Study on the Effect of Different Elevation Angles on GPS P3 Code Time Transfer

In our proposed up-sampling method for GPS P3 code time transfer, we employ a two-step resampling process. The first step involves the down-sampling process, which aims to transform the noisy raw data into accurately down-sampled data by condensing the noisy raw data into a single accurate data point. This step is crucial in reducing the effects of noise and enhancing the overall accuracy of the sampled results. Following the down-sampling process, the second step involves the up-sampling process. The primary objective of this study was to enhance the accuracy of the down-sampled results. We conducted an in-depth analysis by investigating the impact of different elevation angles on the measurement errors. By employing a differential approach between two pairs of observations with comparable elevation angles, we effectively quantified the measurement errors linked to different elevation angles of GPS satellites, thereby mitigating the impact of clock noise. Our analysis revealed that GPS satellites at higher elevation angles exhibited relatively smaller standard deviations, suggesting that assigning higher weights to observations at these angles would yield more precise results. Specifically, we found that the weights should be directly proportional to the fourth power of the sine function of the elevation angle. The modified Allan deviations (MDEV) values at 1 sidereal day of UTC(TL)-IGST using the weighted average method demonstrated significant improvements ranging from 17% to 24% for three different satellites. These results provide valuable insights for future studies on GPS up-sampled all-in-view time transfers.