integration should be applied, as showed in the research.

A ladar can acquire a dense set of 3D coordinates of a scene, a so-called point cloud, in sub-second time from ranges of several kilometers. This paper presents algorithms for segmenting a point cloud into meaningful classes of similar objects, and for identifying a specific object within its respective class. The segmentation algorithm incorporates several low level features derived from surface patches of objects from different classes and the interphases between them. On a mathematical level, it partitions the point cloud in a way that optimally balances these considerations by finding the global minimizer to a so-called variational problem over a graph, utilizing recently published results on general high-dimensional data classification. The subsequent recognition step makes use of higher level features for identifying a particular object, represented by a 3D model, among the respective class of segmented objects. It measures similarity of shape between the 3D model and each observed object, considering them as two pieces in a puzzle. The simulated shadow and visibility of the 3D model are measured for consistency with the point cloud shadows. The recognition step is also formulated as an optimization problem and solved by mathematically well-founded techniques. Results demonstrate that point clouds acquired in maritime, urban and rural scenes can be segmented into meaningful object classes and that individual vessels can be identified with a high confidence.

The space-based detection system is gradually indispensable into situational awareness systems such as near-celestial bodies and space debris because it has the characteristics of being unrestricted by factors such as climate and geography, and can be observed over a long period of time. At present, the international on-orbit detection of near-celestial bodies and space debris is widespread, that is, the lack of measurement system development and design means, and the lack of data sources. The paper focuses on the principle of space debris on-orbit imaging. Three image information extraction methods and two relative attitude determination methods are proposed. The simulation algorithm of space debris on-orbit imaging is constructed, and the feasibility of the simulation scheme is used. Performance, accuracy, data processing efficiency and other performance were evaluated. The results of the paper will contribute to the early analysis and assessment of space debris.

Range-gated viewing systems, which were at first used for object observation under poor visibility conditions, are used now also to determine distances to objects and obtain 3D images. A number of methods were suggested to determine distance. For instruments operating in real time, it is important to use fast methods. Range-intensity correlation methods are such methods because they use only two images. The methods work with rectangular-shaped illumination pulses and rectangular gate pulse shape. However, real pulses may differ from the rectangular ones that may introduce significant error into the distance measurement. To avoid the error one has to use a calibration dependence of the distance on the signal. The calibration curve depends not only on time profiles of the pulse and gate, but also on the gate duration and the difference between delay times of two images. Experimental search for optimal measurement condition through trial and error is a rather cumbersome problem. Therefore, we used numerical simulation and analytical estimates. The pulse time profile could be taken arbitrary. The gate time profile was assumed to be rectangular. The ratio of the energies received by the same pixel in two images depending on distance is used to build calibration curve. With given pulse shape, by varying gate time and delay time difference, we obtain calibration curves with different slope, different position on the distance scale and with different range of the determined distances. It appeared that the greater the slope of the curve, the narrower the range of measured distances and the lower the pixel energy. The conditions were found to get monotonous calibration curve with the highest possible return signal from all points on the distance determination interval.

We report on comparative properties in deep UV region of two types of tunable deep UV lasers for applications in resonance Raman lidar. The first type of the tunable deep UV laser is based on frequency doubling of the output of an optical parametric oscillator (OPO) pumped by the third harmonics of a Q-Switched Nd-YAG laser. The second one is based on the generation of the third and fourth harmonics of a Ti:sapphire (Ti:S) laser, which is pumped by the second harmonics of a Q-Switched Nd-YAG laser. Also, we demonstrated the resonance Raman spectroscopic measurements of SO2 gas using these tunable deep UV lasers.

In this study, a hydrogen leak simulation apparatus was made, and then hydrogen diffusion behavior in the ground and in the atmosphere was measured, in order to clarify how to detect leaked hydrogen or respond after the leakage. The hydrogen leak simulation apparatus was composed of an underground simulation tank of 7 m in diameter and 1.35 m in depth, and an atmospheric simulation tank of 8 m wide x 8 m depth x 3 m height. The pipe was set in the underground simulation tank at the burial depth 1.2 m. A pinhole of 1 mm in diameter was made on the buried pipe, and the diffusion behavior of hydrogen gas released from the pinhole was measured. For the diffusion behavior in the ground, the concentration distribution was measured by 40 sensors buried in decomposed granite soil and crushed stone. For the diffusion behavior in the atmosphere, the concentration distribution was measured by Raman imaging. The hydrogen gas passing through the asphalt and diffusing into the atmosphere was irradiated with the third harmonic generation from the Nd: YAG laser, and the Raman scattering light was visualized by a high sensitivity camera. The characteristics of the hydrogen gas diffusion behavior were found. In addition, the hydrogen diffusion behavior was reproduced by simulation analysis, and compared with the experimental results. As a result, it is confirmed that the simulation of the diffusion behavior in the ground and in the atmosphere is valid even under the condition with pavement.