Latency in augmented vision systems can be defined as the total delay imposed on information propagating through a device with respect to a direct path. Latency is critically important in vision systems as it imposes a delay on reaction time. With the emergence of headborne augmented vision systems for dismounted soldiers and widespread usage of embedded digital processing in vision systems, latency becomes most critical in dynamic operational scenarios. As consequence, latency has been characterized in the recent years for various technologies including AR headsets, VR headsets and pilot helmets with integrated symbology overlay and night vision. These efforts have led to latency requirements that vary according to the application. However, as there is no standardized definition and testing methodology for latency in vision devices, it is difficult to compare latency values across devices and as stated by different manufacturers. We propose that latency be characterized as a set and not as a single value.
Testing of Night Vision Devices (NVD) and I2 tubes are regulated by a long series of US Defense standards (often called military standards or MIL standards). These standards set mandatory testing conditions to be fulfilled. Among others, the radiation source used in the tests shall be a tungsten filament lamp operated at a color temperature of 2856 kelvins (K), ±50 K. In recent years, we have noticed that those tungsten filament lamp with a sufficient spectral shape accuracy and stability have been harder to procure. In this paper, we present our characterization efforts to determine if a commercially available LED-based light source is suitable to replace a tungsten filament lamp for NVDs and I2 tubes testing. A LED-based light source is compared to a 2856 K filament lamp in terms of spectral shape, output power linearity, dynamic range and relative intensity noise (RIN). We also present the pros and cons of the two sources in a perspective of evaluating NVD performance in a controlled environment emulating different representative night sky irradiances in support of military and law enforcement operations.
The last decades have brought significant improvements in materials, microfabrication, manufacturing processes, microelectronic fabrication, optical design tools and microprocessing power. It has allowed the development of novel types and designs of electro-optical (EO) military systems having, among others, the following added capabilities: wide field of view, extended spectral response, multifunction devices, image fusion and embedded image processing. Meanwhile, the international standards that regulate the testing and evaluation of EO systems, developed in the 1990s, have not been updated to include those new capabilities that are important on the battlefield. As a result, those standards are often no longer suitable to characterize current state-of-art EO systems and to support major military EO systems acquisition projects. In this paper, we present an overview of some novel testing capabilities developed over the last decade at DRDCValcartier Research Centre that aim at comparing, in a controlled environment, the performance and limitations of EO military systems under different representative operational conditions. Those novel testing capabilities do not aim at replacing standard testing procedures, but rather at complementing them. Methodologies developed to test thermal imagers, wide-field-of-view night vision google, image intensifier tubes and lasers are described.
Modern thermal imaging systems are widely used because of their broad military and commercial application range. The performance of the first generations of thermal imagers was limited by resolution and thermal sensitivity. Brightness and contrast adjustments were also the crux of the image quality. From a military user perspective, the amount of details and the interpretation of a scene depends, among others, on the experience of the user and on the time available to complete those adjustments. Modern imagers now feature embedded digital processing that can automatically adjust the device parameters in order to optimize the image quality. With the combined improvements in microprocessor power and microfabrication processes, digital processing enhanced the thermal imagers’ performance until they eventually became limited by their ability to react to different operational scenarios. That brings the need for testing the reaction of digital processing in such operational scenarios. Meanwhile, there were no significant modification in testing methodologies and metrics used for the assessment of thermal imagers. In this paper, we present DRDC-Valcartier Research Centre’s efforts to develop a test bench to measure the efficiency of the digital processing embedded in thermal imagers. The purpose of the testing methodology is to provide reliable, repeatable and user-independent metrics. Outputs quantitatively highlight the impact of digital processing for various operational situations and allow the performance of devices to be compared.
Nathalie Roy, Alexandre Vallières, Daniel St-Germain, Simon Potvin, Michel Dupuis, Jean-Claude Bouchard, André Villemaire, Martin Bérubé, Mélanie Breton, Guillaume Gagné
A novel approach is used to characterize and compare the performance of night vision systems in conditions more
representative of night operation in terms of spectral content. Its main advantage compared to standard testing
methodologies is that it provides a fast and efficient way for untrained observers to compare night vision system
performances with realistic illumination spectra. The testing methodology relies on a custom tumbling-E target and on a
new LED-based illumination source that better emulates night sky spectral irradiances from deep overcast starlight to
quarter-moon conditions. In this paper, we describe the setup and we demonstrate that the novel approach can be an
efficient method to characterize among others night vision goggles (NVG) performances with a small error on the photogenerated
electrons compared to the STANAG 4351 procedure.
Measurements of the depolarization ratio of water droplets were performed to study the relationship between layer
integrated depolarization and layer integrated backscattered light for linear and circular polarization illumination. Since
those particles are spherical, the depolarization of the signal is attributed to multiple scattering effects. The experimental
data reported in this article support Hu relationship between the single scattering fraction As and the linear accumulated
depolarization ratio. For circular polarization, a modified Hu relationship is established and it is shown that the use of
the accumulated depolarization parameter instead of the accumulated depolarization ratio allows harmonization of the
linear and circular polarization measurements into a simple mathematical expression.
Relatively inexpensive laser-guided weapons were identified as an important threat to naval platforms operating in littoral environments. Countermeasures (CM) developed against laser-assisted threats in air and land environments are all based on accurate threat detection. Due to the limited performance of current laser detecting capabilities applied to large maritime platforms, there are no known CMs that can be used to protect them. We present a new far off-axis laser detection approach for minimizing the number of laser sensors required to protect a ship. A model predicting the detection of aerosol scattering in the spectral band used by laser threats, exploiting the high humidity conditions present in maritime environments, is described, as well as its limitations and some preliminary results regarding its validation.
A Multiple-Field-Of-View (MFOV) lidar is used to characterize the size and concentration of low concentration of bioaerosol particles. The concept relies on the measurement of the forward scattered light by using the background aerosols at various distances at the back of the sub-visible cloud. It also relies on the subtraction of the background aerosol forward scattering contribution and on the partial attenuation of the first order backscattering. We demonstrate theoretically and experimentally that the MFOV lidar can measure with a good precision the effective diameter of low concentration bioaerosol clouds.
We measure the cross-polarized backscattered light from a linearly polarized laser beam penetrating a cloud made of spherical particles with a gated intensified CCD camera. In accordance with previously published results, we observe a clear azimuthal pattern in the recorded images. We show that the pattern originates from second order scattering, and that higher-order scattering causes blurring that increases with optical depth. We also find that the contrast of the symmetrical features can be related to the measure of the optical depth. Moreover, by identifying and subtracting the blurring contributions, the resulting pattern provides a "pure" second-order scattering measurement that can be used for the retrieval of droplet size. We apply this technique on a stratus cloud located at 1400 m. The extinction values retrieved on the basis of the laboratory quantification of the blurring of the multiple scattering secondary polarization patterns measured from the ICCD images are then compared with the profile of the extinction coefficient obtained using Bissonnette's algorithm, which is based on the multiple-field-of-view (MFOV) lidar returns.
A multiple-scattering lidar technique is used to retrieve simultaneously the extinction coefficient and the effective particle diameter of clouds and precipitation. In addition, the linear depolarization ratio is measured to determine the liquid or solid phase of the particles. The reported measurements were made with a ground-based multiple-field-of-view (MFOV) lidar pointed at zenith. The lidar was fired in 10-s bursts, every minute for periods ranging from 30 min to 3 hours. The vertical resolution was selectable from 1.5 to 6 m but typically set at 3 m. The retrieved profiles are collected in the form of time-height maps of 1 min x 3 m resolution of the extinction coefficient, effective particle diameter, and depolarization ratio. Here, we analyze only the cloud layer and identify, from the statistics of the retrieved extinction coefficient and effective droplet diameter, important physical behaviors of water clouds. The results not only demonstrate the validity of the lidar retrievals but show that systematic lidar probings can yield significant information on cloud physics.
Lidar probing of dense water clouds gives rise to significant multiple scattering contributions. Instead of trying to mitigate the effect, we have developed methods to collect and angularly resolve the multiple scattering returns. The proposed retrieval method combines these measurements with a rapid semi-empirical computation method of the lidar multiple scattering contributions. Solutions are calculated for the extinction coefficient, the effective droplet diameter, the liquid water content and the rain rate. The paper reviews the main measurement methods, discusses briefly the concept and implementation of the retrieval technique, presents validation results obtained from Monte Carlo simulations, and compares lidar solutions for liquid water content and effective droplet diameter with in-cloud aircraft measurements. Good correlation is demonstrated for both simulation and field data. We conclude that multiple-scattering lidar is a practical option for the remote sensing of water cloud microphysical parameters up to the lidar penetration depths of typically 200 m.
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