This PDF file contains the front matter associated with SPIE Proceedings Volume 12737, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Infrared (IR) sensors and photodetector arrays are employed in various imaging applications (such as night vision), remote temperature measurement, and chemical analysis. These applications are in space and environmental sensing, transport, health and medicine, safety, security, defense, industry, agriculture, etc. Optical chemical analysis employs IR absorption spectroscopy which enables the identification and quantification of gases, liquids, and materials based on their unique absorption spectra which are feature-rich in the IR region. State-of-the-art (SoA) quantum photodetectors utilize either photoconductivity or the photovoltaic effect. Commercial quantum photodetectors are widely available in the spectral range from UV to short-wave infrared (SWIR), but in midwave IR (MWIR) and long-wave IR (LWIR), they require exotic materials and cooling to maintain high sensitivity. Thermal detectors (bolometers) are a competing technology that can reach high sensitivities in IR without the need for cooling and can be manufactured using widely available semiconductor technologies. SoA bolometers include resistive bolometers, diode- or transistor-based bolometers, and thermoelectric bolometers. By utilizing nanomaterials and integrated design, we have minimized the thermal mass and demonstrated fast and sensitive nano-thermoelectric IR bolometers with high thermoelectric efficiency. We review the application and development of the silicon-based nano-thermoelectric infrared bolometers: modelling, design, fabrication, and electro-optical characteristics. The enabling materials, silicon nanomembranes, are also discussed, and the first devices used to test the potential of these nanomembranes, the electro-thermal devices, are reviewed and new experimental results are presented.

Microbolometers are well-established sensing elements for uncooled thermal imaging applications. Benefits in both costs and power consumption allow microbolometers to be a competitive alternative as compared to cooled infrared detectors in most common infrared imaging scenarios. Until now, microbolometers are designed and optimized for the long wavelength infrared (LWIR) regime ranging from 8 μm to 14 μm. However, the mid wavelength infrared (MWIR) regime ranging from 3 μm to 5 μm is also of great interest for a wide range of applications that can benefit from the advantages of a technological concept relying on microbolometers. For this reason, Fraunhofer IMS developed an uncooled thermal imager based on microbolometers targeting the wavelength spectrum of the MWIR for high temperature imaging applications. A novel imager technology based on Fraunhofer IMS's microbolometer process for lateral leg bolometers providing QVGA resolution (320 x 240) in case of a pixel pitch of 17 μm but transferred to the MWIR regime will be presented here. In order to increase the sensitivity in the MWIR, the transmission characteristics of the vacuum package have been adopted to meet the requirements of this wavelength region. The resulting spectral sensitivity of our MWIR imagers was verified by means of an electro-optical test setup making use of a high temperature black body radiator. In addition, the actual design of the microbolometer membrane has been optimized to reduce the overall thermal capacitance, resulting in thermal time constants up to 30 % lower than those of our standard LWIR imager.

With the objective of producing high-performance infrared radiation detectors, we have undertaken the study of devices based on the Y-Ba-Cu-O material produced in amorphous film (a-YBCO) by DC sputtering at low temperature (< 150 °C) on p-doped silicon substrates coated with a SiO_x oxide film. Two types of structures have been considered: simple planar structures, where a-YBCO is connected to in-plane metal contacts, and trilayer structures where a-YBCO is sandwiched between the two contacts. The near-infrared response was recorded with a laser source at 850 nm wavelength, amplitude modulated up to 40 MHz. The main characteristics of the responses are: i) a 𝑓⁺² behavior at very low frequency (resulting from two dipolar relaxations); ii) a typically pyroelectric behavior in 𝑓⁺¹ up to a few tens of kHz; iii) a maximum response followed by a decrease in 𝑓^−1/2, reflecting the heat diffusion through the substrate. All of those results could be interpreted with the help of a theoretical model with adjustable parameters. Small size trilayer devices exhibit a very fast response (time constant: 11 ns). Besides, with noise equivalent power levels as low as 8 pW/Hz^1/2 and detectivity values of 8×10⁸ cm⋅Hz^1/2·W⁻¹ at 1 MHz, our uncooled devices are standing at the state-of-the-art both in terms of sensitivity and bandwidth.

The Short Wave Infrared (SWIR) market for defense, aerospace and industry applications is rapidly growing. A wide range of applications is available: From night vision to plastic sorting up to hyperspectral imaging. The classical SWIR detectors, which are based on InGaAs technology, have a cut-off wavelength typically around 1.7 μm. The extended SWIR (eSWIR) technology, with a spectral range up to 2.5 μm however offers significant advantages over traditional SWIR detectors. These are e.g. full exploitation of the nightglow spectrum, enhanced imaging under low light condition or ‘out of band’ operation with laser illuminators with a wavelength >2 μm. In addition, eSWIR technology includes reflective and thermal imaging, which allows detecting thermal target radiation in complete darkness. AIM presents its modules with different array formats and pixel pitches in the eSWIR spectral range from 0.8 μm up to 2.5 μm. Additionally we show that the cut-on wavelength can be lowered down to ~0.4 μm to extend the spectrum to the visible range by removing the detector substrate. A low size, weight and power (SWaP) eSWIR 640x512 10 μm pitch module has been developed and produced by AIM. It is best suited for handheld imaging or hyperspectral imaging applications with e.g. integration in UAVs. Key enabler for low SWaP however is higher operating temperature detector technology. Hence, we present the last improvements on dark current density and electro-optical performance of our eSWIR MCT HOT detector technology.

The detection in short wavelength infrared (SWIR) band, ranging from 1–3 μm, provides a wide range of applications in earth observation, plastics recycling, biology and hyperspectral imaging, gas analysis and defense. In this paper, uncooled InGaAsSb-based detectors for the wavelength range beyond 1.7 μm, the extended SWIR (eSWIR), are investigated for the later use in a thermographic traffic monitoring system that is supposed to localize potentially dangerous overheated hot-spot regions. Up to the wavelength of 1.7 μm, InGaAs lattice-matched with InP is used for photodetection in the SWIR. To reach a longer cutoff wavelength, “extended InGaAs” can be employed. This requires strained growth that leads to more growth defects and reduced yield, though. InGaAsSb, however, provides a tunable bandgap for detection beyond 1.7 μm and still enables lattice-matched growth on GaSb, which makes it a viable alternative for photodetection in the eSWIR. We have demonstrated that the bandgap of InGaAsSb can be tuned in the eSWIR by modifying the stoichiometry for lattice-matched growth on GaSb. Furthermore, we have successfully realized InGaAsSb heterojunction photodiodes with an AlGaAsSb hole barrier. At room temperature, the diodes achieve a dark current density of 0.5 mA/cm² and a responsivity better than 1 A/W resulting in an excellent peak detectivity of 9 x 10¹⁰ cm Hz^1/2/W. Thus, the highperformance detector arrays operating at room temperature are within reach in order to meet application demands.

Optical Whispering Gallery Mode (WGM) of various sizes and axisymmetry-shapes have been studied and used for a variety of optical sensors. Recently, we suggested a new type of WGM resonators with a saddle shape. These structures consist of two resonators with a bridging region resembling a valley. The unique shape of the saddle-shape resonators may allow the coupling of light into the resonator using a tapered fiber, by placing the tapered fiber at the structural minima point of the valley region. This coupling configuration provides high mechanical stability while maintaining the quality (Q) factor of the joint structured resonator. Here we present saddle shape resonators of various shapes and sizes, suitable for a variety of sensing applications.

3D mixed reality displays increase accessibility in personal transportation. Personalized Head-up Display (HUD) layouts and the provision of visual depth cues in the replay field can additionally increase safety and security by retaining the driver’s focus on the road. Current options for commercial displays fail to provide visual depth cues based on their optical system component arrangements. This work presents a compact mixed-reality volumetric display using virtual lenses, a 4K Spatial Light Modulator (SLM), a combiner, and fiber lasers. The generated mixed reality holographic head-up display aims to contextually enhance the user’s perception of the real world with additional information without presenting distractions such as wearable devices or small projections on the windshield. Hence, the optical assembly was designed to be compact such that optical lenses were mostly replaced with virtual Fresnel lenses and the algorithms were accelerated for real-time utilization. Additionally, the accuracy and precision of the replay field results were enhanced with the introduction of pigtailed fiber lasers to reduce speckles. This work has demonstrated 3D ultra-high-definition compact mixed reality holographic replay field results for various applications due to accuracy and precision.

Long range observation through atmospheric turbulence is hampered by spatiotemporally randomly varying shifting and blurring of scene points in recorded imagery. The image quality degradation induced by turbulence will limit the performance of the system. To mitigate the effect, various hardware strategies combining wavefront sensors together with adaptive optics have been proposed. Both components are associated in a control loop designed to compensate in real time for the aberrations induced by turbulence and reach a system performance close to the diffraction limit. Those techniques are designed for observations of punctual sources within a narrow field of view under which the effect of turbulence can be considered as spatially constant. Unfortunately, the majority of long range horizontal path imaging applications deal with extended sources that are wider than the area under which the turbulence effect is assumed constant. For long range horizontal observation, we devise here a method implementing wavefront sensing using a high speed camera. The system relies on two images of the same scene and same atmosphere realization, having one of the images distorted by a controlled aberration. We describe the simulation and the design choices made for the implementation of such a system. We show that this method allows to measure the relevant shape of the wavefront and provides a way to correct for the effect of atmospheric turbulence.

A scanning LIDAR system that uses a single pixel detector can be highly attractive, with simple data processing coupled with low cost and complexity. However, the impact of ambient light noise is much greater than with a multiple pixel system. A potential means of overcoming this is to filter for transverse spatial coherence. Such filters have been discussed and evaluated in the literature, typically based on an axicon or a spiral phase plate that creates a ring with coherent light. Incoherent light, in contrast, smears the light out diffusely, allowing for spatial separation and thus, filtering. The focus of the existing literature tends to be in optical communication or underwater ranging, whereas a free-space LIDAR environment has distinct issues that inhibit the practicality of the filter if a direct replication is performed. This work thus focusses on exploring the practical implementation of these filters in a free-space LIDAR environment.

We have set up a Gated Viewing (GV) system operating at a laser wavelength of 2.09 μm in the short-wave infrared (SWIR) spectral range to experimentally assess the potential of such a system for security and military applications like long-range target identification and intelligence, surveillance and reconnaissance (ISR) in low visibility conditions. In particular, we compare this system with GV systems operating at the widely used SWIR wavelength of 1.57 μm. Our focus is on examining physical effects such as laser reflection and speckles at the target surface as well as atmospheric impacts like transmission and turbulence. Finally, estimates of system ranges are made. The gated viewing camera is based on an array of 640 × 512 mercury cadmium telluride (MCT) avalanche photodiodes (APD) with a pitch of 15 μm. The cut-on and cut-off wavelengths are 0.9 μm and 2.55 μm, respectively, providing sensitivity in the extended SWIR (eSWIR) spectral range. This allows to capture both laser wavelengths 1.57 μm and 2.09 μm with the same GV camera. The camera is equipped with an aspherical F/3 lens with a focal length of 600 mm, resulting in a field-of-view (FOV) of 0.92° × 0.73°. The 1.57 μm laser is based on a commercial flashlamp-pumped Nd:YAG laser combined with an optical parametric oscillator (OPO) with a maximal pulse energy of 65 mJ at 20 Hz pulse repetition frequency (PRF) and a pulse width of τ = 11 ns. The 2.09 μm laser is an in-house developed solution with approximately 20 mJ at 20 Hz PRF and τ = 12 ns.

The ERNST mission will demonstrate infrared detection and missile tracking capabilities with a 12U nanosatellite platform. ERNST will be launched into a 500 km sun-synchronous orbit. The main payload of ERNST is a multispectral cryogenically-cooled infrared imager that was designed for missile early warning demonstration and measurement of the Earth‘s background radiation in the corresponding spectral range. The spectral sensitivity of the mid-wave infrared (MWIR) detector ranges from 2.5 µm to 5.0 µm. Six bandpass filters with a spectral width ranging between 100 and 500 nm are used to subdivide the spectral range of the detector into six narrow spectral ranges. The payload is currently undergoing geometric as well as radiometric calibration. We expect that the images acquired by ERNST during the mission will provide valuable data for early warning research and scientific applications. This paper presents the multispectral MWIR imaging payload of ERNST.

Photonic Doppler Velocimetry (PDV) has become a gold standard technique in materials impact dynamic loading research offered by its high accuracy and resolution in determining the shock wave speed under extreme conditions (shock, explosion, high pressure, etc...). However, this technique is nowadays mostly restrained to surfaces velocities. On the opposite, Radio-Frequency systems may enhance penetration in specific materials, but at the expense of lower spatial and temporal resolutions. To reach adequate penetration depth at high-speed rate measurements, we propose an innovative long-wave (LWIR) infrared Doppler velocimeter architecture to measure shock waves inside a material, operating at a wavelength near 9.5 μm. The system is currently designed to measure velocities up to 4 km/s, with a 750 MHz bandwidth MCT photodetector. Moreover, the measurement is remotely done using a 300 μm diameter Hollow Core fiber with internal dielectric reflective layers. In order to optimize the signal penetration properties into different materials, a wide tunable quantum cascade infrared laser (IR-QCL) operating in the 8-12 μm region is used. As preliminary results, we present measurements at low-speed (<1 m/s) with different targets materials (copper, aluminum and diffuse reflector) in air and transparent medium, in which the sensitivity has been identified at 9.5 μm. Results show that, despite high attenuation components, the system is able to maintain a suitable fringe contrast to ensure the velocity measurement. Further investigation will concern high speed target measurement and wavelength penetration depth optimization for materials of interest.

Low light night vision systems based on I² tubes have been expanding rapidly over the past few years, due to a combination of the growing advancement of this technology and the increased pressure in the current climate. The design of a single optical bench able to fully characterize night vision devices is presented into this paper, focused more specifically on spot defects and goggle axes parallelism tests. These criteria are indeed very important: misalignment between the two binocular images may be one source of visual fatigue and could degrade task performance of the night vision user, and spot defects can act as visual distractions and may be large enough to mask critical information pilots need to conduct normal night vision operations. Thanks to HGH’s IRCOL bench, these two tests are integrated on the same support. Spot defect measurement utilizes machine vision algorithms to determine the size and location of the defects, and the parallelism measurement identifies the angular misalignment between the two channels under test. The spot defect test has also been completely automatized compared to the only visible test previously available All these results will be compiled and directly integrated into a computer-generated report that can be easily used for quality control or for maintenance applications.

Spin-scan and conical-scan tomographic scanning (TOSCA) imagers have produced good-quality and costeffective images and video in both the infrared (IR) and optical wavelengths. A novel rosette-scan implementation of TOSCA single-pixel imaging is presented below. Previous conical-scan TOSCA imagers implemented a reticle with a fixed number of thin slits. This resulted in a fixed angular resolution which implied a fixed image resolution. The feasibility of a rosette-scan implementation using similar processing techniques to conical-scan TOSCA imagers will be demonstrated. The rosette-scan implementation would only require a reticle with a single thin slit, instead of a reticle with a number of thin slits at fixed angles. The single thin-slit reticle can be rotated to be perpendicular to the line-scan angle of each rosette petal. The number of scan angles can be dynamically changed to achieve different trade-offs between resolution and frame rate by varying the rotational speeds of the prisms and the single thin slit reticle.

Range prediction for thermal imagers applying advanced signal processing is still in its infancy. Boost filters are such an advanced signal processing and here it was assessed if the achieved range when using them is in correspondence with predictions based on the Johnson criteria. Equipment in test was an under-sampled MWIR imager operating with and without five different boost filters, four different Laplace- and one Wiener-filter. Range of this imager using the different boost filter was estimated by perception experiments for identification of numbers. These ranges were compared with limiting frequencies derived from Minimum Temperature Difference Perceived (MTDP) measurements including the boost filters. The comparison showed identification range and limiting frequency derived from the MTDP in good correspondence. Thus, the Johnson Criteria should be able to correctly predict range for thermal imagers including boost-filtering. Further work includes extending the comparison to low contrast and to real targets.

A large number of factors may influence the performance of thermal surveillance systems used in any given scenario. Highly accurate predictions of acquisition range for a sensor therefore requires the access to specialized numerical tools with a large number of input parameters. At the other hand, simple range estimations with acceptable accuracy can be made for situations of ideal conditions by applying the Johnson Criteria. However, such an approach completely ignores the effect of low signal contrast and atmospheric attenuation and would therefore be unsuited for many real-world scenarios. This work proposes an alternative method, of medium accuracy and complexity, for estimating the acquisition range of thermal sensors. It relies on the well-known concept of Minimum Resolvable Temperature Difference (MRTD), and the method represents the MRTD information for a given sensor by a parametric curve. The form of the parametric curve is chosen so that the observation range can be estimated from a simple second-order equation. The new method has several advantages. First, uncertainties in calculated acquisition range can easily be estimated based on input parameter uncertainties. Secondly, linear approximations can be made for classes of scenarios by making specific assumptions about thermal contrast and atmospheric attenuation. Thirdly, the method can form the basis for a more generalised solver that can handle an even wider range of scenarios. In this work, the new method called Parameterised MRTD (PMRTD) is outlined. Linear approximations to the solutions are derived. In addition, the solution for relevant examples are shown and discussed.

This work investigates the impact of various types of motion blur on the recognition rate of triangle orientation discrimination (TOD) models. Models based on convolutional neural networks (CNNs) have been proposed as an automated and faster alternative to observer experiments for range performance assessment. They may also give insights into the impact of system degradations on the performance of automated target recognition algorithms. However, the effects of many image distortions on the recognition rate of such models are relatively unknown. The recognition rate of CNN-based TOD models is examined in terms of different forms of motion blur, such as jitter, linear and sinusoidal motion. For model training and validation, simulated images are used. Triangles with four directions and different sizes, positions are used as targets, which are superposed on natural images as background taken from the image database “Open Images V7”. Motion blur of varying strength is applied to both the triangle and the entire image to simulate movements of the target and imager. Additionally, common degradation effects of imagers are applied, such as white sensor noise and blur due to diffraction and detector footprint. The recognition rates of the models are compared for target motion and global motion as well as for the different motion types. Furthermore, dependencies of the recognition rate on blur strength, triangle size and noise level are shown. The study shows interrelationships and differences between target motion and global motion regarding TOD classifications. The inclusion of motion blur in training can also increase model accuracy in validation. These findings are crucial for range performance assessment of thermal imagers for fast-moving targets.

Targeting systems are subject to multiple sources of error when operating in complex environments. To reduce the effect of these errors, modern targeting systems generally include both imaging and RF sensors. Data processing then provides target detection and classification information, and the detection streams are combined using a data fusion scheme to produce an optimal target location estimate with an associated latency. In this paper, the performance of a multi-sensor system in a maritime application is investigated using a mathematical simulator that has been developed to provide the system performance error analysis for different engagement scenarios and test conditions. This simulator is described together with the sources of targeting error such as image motion blur and radar glint. Additionally, the impact of flare and chaff countermeasures on the targeting performance is reviewed in terms of different types of target recognition and tracking algorithms.

Data gathering trials remain an important part of the development and testing of imaging sensor systems. However, the role of trials has evolved to reflect emergent technology, engineering methodologies, operational requirements, and project constraints such as schedule and cost. The changing nature of data gathering trials is reviewed. Although trial programmes are still used for product acceptance, there has been an increased demand for trial data to support the design process. In this paper, the emphasis is on air-to-ground image-based military systems where the timely availability of relevant image data is critical to the development of advanced image processing software which, in turn, underpins the performance of the latest imaging systems. Other factors which affect the nature of trial programmes are also considered. These include the widespread availability of synthetic image generators and the use of low-cost drones as either targets or sensor platforms. Furthermore, the increasing use of AI data processing techniques demands a larger and more diverse image data set for training and evaluation purposes. Against this background of changing requirements, trial planning has become increasingly important. Although the great flexibility of low-cost commercial drones has resulted in them becoming a preferred solution for camera platforms, they present unique challenges, ranging from logistics through to image truthing of target locations. These issues are discussed, and recommendations made based on experience gained through multiple trial programmes.

CI has developed a modular optical system, which provides the sensor stimulus to obtain the required quantitative spectral response of single detectors, detector array engines and camera systems with small to large aperture optics. The system includes interchangeable sources, Circular Variable Filter scanning monochromator (CVF) and collimating and focusing optics to project monochromatic radiation (in focused or collimated configuration, according to need) towards the sensor. When spatial patterns are also used on the focal plane, the Unit Under Test (UUT) is fully characterized in both spectral and spatial domains.

Optical zoom system plays an important role application in high precision opto-electronic imaging for the high-speed moving target imaging. The novel stabilized zoom stabilization system based on deformable mirrors(DMs) has a future application prospect in integrating fast doubling, accurate focusing, image plane stabilization and aberration compensation. In this paper, we design a reflective zoom structure including the front group and the rear group. The double DMs and the reflective mirrors form the Combined Telephoto and Reversed-Telephoto structure, which achieve the zoom of the system and correct the off-axis aberration during the whole focal length. The fixed reflective mirror in rear group is used to compress the optical length and keep the image stabilized. We make full use of effective diameter range of DMs and the flexible deformations amount of actuator strokes to achieve the freeform surfaces in the system. It achieves a high zoom ratio of 14.52 and 5 milliseconds of zooming time from Wide-angle and Telephoto. This optical system is conducive to further achieving high zoom efficiency and high speed in the stabilized zoom system based on DMs.

Automotive LiDAR systems are expected to play a crucial role in the future development of autonomous driving. In the course of the Austrian research project iLIDS4SAM an appropriate LiDAR sensor demonstrator has been designed and developed. Based upon typical requirements for such sensors, e.g. the capability to detect objects of about 10 cm x 13 cm size at a distance of 80 m, a field-of-view of 20° x 90° (V x H) and an image rate of about 17 Hz, a highly innovative 3D laser scanner has been designed which combines state-of-the-art MEMS mirror beam deflection with a rather classical polygon mirror wheel. Integrating a laser diode array of the newest generation, a multipixel APD detector array, waveform digitization as well as online waveform processing, 16 range measurement channels operating simultaneously are realized. The resulting LiDAR sensor offers a range measurement rate of 4.5 million measurements per second, each with the capability to resolve multiple targets. The LiDAR sensor is manufactured as a prototype on the level of an elegant breadboard. This contribution provides insight into the design of the LiDAR sensor and discusses the challenges identified during the design and development phase.

We report a fully-developed theory of laser scanners with rotational Polygon Mirrors (PMs). The deduced scanning function, velocity, and acceleration of PMs have been deduced and discussed in comparison to those of Galvanometer Scanners (GSs). All other characteristic parameters have been obtained, including angular and linear field-of-view (FOV), as well as duty cycle [Proc. of the Romanian Acad. Series A 18, 25-33, 2017]. Although this developed theory considered the laser beams reduced to a single ray (i.e., the center axis of the beam), the specific approach has allowed further on for a complete analysis for scanning laser beams with finite diameters. The multi-parameter optomechanical analysis of these PM functions was performed as well, considering all constructive and functional parameters [Appl. Sci. 12, 5592 (2022)]. The non-linearity of scanning functions (i.e., the non-constant scanning velocities) has been approached. In order to linearize the PM or GS scanning function, a two supplemental mirrors device was developed. This increases the distance between the PM and its objective lens within a reasonable dimension of the system, by folding the scanned laser beam. Rules-of-thumb have been obtained for the design of these scanning heads. The optical part has been completed with a Finite Element Analysis (FEA) of rotational PMs, assessing their structural integrity. An optomechanical design scheme completes the PM scanning heads study, highlighting the links between optical and mechanical aspects. This type of scheme can be utilized for other optomechanical scanners, as well.

The laser-acoustic detection of buried objects, such as landmines, is based on excitation of elastic waves in the ground and creating a vibration image of the ground surface by using a laser Doppler vibrometer (LDV). The technique provides high probability of detection and low false alarm rate. However, traditional LDVs require operation from a stable stationary platform due to their sensitivity to the motion of the vibrometer itself. Recently developed laser Doppler multi-beam differential vibration sensor has low sensitivity to the motion of the sensor itself, while measuring vibration velocity difference between points on the object with interferometric sensitivity. Low sensitivity to the sensor motion allows for vibration measurements from a moving vehicle. Two configurations of the developed sensor: the linear array and the 2D array sensors, are discussed in the paper. The linear array sensor measures velocity difference between points on the object illuminated with a linear array of 30 laser beams, and creates a vibration image of the object by scanning the array of beams in a transverse direction. The 2D array sensor employs an array of 34 x 23 laser beams and measures velocity difference between corresponding points on the object over the whole illuminated area simultaneously. Simultaneous measurements at all points allow for the fast recording of the vibration image of the area of interest, and makes possible calculation of the vibration phase and instantaneous velocity images. Description of the sensors and the experimental results are presented in the paper.

The number of satellites is rapidly growing, hence the demand for increasingly precise knowledge of the satellites’ orbital parameters is essential to avoid collisions, debris, and efficient use of the orbits. Recognizing, cataloging, and measuring with better confidence are actions crucial to preserve the health of crewed and uncrewed flying objects. Moreover, strategies to distinguish them may vary: TNO is developing suitable optical instrumentation for flying object reconnaissance along these two main paths. The satellite license plate (SLP) is a collaborative method based on a tag mounted on the satellite before launch. This plate consists of retroreflectors and wisely arranged bandpass filters. Therefore, it is passive and needs no power as opposed to an onboard radio beacon. Once a ground-based laser terminal illuminates the tag attached to the satellite, it sends back to Earth a signal encoding a unique identifier in the spectral domain. The current activities of TNO focus on proof-of-principle experiments in relevant environments (free-space tests over 2.5 km distances) and system design.

Hyperspectral cameras are optical instruments that are designed for capturing spatial information from a scene in such a way that each pixel contains the spectrum of the corresponding small scene area. One of the important factors when assessing camera performance, is the amount of spatial and spectral information in the acquired hyperspectral data. Traditionally, these are directly communicated to users as spatial pixel count and spectral band count. However, depending on the width of the sampling point spread function (SPSF) and of the spectral response function (SRF), the amount of acquired information may be significantly different for two cameras – even if the specified pixel and band counts are the same. As a better indication of the amount of acquired information, the authors suggest using two new specifications in the camera specification sheet: equivalent pixel count (EPC) and equivalent band count (EBC). Both specifications are derived from an optical resolution criterion such as full width at half-maximum (FWHM) of the SPSF and SRF. With the pixel count being a universally known and intuitive concept, and FWHM being a well-established resolution criterion, EPC and EBC specifications would allow for a quick and easy comparison between cameras with significantly different degree of optical blur, pixel count, and band count. EBC and EPC are drafted to be included in the upcoming standard dedicated to hyperspectral imaging devices. The standard is currently being finalized by P4001 working group, sponsored by the IEEE Geoscience and Remote Sensing Society standards committee.

In view of the application of optical remote sensing disaster emergency rescue under the complex environment of low illumination at night, the optical remote sensing imaging technology under the condition of low illumination and low signal-to-noise ratio was studied. The compressed sensing technology of thin film diffraction grating primary mirror is used to realize large-aperture optical acquisition. The sensing ability of large dynamic range is increased by Geiger pattern imaging technology, and the dim and weak targets are identified by semantic sensing algorithm. The system realizes target recognition under the condition of extremely low image signal-to-noise ratio through the design of the new system's main mirror flattening and the aliasing compression and decoupling of spatial information and spectral information. The technology has completed space-based scheme design and desktop principle verification tests, and the spectral resolution reaches 5nm, realizing fast target search and recognition.

This paper presents the system design of a real-time hyperspectral imager based on tunable Fabry-Pérot interferometer (FPI) filter technology. This passive hyperspectral instrument is able to capture spectral data at a rate corresponding to video-like image feed. The instrument is designed to be suitable for handheld operation as well as for missions carried out using uncrewed aerial vehicles. The frame rate of individual spectral channels of an FPI-based camera, and subsequently the acquisition speed of hyperspectral data, depends on the actuation speed of the FPI filter, exposure time of the sensor, data transfer rate, and all delays between the consecutive operations. In order to minimize the delays when switching between the spectral channels, the large FPI of this instrument is enclosed in a low-pressure housing to reduce air resistance, which would otherwise slow down the mechanical movement of the filter. As various applications require different sets of wavelengths and a variable number of spectral channels to be recorded, the imager enables selecting the desired wavelengths programmatically from within the complete spectral range of the instrument. FPI-based hyperspectral cameras produce a full two-dimensional image for each spectral channel. The spatial information contained in the images may be used to compensate for any desired or undesired movement of the imager. The spatial information available for individual channels can also be used for data analysis, and it enables employing conventional machine vision algorithms for example to detect and track the objects of interest.

A novel method for space object identification is proposed, based on full Stokes spectropolarimetry in the visible and near-infrared wavelength range. Space objects that have been previously detected and are illuminated by the sun can be observed with a telescope to simultaneously obtain intensity, spectra, and polarimetry, and compose light curves of these parameters as function of time. The intention is to thus assign a unique identification, or at least a classification to these objects. Single, double, and multiple reflections of sunlight off the space object (natural or artificial objects, including debris) will introduce spectrally dependent polarisation into the scattered light, the spectral signature of which is affected by the complex refractive index of the scattering materials and the geometry. The simultaneous measurement of the full Stokes vector allows separation of the light source unpolarised spectral signatures on the one hand from the polarisation spectral features on the other hand. To illustrate the concept, we have performed a number of simulations for double scattering off a small selection of materials, for a large range of scattering geometries. Examples of individual scattering geometries and statistical summaries of all geometries are presented. A demonstrator spectropolarimeter is being built, we present an overview of the design and the high level planning, as well as some predicted performance parameters.

Two compact and portable SWIR active imaging instrument configurations aiming at vision enhancement in indoor applications are tested and compared, working at 1300 nm and 1550 nm, respectively. Both configurations are in-house developments, but based on a limited number of standard and commercially available components (cameras, LEDs). The instruments provide images (640×512, resp. 1280×1024 pixels) at a rate of ca. 17 Hz (live stream) that can be displayed either directly on an integrated display or send via (wireless) network. Key specifications (optical power, field of view, heat development) have been characterized in laboratory tests. The performance of the two system configurations in terms of vision enhancement is compared both practically (field tests) and theoretically (Mie scattering theory). The 1300 nm illuminator has almost double power compared to the 1550 nm illuminator. However, Mie calculations predict more backscatter and less transmission through fog and smoke, which is highly depending on the particle size. Field tests using artificial fog and an in-house developed transmissiometer have been performed to validate the findings from modeling and found a vision enhancement in the order of one magnitude due to use of SWIR (instead of the Visible) for use in typical environments for which the instruments are designed for. A substantial additional improvement in terms of vision enhancement could be achieved by using polarized light and polarization optics to reduce the backscatter signal. In contrast to other research studies, this vision enhancement is not based on polarization difference imaging but on reducing the backscatter component only, enabling a robust and simple system design.

We present an overview of our on-going work in the domain of optical choppers with rotational shafts, which we proposed and patented. The different constructive solutions are presented and discussed referring to the shape of the shafts and of the slits. Our Finite Element Analyses (FEA), developed as a multi-parameter approach considering all the material, constructive and functional characteristics of the devices is briefly presented – regarding both the structural integrity and the level of deformation of fast rotational shafts with multiple holes. The potential of this novel type of optomechanical choppers is pointed out, in comparison to classical solutions of choppers with rotational disks.