## 6 Positioning Analysis
### NRCan PPP Results  
With the online service NRCan (National Resources Canada) PPP [18], the ionosphere-free linear combination of \(L_{1}\) and \(L_{2}\) phase observations (\(L_{IF}\)) is applied. The resulting mean phase center is consequently adjusted to the linear combination of the \(L_{1}\) and \(L_{2}\) phase centers. This experiment allows us to estimate the \(L_{IF}\) PCO and the impact of the PCVs on the height estimations. The NRCan service uses IGS products and applies the type mean antenna phase center corrections from the current IGS ANTEX file. The estimated height of the rover LEIAR antenna, with antenna corrections from the IGS ANTEX file applied by the PPP engine, is used as the reference value for the height. Moreover, for the TRM5 antenna, which has an entry in the IGS ANTEX file, the PPP engine applies antenna corrections automatically. This antenna serves as an additional reference. The PPP analysis is done by submitting several dual-frequency RINEX files of one full day. Since the high-rate (1 Hz) data sampling rate is not required for the static PPP processing, the data are down-sampled to a 30-s interval. Ocean loading parameters for the station location from the FES2004 model [19] are provided in an external file. Final GPS orbit and clock parameters are used by the engine. The antenna corrections (PCO and PCVs) are automatically applied to the receiver antenna provided that the antenna name is given in the RINEX header and an entry for this antenna (and radome) exists in the IGS ANTEX file. The engine also applies the satellite antenna corrections. Except for the input RINEX data, all conducted tests use the same configuration parameters. To verify the implementation of the corrections to the RINEX data, the reference antennas LEIAR and TRM5 are processed by the PPP engine using different input data configurations. The results can be found in Table 2.  
The first line shows the offsets using the original RINEX data without antenna metadata. No receiver antenna correction is applied, therefore yielding the position of the mean phase centers of the \(L_{IF}\) of the combined PCO and PCV effects. The resulting offsets are 183 and 71 mm. The second line shows the height differences with automatically applied IGS PCO and PCV corrections. Obviously, no height error is found for the LEIAR antenna since it serves as our reference measurement. A difference of \(-8\) mm compared to the LEIAR ARP position is observed for the second antenna. Though the same mounting adaptor was used for both antennas, this antenna could not be fully screwed into the screw hole and the height offset was measured manually and corrected by 10 mm. This is already taken into account in the values given in the table. The higher uncertainty of the manually measured height could play a role in this observed offset of \(-8\) mm, but another, more likely reason is that, because the LEIAR and TRM5 were mounted on different days, the difference is simply due to noise in the data. The third line shows the height differences after manually applying the IGS ANTEX PCV (but no PCO) corrections to the RINEX files according to Equation (2). The RINEX modification is necessary since it is not possible to supply your own ANTEX file to the NRCan online service. To be consistent with the IGS ANTEX resolution, this analysis is performed using an angular resolution of 5\({}^{\circ}\). The implemented interpolation strategy in the NRCan software is unknown to us. For our cases, we use linear interpolation to the respective satellites to obtain the phase corrections. The resulting offsets respect the PCVs and return an estimate of the \(L_{IF}\) PCOs. The result of the LEIAR antenna is equal to the IGS ANTEX \(L_{IF}\) PCO of 167 mm. In the case of the TRM5 antenna, the \(L_{IF}\) PCO according to the ANTEX entries is 80 mm. Compared to the manual PCV applied result of 72 mm, a bias of 8 mm persists, which is consistent with the result on the second row.