# Improving Low Earth Orbit (LEO) Prediction with Accelerometer Data
## 3 Analysis of Dynamic Parameters  
In this section, we first checked the precision of LEO orbits by using precise GNSS products with those three strategies. Here, we used CODE (Center for Orbit Determination in Europe) precise GPS orbit and 30 s clock products since there was no real time precise orbit and clock products in 2007 ([[ftp://cddis.gsfc.nasa.gov/pub/gps/products](ftp://cddis.gsfc.nasa.gov/pub/gps/products)]([ftp://cddis.gsfc.nasa.gov/pub/gps/products](ftp://cddis.gsfc.nasa.gov/pub/gps/products)), [41]). Furthermore, one has to collect and store real time \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Force Models** & **Description** & **ACC\_B\_K** & **ACC\_B** & **EMP** \\ \hline Earth gravity & EIGEN+GC [32] 120 x 120 & \(\surd\) & \(\surd\) & \(\surd\) \\ N-body & JPL DE405 [33] & \(\surd\) & \(\surd\) & \(\surd\) \\ Solid earth tide & IERS Conventions 2010 [34] & \(\surd\) & \(\surd\) & \(\surd\) \\ Ocean tide & EOT11a [35] & \(\surd\) & \(\surd\) & \(\surd\) \\ Relativity effect & IERS Conventions 2010 [32] & \(\surd\) & \(\surd\) & \(\surd\) \\ Atmosphere drag & DTM94 [36] & \(\times\) & \(\times\) & \(\surd\) \\ Solar radiation & Macro model [37] & \(\times\) & \(\times\) & \(\surd\) \\
**Observation models** & & & \(\surd\) & \(\surd\) \\ Observation & Un-differenced ionosphere-free code and phase combination & \(\surd\) & \(\surd\) & \(\surd\) \\ Arc length & 24 h & \(\surd\) & \(\surd\) & \(\surd\) \\ Sampling rate & 30 s & \(\surd\) & \(\surd\) & \(\surd\) \\ Cutoff elevation & 3\(\degr\) & \(\surd\) & \(\surd\) & \(\surd\) \\ Phase wind up & Applied [38] & \(\surd\) & \(\surd\) & \(\surd\) \\ LEO phase centre offset & Applied [39] & \(\surd\) & \(\surd\) & \(\surd\) \\ GPS phase centre offset & ig80.4\% [40] & \(\surd\) & \(\surd\) & \(\surd\) \\ Relativity effect & IERS Conventions 2010 [32] & \(\surd\) & \(\surd\) & \(\surd\) \\ Tropospheric delay & Not relevant & \(\times\) & \(\times\) & \(\times\) \\ Parameters & & & & \\ LEO orbits & Initial conditions (positions and velocities) & \(\surd\) & \(\surd\) & \(\surd\) \\ Receiver clock & Estimated as white noise & \(\surd\) & \(\surd\) & \(\surd\) \\ Atmosphere drag & A scale factor estimated every one cycle per revolution (1.5 h) & \(\times\) & \(\times\) & \(\surd\) \\  & Ca, Sa, Cc, and Sc for along- and cross-track directions (cosine/sine) & \(\times\) & \(\times\) & \(\surd\) \\ Empirical force & every one cycle per revolution & & & \\ Accelerometer scale & \(\text{K}_{\text{X}_{\text{V}}}\), \(\text{K}_{\text{Y}}\), and \(\text{K}_{\text{Z}}\), one set for one arc & \(\surd\) & \(\times\) & \(\times\) \\ Accelerometer bias & \(\text{B}_{\text{X}_{\text{V}}}\), \(\text{B}_{\text{Z}}\), one set for one arc for ACC\_B\_K, every 60 min for ACC\_B & \(\surd\) & \(\times\) \\ Phase ambiguity & One per satellite per pass (float solution) & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Force models, observation models, and estimated parameters of LEO POD with different strategies. orbit and clock corrections by themselves since no public archive is available for the storage of previous real time orbit and clock products. More details about the impact on LEO POD with real time products and final products can be found in the Appendix A. The Precise Science Orbits (PSO) of GRACE-A provided by Jet Propulsion Laboratory (JPL) was used as references for our orbit evaluation in this article ([[https://podaac-tools.jpl.nasa.gov/drive/files/allData/grace/L1B/JPL](https://podaac-tools.jpl.nasa.gov/drive/files/allData/grace/L1B/JPL)]([https://podaac-tools.jpl.nasa.gov/drive/files/allData/grace/L1B/JPL](https://podaac-tools.jpl.nasa.gov/drive/files/allData/grace/L1B/JPL))). Then the accelerometer calibration parameters as well as the parameters of empirical models were also investigated for the first two strategies. Figure 3 shows the averaged Root Mean Square (RMS) values for along-track, cross-track, and radial directions with the three strategies, respectively.