Sensor Line Of Sight Research Articles

The Impact of Line-of-Sight and Connected Vehicle Technology on Mitigating and Preventing Crash and Near-Crash Events.

Line-of-sight (LOS) sensors developed in newer vehicles have the potential to help avoid crash and near-crash scenarios with advanced driving-assistance systems; furthermore, connected vehicle technologies (CVT) also have a promising role in advancing vehicle safety. This study used crash and near-crash events from the Second Strategic Highway Research Program Naturalistic Driving Study (SHRP2 NDS) to reconstruct crash events so that the applicable benefit of sensors in LOS systems and CVT can be compared. The benefits of CVT over LOS systems include additional reaction time before a predicted crash, as well as a lower deceleration value needed to prevent a crash. This work acts as a baseline effort to determine the potential safety benefits of CVT-enabled systems over LOS sensors alone.

Velocity Estimation for Space Infrared Dim Targets Based on Multi-Satellite Observation and Robust Locally Weighted Regression

Velocity estimation of space moving targets is a key part of space situational awareness. However, most of the existing methods do not consider the satellite observation process, and the performance mainly depends on the preset target motion state, which has great limitations. To accurately obtain the motion characteristics of space infrared dim targets in space-based infrared detection, a velocity estimation method based on multi-satellite observation and robust locally weighted regression is proposed. Firstly, according to parameters such as satellite position, satellite attitude angle, and sensor line of sight, the overall target observation model from the sensor coordinate frame to the Earth-centered inertial coordinate frame is established, and the pixel coordinates of the target imaging point are extracted using the gray-weighted centroid method. Then, combined with the least squares criterion, the position sequence of the space target is obtained. Finally, a robust locally weighted regression operation is performed on the target position sequence to estimate the velocity. This study verified the feasibility of the proposed method through simulation examples, with the results showing that the Mean Absolute Error (MAE) and Root Mean Square Error (RMSE) of the method were only 0.0733 m/s and 1.6640 m/s without measurement error. Moreover, the velocity estimation accuracy was better than that of other methods in most scenarios. In addition, the estimation accuracy under the impact of various measurement errors was analyzed, and it was found that the pixel coordinate extraction error had the greatest impact on velocity estimation accuracy. The proposed method provides a technical basis for the recognition of space infrared dim moving targets.

A geometrical approach for the angular velocity determination using a star sensor

In this paper, a geometrical investigation of the star sensor image is performed under dynamic conditions where the angular velocity effects are non-negligible. It is shown that, when the spacecraft is rotating, the streaks left by the stars’ signal onto the star sensor detector belong to portions of conic sections which features depend on the angles between the instantaneous rotation axis, the sensor line of sight and the stars’ direction. The geometrical properties discussed in the first part of the paper can be used to develop new numerical methods for the evaluation of the angular velocity. Hence, the chord method is proposed and discussed. This approach needs at least two stars in two successive images and, despite its simplicity, is quite effective to get a preliminary estimation of the spacecraft angular velocity in terms of direction and magnitude. Using the stars’ centroids from two successive images, the chord method evaluates the angular velocity direction as the intersection of the normals to the streaks. The proposed method is firstly presented by means of simple examples using some reference geometries, and then it is applied to real scenarios by using a high fidelity star sensor simulator. The pre-processing and processing of simulated images are discussed, presenting the geometrical techniques used to cluster the streaks and compute the centroids. Results are presented and discussed, validating the reported theoretical speculations.

Dynamic model‐based feature aided data association filter in target tracking

In this study, the authors consider the data association problem where the feature of a target is available. Most existing data association filters mainly use a statistical or simple model of the feature without explicitly considering the correlation between the target behaviour and feature characteristics. The inaccurate model of the feature could lead to divergence of the estimation error or the loss of a target in heavily cluttered and/or low signal-to-noise ratio environments. To address the problem, they first develop feature models (e.g. target dimensions) dependent on the target behaviour (i.e. the distance between the sensor and the target, and the aspect angle between the longitudinal axis of the target and the axis of sensor line of sight). Then they propose a data association filter which can facilitate the feature models dependent on the target kinematics to reduce the misassociations. The performance of the proposed feature models and data association filter are demonstrated with illustrative target tracking scenarios.

Review of the Book Predicting Vehicle Trajectory [Book Review

The book concentrates on the improvement of the prediction of a future vehicle trajectory, giving emphasis on the cases of non-straight paths. The trajectory is the path that a moving object (in our case a vehicle) follows through space as a function of time. In several cases in our physical world, trajectories can be described mathematically either by the geometry of the path or as the position of the object over time. However, in intelligent transportation systems this is not applicable and therefore having a reliable prediction of a vehicle position in the very near future is crucial to determine possible path intersections, collisions of vehicles or diversion from the road. As stated in the book “The US Department of Transportation will be mandating that all vehicle manufacturers begin implementing Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) systems, so very soon collision avoidance systems will no longer rely on line of sight sensors, but instead will be able to take into account another vehicle’s spatial movements to determine if the future trajectories of the vehicles will intersect at the same time”. To this end, this book offers the reader some improvements for predicting the future trajectory of a vehicle and presents a novel temporary solution on how to speed up the implementation of such V2V collision avoidance systems. Additionally, the book evaluates whether smartphones can be used for trajectory predictions, to populate a V2V collision avoidance system faster than a vehicle manufacturer can.

Investigating uplift in Lesina Marina (Southern Italy) with the aid of persistent scatterer SAR interferometry and in situ measurements

We apply persistent scatterer interferometry (PSI) techniques to synthetic aperture radar (SAR) data from ERS and ENVISAT satellites on the Lesina Marina area, a coastal tourist village in Apulia, Southern Italy, where the excavation of a canal exposed grey micro- and meso-crystalline gypsum which is now showing a high density of cavities and sinkholes due to gravitational collapse processes. We observe PS objects undergoing displacements, along the sensor line of sight, forming the same relatively smooth pattern in all the processed data stacks. Vertical displacement rates, derived through integration of ascending and descending geometries, reach about 4 mm/year on locations adjacent to the canal, gently decreasing towards the western end of the built-up area . High-precision leveling measurements, performed in 1999 and 2010, reveal a substantial agreement with the ENVISAT PSI data, taking into account a small bias due to the choice of the leveling reference point. The dataset, thus validated, suggests the presence of an uplift phenomenon going on steadily for the entire timespan covered by the SAR observations (1992–2009). These observations, supported by petrographic data and in situ investigations, seem only in part compatible with a residual diapirism, and hint instead to more complex processes, such as a combination of diapirism and the hydration of the residual anhydrite in the core of the gypsum mass. These results confirm the importance of the integration between in situ, geologic and geophysical, remotely sensed investigations, as the latter often represent an essential tool to infer whether a given phenomenon, which can be hypothesized by the former, is presently under development.

Inertially stabilized platforms for optical imaging systems

Optical imaging sensors, such as television or infrared cameras, collect information about targets or target regions. It is thus necessary to control the sensor's line-of-sight (LOS) to achieve accurate pointing. Maintaining sensor orientation toward a target is particularly challenging when the imaging sensor is carried on a mobile vehicle or when the target is highly dynamic. Controlling an optical sensor LOS with an inertially stabilized platform (ISP) can meet these challenges.A target tracker is a process, typically involving image processing techniques, for detecting targets in optical imagery. This article describes the use and design of ISPs and target trackers for imaging optical sensors.

Acoustic array tracking performance under moderately complex environmental conditions

The direction-of-arrival (DOA) tracking performance of microphone arrays having aperture sizes ranging from 0.3 to 34 m is examined for an experiment involving a vehicle traversing a moderately complex terrain. A segment of the vehicle’s path was obscured behind a small, 6.7-m high, vegetated hill. The combination of the hill and upwind propagation created an acoustic shadow during this segment. DOA tracks were estimated with a minimum-variance distortionless response (MVDR) beamformer operating in two frequency bands: 25–60 Hz and 60–105 Hz. In the lower frequency band, array sizes between 1 and 8 m gave the best results, with DOA errors between 2° and 5°. Furthermore, in this band shadowing from the hill and wind refraction had a minimal affect on DOA error. In the higher frequency band, the acoustic shadow zone produced a distinct interval of high DOA error, with the 8-m array giving the best overall performance. Modeling of the beamforming process shows that high DOA errors corresponded to MVDR wavenumber patterns that are degraded by distortions to the propagating wavefronts. Our experimental results indicate that small acoustic arrays with apertures less than 0.3 m, operating at frequencies above 100 Hz, should be considered line of sight sensors. Given the moderate complexity of the test conditions, it is anticipated that the observed effects are likely to be present in most attempts to localize outdoor sound sources.

Radio frequency identification in the UK: opportunities and challenges

Radio frequency identification (RFID) is the generic name for technologies that use radio waves to automatically identify individual items that carry such identification tags. Unlike barcodes, which need line of sight sensors, RFID tags do not. As the cost of this new technology falls, the take‐up rate by the retail industry will be significant, revolutionizing retailers’ control of the product supply chains and knowledge about the consumer. The paper argues that the opportunities and challenges for RFID tags for retailers are significant, and reports on a number of trials that have been conducted by retailers in the UK in the management and introduction of this technology. The paper also examines some of the issues facing retailers in terms of the widespread use of RFID tags and the privacy concerns that are linked to data capture and data usage by retailers and third parties.

A model for atmospheric background radiance structures

Infrared radiance fluctuations in the atmosphere result from fluctuations in the density of atmospheric species, individual molecular state populations, and kinetic temperatures along the sensor line of sight (LOS). As part of the SHARC-4 development program, a model for the prediction of atmospheric background radiance fluctuations was constructed. It predicts a two dimensional radiance spatial covariance function and power spectral density (PSD) from the underlying 3D atmospheric structures. Inputs to the model include the parameters of an atmospheric temperature fluctuation model and vertical atmospheric profiles. The model can be applied for arbitrary sensor viewing geometries, including limb viewing. In the upper atmosphere non-equilibrium effects are important. Fluctuations in kinetic temperature can result in correlated or anti-correlated fluctuations in vibrational state temperatures. The model accounts for these effects and predicts spatial covariance functions and PSD's for molecular state number densities and vibrational temperatures. SHARC is used to predict the non-equilibrium dependence of molecular state number density fluctuations on kinetic temperature and density fluctuations, and to calculate mean LOS radiances and radiance derivatives. The goal is to understand the origin of LOS radiance fluctuations and the prediction of fluctuation statistics based on local fluctuations in gas kinetic temperatures, and densities. The modeling capabilities are illustrated with a sample image prediction for the Midcourse Space Experiment (MSX) having an MSX sensor bandpass and field-of-view (FOV).

The Effect of Scene Rotation on Target Acquisition

Studies were performed to determine the effects of scene rotation on target acquisition performance. Video tapes of simulated straight approaches to surface vehicular targets were made at constant offset, altitude, and speed using a terrain table (600:1) and a gimbal mounted TV camera. Detection and (separate) recognition tests were then made under load (button-pushing) and no-load conditions. No differences in detection slant range and erroneous detections were found between the rotated (roll-pitch) and non-rotated (yaw-pitch gimbal order) conditions or between the load/no-load conditions. Statistically significant differences were found between the recognition ranges and error scores for gimbal order but again not between load/no-load conditions. It was concluded that the sensor line of sight should be stabilized or derolled if maximum recognition performance is to be realized using airborne electro-optical systems in ground target acquisition.