# Feasibility of Using Low-Cost Dual-Frequency GNSS Receivers for Land Surveying
## 2 Materials and Methods
### Experiment Setup and Processing Strategies  
#### 2.3.1 Static Measurements  
Measurements were performed in five control points in two areas, i.e., one point (S1) in a rural area (on 21 September 2020) and four points (S2, S3, S4, and S5) in an urban area (on 25 October 2020). The rural area was in the counryside Suliszewicz, near Sieradz city, Poland (Figure 1a), characterized by open-sky conditions. The point was measured for 5.5 h. The two nearest ASG-EUPOS stations were KALI (26 km far) and WIEL (50 km far). The urban area was in Wroclaw city, Poland, around the University campus, near buildings of different heights (up to 85 m), thus representing more challenging surveying conditions (Figure 1b). WROC station was located in the central part of this testing area. The longest baseline between a test point and the reference station was 385 m. Each point was measured for 1 h. Moreover, on 22 September 2020, a 24-h long measurement was performed near WROC station (roof of a building, open-sky conditions), which was used for analyzing the signal acquisition by a low-cost receiver.  
In order to investigate the performance of a low-cost patch antenna and the signal acquisition by a low-cost receiver, the dependence of the carrier-to-noise ratio (C/N\({}_{0}\)) on the satellite elevation, GNSS and frequency was investigated. Then, the open-source RTKLib software ([[http://www.rtklib.com](http://www.rtklib.com)]([http://www.rtklib.com](http://www.rtklib.com))) was used for post-processing the data logged in the relative positioning. CSRS-PPP online service ([[https://webapp.geod.nrcan.gc.ca/geod/tools-utils/PPP.php](https://webapp.geod.nrcan.gc.ca/geod/tools-utils/PPP.php)]([https://webapp.geod.nrcan.gc.ca/geod/tools-utils/PPP.php](https://webapp.geod.nrcan.gc.ca/geod/tools-utils/PPP.php))) was used for the absolute positioning. Table 1 shows the  
Figure 1: Location of control points and reference stations in (**a**) countryside and (**b**) urban areas.  
details of both processing strategies. Moreover, in order to evaluate the impact of session length on the estimation of coordinates (both in relative and absolute positioning), the measurements in S1 were split into shorter and independent sessions, i.e., two sessions of 2.5 h, five sessions of 1 h, 11 sessions of 30 min and 22 sessions of 15 min. For relative positioning, the ambiguity fixing ratio was investigated. Finally, the uncertainty (i.e., the a posteriori standard deviation of estimated coordinates) and accuracy (i.e., the difference with respect to known coordinates) were evaluated for relative and absolute positioning, by using the measurements obtained during sessions of 1 h. In S1, the first one hour of observations was used, in order to have a fair comparison with measurements in the urban area. In the relative positioning, S1 coordinates were determined by using both the reference stations, in order to evaluate the impact of baseline length on the accuracy. The coordinates of S2, S3, S4, and S5 were determined with respect to the WROC station, without network adjustment, because a single point was measured in a time.