• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.535-540
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• 2006

The relationship between the observable noise model and the satellite elevation angle can be modeled quite well by an exponential function.[Jin, 1996] Noise size and dependence on the elevation angle are, however, different for each observation and receiver type. Therefore, the coefficient determination of this model is an issue, and various methods including PR-CP, single difference, and time difference have been suggested. The limitations of them are difficulty to model the carrier phase noise and to eliminate bias. To overcome these disadvantages for using Jin's model, we suggest zero baseline double difference (DD) and noise sorting algorithm. Data DD technique in zero baseline is useful to eliminate all the troublesome GPS biases, and the remaining error is the sum of GPS measurement noises from two satellites. These DD residuals for hours should be sorted by the combination of satellite elevation angles, and then variance value of the residual for each combination can be estimated. Using these values, we construct an over-determined linear equation whose solution is a set of noise variance for each satellite elevation angle. With 24hr Trimble 4000ssi data, we easily worked out the coefficients of the noise model not only for pseudorange but also for carrier phase. We estimated the standard deviation of the measurement DD using our model, and plotted 1 and 3 sigma lines for every epoch to verify the representation of the residual error. 63.3% of pseudorange residual and 65.9% of phase error did not exceed the 1 sigma lines. Additionally, 99.2% and 99.5% of them lied within 3sigma line. These figures prove that the Gaussian property of measurement noise, and that the suggested model by our algorithm corresponds to the observable noise information.

• Journal of Astronomy and Space Sciences
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• v.32 no.4
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• pp.403-409
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• 2015

The Quasi-Zenith Satellite System (QZSS), a dedicated regional Japanese satellite system currently under development, was designed to complement the performance of the Global Positioning System (GPS). The high elevation angle of the QZSS satellite is expected to enhance the effectiveness of GPS in urban environments. Thus, the work described in this paper, aimed to investigate the effect of QZSS on GPS performance, by processing the GPS and QZSS measurements recorded at the Bohyunsan reference station in South Korea. We used these data, to evaluate the satellite visibility, carrier-to-noise density (C/No), performance of single point positioning, and Dilution of Precision (DOP). The QZSS satellite is currently available over South Korea for 19 hours at an elevation angle of more than 10 degrees. The results showed that the impact of the QZSS on users' vertical positioning is greatest when the satellite is above 80 degrees of elevation. As for Precise Point Positioning (PPP) performance, the combined GPS/QZSS kinematic PPP was found to improve the positioning accuracy compared to the GPS only kinematic PPP.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.3
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• pp.365-372
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• 2013

The multibeam surveillance radar is a state-of-art of 3D radar technology. It applies the stacked beams realized by a digital beamformer. In this paper, a hybrid compensation technique on elevation angle errors for low elevation angle targets over the sea in multipath radar environments is proposed. The proposed method can be applied to stacked beam radars. Double null algorithm based on maximum likelihood method in 3-D beamspace domain works well unless the phase difference between the two rays(direct and specular path) is close to $0^{\circ}$ and the magnitude of reflection coefficient is close to 0. To overcome these problems, we propose a hybrid compensation technique which uses the selective double null algorithm and the beam-ratio compensation technique for low-elevation errors on a log scale. Results of computer simulation show that the proposed method outperform conventional monopulse method and double null algorithm only under various multipath environments.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.12 no.1
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• pp.44-50
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• 2006

The purpose of this study is to assess the radiographic effects of normal person with contact laterally wedged insoles with strapping of varying elevations. Eight person who were randomized into group according to their birth dates and wedge elevation, participants wore contact laterally wedged insoles with strapping with elevation of 9, 15, 21mm. Standing radiographs were used to analyze the femorotibial angle for each subject, The result of repeated measures ANOVA's reveled that laterally wedged insoles with strapping of varying elevations produced significantly the femorotibial angle. The degree of change in femorotibial angle with the insole with strapping was effected by the tilt of the lateral wedge(P<0.05). We suggest that these results may be beneficial for manufacturing foot orthotic devices, such as wedged insoles, to control medial and later compartment forces in the knee varus-valgus deformity.

• Journal of Navigation and Port Research
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• v.37 no.5
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• pp.463-469
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• 2013

This paper focuses on GPS positioning accuracy variations according to locations of obstacles which surround GPS station. We derived precise coordinates of a GPS station which has a good visibility. Its observation data was rewritten by assuming signal blocking due to obstacle in the elevation angle of $10^{\circ}$ to $70^{\circ}$. We processed daily and hourly data for 10 days. In the results using daily data, RMSE was at 10mm level. And RMSE increased to 100mm levels in case of hourly data. As the elevation angle of obstacle increased, the horizontal and vertical RMSE increased, while the height estimates decreased. These results showed the higher the elevation angle of the obstacle increased the loss of large amounts of data by blocking satellite signals direction. In terms of the direction, when the blocking thing was located in the east or west, the coordinate has larger error in the east-west direction. And if signal was blocked at the south direction, the difference between the east-west error and the south-north position error was reduced.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11A
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• pp.1078-1084
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• 2010

The tracking performance of a big parabola tracking antenna system for tracking and receiving of the signal from the vehicle is impacted by many factors of the internal and the external of the system. In this paper, we analyze the tracking error due to the radio refraction in the application of the tracking and positioning of the vehicle by using radio frequency. The real measurement data are used for the analysis which had been acquired by using GPS and the tracking systems of C- and S-band frequencies in NARO Space centre. To verify the correlation between the tracking errors measured and the radio refraction, we review the error factors and the accuracies of the tracking systems, and the characteristics of the refractivity. The analysis shows that there are angular errors which are due to the radio refraction and not to be neglected, compared to the accuracies of the tracking systems, in case of low elevation angle less than 10 degrees. Also, the tracking errors depend on the target altitude as well as the elevation angle for the case of the target in the troposphere. It is recommended to correct the tracking angle considering the target altitude and elevation angle for the precise target positioning.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.2
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• pp.294-300
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• 2017

This paper proposes a method for 3-D sound source localization (SSL) using region selection and TDOA. 3-D SSL involves the estimation of an azimuth angle and an elevation angle. With the aim of reducing the computation time, we compare signal energies to select one out of three regions. In the selected region, we compute only one TDOA value for the azimuth angle estimation. Also, to estimate the vertical angle, we choose the higher energy signal from the selected region and pair it up with the elevated microphone's signal for TDOA computation and elevation angle estimation. Our experimental results show that the proposed method achieves average error values of $0.778^{\circ}$ in azimuth and $1.296^{\circ}$ in elevation, which is similar to other methods. The method uses one energy comparison and two TDOA computations therefore, the total processing time is reduced.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.3
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• pp.15-21
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• 2017

In the active SONAR system, various studies have been carried out to enhance the resolution of a received signal. In order to obtain higher resolution for detecting a bottoming cylindrical object, the design of a planar array for SONAR is investigated in this paper. It is necessary to employ planar structures for SONAR array to obtain narrower beam pattern which gives high resolution. In this study, the transmit frequency of each acoustic transducer, which consists of an array is 13 kHz. For efficient detection of a target of an asymmetric size, the concept of areal angle is applied, which considers resolution according to both azimuth and elevation angles in array design. In the design, the areal angle is first investigated to satisfy the resolution requirements, and then based on the value of areal angles, the azimuth angle and the elevation angle are calculated respectively to design an array.

• Journal of the Korea Society for Simulation
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• v.28 no.3
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• pp.75-82
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• 2019

A Satellite Communication (SATCOM), which is applied to various systems to communicate with other systems at the limited wired communication situation, is required to head at a stable point of the space, because this system uses a geostationary satellite. It is important to know satellite tracking heading angles such as elevation angle and azimuth angle for the immovable antenna's latitude, longitude, and altitude. Moreover, calculation of heading angle is critical for SATCOM antenna on a moving platform. In this study, a antenna heading angle calculation method is applied to compute elevation and azimuth angle for a SATCOM antenna and the heading angle simulation is executed for the Korea peninsula and surrounding areas. To verify this simulation, satellite tracking test is conducted using a SATCOM antenna which uses monopulse signal tracking method. The simulation is confirmed by comparing this test result with the simulation. And we make a suggestion for calculation of polarization angle of this antenna.

• Progress in Medical Physics
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• v.27 no.1
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• pp.14-24
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• 2016

Since the head and neck region is densely located with organs at risk (OAR), OAR-sparing is an important issue in the treatment of head and neck cancers. This study-in which different treatment plans were performed varying the head tilt angle on brain tumor patients-investigates the optimal head elevation angle for sparing normal organs (e.g. the hippocampus) and further compares the dosimetric characteristics of different types of radiation equipment. we performed 3D conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), and tomotherapy on 10 patients with brain tumors in the frontal lobe while varying the head tilt angle of patients to analyze the dosimetric characteristics of different therapy methods. In each treatment plan, 95% of the tumor volume was irradiated with a dose of 40 Gy in 10 fractions. The step and shoot technique with nine beams was used for IMRT, and the same prescription dose was delivered to the tumor volume for the 3D-CRT and tomotherapy plans. The homogeneity index, conformity index, and normal tissue complication probability (NTCP) were calculated. At a head elevation angle of $30^{\circ}$, conformity of the isodose curve to the target increased on average by 53%, 8%, and 5.4%. In 3D-CRT, the maximum dose received by the brain stem decreased at $15^{\circ}$, $30^{\circ}$, and $40^{\circ}$, compared to that observed at $0^{\circ}$. The NTCP value of the hippocampus observed in each modality was the highest at a head and neck angle of $0^{\circ}$ and the lowest at $30^{\circ}$. This study demonstrates that the elevation of the patients' head tilt angle in radiation therapy improves the target region's homogeneity of dose distribution by increasing the tumor control rate and conformity of the isodose curve to the target. Moreover, the study shows that the elevation of the head tilt angle lowers the NTCP by separating the tumor volume from the normal tissues, which helps spare OARs and reduce the delivered dose to the hippocampus.