Correction Model of BDS-3 Satellite Pseudorange Multipath Delays and Its Impact on Single-Frequency Precise Point Positioning

Precise point positioning (PPP) is used in many fields. However, pseudorange multipath delay is an important error that restricts its accuracy. Pseudorange multipath delay can be considered as the combination of effective information and observation noise; it can be modeled after removing the observation noise. In this work, elastic nets (EN) regularization denoising method is proposed and compared with L2-norm regularization denoising method. Then, quadratic polynomial (QP) model plus autoregressive (AR) model (QP + AR) are used to model the denoised pseudorange multipath delays. Finally, the modeling results are corrected to the observations to verify the improvement of BDS-3 single-frequency PPP accuracy. Three single-frequency PPP schemes are designed to verify the effectiveness of denoising method and QP + AR model. The experimental results show that the accuracy improvement of B3I and B2a is more obvious than that of B1I and B1C when the modeling values are corrected to the pseudorange observations. The improvement of B3I and B2a in the east (E) and up (U) directions can reach 10.6%∼34.4% and 5.9%∼65.7%, and the improvement of the north (N) direction is mostly less than 10.0%. The accuracy of B1I and B1C in E and U directions can be improved by 0%∼30.7% and 0.4%∼28.6%, respectively, while the accuracy of N direction can be improved slightly or even decreased. Using EN regularization denoising and QP + AR model correction, single-frequency PPP performs better at B3I and B2a, while L2-norm regularization denoising and QP + AR model correction perform better at B1I and B1C. The accuracy improvement of B2a and B3I is more obvious than that of B1I and B1C. The convergence time after MP correction of each frequency is slightly shorter. Overall, the proposed pseudorange multipath delays processing strategy is beneficial in improving the single-frequency PPP of BDS-3 satellite.

Vocational awareness and aspiration of seafaring students in Taiwan

Purpose This study aims to examine variables and factors in vocational awareness and attitudes that affect the vocational aspiration of seafaring course students who are potential future seafaring employees. Design/methodology/approach A literature review was conducted to identify factors that prompt students in seafaring courses to pursue seafaring careers, followed by a design of preliminary questionnaire questions to survey students’ perception on the conditions of seafaring careers (i.e. vocational awareness) and their intention to pursue a seafaring career (i.e., vocational aspiration). A total of 744 seafaring course students in four Taiwanese universities completed a questionnaire developed according to the previous studies. A structured equation modelling was conducted in this research including model validity, goodness of fit, model correction and mediation effects. Findings With a model consisting of four factors for vocational awareness, three factors for overall attitudes and vocational aspiration as a dependent variable, the results showed that factors of vocational awareness and students’ overall attitudes were significantly correlated, and the factors of overall attitudes exhibit strong mediation effects on vocational aspiration from vocational awareness. The results confirmed that the factors are important determinants for the vocational aspiration of students. Originality/value The findings of this study provide a comprehensive approach to understand students’ seafaring aspiration for the universities, governments and shipping companies. Seafaring policies and management are discussed from the research findings.

Ionosphere Models and Their Correction Using Operational Data from the Ionospheric Observation Network

A possibility of correcting ionosphere climate models based on data from a single observation station equipped with the vertical radio sounding ionosonde is studied to monitor the Earth plasma shell in the vicinity of this measuring instrument. The SIMP-STANDARD and IRI models are used for the study. The probabilities of the fact that relative deviations of corrected models are below 10% are taken as criteria of the efficiency of ionosphere climate model correction. The size of the areas around each ionosonde of the state ionospheric network is determined, where an increase in the quality of ionospheric monitoring is possible by correcting the ionosphere climate model based on the data of this particular ionosonde.