Abstract
Precise point positioning with ambiguity resolution (PPP-AR) based on multiple global navigation satellite system (multi-GNSS) constellations is an important high-precision positioning tool. However, some unmodeled satellite and receiver biases (such as errors in satellite attitude) make it difficult to fix carrier-phase ambiguities. In order to fix ambiguities of eclipsing satellites, accurate integer clock and satellite attitude products (i.e., attitude quaternion) have been provided by the International GNSS Service (IGS). Nevertheless, the quality of these products and their positioning performance in multi-GNSS PPP-AR have not been investigated yet. Using the PRIDE PPP-AR II software associated with the corresponding rapid satellite orbit, integer clock and attitude quaternion products of Wuhan University (WUM), we carried out GPS/BDS PPP-AR using 30 days of data in an eclipsing season of 2020. We found that about 75% of GPS, 60% of BDS-2 and 57% of BDS-3 narrow-lane ambiguity residuals after integer clock corrections fall within ±0.1 cycles in the case of using nominal attitudes. However, when using attitude quaternions, these percentages will rise to 80% for GPS, 70% for BDS-2 and 60% for BDS-3. GPS/BDS daily kinematic PPP-AR after integer clock and nominal attitude corrections can usually achieve a positioning precision of about 10, 10 and 30 mm for the east, north and up components, respectively. In contrast, the counterparts are 8, 8 and 20 mm when using attitude quaternions. Compared with the case of using attitude quaternions only at the network end for the integer clock estimation, using attitude quaternions only at the user end shows a pronounced improvement of 15% in the east component and less than 10% in the north and up components. Therefore, we suggest PPP users apply integer clock and satellite attitude quaternion products to realize more efficient ambiguity fixing, especially in satellite eclipsing seasons.
Highlights
With the development of precise point positioning (PPP) [1], multi-constellations have become a research hotspot [2,3,4,5]
We demonstrate that the integer clock products generated with attitude quaternions have better performance in recovering integer PPP ambiguities
Strategy (d) achieves the highest fixing rates of all, about 90, 79 and 77% for GPS, BDS-2 and BDS-3, respectively. This strategy can lead to an improvement of about 10% for BDS-2 while GPS and BDS-3 satellites show modest improvements of less than 5% compared to other strategies. It shows that the attitude quaternions we used are helpful to improve the performance of fixing ambiguities, especially for BDS-2
Summary
With the development of precise point positioning (PPP) [1], multi-constellations have become a research hotspot [2,3,4,5]. After the first BLOCK IIR satellite was fully operational, Bar-Sever [18] added the non-nominal attitude model for this satellite type/block In this model, there are no yaw biases or shadow crossing maneuvers, and the yaw rate is larger than that of former GPS satellites. In order to obtain high-precision solutions, an analysis center has to establish a satellite model that describes the true attitude of GPS and BDS. In the processing of PPP model, the errors of satellite yaw attitude can influence the accuracy of phase center variation/offset and phase wind-up, leading to a low-precision positioning performance. In order to solve this problem, exchanging multi-GNSS satellite attitude information in the ORBit EXchange (ORBEX) format is being tested [14,28,29] Based on this format, Wuhan University (WUM) generated attitude quaternion products, associated with satellite integer clock and orbit products for users [30].
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