To overcome signal obstruction and improve positioning accuracy in near-island waters, the marine satellite navigation system must first optimize the design of its satellite receiving hardware to enhance signal acquisition and anti-obstruction capabilities. The system's satellite receiving antenna utilizes a multi-element array layout, rather than a single receiving element. Multiple antenna elements face different airspaces. Even if some elements are blocked by islands, others facing open airspace (such as the sea surface or between islands) can still capture satellite signals. This preferential selection of signals between antenna elements mitigates the impact of single obstructions on overall signal reception. Furthermore, the antenna is designed with a low profile and wide beam to expand the signal reception angle. This allows for effective signal acquisition even when the vessel is slightly tilted while navigating between islands, or when satellite signals are transmitted at low angles between islands, avoiding signal loss due to angular limitations.
To address the "multipath effect" common in near-island waters (where satellite signals reflect off islands and the sea surface and overlap with direct signals, interfering with positioning accuracy), the marine satellite navigation system optimizes its signal processing algorithms to filter out interfering signals and purify valid positioning data. The system's signal processor analyzes received satellite signals in real time, identifying the characteristic differences between direct and reflected signals. Direct signals have a stable propagation path and consistent phase, while reflected signals exhibit characteristics such as delay and phase distortion. Based on these differences, the algorithm constructs an interference signal model, separating and removing the reflected signal from the overall signal. Furthermore, the processor employs dynamic threshold adjustment technology. When it detects a high proportion of reflected components in the signal, it automatically increases the stringency of signal screening to ensure that only pure direct signals are included in the positioning calculation, reducing positioning errors caused by multipath effects.
The coordinated integration of multiple satellite systems is a key means of addressing island obstruction and ensuring positioning continuity. The marine satellite navigation system does not rely on a single satellite navigation system (such as GPS), but is compatible with multiple global satellite navigation systems, including Beidou, GLONASS, and Galileo. Satellites from different systems have varying coverage in near-shore airspace. Satellites from one system may be obscured by islands, while satellites from another system may be in open air. The system monitors the signal quality of each satellite system in real time, automatically switching to the one with the better signal or integrating valid satellite signals from multiple systems for joint positioning. This multi-system redundant design significantly reduces the risk of positioning interruptions caused by signal obstruction in a single system. Furthermore, the complementary data from multiple systems improves the stability and accuracy of positioning results.
Interoperability with other onboard navigation equipment allows for auxiliary positioning when satellite signals are obstructed, compensating for the shortcomings of single-satellite navigation. The marine satellite navigation system integrates deeply with the ship's radar, Automatic Identification System (AIS), and electronic nautical chart system. Radar detects the location and distance of surrounding islands in real time, combining this with island geographic information stored in electronic nautical charts to derive the ship's relative position to known islands. The AIS receives position information transmitted by nearshore beacons and other ships for positioning reference. When satellite signals weaken or accuracy degrades due to obstruction, the system automatically incorporates auxiliary data from radar and AIS to correct the satellite positioning results. For example, the radar-derived distance from the ship to an island can be used to adjust for potential deviations in satellite positioning. This ensures high positioning accuracy even when satellite signals are poor, preventing the ship from deviating from its course due to positioning errors.
The application of nearshore differential enhancement technology further offsets positioning errors caused by signal obstruction, improving positioning accuracy in local areas. In nearshore waters with numerous islands, relevant authorities deploy shore-based differential reference stations. These stations accurately receive satellite signals and calculate satellite positioning errors in the area (such as local errors caused by ionospheric delay, tropospheric delay, and signal obstruction). These stations then broadcast these error corrections in real time via radio or satellite links. The marine satellite navigation system receives and applies these corrections to calibrate its own positioning calculations, offsetting errors caused by factors such as island obstruction and atmospheric changes. This differential enhancement technology can achieve even higher levels of positioning accuracy in nearshore waters. It is particularly suitable for applications such as port entry and berthing, where positioning accuracy is extremely critical. It can meet precise navigation requirements even in densely populated areas.
Dynamic route prediction and signal status warning mechanisms help ships proactively avoid areas with strong signal obstruction, reducing the need for reactive responses. The marine satellite navigation system, combined with island distribution data from electronic nautical charts, proactively analyzes satellite signal obstruction risks along planned routes. It identifies areas prone to signal obstruction, such as the shady sides of islands and narrow island-reef channels. It then prompts the vessel to adjust its route, prioritizing routes with wide satellite signal coverage (such as the main channel between islands and waters away from densely populated islands and reefs). The system also monitors the number of satellites currently being received and signal strength in real time. If it predicts a vessel is about to enter an obstruction zone, it issues a warning, alerting the crew to changes in positioning status. It automatically activates backup positioning strategies, such as multi-system fusion and device linkage, to ensure positioning mode switching is completed before entering the obstruction zone, avoiding accuracy fluctuations caused by temporary switching.
Optimizing antenna mounting locations and protective design can also indirectly improve signal reception and minimize the effects of obstruction. The marine satellite navigation system's receiving antenna is preferably installed high on the ship's superstructure (such as the bridge or masttop), avoiding obstruction from ship structures such as chimneys and cranes. This maximizes the antenna's field of view and minimizes the effect of island obstruction exacerbated by the ship's own hull. At the same time, the antenna shell will be made of salt spray and corrosion-resistant materials to adapt to the high humidity and high salinity environment of nearshore waters, avoiding the decline in signal reception capability due to antenna hardware failure; the antenna base will be designed as a fine-tunable structure, and the crew can adjust the direction of the antenna appropriately according to the distribution of islands in the navigation area, further optimizing the signal capture effect and ensuring that the antenna can continuously and stably receive satellite signals in the complex nearshore multi-island environment.
