## 4 Discussion  
Comparing the best and worst TVU values (0.00 and 0.21 m) reported in Table 13 with the TVU IHO standards [17] (see Table 15), it can be seen that the Deeper Smart Sonars produced depth measurements with a TVU between the Exclusive Order and the Special Order. Regarding the geolocation of the devices in the static tests, it can be observed that in the SPP (Table 9 and Figures 11, A1 and A2) the G \(>\) S \(>\) P Sys was superior in comparison to the Deeper Smart Sonars. In the post-processing (Table 10, Figures 13 and A4) the static was superior compared to the PPP static. In the dynamic tests, analysing the THU values of the Deeper Smart Sonars, as shown in Table 11 (1.180 and 4.682 m), and comparing them with the reference THU standards values in Table 15 [17], it can be observed that the Deeper Smart Sonars obtained values between the Special Order and the Order 1. Observing the values of the G \(>\) S \(>\) P Sys shown in Tables 11 and 12 and Figure 14, it can be seen that in all types of positioning performed (SPP, PPP kinematic and PPK), the THU values are compatible with the Exclusive Order (the worst value is in fact 0.956 m). The dispersion of the surveyed points (Figure A5) in SPP had a minor dispersion compared to the Deeper Smart Sonars. In addition, an analysis of Figures 12 and A3 reveals that the SNR of the G \(>\) S \(>\) P Sys is in each case better than the internal GNSS receiver of the Huawei P30 Pro. Considering overall the THU and TVU values of the Deeper Smart Sonars it can be deduced that these sensors can express uncertainty values that in the worst case are compatible with the Order 1 and in the best case with the Special Order. Instead, the G \(>\) S \(>\) P Sys in the worst case can express uncertainty values compatible with the Special Order and in the best case with the Exclusive Order. In TVU, \(a\) is the portion of the uncertainty that does not vary with depth, \(b\) is a coefficient representing the portion of uncertainty that varies with depth and \(d\) is the depth. The \(\mu\)2D values of the Deeper Smart Sonar internal GNSS receivers reported in Table 11 (2.007 and 0.700 m) proved to be better than the accuracy estimated in [PERSON] et al. [7] and more in accordance with [PERSON] et al. [10]. It seems improper to define the Deeper Smart Sonar internal GNSS receiver as \"highly accurate\" as in [PERSON] et al. [9]. However, it proved to have good accuracy. The \(\Delta\)V values reported in Table 13 (between 0.01 and 0.04 m) showed accuracy in measuring depth in shallow water better than the accuracy estimated in [PERSON] et al. [11] and more in accordance with [PERSON] et al. [7]. The differences and similarities found may depend on the different measurement methods used and the technological advancement of the sensors studied. The \(\mu\)2D values of the G \(>\) S \(>\) P Sys in PPK positioning reported in Tables 11 and 12 (0.043 and 0.037 m) proved that the G \(>\) S \(>\) P Sys is more accurate than the method presented in [PERSON] et al. [7] and logistically not strictly dependent on the use of a UAV. Compared to the system proposed in [PERSON] et al. [16], the G \(>\) S \(>\) P Sys allows excellent real-time geolocation in SPP compatible with the THU value of the Exclusive Order. Furthermore, the synchronisation principle of the G \(>\) S \(>\) P Sys is potentially applicable to other sensors (e.g., optical sensors) that use the smartphone for geolocation. The implementation of sensors via smartphones had the advantage of prototyping and operating the system easily, and quickly and saving microchips during the semiconductor crisis. In addition, as the system is lightweight, it can also be moved by UAVs and USVs [41]. However, it must be considered that the system