## Materials and Methods
### RTKLib Software
Indeed, the tested PPP-AR processing mode is considered \"experimental\" in the RTKLib manual. For this reason, the results will not show in the current research. The CNES/CLS center provides ephemeris at 15-minute intervals with clock corrections every 5 min (in \".sp3\" format) and also clock corrections every 30 s (in \".clk\" format). The combined use of \".sp3\" and \".clk\" products is useful both for real-time applications and for fixing ambiguity. In RTKPOST different ionospheric error correction models can be chosen, including using ionospheric parameters broadcast in the navigation message, iono-free linear combination (possible only if observation data on both L1 and L2 frequencies are available and no triple frequency combinations are allowed) named Iono-Free LC, using the estimated ionospheric parameters STEC (Slant Total Electron Content), or IONEX TEC data. In the current analysis, Iono-Free LC is used as an ionospheric correction model in the IF combination of DF carrier phases and pseudoranges used in the adopted PPP measurement model. It is well known that the Iono-Free LC is able to eliminate errors of about 99.9% of ionospheric delay as shown by several studies [12; 14; 20], highlighting the achievement of satisfactory positioning results. Since the test is carried out in Palermo, located about 1 km from the coast, and since high precision values are desired, the effects due to the tide are also included in the processing. Many models have been developed to correct this effect and are available free of charge as a \".blq\" file on the website [44], managed by the Onsala Space Observatory (OSO), Swedish national infrastructure for astronomy. The best results can be obtained with the latest models, including: GOT4.7, FES2004, TPXO_Atlas, HAMTIDE, and DTU10, and it is also possible to view the models not available for specific areas on the OSO website (Figure 5). Among the various available models, the GOT4.7 model is chosen, which is the latest version of [PERSON]'s tide models and is one of the standard tide models, in addition to FES2004, used for satellite altitude corrections [46]. Figure 5: Map of areas where ocean tide patterns are missing, taken from [45]. For the correction of the tropospheric delay, models commonly adopted for geodetic applications are used. These models are precise and complex [47], because they are based on satellite elevation angle and weather data, which cannot be easily determined. Based on literature considerations, in the current research a comparison between the Saastamoinen and Estimate ZTD (Zenith Total Delay) models is performed. Finally, additional settings are set to obtain the desired PPP-static solution, including (Figure 6):  
* Phwindup (phase wind-up), to correct the delay caused by the relative rotation between the satellite and receiver antennas;
* Reject Ecl, to exclude the GPS Block IIA satellites in eclipsed, that degrade the PPP solutions due to unpredicted behavior of yaw-attitude;
* RAIM (receiver autonomous integrity monitoring) FDE (fault detection and exclusion) to detect and exclude possible outliers from the measurements set used for the solution computation;
* Sat PCV e Rec PVC, to consider the phase center variations of the satellite and the receiver, respectively, feature allowed by uploading the \"igs14.atx\" file, provided by the IGS, containing the correction parameters of several types of antenna;
* a GDOP threshold is set to reject solution with GDOP value higher than 30, and a mask-angle equal to 10\({}^{\circ}\) is applied;
* no ambiguity resolution strategy is used;
* DCB multi-GNSS product, provided by the German aerospace center DLR, in \".bsz\" format, is also used as an input (Figure 6).