Today, the GNSS （global navigation satellite system） is used for more complicate and accurate applications such as monitoring or stake out works. The truth lies in the fact that in the most of the times not enough a...Today, the GNSS （global navigation satellite system） is used for more complicate and accurate applications such as monitoring or stake out works. The truth lies in the fact that in the most of the times not enough attention is paid to the antenna＇s setup. Usually, gross errors are found in the antenna＇s centering, leveling and in the measurement of its height, which are significant. In this paper, a thoroughly analysis of the above mentioned errors is carried out. The influence of these errors in the calculation of the X, Y, Z Cartesian geocentric coordinates and the ~, 2, h ellipsoid geodetic coordinates of a point P on the earth＇s surface, is analyzed and is presented in several diagrams. Also a new convenient method for the accurate measurement of the antenna＇s height is presented and it is strongly proposed. The conclusions outline the magnitude of these errors and prove the significance of the antenna＇s proper setup at the accurate GNSS applications.展开更多
The ionosphere is one of the major error sources in Global Navigation Satellite System （GNSS） posi- tioning, navigation and timing. Estimating the ionospheric delays precisely is of great interest in the GNSS commun...The ionosphere is one of the major error sources in Global Navigation Satellite System （GNSS） posi- tioning, navigation and timing. Estimating the ionospheric delays precisely is of great interest in the GNSS community. To date, GNSS observables for ionospheric estimation are most commonly based on carrier phase smoothed code measurements. However, leveling errors, which affect the performance of ionospheric modeling and differential code bias （DCB） estimation, exist in the carrier phase smoothed code observations. Such leveling errors are caused by the multipath and the short-term variation of DCB. To reduce these leveling errors, this paper investigates and estimates the ionospheric delays based on carrier phase measurements without the leveling errors. The line-of-sight ionospheric observables with high precision are calculated using precise point positioning （PPP） techniques, in which carrier phase measurements are the principal observables. Ionosphere-free and UofC PPP models are applied and compared for their effectiveness to minimize the leveling errors. To assess the leveling errors, single difference of ionospheric observables for a short baseline is examined. Results show that carrier phase- derived ionospheric observables from PPP techniques can effectively reduce the leveling errors. Furthermore, we compared the PPP ionosphere estimation model with the conventional carrier phase smoothed code method to assess the bias consistency and investigate the biases in the ionospheric observables.展开更多
This work analyzes the quality of crustal tilt and strain observations during 2014, which were acquired from 269 sets of ground tiltmeters and 212 sets of strainmeters. In terms of data quality, the water tube tiltmet...This work analyzes the quality of crustal tilt and strain observations during 2014, which were acquired from 269 sets of ground tiltmeters and 212 sets of strainmeters. In terms of data quality, the water tube tiltmeters presented the highest rate of excellent quality,approximately 91%, and the pendulum tiltmeters and ground strainmeters yielded rates of81% and 78%, respectively. This means that a total of 380 sets of instruments produced high-quality observational data suitable for scientific investigations and analyses.展开更多
Introduction Errors are unavoidable in language learning, however, to a great extent, teachers in most middle schools in China regard errors as undesirable, a sign of failure in language learning. Most middle schools ...Introduction Errors are unavoidable in language learning, however, to a great extent, teachers in most middle schools in China regard errors as undesirable, a sign of failure in language learning. Most middle schools are still using the grammar-translation method which aims at encouraging students to read scientific works and enjoy literary works. The other goals of this method are to gain a greater understanding of the first language and to improve the students’ ability to cope with difficult subjects and materials, i.e. to develop the students’ minds. The practical purpose of using this method is to help learners pass the annual entrance examination. "To achieve these goals, the students must first learn grammar and vocabulary,... Grammar is taught deductively by means of long and elaborate explanations... students learn the rules of the language rather than its use." (Tang Lixing, 1983:11-12)展开更多
文摘Today, the GNSS （global navigation satellite system） is used for more complicate and accurate applications such as monitoring or stake out works. The truth lies in the fact that in the most of the times not enough attention is paid to the antenna＇s setup. Usually, gross errors are found in the antenna＇s centering, leveling and in the measurement of its height, which are significant. In this paper, a thoroughly analysis of the above mentioned errors is carried out. The influence of these errors in the calculation of the X, Y, Z Cartesian geocentric coordinates and the ~, 2, h ellipsoid geodetic coordinates of a point P on the earth＇s surface, is analyzed and is presented in several diagrams. Also a new convenient method for the accurate measurement of the antenna＇s height is presented and it is strongly proposed. The conclusions outline the magnitude of these errors and prove the significance of the antenna＇s proper setup at the accurate GNSS applications.
文摘The ionosphere is one of the major error sources in Global Navigation Satellite System （GNSS） posi- tioning, navigation and timing. Estimating the ionospheric delays precisely is of great interest in the GNSS community. To date, GNSS observables for ionospheric estimation are most commonly based on carrier phase smoothed code measurements. However, leveling errors, which affect the performance of ionospheric modeling and differential code bias （DCB） estimation, exist in the carrier phase smoothed code observations. Such leveling errors are caused by the multipath and the short-term variation of DCB. To reduce these leveling errors, this paper investigates and estimates the ionospheric delays based on carrier phase measurements without the leveling errors. The line-of-sight ionospheric observables with high precision are calculated using precise point positioning （PPP） techniques, in which carrier phase measurements are the principal observables. Ionosphere-free and UofC PPP models are applied and compared for their effectiveness to minimize the leveling errors. To assess the leveling errors, single difference of ionospheric observables for a short baseline is examined. Results show that carrier phase- derived ionospheric observables from PPP techniques can effectively reduce the leveling errors. Furthermore, we compared the PPP ionosphere estimation model with the conventional carrier phase smoothed code method to assess the bias consistency and investigate the biases in the ionospheric observables.
基金supported by Special Foundation of Earthquake Science(201408006)Director Foundation of Institute of Seismology,China Earthquake Administration(201516214)
文摘This work analyzes the quality of crustal tilt and strain observations during 2014, which were acquired from 269 sets of ground tiltmeters and 212 sets of strainmeters. In terms of data quality, the water tube tiltmeters presented the highest rate of excellent quality,approximately 91%, and the pendulum tiltmeters and ground strainmeters yielded rates of81% and 78%, respectively. This means that a total of 380 sets of instruments produced high-quality observational data suitable for scientific investigations and analyses.
文摘Introduction Errors are unavoidable in language learning, however, to a great extent, teachers in most middle schools in China regard errors as undesirable, a sign of failure in language learning. Most middle schools are still using the grammar-translation method which aims at encouraging students to read scientific works and enjoy literary works. The other goals of this method are to gain a greater understanding of the first language and to improve the students’ ability to cope with difficult subjects and materials, i.e. to develop the students’ minds. The practical purpose of using this method is to help learners pass the annual entrance examination. "To achieve these goals, the students must first learn grammar and vocabulary,... Grammar is taught deductively by means of long and elaborate explanations... students learn the rules of the language rather than its use." (Tang Lixing, 1983:11-12)
