Horizontal Distance Measurements Research Articles

Ultrasound-based horizontal ranging in the localization of fetal conus medullaris.

Currently, there are a variety of methods for ultrasound to localize the conus medullaris. A concern is that measured values can be influenced by variations in spinal flexion and extension. To overcome this limitation, the present study measures the horizontal distance (HD) between the end of the conus medullaris and the caudal edge of last vertebral body ossification in normal fetus at different gestational weeks, and analyzes the relationship between the measured value and fetal growth, as well as the utility of these measurements in assessing the position of the conus medullaris. A total of 655 fetuses at gestational weeks 18-40, who underwent routine prenatal ultrasound, were selected in the study. We measured the distance between the end of the cone of the fetal spinal cord and the caudal end of the final vertebral ossification center (Distance1, D1), the distance between the end of the spinal cord cone and the intersection of the extension of D1 with the caudal skin (Distance2, D2), and HD. We analyzed the correlation between the measurements and gestational weeks, established normal reference values, the ratio of D1, D2 and HD to the commonly used growth parameters was calculated. The ratios of D1, D2, HD and the application value of each ratio phase were analyzed, and the reliability analysis of repeated measurement results among physicians was performed. D1, D2 and HD exhibited strong linear correlations with gestational weeks. Among the ratios of D1, D2 and HD to common growth parameters, D2/FL stabilized after 20 weeks of gestation and consistently exceeded 1. Repeatability tests between D1, D2 and HD showed good reliability (P> 0.05). D1, D2 and HD are significantly correlated with gestational age. Horizontal distance measurement can effectively determine the position of fetal conus medullaris, enabling rapid prenatal evaluation of low position of conus medullaris and excluding the possibility of tethered cord.

Stereoscopic imaging with spherical panoramas for measuring tree distance and diameter under forest canopies

This study is the first to adapt stereoscopic imaging to measure tree distance and diameter under forest canopies with spherical panoramas. The proposed stereoscopy method requires two spherical panoramas taken at a known distance directly on top of each other. The geometry was comprehensively laid out. Twenty-three plots were randomly established in planted forests. Sample trees were selected with a small basal area factor (BAF) for diameter at breast height and horizontal distance measurement. A larger BAF was used to subsample trees for upper stem diameters. Only fully visible trees were used in the analysis. Results showed that precision decreased with increasing distance from plot centre. Tree distance could be accurately and precisely estimated up to a distance of ~10 m from plot centre. For tree diameters, better accuracy and precision was achieved when a tree was within 5 m from plot centre or its diameter was less than 20 cm. Maintaining the required vertical displacement between panoramas was challenging in the field due to difficult terrain and heavy equipment, which are likely sources of error. With continued advancement in photography equipment, shooting spherical panorama becomes easier. Our proposed method could potentially lead to a citizen science based forest resources monitoring programme.

A stingless bee can use visual odometry to estimate both height and distance

Bees move and forage within three dimensions and rely heavily on vision for navigation. The use of vision-based odometry has been studied extensively in horizontal distance measurement, but not vertical distance measurement. The honey bee Apis mellifera and the stingless bee Melipona seminigra measure distance visually using optic flow-movement of images as they pass across the retina. The honey bees gauge height using image motion in the ventral visual field. The stingless bees forage at different tropical forest canopy levels, ranging up to 40 m at our site. Thus, estimating height would be advantageous. We provide the first evidence that the stingless bee Melipona panamica utilizes optic flow information to gauge not only distance traveled but also height above ground, by processing information primarily from the lateral visual field. After training bees to forage at a set height in a vertical tunnel lined with black and white stripes, we observed foragers that explored a new tunnel with no feeder. In a new tunnel, bees searched at the same height they were trained to. In a narrower tunnel, bees experienced more image motion and significantly lowered their search height. In a wider tunnel, bees experienced less image motion and searched at significantly greater heights. In a tunnel without optic cues, bees were disoriented and searched at random heights. A horizontal tunnel testing these variables similarly affected foraging, but bees exhibited less precision (greater variance in search positions). Accurately gauging flight height above ground may be crucial for this species and others that compete for resources located at heights ranging from ground level to the high tropical forest canopies.

A long-term seafloor experiment using an acoustic ranging system: Precise horizontal distance measurements for detection of seafloor crustal deformation

We have developed a seafloor acoustic ranging system to monitor local seafloor crustal deformation. In August 2007 we carried out an experiment to estimate the long-term stability of acoustic measurements collected by the system. We deployed four precision acoustic transponders with about 920m and 590m spacing at the depth of 2035m in Kumano-nada, southeast coast Japan, and we collected acoustic ranges for 4months. The observed round-trip travel times showed a variation with peak-to-peak amplitude of about 0.75m in the range. It was confirmed that most of the variation could be explained by changes in sound speed. The standard deviation in the acoustic measurements was about 1.0cm after the correction for sound speed, and the average value of the ranges remained constant within 1cm.

Reproducibility of phantom-based quality assurance parameters in real-time ultrasound imaging

In a large radiological center, the ultrasound (US) quality assurance (QA) program involves several professionals. Although the operator and the parameters utilized can contribute to the results, the selected QA parameters should still reflect the quality of the US scanner, not the measuring process. To evaluate the reproducibility of recommended phantom-based US QA parameters in a realistic environment. Six sonographers measured six high-end US scanners with 20 transducers using a general purpose phantom. Every transducer was measured altogether seven times, using one frequency per transducer. The QA parameters studied were homogeneity, visualization depth, vertical and horizontal distance measurements, axial and lateral resolution, and the correct visibility of anechoic and high-contrast masses. The evaluation of the homogeneity was based on visual observations. Inter-observer interquartile ranges were computed for the grading of the masses. For the other QA parameters, the mean inter- and intra-observer coefficients of variation (CoV) were calculated. In addition, the symmetry of the reverberations when imaging air with a clean transducer was checked. The mean inter-observer CoVs were: visualization depth 11 ± 4%, vertical distance 1.7 ± 0.4%, horizontal distance 1.4 ± 0.6%, axial resolution 22 ± 7%, and lateral resolution 16 ± 8%. The mean intra-observer values were about half of these values with similar standard deviations. The visual evaluation of the homogeneity and the symmetry of the reverberations produced false-positive findings in 5% of the cases, but were found useful in detecting a defective transducer. The grading of the masses had mean interquartile ranges of 20-30% of the grading scale. The inter-observer variability in measuring phantom-based QA parameters can be relatively high. This should be considered when implementing a phantom-based QA protocol and evaluating the results.

A deep-sea observatory experiment using acoustic extensometers: precise horizontal distance measurements across a mid-ocean ridge

In July 2000, an array of instruments called acoustic extensometers was deployed at the Cleft segment of the southern Juan de Fuca Ridge, a seafloor observatory site selected by the National Science Foundation RIDGE Program. These instruments are designed to precisely measure horizontal deformation across the axis of a mid-ocean ridge in order to detect and quantify seafloor spreading events. The instruments were deployed in semipermanent seafloor benchmarks in a linear array that is 1.2-km long and spans the floor of the axial valley. The instruments make daily measurements of distance to their neighbors in the array by recording the round trip travel time of 100-kHz acoustic pulses, and simultaneous temperature measurements are used to correct the ranges for sound speed variations. The instruments are expected to have lifetimes of at least five years. In addition, precise pressure measurements have been made at each benchmark with a remotely operated vehicle in order to monitor for vertical deformation across the array. Preliminary results show that the resolution of the acoustic measurements is /spl plusmn/1-2 cm and that no abrupt deformation events occurred during the first year.

Heighting and Distance Accuracy with Electronic Digital Levels

A Leica NA3000 electronic digital level, one of the newly-introduced heighting equipment, was evaluated for vertical and horizontal distance measurement. A well protected 170 m long 17-section test line was first established for this purpose using geodetic surveying techniques. The test instrument was then used to remeasure the line. Two approaches were followed. In the first, closed loops were run from one end of the line to each of the pegs on the line and back to the starting point in an out-and-back manner. Misclosure errors of loops were then computed and compared to known levelling standards. In the second approach, heights of some pegs on the line were re-established several times with the instrument erected on the one end of the line. Standard deviations of height measurement of each peg were then computed and compared with known standards. The results showed that in the first approach, the test instrument was able to achieve accuracy values commensurate with first order class I levelling standards as set out by the U.S.A.-based Federal Geodetic Control Committee (FGCC), i.e. better than ±3.0k mm. In the second approach, for distances up to 64 m, standard deviations better than ± 60 microns could easily be obtained. Again, this is within the requirements of first order class I levelling standards. Overall, therefore, it can be said that digital electronic levels, as exemplified by the Leica NA3000 model, could be used to support high accuracy levelling operations being them of the geodetic or ordinary type.The distance measuring stage of the test showed that, for up to 64 m from instrument station, the test instrument is capable of measuring distances to accuracy values better than 1/2000. This is sufficient accuracy for some localized survey works, e. g. site preparation in construction industry, pavement maintenance surveys, sewer pipe placement and monitoring etc. where distance errors of a few centimeters in several tens of meters are tolerable.

Nearshore Surveying: Accuracy and Techniques for Improvement

Various concerns of beach and nearshore survey accuracy including methodologies and equipment are addressed. First, four types of horizontal distance measurement apparatus (survey tape, infrared apparatus, microwave and optical range finder) are evaluated through intercomparison of field measurements. Second, analysis methods are developed and applied to horizontal positioning data obtained from triangulation surveys. The method provides the most probable location accompanied with a measure of uncertainty based on general characteristics of arc intersections. Finally, methods are developed for the postprocessing of standard bathymetric data obtained from a combination of land and boat surveys with a certain overlap region. The general method considers adjustments to both the vertical and horizontal positions obtained by a Fathometer and a microwave system, respectively, through offsets and linear scale factors such that for each profile line, there is a maximum of four free parameters to be optimized. The method is applied to a set of field data and compares the improvements obtained by allowing different numbers of free parameters.

Location and orientation of eruptive fissures and feederdykes at Mount Etna; influence of gravitational and regional tectonic stress regimes

Lava extrusion from fissures on the flanks of the Etna volcano is a common feature of recent activity, as evidenced by the eruptions of 1971, 1981, 1983, and 1985, and was of similar importance during prehistoric times. We propose here a model within which the location and orientations of the large majority of historic eruptive fissures on Etna's flanks, together with their feeder-dykes, are explained within the framework of a gravitational stress regime. Stress orientations within this regime are controlled largely by the gross morphology of the volcano, but are significantly modified by local topographic anomalies. We propose that the gravitational stress regime largely supercedes an earlier developed regional tectonic stress regime, which still operates in the sub-volcanic basement, and may remain the dominant control of eruptive fissure and feeder-dyke disposition at lower altitudes on the flanks. The proposed model is supported by: (1) detailed examination of fissure locations and orientations, and the relationship between fissure azimuths and topography; (2) precise horizontal distance measurement and vertical ground deformation studies of a recent eruption; and (3) qualitative physical modelling experiments in which coloured water is injected into solidified gelatine solutions representing variously shaped volcanic constructs. A cautious approach is advocated when extrapolating trends of spatially limited fissure segments for the purpose of locating potential sites of magma ascent, and implications of the model for hazard analysis are outlined.

Crustal deformation and gravity changes during the first ten years of exploitation of the new travale — radicondoli geothermal field, Italy

The results of precise levelling measurements on a specially constructed network of benchmarks in the Travale geothermal area (Tuscany, Italy) revealed that the central part of this area is subsiding and that the average rate of subsidence in the period 1973–1983 was 20–25 mm/year. Three series of horizontal distance measurements were carried out (1980, 1981, 1982) to monitor variations in the coordinates of the bases of a horizontal control net. The variations noted in this time interval range between 13 and 36 mm, slightly exceeding the semi-axis values of their error ellipses. A series of gravity measurements was carried out annually between 1979 and 1982 on a network of gravity benchmarks coinciding with part of the topographic benchmarks. The g variations observed reached a maximum of 40 μGal. A tentative correlation of these data with field exploitation data indicates a possible means of interpreting the variations observed during these surveys.

Analysis of surface deformation data, Kilauea Volcano, Hawaii: October 1966 to September 1970

A least squares inversion technique has been applied to surface displacement measurements made at Kilauea Volcano, Hawaii, in an attempt to locate centers of intrusive activity. Utilizing analytic expressions for the displacement field arising from dilatational sources in an elastic half space, this technique allows for the simultaneous inversion of level, tilt, and horizontal distance measurements in terms of the location and volume of the intrusive body. A variety of simple elastic model geometries, representing possible shapes for intrusive bodies in the summit region of Kilauea, were examined. None of the model geometries considered significantly improved the quality of the model fit to the available data over that obtained by a point source model. Calculations based on elastic models to consecutive level surveys were compared to available tilt data and horizontal distance measurements. These comparisons indicate occasional departures from ideal elastic behavior. The departure of measured tilt patterns from calculated tilt values may be the result of earthquake activity or episodic block movements superimposed on larger elastic displacements. The departure of measured and calculated horizontal measurements reveals a gradual north‐south extensional strain across the summit caldera of Kilauea in addition to the elastic uplift and subsidence patterns determined from level surveys. A minimum estimate for the magma supply rate to Kilauea is provided by the elastic models to the level data. The average rate for the period from October 1966 to September 1970 was 0.07 km3 per year.

Resolution and accuracy in two dimensional echocardiography

The resolution and accuracy of commercially available two dimensional echocardiographic systems were tested by Imaging two types of in vitro test objects. One consisted of a series of fine parallel threads spaced at known intervals and the other was a tissue phantom in which a series of holes of known size had been cut. The echocardiographic systems tested included a mechanical single element sector scanner, a three element rotary sector scanner and a phased array system. Azlmuthal resolution, lateral resolution and accuracy of horizontal distance measurements were assessed at depths of 2 and 6 cm. For each system, azimuthal resolution was better than lateral resolution, especially when assessed with use of the parallel threads. When the tissue phantom was imaged, the best resolution (2 mm in azimuthal and lateral directions) was obtained with the highest frequency transducer tested (3.5 MHz). The apparent size of a tissue defect was sensitive to gain settings, especially at a depth of 2 cm with lower frequency transducers; at a depth of 6 cm, echographic measurements of defect size were accurate to within 2.5 mm. Recent applications of two dimensional echocardiography require resolution near the apparent limits of current equipment. It Is recommended that the highest frequency transducer and lowest possible gain settings be used in these situations.