## 2 Characteristics of SNR
The data span, including dates, in addition to the elevation cutoff angle, is as follows: (a) IHU4: 24 h on DOY 111 (21 April 2014), and the elevation cutoff angle is 10 degrees; (b) SOND: about three hours on DOY 245 (2 September 2014), and the elevation cutoff angle is five degrees; and (c) TEHE: 24 h on DOY 035 (4 February 2014), and the elevation cutoff angle is five degrees. Figure 1: SNR values in dB-Hz, averages, and standard deviations at 1-degree intervals according to the receiver type: (**a**) NovAtel—SNR values against the elevation angle; (**b**) NovAtel—SNR averages and standard deviations against the elevation angle; (**c**) u-blox—SNR values against the elevation angle; (**d**) u-blox—SNR averages and standard deviations against the elevation angle. Figure 2 shows the SNR measurements at the three sites in a sky plot. To help determine the direction of the signal-blocking structures and understand their relation to the SNR observations, aerial photographs are also included in the figure. As shown in Figure 2a, the SNR is high at higher elevation angles, regardless of the azimuthal direction, and decreases as the elevation angle decreases. From Figure 2b,c on the contrary, one can see that SNR is high only along the street directions because the satellite visibility is maintained through the limited range of open sky along the street. In the cases of CS and UC, even those satellites whose visibility should be blocked by nearby buildings are observed, possibly through multiple paths, but show a very low SNR. The SNR variability was statistically evaluated in terms of the average and standard deviation according to the elevation angle. In Figure 3, the scatter plot of the SNR with respect to the elevation angle shows distinctive features. As the satellite visibility worsens, the standard deviation increases. Under the OS environment at IHU4, \(\sigma_{SNR}\) is not dependent on the elevation angle at all and varies in the range of 0.8-2.4 dB-Hz. Meanwhile, at SOND, \(\sigma_{SNR}\) remains nearly constant at 0.7 when the elevation angle is higher than 55\({}^{\circ}\)  
Figure 2: SNR values on a skylot and aerial photographs by each observation environment: (**a**) open sky (IHU4); (**b**) typical city streets (SOND); (**c**) urban canyons (TEHE). but becomes quite variable below it. This characteristic matches the height and density of the surrounding buildings at the site. Lastly, at TEHE, \(\sigma_{SNR}\) fluctuates tremendously in all elevation angles except for the zenith direction of 80-90\({}^{\circ}\). As mentioned before, a larger variability of \(\sigma_{SNR}\) means the site is more affected by the multipath effect. From the analysis of the behavior of the SNR variability patterns according to the signal-reception environment classified as OS, CS, or UC, we found that the magnitude and standard deviation of the SNR were highly dependent on the environment. Repeating patterns on two consecutive days can be used to prove that SNR variations are not determined by chance and are closely related to the environment. According to [18; 19], multipath and phase center variations are the two most well-known error factors repeating on a sidereal day basis. [PERSON] et al. [20] used satellite repeat times to show that the SNR patterns repeat exactly when the satellite returns to the same location in the sky after a  
Figure 3: SNR values, averages, and standard deviations at 1-degree intervals according to the observation environment: (**a1**) IHU4—SNR values against the elevation angle; (**a2**) IHU4—SNR averages and standard deviations against the elevation angle; (**b1**) SOND—SNR values against the elevation angle; (**b2**) SOND—SNR averages and standard deviations against the elevation angle; (**c1**) TEHE—SNR values against the elevation angle; (**c2**) TEHE—SNR averages and standard deviations against the elevation angle. sidereal day.