Workshop 2018
Chao Hu - Accuracy analysis of the observed GNSS ultra-rapid orbit and its correction - October 29, 2018 • 31 Views
For ultra-rapid orbits provided by the Global Navigation Satellite System (GNSS), the key parameters, accuracy and timeliness, must be taken into consideration for real-time and near real-time applications. However, from an accuracy analysis of these orbits, orbit errors of the initial observed part were found to increase along with later epochs, imposing concerns on orbit prediction. Furthermore, the observed ultra-rapid orbit was analyzed for data quality and availability in orbit determination; insufficient observations in later epochs appear to generate low accuracy in observed orbits, for which a correlation between the Dilution Of Precision (DOP) of the orbit parameters and their accuracy is found. To correct the observed GNSS ultra-rapid orbit, a correction method based on the DOP values is proposed by building the function models between DOP values and the orbit accuracy. The highly accurate predicted DOP values were then reinserted into the function models to calculate the orbit corrections. With 10-day orbit determination experiments, the results show that the observed ultra-rapid-orbit errors, generated by insufficient observations, can be corrected by 12.35%–22.02% for the last 3 hours of the observed orbits. However, considering the timeliness constraints in ultra-rapid-orbit determination, the orbit accuracy is influenced by with the decrease in the number of stations, thereby reducing the correlation between orbit accuracy and DOP values. A DOP amplification factor is defined to weigh the contribution of each tracking station and optimize the station distribution in the orbit determination procedure. Finally, six schemes are designed to verify the method and strategy in determining the ultra-rapid orbit based on one-month observations. We conclude: (1) with increasing amplification factor, the orbit accuracy decreases by 1.27–6.34 cm; (2) compared with the orbit accuracy of the scheme of 90 stations selected at random, orbit corrections are more accurate using the DOP optimization strategy; (3) a better-corrected observed ultra-rapid orbit is acquired with less stations than the GFZ (German Research Center for Geosciences) uses. Thus, the observed ultra-orbit correction method proposed is ideal when considering accuracy and timeliness in ultra-rapid-orbit determination.


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