High-quality satellite orbits and clocks are necessary for multi-GNSS precise point positioning and timing. In undifferenced GNSS solutions, the quality of orbit and clock products significantly influences the resulting position accuracy; therefore, for precise positioning in real time, the corrections for orbits and clocks are generated and distributed to users. In this research, we assess the quality and the availability of real-time CNES orbits and clocks for GPS, GLONASS, Galileo, and BeiDou-2 separated by satellite blocks and types, as well as the product quality changes over time. We calculate the signal-in-space ranging error (SISRE) as the main orbit and clock quality indicator. Moreover, we employ independent orbit validation based on satellite laser ranging. We found that the most accurate orbits are currently available for GPS. However, Galileo utmost stable atomic clocks compensate for systematic errors in Galileo orbits. As a result, the SISRE for Galileo is lower than that for GPS, equaling 1.6 and 2.3 cm for Galileo and GPS, respectively. The GLONASS satellites, despite the high quality of their orbits, are characterized by poor quality of clocks, and together with BeiDou-2 in medium and geosynchronous inclined orbits, are characterized by SISRE of 4–6 cm. BeiDou-2 in geostationary orbits is characterized by large orbital errors and the lowest availability of real-time orbit and clock corrections due to a large number of satellite maneuvers. The quality of GNSS orbit and clock corrections changes over time and depends on satellite type, block, orbit characteristics, onboard atomic clock, and the sun elevation above the orbital plane.

中文翻译：

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实时多GNSS解决方案的轨道和时钟质量的演变

高质量的卫星轨道和时钟对于多GNSS的精确点定位和计时是必需的。在无差异的GNSS解决方案中，轨道和时钟产品的质量会显着影响所产生的位置精度。因此，为了实时进行精确定位，会生成轨道和时钟的校正并分发给用户。在这项研究中，我们评估了GPS，GLONASS，Galileo和BeiDou-2（按卫星块和类型分开）的实时CNES轨道和时钟的质量和可用性，以及产品质量随时间的变化。我们计算空间信号测距误差（SISRE）作为主要轨道和时钟质量指标。此外，我们采用基于卫星激光测距的独立轨道验证。我们发现，目前最精确的轨道可用于GPS。然而，伽利略号最稳定的原子钟弥补了伽利略号轨道中的系统误差。结果，伽利略的SISRE低于GPS的SISRE，伽利略和GPS的SISRE分别等于1.6厘米和2.3厘米。尽管GLONASS卫星的轨道质量很高，但其时钟质量较差，而在中等和地球同步倾斜轨道上的BeiDou-2卫星，其SISRE为4–6 cm。对地静止轨道上的北斗二号的特点是轨道误差大，由于有大量的卫星操纵，实时轨道和时钟校正的可用性最低。GNSS轨道和时钟校正的质量会随时间变化，并取决于卫星类型，块，轨道特性，机载原子钟以及轨道平面上方的太阳高度。