Offset Measurements Research Articles

Evaluation of the Use of Sub-Pixel Offset Tracking Techniques to Monitor Landslides in Densely Vegetated Steeply Sloped Areas

Sub-Pixel Offset Tracking (sPOT) is applied to derive high-resolution centimetre-level landslide rates in the Three Gorges Region of China using TerraSAR-X Hi-resolution Spotlight (TSX HS) space-borne SAR images. These results contrast sharply with previous use of conventional differential Interferometric Synthetic Aperture Radar (DInSAR) techniques in areas with steep slopes, dense vegetation and large variability in water vapour which indicated around 12% phase coherent coverage. By contrast, sPOT is capable of measuring two dimensional deformation of large gradient over steeply sloped areas covered in dense vegetation. Previous applications of sPOT in this region relies on corner reflectors (CRs), (high coherence features) to obtain reliable measurements. However, CRs are expensive and difficult to install, especially in remote areas; and other potential high coherence features comparable with CRs are very few and outside the landslide boundary. The resultant sub-pixel level deformation field can be statistically analysed to yield multi-modal maps of deformation regions. This approach is shown to have a significant impact when compared with previous offset tracking measurements of landslide deformation, as it is demonstrated that sPOT can be applied even in densely vegetated terrain without relying on high-contrast surface features or requiring any de-noising process.

Informativeness, Timing and Tempo in Lexical Self-Repair.

This paper presents a study of the temporal organization of lexical repair in spontaneous Dutch speech. It assesses the extent to which offset-to-repair duration and repair tempo can be predicted on the basis of offset timing, reparandum tempo and measures of the informativeness of the crucial lexical items in the repair. Specifically, we address the expectations that repairs that are initiated relatively early are produced relatively fast throughout, and that relatively highly informative repairs are produced relatively slowly. For informativeness, we implement measures based on repair semantics, lexical frequency counts and cloze probabilities. Our results highlight differences between factual and linguistic error repairs, which have not been consistently distinguished in previous studies, and provide some evidence to support the notion that repairs that are initiated relatively early are produced relatively fast. They confirm that lexical frequency counts are rough measures of contextual predictability at best, and reveal very few significant effects of our informativeness measures on the temporal organization of lexical self-repair. Moreover, although we can confirm that most repairs have a repair portion that is fast relative to its reparandum, this cannot be attributed to the relative informativeness of the two portions. Our findings inform the current debate on the division of labour between inner and overt speech monitoring, and suggest that, although the influence of informativeness on speech production is extensive, it is not ubiquitous.

Automatic tuning of digitally-controllable positive-feedback OTAs in continuous-time sigma–delta modulators

This paper proposes a technique suitable for on-chip tuning of digitally-tunable positive-feedback operational transconductor amplifiers in a continuous-time sigma---delta modulator (CT-SDM) with active-RC integrator stages. The work we present relies on phase shift and offset measurement of individual active-RC integrator stages output using comparators to estimate output conductance, DC-gain, and common mode level of the differential output signals. The tuning methodology aims to tune the integrator stages to achieve sufficient DC-gain as required by the SDM. We present experimental results to confirm the correlation of our integrator phase and output offset detection technique with the operational transconductance amplifier (OTA) DC gain. We employ this technique in a tuning process of two digitally-tunable OTA chips implemented in complementary metal-oxide semiconductor 180 nm process configured in a second-order CT-SDM circuit with discrete components. The tuning algorithm results in a measured signal-to-noise and distortion ratio (SNDR) of 46.97 dB, which is close to the maximum SNDR of 47.83 dB achievable across a subset of the digitally-tunable OTA code space. High-speed operation of the CT-SDM and tuning circuitry has been verified through circuit simulations.

An Algorithm for Accurate Distributed Time Synchronization in Mobile Wireless Sensor Networks from Noisy Difference Measurements

AbstractWe propose a distributed algorithm for time synchronization in mobile wireless sensor networks. The problem of time synchronization is formulated as nodes estimating their skews and offsets from noisy difference measurements of offsets and logarithm of skews; the measurements acquired by time‐stamped message exchanges between neighbors. The algorithm ensures that the estimation error is mean square convergent (variance converging to 0) under certain conditions. A sequence of scheduled update instants is used to meet the requirement of decreasing time‐varying gains that need to be synchronized across nodes with unsynchronized clocks. Moreover, a modification on the algorithm is also presented to improve the initial convergence speed. Simulations indicate that highly accurate global time estimates can be achieved with the proposed algorithm for long time durations, while the errors in competing algorithms increase over time.

Characterization of patellar maltracking using dynamic kinematic CT imaging in patients with patellar instability.

Little has been reported on the relationship between patellar maltracking and instability. Patellar maltracking has been subjectively described with the "J sign" but is difficult to assess objectively using traditional imaging. Dynamic kinematic computed tomography (DKCT) allows dynamic assessment of the patellofemoral joint. DKCT was used to visualize and quantify patellar maltracking patterns, and severity of maltracking was correlated with the presence or absence of patellar instability symptoms. Seventy-six knees in 38 patients were analysed using DKCT. Maltracking was defined as deviation of the patella from the trajectory of the trochlear groove and was characterized by patellar bisect offset, which was measured at 10° intervals of knee flexion during active flexion and extension. Bisect offset measurements were grouped by number of quadrants of maximum lateral patellar motion, with one, two, and three quadrants corresponding to 75-99, 100-125, and >125%, respectively. Patellar instability symptoms were correlated with maltracking severity. Two knees were excluded because of poor imaging quality. Fifty of 74 knees had patellar instability, and 13 patients had bilateral symptoms. Of these, four (8%) had normal tracking patterns; 41 (82%) had increased lateral translation in extension, which we termed the J-sign pattern; 4 (8%) had persistent lateralization of the patella throughout range of motion; and 1 had increased lateral translation in flexion. In knees with the J-sign pattern, degree of maltracking was graded by severity: J1 (n=24), J2 (n=19), and J3 (n=15). The sensitivities of J-sign grades in predicting patellar instability symptoms were 50% (J1), 80% (J2), and 93% (J3) (p<0.01). There were significant differences in sensitivity between knees with no J sign or J1 versus J2 or J3 (p=0.02). DKCT showed several patellar maltracking patterns in patients with patellar instability. A J-sign pattern with more than two quadrants of lateral translation correlated with the presence of patellar instability symptoms. Incorporation of this approach of objectively quantifying maltracking patterns is recommended in the evaluation of patellofemoral instability. IV.

DMD-based software-configurable spatially-offset Raman spectroscopy for spectral depth-profiling of optically turbid samples.

Spectral depth-profiling of optically turbid samples is of high interest to a broad range of applications. We present a method for measuring spatially-offset Raman spectroscopy (SORS) over a range of length scales by incorporating a digital micro-mirror device (DMD) into a sample-conjugate plane in the detection optical path. The DMD can be arbitrarily programmed to collect/reject light at spatial positions in the 2D sample-conjugate plane, allowing spatially offset Raman measurements. We demonstrate several detection geometries, including annular and simultaneous multi-offset modalities, for both macro- and micro-SORS measurements, all on the same instrument. Compared to other SORS modalities, DMD-based SORS provides more flexibility with only minimal additional experimental complexity for subsurface Raman collection.

SU‐F‐J‐142: Proposed Method to Broaden Inclusion Potential of Patients Able to Use the Calypso Tracking System in Prostate Radiotherapy

Purpose:To introduce a non‐standard method of patient setup, using BellyBoard immobilization, to better utilize the localization and tracking potential of an RF‐beacon system with EBRT for prostate cancer.Methods:An RF‐beacon phantom was imaged using a wide bore CT scanner, both in a standard level position and with a known rotation (4° pitch and 7.5° yaw). A commercial treatment planning system (TPS) was used to determine positional coordinates of each beacon, and the centroid of the three beacons for both setups. For each setup at the Linac, kV AP and Rt Lateral images were obtained. A full characterization of the RF‐beacon system in clinical mode was completed for various beacons’ array‐to‐centroid distances, which includes vertical, lateral, and longitudinal offset data, as well as pitch and yaw offset measurements for the tilted phantom. For the single patient who has been setup using the proposed BellyBoard method, a supine simulation was first obtained. When abdominal protrusion was found to be exceeding the limits of the RF‐Beacon system through distance‐based analysis in the TPS, the patient is re‐simulated prone with the BellyBoard. Array to centroid distance is measured again in the TPS, and if found to be within the localization or tracking region it is applied.Results:Characterization of limitations for the RF‐beacon system in clinical mode showed acceptable consistency of offset determination for phantom setup accuracy. The nonstandard patient setup method reduced the beacons’ centroid‐to‐array distance by 8.32cm, from 25.13cm to 16.81cm; completely out of tracking range (greater than 20cm) to within setup tracking range (less than 20cm).Conclusion:Using the RF‐beacon system in combination with this novel patient setup can allow patients who would otherwise not be candidates for beacon enhanced EBRT to now be able to benefit from the reduced PTV margins of this treatment method.

Identificación de sitios de cruce de fauna en la ruta 415, en el "Paso del Jaguar", Costa Rica.

La Iniciativa del Corredor del Jaguar pretende mantener la conectividad de esta especie. En Costa Rica, esta iniciativa inició en el Subcorredor Biológico Barbilla-Destierro. En este Subcorredor, se ha identificado la pavimentación de un camino de lastre (asociado a las obras de mitigación social del Proyecto Hidroeléctrico Reventazón), como una potencial barrera para la conectividad del jaguar (Panthera onca) y otras especies. Este estudio sugiere un método para identificar los cruces de fauna sobre el camino. Se tomaron datos de junio del 2011 a enero del 2012. Se compararon los registros de avistamientos y atropellos entre una sección de lastre y una de pavimento del mismo camino. Para identificar los pasos de fauna se sobrepusieron distintas fuentes de información: recorridos, entrevistas y conectividad estructural. Al comparar los caminos se encontró que en el pavimento circulan más vehículos, hay más casas, hay más atropellos y se registran menos especies y avistamientos de fauna. Se identificaron tres sitios de cruces de fauna y cinco sectores. Se registró el cruce del camino por jaguar y caucel (Leopardus wiedii) y el uso de una alcantarilla por mapaches (Procyonlotor). Esta metodología puede ser implementada por proyectos viales para identificar los sitios de cruce de fauna y brindar recomendaciones sobre las medidas ambientales de mitigación a implementar asociadas a mejoras o construcción de caminos.

Continent-Wide 2-D Co-Seismic Deformation of the 2015 Mw 8.3 Illapel, Chile Earthquake Derived from Sentinel-1A Data: Correction of Azimuth Co-Registration Error

In this study, we mapped the co-seismic deformation of the 2015 Mw 8.3 Illapel, Chile earthquake with multiple Sentinel-1A TOPS data frames from both ascending and descending geometries. To meet the requirement of very high co-registration precision, an improved spectral diversity method was proposed to correct the co-registration slope error in the azimuth direction induced by multiple Sentinel-1A TOPS data frames. All phase jumps that appear in the conventional processing method have been corrected after applying the proposed method. The 2D deformation fields in the east-west and vertical directions are also resolved by combing D-InSAR and Offset Tracking measurements. The results reveal that the east-west component dominated the 2D displacement, where up to 2 m displacement towards the west was measured in the coastal area. Vertical deformations ranging between −0.25 and 0.25 m were found. The 2D displacements imply the collision of the Nazca plate squeezed the coast, which shows good accordance with the geological background of the region.

Rupture model of Mw 7.8 2015 Gorkha, Nepal earthquake: Constraints from GPS measurements of coseismic offsets

We estimate coseismic offsets at 20 sites in India due to the 25 April 2015 Gorkha, Nepal (Mw 7.8) earthquake. Only four sites in the Indian region, immediately to the south of the rupture, showed discernible coseismic horizontal offsets ranging between 3 and 7mm toward north. We invert these offsets along with 13 other offsets at GPS sites in Nepal and 33 offsets at sites in China, for the estimation of slip distribution on the causative rupture. We assume that rupture occurred on the Main Himalayan Thrust (MHT). In our estimated slip model, high slip reaching ∼5m occurred east of the mainshock epicenter, and the slip on rupture terminated close to the Main Boundary Thrust (MBT). Thus the rupture for this earthquake remained blind, increasing the potential for future earthquake in the shallow, updip unruptured part of the MHT.

Improving marine biodiversity offsetting: A proposed methodology for better assessing losses and gains

Although the limitations of implementing the mitigation hierarchy have been widely discussed in scientific literature, these studies have drawn mainly on feedback concerning terrestrial ecosystems. In the case of development projects in marine and coastal environments, certain issues must be tackled to improve existing practice. This article focuses on the methodologies used to assess both the ecological losses resulting from a development project and the ecological gains generated by an offset measure. The originality of this article is to propose a standardized, operational approach regardless of the development project and the ecosystem impacted that (i) enhances avoidance and reduction efforts and (ii) assesses biodiversity offset needs based on data available in Environmental Impact Assessments (EIAs). The proposed hybrid method combines a multi-criteria analysis of the state of the environment, inspired by the Unified Mitigation Assessment Method (UMAM), and a more accurate assessment at indicator level inspired by Habitat Equivalency Analysis (HEA). The steps of the method, from the selection of biophysical indicators to offset sizing, are described and are then applied to two EIA case studies: one related to a port extension and the other to an offshore wind farm.

How to best measure femoral length and lateralisation after total hip arthroplasty on antero-posterior pelvic radiographs.

Various methods exist for measuring limb length and lateralisation after total hip arthroplasty. Most of them utilise standard anteroposterior (AP) pelvic radiographs, but their results can be affected by patient position during imaging and thus the position of the lower limb on the coronal plane. The aim of this study is to evaluate how commonly used measuring methods of limb lengthening and femoral offset are affected by the position of the lower limb in the coronal plane. A standing pelvic AP radiograph post implantation of a right total hip prosthesis was digitised. The right femur and its femoral stem were digitally segmented, such that they could be positioned orthogonal to the pelvis horizontal reference, with 10° of adduction, and with 10° of abduction, with respect to the centre of rotation. Various limb lengths and implant lateralisation were also digitised. We obtained nine x-rays differing one to three variables. Twice four independent surgeons performed three femoral length measurement methods and femoral offset measurement methods. Intra and inter-observer error as well as the effect of the femoral position on the measurements were studied. With respect to length measurements, the distance between the centre of rotation (C) and the tip of the lesser trochanter (LT) increased by 3mm per cm of lateralisation. This measurement was not affected by the hip position in abduction or adduction. The distance between the tip of the lesser or greater trochanter (GT) and the horizontal passing through the centre of rotation was strongly affected by the hip position in abduction or adduction. With respect to offset, the distance between the centre of rotation and the greater trochanter (C-GT) was the most consistent and was not affected by variations in lengths or femoral axis. At the level of the lesser trochanter, the distance of the femoral anatomical axis and to Perkin's line was heavily influenced by the femoral position. The C-LT distance was consistent in measuring limb length and the C-GT distance was reliable in determining femoral offset regardless of the relative position of the femur.

Application of UAV Photography to Refining the Slip Rate on the Pyramid Lake Fault Zone, Nevada

The Pyramid Lake fault zone (PLFZ) is a 50‐km‐long, active northwest‐trending right‐lateral fault in the northern Walker Lane, located ∼30 km east of Reno, Nevada. Previous paleoearthquake and slip‐rate studies report that the Pyramid Lake fault has produced four surface‐rupturing paleoearthquakes since 15,475±720 cal B.P., three of which occurred after 8980±260 cal B.P., and has had an average minimum slip rate of 2.6±0.3 mm/yr since the late Pleistocene. These observations imply that coseismic offset for each paleoearthquake averaged 7–9 m, larger than expected from empirical scaling relationships for a strike‐slip fault of its length. To reconcile this discrepancy, we used a small camera‐mounted unmanned aerial vehicle to develop high‐resolution digital elevation models and interpret previously unreported right‐laterally offset geomorphic features along the northern section of the PLFZ. Offset measurements at seven sites range from 8 to 21 m. The ages of displaced features are interpreted from previous lake level and mapping studies of Lake Lahontan. From these observations, slip‐rate estimates at the sites range between 0.5 and 1.6 mm/yr. These lower values of slip rate require that coseismic displacements associated with previously reported paleoearthquakes average only 3–5 m, within the range that would be predicted from empirical scaling relationships of rupture length and coseismic displacement.

背部偏荷重を考慮したパワーアシストスーツの歩行制御の研究

A powered exoskeleton which is mechanical equipment used for assisting and increasing human power, and usage of them has been considered in nuclear facility. Moreover, the method that develops upper PE and base PE separately has been devised. Connecting the general use base PE and varieties of upper PE designed for work contents, it's expected to decrease overall development cost and term. However, due to connecting the upper PE, an offset load happens and the operator feels as being pulled backward. It hinders the operator's motion and the strength relies on the structure of the upper PE, the control system corresponding to any upper PE is needed for development of PE. Therefore, in this research, we propose control method to compensate the offset load and measure effects of decreasing it with some experiments.

Intraoperative Measurement of Femoral Offset in Primary Total Hip Arthroplasty

Intraoperative Measurement of Femoral Offset in Primary Total Hip Arthroplasty

Late Quaternary Tectonic Deformation of the Eastern End of the Altyn Tagh Fault

AbstractThe Quaternary activity of the faults at the eastern end of the Altyn Tagh fault, including the Dengdengshan–Chijiaciwo, Kuantanshan and Heishan faults, was studied on the basis of interpretation of satellite images, trenching, geomorphologic offset measurements and dating. The Altyn Tagh fault has extended eastwards to Kuantanshan Mountain. The left–slip rates of the Altyn Tagh fault decreased through the Qilianshan fault and were transformed into thrust and folds deformation of many NW– trending faults within the Jiuxi basin. Meanwhile, under NE–directed compression of the Tibetan plateau, thrust dominated the Dengdengshan–Chijiaciwo fault northeast of the Kuantanshan uplift with a rate lower than that of every fault in the Jiuxi basin south of the uplift, implying that tectonic deformation is mainly confined to the plateau interior and the Hexi Corridor area. From continual northeastward enlargement of the Altyn Tagh fault, the Kuantanshan uplift became a triangular wedge intruding to the east, while the Kuantanshan area at the end of this wedge rose up strongly. In future, the Altyn Tagh fault will continue to spread eastward along the Heishan and Jintananshan faults. The results have implications for understanding the propagation of crustal deformation and the mechanism of the India–Eurasian collision.

Lateral Offset Quality Rating along Low Slip Rate Faults: Application to the Alhama de Murcia Fault (SE Iberian Peninsula)

Seismic hazard assessment of strike-slip faults is based partly on the identification and mapping of landforms laterally offset due to fault activity. The characterization of these features affected by slow-moving faults is challenging relative to studies emphasizing rapidly slipping faults. We propose a methodology for scoring fault offsets based on subjective and objective qualities. We apply this methodology to the Alhama de Murcia fault (SE Iberian Peninsula) where we identify 138 offset features that we mapped on a high-resolution (0.5 × 0.5 m pixel size) Digital Elevation Model (DEM). The amount of offset, the uncertainty of the measurement, the subjective and objective qualities, and the parameters that affect objective quality are independent variables, suggesting that our methodological scoring approach is good. Based on the offset measurements and qualifications we calculate the Cumulative Offset Probability Density (COPD) for the entire fault and for each fault segment. The COPD for the segments differ from each other. Tentative interpretation of the COPDs implies that the slip rate varies from one segment to the other (we assume that channels with the same amount of offset were incised synchronously). We compare the COPD with climate proxy curves (aligning using the very limited age control) to test if entrenchment events are coincident with climatic changes. Channel incision along one of the traces in Lorca-Totana segment may be related to transitions from glacial to interglacial periods.

Validation of meter-scale surface faulting offset measurements from high-resolution topographic data

Studies of active fault zones have flourished with the availability of high-resolution topographic data, particularly where airborne light detection and ranging (lidar) and structure from motion (SfM) data sets provide a means to remotely analyze submeter-scale fault geomorphology. To determine surface offset at a point along a strike-slip earthquake rupture, geomorphic features (e.g., stream channels) are measured days to centuries after the event. Analysis of these and cumulatively offset features produces offset distributions for successive earthquakes that are used to understand earthquake rupture behavior. As researchers expand studies to more varied terrain types, climates, and vegetation regimes, there is an increasing need to standardize and uniformly validate measurements of tectonically displaced geomorphic features. A recently compiled catalog of nearly 5000 earthquake offsets across a range of measurement and reporting styles provides insight into quality rating and uncertainty trends from which we formulate best-practice and reporting recommendations for remote studies. In addition, a series of public and beginner-level studies validate the remote methodology for a number of tools and emphasize considerations to enhance measurement accuracy and precision for beginners and professionals. Our investigation revealed that (1) standardizing remote measurement methods and reporting quality rating schemes is essential for the utility and repeatability of fault-offset measurements; (2) measurement discrepancies often involve misinterpretation of the offset geomorphic feature and are a function of the investigator’s experience; (3) comparison of measurements made by a single investigator in different climatic regions reveals systematic differences in measurement uncertainties attributable to variation in feature preservation; (4) measuring more components of a displaced geomorphic landform produces more consistently repeatable estimates of offset; and (5) inadequate understanding of pre-event morphology and post-event modifications represents a greater epistemic limitation than the aleatoric limitations of the measurement process.

Finite fault slip models for the 11 August 2012 Varzaghan-Ahar, NW Iran earthquakes (Mw 6.4 and 6.3) from near-field GPS measurements of coseismic offsets

We use coseismic offsets, derived from continuous GPS measurements at six nearby sites, due to the twin Varzaghan-Ahar earthquakes (northwest Iran) of 11 August 2012 (Mw 6.4 and 6.3) to constrain slip distribution on the ruptures of two earthquakes. We assume that slip during the two earthquakes occurred on conjugate faults. Majority of the slip occurred during the first earthquake which involved dextral slip on the east west trending vertical plane. The earthquake involved slip at shallow depth which reached up to ∼0.9m at the surface, consistent with the evidence of surface rupture and the observed offsets. During the second earthquake oblique slip occurred on a north–south rupture having steep dip towards east and extending towards north from the eastern edge of the first earthquake. Maximum slip of ∼0.4m occurred at depth of ∼6–8km. Derived moment magnitude of the first earthquake (6.45) from our analysis is consistent with the reported moment magnitude, while that of the second earthquake (6.1) is slightly underestimated from our analysis.

Role of sills in the development of volcanic fields: Insights from lidar mapping surveys of the San Rafael Swell, Utah

Analysis of airborne and terrestrial lidar data demonstrates that >0.4 km 3 of magma cooled in sills at shallow (<1 km) depth in the now-eroded Pliocene San Rafael Swell distributed volcanic field, Utah (USA). The volumes of each of seven sills are estimated from three-dimensional (3-D) models of the lidar data and range from 10 –4 to 10 –1 km 3 . Directions of magma flow during emplacement are interpreted from precise sill thickness measurements and measurements of linear vertical offsets within the sills, helping to identify feeder conduits and dikes; 3-D map relationships derived from lidar data demonstrate that magma flowed into and out of sills from these active dikes and eruptive conduits. Mapped sill volumes account for >92% of intrusive material within the 50 km 2 study area. We conclude that sills played a significant role in modifying eruption dynamics during activity in San Rafael, and suggest that monitoring of sill inflation and deflation in active distributed volcanic fields may provide key information about unrest and potential eruption dynamics.