Using Crash Detection and Alert Beacons on an Electronic Device to Increase Survival of Snow Immersion Victims

This publication describes systems and techniques for crash detection on an electronic device to trigger transmitting alert beacons with the electronic device. The alert beacons may be received by nearby electronic devices to alert the users of those electronic devices of a snow immersion victim. A crash is detected by monitoring one or more sensors on an electronic device for a tumbling or inversion of the electronic device that indicates a snow immersion accident. Additionally, location and weather may also be monitored to detect a snow immersion accident and support a crash detection. After a crash is detected, a user of the electronic device may be provided with a notification to dismiss triggering alert beacons. If the user does not dismiss the notification, the electronic device may trigger transmitting alert beacons to alert others via wireless signal that the user has been in a snow immersion accident. The alerts may be provided via a peer-to-peer system tagged with location information of the snow immersion accident. The alerts can assist others in locating the snow immersion accident victim more quickly

Correction of image radial distortion based on division model

This paper presents an approach for estimating and then removing image radial distortion. It works on a single image and does not require a special calibration. The approach is extremely useful in many applications, particularly those where human-made environments contain abundant lines. A division model is applied, in which a straight line in the distorted image is treated as a circular arc. Levenberg–Marquardt (LM) iterative nonlinear least squares method is adopted to calculate the arc’s parameters. Then “Taubin fit” is applied to obtain the initial guess of the arc’s parameters which works as the initial input to the LM iteration. This dramatically improves the convergence rate in the LM process to obtain the required parameters for correcting image radial distortion. Hough entropy, as a measure, has achieved the quantitative evaluation of the estimated distortion based on the probability distribution in one-dimensional θ Hough space. The experimental results on both synthetic and real images have demonstrated that the proposed method can robustly estimate and then remove image radial distortion with high accurac

An ASIFT-based local registration method for satellite imagery

Imagery registration is a fundamental step, which greatly affects later processes in image mosaic, multi-spectral image fusion, digital surface modelling, etc., where the final solution needs blending of pixel information from more than one images. It is highly desired to find a way to identify registration regions among input stereo image pairs with high accuracy, particularly in remote sensing applications in which ground control points (GCPs) are not always available, such as in selecting a landing zone on an outer space planet. In this paper, a framework for localization in image registration is developed. It strengthened the local registration accuracy from two aspects: less reprojection error and better feature point distribution. Affine scale-invariant feature transform (ASIFT) was used for acquiring feature points and correspondences on the input images. Then, a homography matrix was estimated as the transformation model by an improved random sample consensus (IM-RANSAC) algorithm. In order to identify a registration region with a better spatial distribution of feature points, the Euclidean distance between the feature points is applied (named the S criterion). Finally, the parameters of the homography matrix were optimized by the Levenberg–Marquardt (LM) algorithm with selective feature points from the chosen registration region. In the experiment section, the Chang’E-2 satellite remote sensing imagery was used for evaluating the performance of the proposed method. The experiment result demonstrates that the proposed method can automatically locate a specific region with high registration accuracy between input images by achieving lower root mean square error (RMSE) and better distribution of feature points

Evaluation of positioning error-induced pixel shifts on satellite linear push-broom imagery

Georeferencing is one of the major tasks of satellite-borne remote sensing. Compared to traditional indirect methods, direct georeferencing through a Global Positioning System/inertial navigation system requires fewer and simpler steps to obtain exterior orientation parameters of remotely sensed images. However, the pixel shift caused by geographic positioning error, which is generally derived from boresight angle as well as terrain topography variation, can have a great impact on the precision of georeferencing. The distribution of pixel shifts introduced by the positioning error on a satellite linear push-broom image is quantitatively analyzed. We use the variation of the object space coordinate to simulate different kinds of positioning errors and terrain topography. Then a total differential method was applied to establish a rigorous sensor model in order to mathematically obtain the relationship between pixel shift and positioning error. Finally, two simulation experiments are conducted using the imaging parameters of Chang’ E-1 satellite to evaluate two different kinds of positioning errors. The experimental results have shown that with the experimental parameters, the maximum pixel shift could reach 1.74 pixels. The proposed approach can be extended to a generic application for imaging error modeling in remote sensing with terrain variation

Complete initial solutions for iterative pose estimation from planar objects

Camera pose estimation from the image of a planar object has important applications in photogrammetry and computer vision. In this paper, an efficient approach to find the initial solutions for iterative camera pose estimation using coplanar points is proposed. Starting with homography, the proposed approach provides a least-squares solution for absolute orientation, which has a relatively high accuracy and can be easily refined into one optimal pose that locates local minima of the according error function by using Gauss-Newton scheme or Lu's orthogonal iteration algorithm. In response to ambiguities that exist in pose estimation from planar objects, we propose a novel method to find initial approximation of the second pose, which is different from existing methods in its concise form and clear geometric interpretation. Thorough testing on synthetic data shows that combined with currently employed iterative optimization algorithm, the two initial solutions proposed in this paper can achieve the same accuracy and robustness as the best state-of-the-art pose estimation algorithms, while with a significant decrease in computational cost. Real experiment is also employed to demonstrate its performance

2,2-Dibromo-N-(4-fluoro­phen­yl)acetamide

In the crystal structure of the title compound, C8H6Br2FNO, C—H⋯O and N—H⋯O hydrogen bonding results in six-membered rings and links the mol­ecules into chains running parallel to the c axis. The dihedral angle between the fluoro­phenyl ring and the acetamide group is 29.5 (5)°

Panoramic mosaics from Chang’E-3 PCAM images at Point A

This paper presents a unique approach for panoramic mosaics based on Moon surface images from the Chang’E-3 (CE-3) mission, with consideration of the exposure time and external illumination changes in CE-3 Panoramic Camera (PCAM) imaging. The engineering implementation involves algorithms of image feature points extraction by using Speed-Up Robust Features (SURF), and a newly defined measure is used to obtain the corresponding points in feature matching. Then, the transformation matrix is calculated and optimized between adjacent images by the Levenberg–Marquardt algorithm. Finally, an image is reconstructed by using a fade-in-fade-out method based on linear interpolation to achieve a seamless mosaic. The developed algorithm has been tested with CE-3 PCAM images at Point A (one of the rover sites where the rover is separated from the lander). This approach has produced accurate mosaics from CE-3 PCAM images, as is indicated by the value of the Peak Signal to Noise Ratio (PSNR), which is greater than 31 dB between the overlapped region of the images before and after fusion

Fault slippage and its permeability evolution during supercritical CO2 fracturing in layered formation

International audienceUnderstanding the hydromechanical responses of faults during supercritical CO2 fracturing is important for reservoir management and the design of energy extraction systems. As small faults are widespread in Chang 7 member of the Yanchang Formation, Ordos Basin, China, supercritical CO2 fracturing operation has the potential to reactive these undetected small faults and leads to unfavorable fracking fluid migrate. In this work, we examined the role of fault slippage and permeability evolution along a small fault connecting the pay zone and the confining formation during the whole process of fracturing and production. A coupled hydromechanical model conceptualized from actual engineering results was introduced to address the main concerns of this work, including, (1) whether the existence of a undetected small fault would effectively constrain the hydraulic fracture height evolution, (2) what the magnitude of the induced microseismic events would be and (3) whether the permeability change along the fault plane would affect the vertical conductivity of the confining formation and thus increase the risk for the fracturing fluid to leak. Our results have shown that the initial hydrofracture formed at the perforation and propagated upward, once it merged with the fault surface, the existence of an undetected small fault would effectively constrain the hydraulic fracture height evolution. As fracturing continued, further slippage spread from the permeability increase zone of high permeability to shallower levels, and the extent of this zone was dependent on the magnitude of the fault slippage. At the end of extraction, the slip velocity decreases gradually to zero and the fault slippage finally reaches stabilization. In general, undetected small faults in targeted reservoir may not be the source of large earthquakes. The induced microseismic events could be considered as the sources of acoustic emission events detected while monitoring the fracturing fluid front. Due to the limited fault slippage and lower initial permeability, the CO2 fracturing operation near undetected small faults could not conduct preferential pathway for upward CO2 leakage or contaminate overlying shallower potable aquifers