A Three-Step Method for Determining Unhealthy Time Period of GPS Satellite Orbit in Broadcast Ephemeris and Its Preliminary Applications for Precise Orbit Determination

Abstract

Abnormal information of satellite orbits inevitably appears in the broadcast ephemeris. Failure to obtain unhealthy information on GPS satellite orbits in precise orbit determination (POD) degrades GPS service performance. At present, the reliable unhealthy information published by the Center for Orbit Determination in Europe (CODE) is usually used, but it has at least one-day latency, and the current level of unhealthy information cannot fully meet the requirements of rapid and real-time geodetic applications, especially for non-IGS (International global navigation satellite systems (GNSS) Service) analysis centers and BeiDou navigation satellite system (BDS) users. Furthermore, the unhealthy orbit information detected by the traditional method, which is based on the synchronized pseudo-range residuals and regional observation network, cannot meet the requirement of setting separate sub-arcs in POD. In view of these problems, we propose a three-step method for determining unhealthy time periods of GPS satellite orbit in broadcast ephemeris during POD to provide reliable unhealthy information in near-real time. This method is a single-epoch solution, and it can detect unhealthy time periods in each sampling of observation in theory. It was subsequently used to detect unhealthy time periods for satellites G09 and G01 based on the 111 globally distributed tracking stations in the IGS. The performance of the new method was evaluated using cross-validation. Based on the test results, it detected an orbital leap for G09 in the broadcast ephemeris from 09:59:42 to 14:00:42 on 25 August 2017. Compared to the traditional method, the unhealthy start time using the three-step method was in better agreement with the information provided by CODE’s satellite crux files. G01 did not appear to have an orbital leap on the specified date, but it was misjudged by the traditional method. Furthermore, compared to the traditional method, the three-step method can perform unhealthy time period detection for a satellite all day long. In addition, precise orbit determination for unhealthy satellites is realized successfully with the unhealthy orbit arc information identified in this study. Compared to the CODE orbit, the root mean square and standard deviation of the new method for G09 are less than 2 cm, and the three-step method shows an improvement in accuracy compared with the traditional method. From the above results, it can be seen that this study can provide a feasible approach to meet the real-time unhealthy time period detection requirements of a satellite orbit in a broadcast ephemeris during POD. Furthermore, compared to waiting for updates of CODE’s satellite crux files or for accumulating delayed observation data, it has the potential to provide additional information in the process of generating ultra-rapid/real-time orbits.

Optimising the Use of National CORS Data in the Context of Thailand

“…The green points are the stations with the last 10-day update, the yellow rectangles are the stations with the last 30-day update, and the red triangles are the unhealthy stations. The unhealthy stations may have problems with no or unreliable signal transmission (De Groot, 2017) or obtaining unreliable ephemeris information (Ye et al, 2019). CORS networks that are part of the IGS network must be standardised according to the IGS guideline (International GNSS Service Infrastructure Committee, 2015).…”

Impact analysis of arc length in multi-GNSS ultra-rapid orbit determination based on the one-step method

“…Compared to real-time kinematic positioning [1,2], satellite ultra-rapid orbit products are some of the most important products for positioning, navigation, and timing users to obtain real-time and near real-time precise services in a single point mode [3,4]. Several research projects have been focused on improving the accuracy of satellite ultra-rapid orbit products as this has always been a difficulty in the field of global navigation satellite systems (GNSSs) [5][6][7][8]. Development over decades has led to improvements in the updating rate of GPS satellites' ultra-rapid orbit products provided by the International GNSS Service (IGS), from 12 h initially to the current 6 h. Orbit accuracy (one-dimensional mean RMS values in the three XYZ geocentric components) has also been reduced from dozens of cm initially to approximately 5 cm.…”

“…5 Natural Resources Canada 6 , the U.S. Naval Observatory AC 7 , Geodetic Observatory Pecný in the Czech Republic [7,9,10] and Wuhan University (WHU) 8 [24] use 48-72, 27, 72, and 24 h orbit arc lengths to provide ultra-rapid orbit products, respectively. Additionally, to develop a prediction strategy that contributes to the IGS ultra-rapid product combination, Choi et al [21] analyzed the impact of orbit arc length on ultra-rapid orbits based on the GPS rapid orbit products provided by the IGS, and it was concluded that the most stable and accurate ultra-rapid GPS satellite orbits can be obtained with an orbit arc length of 40-45 h [21].…”

Editorial for the Special Issue: “High-Precision GNSS: Methods, Open Problems and Geoscience Applications”

“…Aiming to shorten the interruption period of BDS broadcast ephemerides after satellite maneuverings and improve the ephemeris accuracy, Qiao et al [12] proposed a two-step orbit recovery strategy based on a piecewise linear thrust model. In another contribution from Ye et al [13], the authors presented a three-step method for determining unhealthy time periods of GPS satellite orbit in broadcast ephemeris during POD to provide reliable information in near-real time. For the purpose of improving the ultra-rapid orbit accuracy for BDS-2/BDS-3, Wang et al [14] linked the predicted clock offsets into the POD as constraints to strengthen the estimation.…”