A Real-Time Dynamic Assessment Method for the Range of AIS Physical Navigation Marks Based on Opportunity Vessels

Abstract

This invention belongs to the field of navigational aid signal monitoring technology and proposes a real-time dynamic assessment method for the effective range of AIS physical navigational aids based on opportunistic vessels. The method includes the following steps: receiving AIS messages broadcast by vessels within the coverage area of ​​the target AIS physical navigational aid and obtaining the actual received signal strength; comparing this strength with the theoretical value calculated by the standard propagation model to deduce the propagation deviation factor for each vessel at its position; calculating the static reference signal strength at each spatial location point within the assessment area to generate a static reference coverage model; performing spatial interpolation processing to ensure that each spatial location point within the assessment area corresponds to a propagation deviation factor; and superimposing the propagation deviation factor corresponding to each location with the static reference coverage model to obtain a real-time dynamic effective range map of the target AIS physical navigational aid. This method enables low-cost, long-term, continuous, real-time, and dynamic assessment of the effective range of AIS physical navigational aids.

Description

Technical Field

[0001] This invention belongs to the field of navigational signal monitoring technology and relates to a real-time dynamic assessment method for the effective range of AIS physical navigational aids based on opportunistic vessels. Background Technology

[0002] Automatic Identification System (AIS) physical navigation marks (AIS AtoNs), as an intelligent upgrade of traditional physical navigation marks, provide surrounding vessels with critical navigational information such as identified obstructions or channel boundaries by periodically broadcasting AIS messages. They have become an indispensable component of modern maritime safety systems and Vessel Traffic Services (VTS). The effective service area of ​​a navigation mark is its most critical performance indicator, directly determining the geographical area in which it can perform its navigational aid functions, and thus impacting navigational safety.

[0003] Currently, the assessment of the effective range of AIS physical navigation aids mainly relies on two traditional methods, both of which have significant and inherent limitations: The first is the theoretical calculation method. This method is based on radio propagation models and calculates an idealized circular coverage area based on parameters such as the beacon's transmission power and antenna height. The fundamental flaw of this method lies in its static and idealized nature. It completely ignores the dynamic impact of the real, complex, and ever-changing marine environment on VHF radio signal propagation. For example, atmospheric ducting can cause signals to propagate beyond line of sight, significantly expanding the actual effective range; while multipath fading caused by severe sea conditions and signal absorption attenuation due to meteorological conditions such as heavy rain can cause a sharp drop in signal strength, making the actual coverage area much smaller than the theoretical value. Therefore, the prediction results of theoretical models often deviate greatly from the actual situation and cannot truly reflect the real-time service capability of navigation aids, resulting in blind spots in safety management decisions made based on this.

[0004] The second method is on-site surveying. This method involves dispatching test vessels equipped with specialized signal receiving equipment to conduct cruise measurements in the waters surrounding the navigational aid, collecting signal strength data at different locations to map the actual coverage boundaries. While this method can obtain relatively accurate instantaneous data, its drawbacks are significant: high cost, low efficiency, and unsustainability. Surveying operations are constrained by weather and sea conditions, are time-consuming and labor-intensive, and the results are only instantaneous snapshots under specific environmental conditions, failing to achieve long-term, continuous monitoring. The dynamic changes in navigational aid performance with the environment cannot be captured. For the need to monitor the operational status of navigational aids in real time, this method is impractical and cannot meet the demands of modern, intelligent maritime safety assurance.

[0005] In summary, existing technologies cannot provide an effective solution for low-cost, long-term, continuous, real-time, and dynamic assessment of the effective range of AIS physical navigation marks. Summary of the Invention

[0006] This invention proposes a real-time dynamic assessment method for the effective range of AIS physical navigation marks based on opportunity vessels. This method utilizes low-cost and readily available data sources to achieve accurate, long-term, continuous, real-time, and dynamic assessment of the effective range of AIS physical navigation marks.

[0007] The technical solution of this invention is implemented as follows:

[0008] Technical Topic 1

[0009] This invention provides a real-time dynamic assessment method for the effective range of AIS physical navigation marks based on opportunity vessels, comprising the following steps:

[0010] A. Receive AIS messages broadcast by vessels within the coverage area of ​​the target AIS beacon, parse and obtain the location information of each vessel and the actual received signal strength (RSSI) corresponding to the AIS message. actual ;

[0011] B. Based on the position information of each ship, calculate the theoretical received signal strength (RSSI) at each ship's location using a radio wave propagation model. t According to RSSI actual With RSSI t The difference is used to determine the environmental calibration factor at each ship's location, thus obtaining an environmental calibration factor database;

[0012] C. Based on the target AIS beacon's own parameters, calculate the static reference signal strength (RSSI) at each spatial location point within the evaluation area using the radio wave propagation model. t (x,y), generate a static baseline coverage model;

[0013] D. Perform spatial interpolation processing on the environmental calibration factor database described in step B, so that each spatial location point in the evaluation area corresponds to an environmental calibration factor; superimpose the environmental calibration factor corresponding to each location with the static benchmark coverage model to obtain the real-time dynamic range map of the target AIS entity beacon.

[0014] Preferably, the theoretical received signal strength RSSI t The calculation formula is as follows:

[0015] ;

[0016] Where P tx This refers to the ship's nominal transmission power.

[0017] G tx Standard gain for shipboard AIS transmitting antennas;

[0018] Grx The receiving antenna gain of the target AIS beacon in the corresponding ship direction;

[0019] L misc It is the sum of the inherent feeder and connector losses, which are typically between 0.5dB and 2dB.

[0020] d represents the distance between the transmitter and receiver, which can be obtained from the ship's latitude and longitude and the location of the target AIS beacon itself.

[0021] h t This indicates the height of the transmitting antenna, specifically the vertical height of the AIS equipment antenna on the ship above the sea level.

[0022] h r This indicates the height of the receiving antenna, specifically the vertical distance between the antenna on the AIS physical beacon and the sea level.

[0023] Preferably, the environmental calibration factor ΔRSSI' = RSSI actual -RSSI t .

[0024] Preferably, generating the static benchmark coverage model includes the following steps:

[0025] S1. Using the geographic coordinates of the target AIS entity beacon as the center, the evaluation area is discretized into a two-dimensional grid; each spatial location point within the evaluation area corresponds to the center point of each grid cell in the two-dimensional grid.

[0026] S2. Traverse each grid cell in the two-dimensional grid and calculate the distance d and azimuth angle of the center point of each grid cell relative to the target AIS entity beacon;

[0027] S3. Assuming the ship is located at the center point (x, y) of the grid cell, based on the azimuth angle calculated in step S2, query the radiation pattern data of the target AIS beacon antenna to obtain the receiving antenna gain G of the target AIS beacon in the direction corresponding to the azimuth angle calculated in step S2. rx (x,y);

[0028] S4. Calculate the theoretical received signal strength, i.e., the static reference signal strength RSSI, for the center point (x, y) of each grid cell. t (x,y), traverse all grid cells and complete the static reference signal strength RSSI t After calculating (x,y), a static benchmark coverage model covering the entire evaluation area can be generated.

[0029] Preferably, the superposition calculation is achieved using the following formula: RSSI d(x,y,t)=RSSI t (x,y)+ΔRSSI'(x,y,t);

[0030] Among them: RSSI d (x,y,t) is the final dynamic prediction signal strength at time t and location (x,y);

[0031] RSSI t (x,y) is the static reference signal strength of the target AIS entity beacon at the center point (x,y) of the grid cell;

[0032] ΔRSSI'(x,y,t) is the environmental calibration factor of the center point (x, y) of the grid cell obtained by spatial interpolation.

[0033] Preferably, the static reference signal strength RSSI t The calculation of (x,y) is as follows:

[0034] ;

[0035] Among them, P tx This refers to the ship's nominal transmission power.

[0036] G tx Standard gain for shipboard AIS transmitting antennas;

[0037] G rx The receiving antenna gain of the target AIS beacon in the corresponding ship direction;

[0038] L misc It is the sum of the inherent feeder and connector losses, which are typically between 0.5dB and 2dB.

[0039] d represents the distance between the transmitter and receiver, which can be obtained from the ship's latitude and longitude and the location of the target AIS beacon itself.

[0040] h t This indicates the height of the transmitting antenna, specifically the vertical height of the AIS equipment antenna on the ship above the sea level.

[0041] h r This indicates the height of the receiving antenna, specifically the vertical distance between the antenna on the AIS physical beacon and the sea level.

[0042] Preferably, after step D, the method further includes step E: in the real-time dynamic range map, according to a preset signal strength threshold, the dynamic range boundary of the target AIS entity beacon in the current marine environment is drawn and visualized.

[0043] Preferably, when the dynamic range of action is less than the preset service distance, an early warning message is automatically sent to the VTS or navigation mark maintenance system.

[0044] Preferably, the spatial interpolation employs the inverse distance weighted interpolation method to convert the discrete environmental calibration factor database data into environmental calibration factors corresponding to each spatial location point within the evaluation area.

[0045] Technical Theme Two

[0046] The present invention also provides an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the program, performs the steps of the method as described in any one of the technical subjects.

[0047] The beneficial effects of the present invention using the above technical solution are as follows:

[0048] 1. This invention creatively utilizes environmental perception and inversion to treat numerous ships sailing on the sea as mobile, non-cooperative radio probes. By receiving AIS messages from these passing ships, its location and actual received signal strength (RSSI) can be obtained. actual And compared with the theoretical value RSSI calculated by the standard propagation model t By comparing data, the propagation deviation factor (i.e., environmental calibration factor ΔRSSI') of each ship at its location is derived, resulting in an environmental calibration factor database with geographic tags and timestamps. These discrete environmental calibration factor database data points constitute a real-time snapshot of the current marine radio environment, quantifying the real impacts of atmospheric waveguides and multipath fading. Simultaneously, the method evaluates the target AIS beacon itself, comprehensively considering key information such as ship transmit power, antenna precision altitude, and especially the non-isotropic antenna pattern. Using a high-precision propagation model, the theoretical spatial distribution of the beacon signal strength under ideal, interference-free conditions is calculated. Finally, the discrete and irregular environmental calibration factor ΔRSSI' snapshot data derived from the propagation path is processed into a continuous environmental correction factor covering the entire evaluation area. Through simple raster algebra operations, the environmental calibration factors corresponding to each spatial location point within the evaluation area are superimposed and corrected with a static reference map, thereby generating a dynamic range map that reflects the real-time changes in beacon performance under actual marine conditions. A clear service boundary can also be plotted based on preset thresholds. The method enables low-cost, long-term, continuous, real-time, and dynamic assessment of the effective range of AIS physical navigation marks.

[0049] 2. The method provided by this invention enables real-time, dynamic monitoring of navigational aid performance: management agencies can monitor it much like checking the weather. Figure 1In this way, the actual coverage of each AIS entity beacon can be seen intuitively over time on the VTS system or electronic chart (ECDIS), completely changing the previous blind-men-and-fellows management model;

[0050] 3. The method provided by this invention improves the level of maritime safety: when the method detects that the effective coverage area of ​​a navigational aid in a key waterway direction is continuously lower than its set service level requirements due to equipment failure or abnormal propagation environment, it can immediately issue an early warning to the management agency. This makes preventive maintenance and emergency response possible, effectively avoiding safety accidents caused by navigational aid failure;

[0051] 4. The method provided by this invention has extremely low operating costs: the method relies entirely on passive data acquisition, without the need to dispatch ships or deploy additional hardware, and can be operated using existing AIS shore-based facilities and ubiquitous merchant ships, resulting in extremely low costs.

[0052] 5. The method provided by this invention provides valuable data for marine environmental research: the environmental calibration factor database derived by the method is itself a valuable long-term, high spatiotemporal resolution observational data of the marine atmospheric radio environment, which can be used for research in the fields of marine physics and radio communication. Attached Figure Description

[0053] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0054] Figure 1 The flowchart shows the real-time assessment method for the effective range of AIS physical navigation marks, which is the objective of this invention.

[0055] Figure 2 The flowchart shows the theoretical model of the static coverage range of the target AIS physical navigation beacon in this invention.

[0056] Figure 3 This is a diagram showing the real-time dynamic range of action of the present invention. Detailed Implementation

[0057] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0058] Example 1

[0059] like Figure 1The diagram shown is a flowchart of the real-time dynamic evaluation method for the effective range of AIS physical navigation aids based on opportunity vessels according to the present invention. Its core principle is to correct the static theoretical model in real time using dynamic environmental measurement data, ultimately generating an accurate and real-time updated dynamic map of the navigation aid's effective range. The method includes the following steps:

[0060] 1. Inversion of the propagation environment within the coverage area of ​​the target AIS physical beacon

[0061] The propagation environment inversion method transforms the vast number of ships operating in a wide sea area into a dynamic, distributed, and cost-free marine atmospheric physics detection network. Specifically, by analyzing these moving signals, the target AIS beacon obtains the theoretical signal strength of the ship information received by the beacon. The difference between this theoretical signal strength and the actual received signal strength can then be used to infer the propagation characteristics of VHF radio waves in a real marine environment in real time.

[0062] 1.1 Receive AIS messages broadcast by ships within the coverage area of ​​the target AIS entity navigation mark.

[0063] The target AIS beacon receives AIS information broadcast by ships within its coverage area and parses each received AIS message (Message 1, 2, 3, 5, 18, 19) to extract the following ship information:

[0064] Ship MMSI, latitude and longitude coordinates, UTC timestamp, AIS equipment type (Class A / B) in static information, standard gain of transmitting antenna, nominal transmit power, such as 12.5W for Class A;

[0065] Determine the target AIS entity's own parameters: geographical coordinates, altitude, receiving antenna gain in the corresponding ship direction, feeder loss, etc.

[0066] The target AIS beacon can calculate the actual received signal strength (RSSI) of each received AIS message in real time. actual， Unit: dBm.

[0067] 1.2 Theoretical Calculation of Received Signal Strength in Propagation Inversion

[0068] The inversion process of the propagation environment first requires constructing a standard radio wave propagation model to calculate the theoretical baseline for VHF signal transmission. This radio wave propagation model can be selected and configured according to the evaluation accuracy requirements, marine environmental characteristics, and available computing resources. It includes, but is not limited to, free-space propagation models, two-ray ground reflection models, Egli models considering Earth's curvature, or empirical models recommended by ITU-R suitable for VHF band propagation at sea. This invention combines a two-ray ground reflection model based on Earth's curvature and standard atmospheric refraction to calculate the theoretical received signal strength RSSI between the ship and the base station. t The calculation formula is as follows:

[0069] (1)

[0070] Where P tx This refers to the ship's nominal transmission power.

[0071] G tx Standard gain for shipboard AIS transmitting antennas;

[0072] G rx The receiving antenna gain of the target AIS beacon in the corresponding ship direction;

[0073] L misc It is the sum of inherent feeder and connector losses, which are typically between 0.5dB and 2dB, depending on the specific hardware configuration of the target AIS beacon.

[0074] d represents the distance between the transmitter and receiver, which can be obtained from the ship's latitude and longitude and the location of the target AIS beacon itself.

[0075] h t This indicates the height of the transmitting antenna, specifically the vertical distance from the sea level to the antenna of the AIS equipment on the ship; ship antenna height h t The methods for obtaining the antenna height include: querying the standard antenna height corresponding to the ship's MMSI from the ship static information database; estimating the typical antenna height based on the ship type and size information in the ship's AIS message through a preset mapping table; or using it as a statistical parameter to be calibrated and learning it through historical data.

[0076] h r This indicates the height of the receiving antenna, specifically the vertical height of the antenna on the target AIS beacon above the sea level.

[0077] 1.3 Quantification of Propagation Inversion Anomalies

[0078] The actual received signal strength (RSSI) recorded by the target AIS beacon.actual The theoretical received signal strength RSSI calculated by the model t By comparing these factors, the anomalous impact of the real-world propagation environment can be quantified. This impact is defined as the propagation deviation factor, or environmental calibration factor ΔRSSI'.

[0079] ΔRSSI' = RSSI actual -RSSI t (2)

[0080] ΔRSSI' reveals the deviation between the real propagation environment and the ideal model. Further analysis can be performed based on the sign of ΔRSSI'.

[0081] If RSSI actual RSSI t For a strong positive anomaly, if multiple ship signals exhibit strengths significantly stronger than the theoretically received signal strength over a wide sea area (e.g., an increase of 10-20 dB or more), the method will confidently identify it as an atmospheric waveguide event. This indicates the presence of a low-loss radio waveguide layer.

[0082] If RSSI actual <RSSI t A strong negative anomaly, where the signal is generally and continuously weaker than the theoretically received signal strength, may be attributed to severe multipath fading caused by adverse sea conditions, or signal absorption and attenuation caused by large-scale dense fog or heavy rain.

[0083] After the above calculations, this method obtains a structured environmental calibration factor database with geographic labels and timestamps through propagation environment inversion. This database constitutes a series of real-time snapshots of the actual marine radio environment, transforming raw, unordered AIS data into a basis for subsequent dynamic corrections, laying a solid data foundation for the final generation of a real-time dynamic coverage assessment map. Each piece of information recorded in the database includes the following: timestamp, longitude, latitude, ΔRSSI', inferred bias type, and quantitative value of the influencing factor.

[0084] 2. Calculate the theoretical static coverage area of ​​the target AIS entity navigation beacon.

[0085] Before dynamically assessing the effective range of AIS beacons, it is essential to first establish an accurate and reliable static theoretical baseline. This involves building a model of how the radio signals of a target AIS beacon are distributed in space under ideal conditions free from time-varying environmental interference. Therefore, constructing a high-resolution, static baseline coverage prediction model is fundamental for subsequent dynamic calibration. The modeling process is as follows: Figure 2As shown, the entire modeling process is divided into four stages: defining the model input parameters, meshing the computational domain, selecting and calculating the propagation model, and visualizing the final results.

[0086] 2.1 Precise Definition of Model Input Parameters

[0087] The effectiveness of the model is highly dependent on the accuracy of the input parameters. To ensure the accuracy of theoretical calculations, all key parameters related to signal transmission and propagation must be precisely defined and acquired. These parameters can be categorized into three main types:

[0088] (1) Transmitter parameters.

[0089] P tx This refers to the ship's nominal transmission power; this parameter is usually determined by the equipment specifications and is converted to logarithmic units dBm or dBW in calculations.

[0090] (2) Parameters of navigation beacon antenna.

[0091] The antenna's geographical coordinates and altitude, and the precise latitude and longitude of the antenna's radiation center, are the geographical origin for coverage analysis. Its altitude relative to the mean sea level is a key factor in determining the line-of-sight distance of radio signals.

[0092] Antenna pattern: The antenna pattern describes in detail the gain change of the antenna at each emission angle within 360 degrees in the horizontal and vertical planes. Only by importing the actual antenna pattern can the directional radiation characteristics of the antenna be accurately reproduced in the model.

[0093] (3) Feeder and connector losses

[0094] Throughout the signal transmission process from the transmitter cabinet to the antenna radiating unit, power attenuation will inevitably occur due to the non-ideal characteristics of the feeder and various connectors; these losses can be calculated by summing them up based on the specific cable type, length, and number of connectors used.

[0095] 2.2 Theoretical Computational Model and Implementation

[0096] After precisely defining the various input parameters of the model, spatial discretization and iterative link budget calculation based on the discretized grid are used to transform the input physical parameters into a high-resolution signal strength prediction map covering the entire target sea area.

[0097] Step 1: Discretization of the computational domain

[0098] Since continuous spatial computation is not feasible, the target geographic region is first transformed into a processable, finite, discretized model through grid processing. Specifically, a two-dimensional grid covering the surrounding sea area is created, centered on the geographic coordinates of the target AIS beacon. Taking a low-power AIS beacon mounted on a buoy as an example, assuming its radiation radius is 15km, the two-dimensional grid range of the evaluation area is set to 30km × 30km, centered on the target AIS beacon. After the area is defined, it is discretized, that is, the physical size of each smallest computational unit in the grid is defined. The choice of resolution is a key trade-off between computational accuracy and resource cost. High resolution can finely depict subtle changes in signals in complex port environments, but leads to a geometric increase in computational load; while low resolution is faster and suitable for macroscopic evaluation in open sea areas. Taking an open sea area as an example, we select 500m as the unit, thus subdividing the 30km × 30km grid into 3600 grid units to discretize the computation area. Each spatial location point within the evaluation area corresponds to the center point of each grid unit in the two-dimensional grid.

[0099] Step 2: Grid-based iterative computation and propagation modeling

[0100] After defining the computational grid, iterate through each grid cell and independently solve for its theoretical received signal strength (RSSI). For any given grid cell, the theoretical received signal strength (RSSI) is calculated. t The calculation follows the following logic:

[0101] First, assuming a ship with standard parameters is located at the center point (x, y) of a grid cell, the method calculates the precise distance *d* and azimuth angle *θ* of this grid cell's center point relative to the target AIS beacon antenna. Then, based on the azimuth angle *θ*, the beacon receiving antenna gain *G* in the direction corresponding to the azimuth angle is retrieved from the imported target AIS beacon antenna pattern data file. rx (x,y); simultaneously, based on preset ship standard parameters, determine the standard gain G of the ship's AIS transmitting antenna. tx (x,y);

[0102] Next, the ship's nominal transmission power P tx Standard gain G of ship AIS transmitting antenna tx The receiving antenna gain G of the target AIS beacon in the corresponding ship direction. rx、 The sum of inherent feeder and connector losses L misc Distance d, height h of transmitting antenna t and the height h of the receiving antenna rSubstituting these parameters into the complete link budget equation, the theoretical received signal strength at the center point (x, y) of the grid cell, i.e., the static reference signal strength RSSI, can be obtained. t (x,y):

[0103] (3)

[0104] Among them, L misc This is the sum of inherent feeder and connector losses, typically between 0.5dB and 2dB. Repeat the above calculation process until each grid cell is filled with a static reference signal strength (RSSI). t (x,y) generates a two-dimensional matrix containing massive amounts of prediction data, which is the target AIS entity beacon reference coverage model map. This model map is a static reference coverage model that covers the entire evaluation area and reflects the expected signal strength under ideal standard conditions.

[0105] 3. Real-time dynamic generation of the navigation mark's effective range

[0106] The target AIS physical beacon obtained the discrete theoretical received signal strength (RSSI) uniformly distributed within its evaluation area. t The environmental calibration factor ΔRSSI', derived from the propagation environment inversion quantification value of the actual receiving range of ship signals from the target AIS entity navigation beacon, forms an environmental calibration factor database. Since ship navigation distribution is discrete and non-uniform, directly using these point data points cannot provide a complete assessment of the corresponding sea area. Therefore, a spatial interpolation algorithm is used to spatially interpolate these discrete data points ΔRSSI', generating a continuous environmental correction factor covering a 30km × 30km assessment area using a two-dimensional grid. Each grid point contains a real-time calibration value ΔRSSI'(x,y,t). During spatial interpolation, for grid cells without valid ship observation data within the search radius, one of the following strategies can be adopted: assigning its environmental calibration factor ΔRSSI'(x,y,t) to 0 (i.e., assuming the environment at that location is consistent with the standard model); or using a spatiotemporal joint interpolation / prediction method, filling in the gaps using historical data and interpolation results from adjacent time slices; or temporarily marking the area as an assessment uncertainty zone and displaying it in a special style on the visualization map.

[0107] At this point, the environmental calibration factor corresponding to each location is superimposed on the target AIS entity beacon reference coverage model, and each grid point within the coverage two-dimensional grid area is evaluated and corrected to generate a real-time dynamic range map of the target AIS entity beacon.

[0108] The superposition calculation is achieved through the following formula:

[0109] RSSI d(x,y,t)=RSSI t (x,y)+ΔRSSI'(x,y,t) (4);

[0110] Among them: RSSI d (x,y,t) is the final dynamic prediction signal strength at time t and location (x,y);

[0111] RSSI t (x,y) is the static reference signal strength of the target AIS entity beacon at the center point (x,y) of the grid cell;

[0112] ΔRSSI'(x,y,t) is the environmental calibration factor of the center point (x, y) of the grid cell obtained by spatial interpolation.

[0113] The above method can generate a dynamic, real-time prediction-calibration coverage map, and the map can be marked with the dynamic predicted signal strength (RSSI) at different locations. d (x, y, t). To clearly show the actual effective range of the target AIS beacon, contour lines were drawn using the internationally standard -107dBm signal strength threshold, and visualized in a dynamic graph. Specifically, as follows... Figure 3 As shown. Therefore, the effective range of the navigational aid obtained by this method is no longer a static theoretical circle, but an irregular shape that changes in real time according to the actual marine environment, accurately reflecting the actual service capability of the navigational aid in the current environment. The method continuously updates the dynamic effective range of the navigational aid at a frequency of minutes to ensure the real-time nature of the assessment results.

[0114] Figure 3 The blue area represents the real-time dynamic map of the test beacon, calibrated based on the inversion value of the propagation environment according to the theoretical coverage calculation model. The green contour lines dynamically delineate the coverage areas within the actual coverage range of the test beacon where the received signal level is higher than -107dBm, using -107dBm as the standard. In practice, the map shows multiple irregular real-time dynamic beacon coverage areas depending on the different signal levels.

[0115] Because the distribution of ships navigating on the sea surface is random and discrete, this invention employs an inverse distance weighted interpolation algorithm to obtain continuous environmental calibration factors covering the entire 30km × 30km evaluation area. The details are as follows:

[0116] For any grid point P(x,y) to be determined in the evaluation area grid, its corresponding real-time environmental calibration factor ΔRSSI'(x,y,t) is derived from the known ship observation points P in its vicinity. i Deviation value ΔRSSI i It is obtained by weighted average. The calculation formula is as follows:

[0117] (5)

[0118] Among them, weight It depends on the distance between the point to be determined and the observation point:

[0119] (6)

[0120] in, It is the first The Euclidean distance between a ship observation point and the grid point to be determined;

[0121] This is the number of valid observation points (ships) participating in the calculation, taken as the number of valid ship observation points within a 5km search radius centered on the grid point to be calculated;

[0122] It is a distance power parameter, usually taken as 2, which determines the rate at which the weight decays as the distance increases. The larger the value, the more concentrated the influence of the close-range observation point.

[0123] Example 2

[0124] This embodiment simulates the real-world performance of an AIS beacon located in a complex nearshore environment, under the combined influence of local atmospheric waveguide and sea surface multipath fading. The method continuously receives AIS messages from passing vessels, dynamically inverts environmental changes, and updates the beacon's dynamic range map in real time. During a continuous 6-hour monitoring period, the method executes step AD from Embodiment 1 every minute. Initially, ΔRSSI'(x,y,t) fluctuates around 0 dB, and the dynamic map approximates a static reference circle. In the second hour, the method receives messages from multiple vessels, and the calculated ΔRSSI' is generally +6 dB to +12 dB. The environmental correction factor generated after spatial interpolation exhibits a high value region in this direction. After superposition, the -107 dBm contour line of the dynamic range map significantly expands outward, forming an irregular bulge. In the fourth hour, the inverted ΔRSSI'(x,y,t) from vessel data in the northwest direction is approximately -5 dB, and the contour lines of the dynamic map correspondingly contract in this direction. The visualization system continuously updates this dynamic irregular boundary map. The following shows the calculation process when ΔRSSI'(x,y,t) is generally +6dB.

[0125] 1. Test Setup and Initial Benchmark

[0126] AIS physical navigation mark: a guide buoy at the entrance of a port.

[0127] Its own fixed parameters:

[0128] Antenna height h r4 meters above sea level.

[0129] System loss L misc 2 dB.

[0130] Standard ship parameters:

[0131] Ship nominal transmission power P tx 2W = 33 dBm.

[0132] Ship antenna height h t 10 meters.

[0133] It is 4dB.

[0134] Assessment area: 30km x 30km sea area centered on the AIS physical navigation beacon.

[0135] Signal reception threshold: -107 dBm.

[0136] 2. Through propagation model calculations, the theoretical coverage radius required to reach the -107 dBm threshold under ideal standard atmospheric conditions can be derived. Approximately 12.11 nautical miles:

[0137]

[0138] Substituting -107dBm into the formula:

[0139]

[0140]

[0141]

[0142]

[0143]

[0144] However, in practice, the coverage area of ​​AIS physical beacons can be affected by environmental factors, which can lead to an increase or decrease in signal reception level. This is due to the existence of the environmental calibration factor ΔRSSI'(x,y,t), which in turn causes the actual coverage area of ​​AIS physical beacons to increase or decrease.

[0145] 3. The method continues to run, detecting that the propagation deviation factor of a certain area of ​​the AIS entity beacon changes to +6dB, indicating an increase in the current atmospheric refractive index, which is beneficial for signal transmission. A spatial interpolation algorithm is used to assign an environmental calibration factor to each spatial location point within the evaluation area; the environmental calibration factor corresponding to each location is then superimposed with the static reference coverage model to generate a continuous, real-time dynamic range map covering the evaluation area.

[0146] ΔRSSI' = RSSI actual -RSSI t

[0147] RSSI actual =RSSI t +ΔRSSI'(x,y,t)

[0148] The calculation process is the same as above, as follows:

[0149]

[0150]

[0151]

[0152] Therefore, the actual coverage area of ​​the buoy is 17.11 nautical miles.

[0153] As the atmospheric waveguide phenomenon dissipates, the ΔRSSI'(x,y,t) retrieved from the subsequently received ship data gradually returns to a small fluctuation close to 0 dB. The dynamic range diagram also adaptively and gradually recovers to a shape close to the initial static baseline.

[0154] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A real-time dynamic assessment method for the effective range of AIS physical navigation marks based on opportunity-based vessels, characterized in that, Includes the following steps: A. Receive AIS messages broadcast by vessels within the coverage area of ​​the target AIS beacon, parse and obtain the position information of each vessel and the actual received signal strength (RSSI) corresponding to the AIS message. actual The vessel in question is a passing vessel. B. Based on the position information of each ship, calculate the theoretical received signal strength (RSSI) at each ship's location using a radio wave propagation model. t ; By using the inversion method, based on RSSI actual With RSSI t The difference is used to determine the environmental calibration factor at each ship's location, thus obtaining an environmental calibration factor database. The methods for obtaining the ship's antenna height include: querying the standard parameters corresponding to the ship's MMSI from the ship's static information database; estimating it based on the ship type and size information in the AIS message using a preset mapping table; or calibrating it using statistical parameters learned from historical data. C. Based on the target AIS beacon's own parameters, and using the radio wave propagation model, calculate the theoretical received signal strength (RSSI) at each spatial location point within the evaluation area. t (x,y), generate a static baseline coverage model; D. Perform spatial interpolation processing on the environmental calibration factor database described in step B, so that each spatial location point in the evaluation area corresponds to an environmental calibration factor; superimpose the environmental calibration factor corresponding to each location with the static benchmark coverage model to obtain the real-time dynamic range map of the target AIS entity navigation mark; the spatial interpolation adopts the inverse distance weighted interpolation method. For any grid point P(x,y) to be determined in the evaluation area grid, its corresponding real-time environmental calibration factor ΔRSSI'(x,y,t) is determined by the surrounding known ship observation points P. i Deviation value ΔRSSI i The weighted average is obtained, and the calculation formula is as follows: ； Among them, weight It depends on the distance between the point to be determined and the observation point: ； in, It is the first The Euclidean distance between a ship observation point and the grid point to be determined; This refers to the number of valid observation points involved in the calculation; It is a distance power parameter; For grid cells without valid ship observation data within the search radius, one of the following strategies is adopted: assigning an environmental calibration factor ΔRSSI'(x,y,t) of 0, or using a spatiotemporal joint interpolation / prediction method to fill the area with interpolation results from historical data and adjacent time slices, or temporarily marking the area as an evaluation uncertainty zone.

2. The method for real-time dynamic evaluation of the effective range of AIS physical navigation marks based on opportunity vessels according to claim 1, characterized in that, The theoretical received signal strength RSSI t The calculation formula is as follows: ； Where P tx This refers to the ship's nominal transmission power. G tx Standard gain for shipboard AIS transmitting antennas; G rx The receiving antenna gain of the target AIS beacon in the corresponding ship direction; L misc It is the sum of inherent feeder and connector losses; d is the distance between the transmitter and receiver; h t Indicates the height of the transmitting antenna; h r This indicates the height of the receiving antenna.

3. The method for real-time dynamic evaluation of the effective range of AIS physical navigation marks based on opportunity vessels according to claim 1, characterized in that, The generation of the static benchmark coverage model includes the following steps: S1. Using the geographic coordinates of the target AIS entity beacon as the center, the evaluation area is discretized into a two-dimensional grid; each spatial location point within the evaluation area corresponds to the center point of each grid cell in the two-dimensional grid. S2. Traverse each grid cell in the two-dimensional grid and calculate the distance d and azimuth angle of the center point of each grid cell relative to the target AIS entity beacon; S3. Assuming the ship is located at the center point (x, y) of the grid cell, based on the azimuth angle calculated in step S2, query the radiation pattern data of the target AIS beacon antenna to obtain the receiving antenna gain G of the target AIS beacon in the direction corresponding to the azimuth angle calculated in step S2. rx (x,y); S4. Calculate the theoretical received signal strength, i.e., the static reference signal strength RSSI, for the center point (x, y) of each grid cell. t (x,y), traverse all grid cells and complete the static reference signal strength RSSI t After calculating (x,y), a static benchmark coverage model covering the entire evaluation area can be generated.

4. The method for real-time dynamic evaluation of the effective range of AIS physical navigation marks based on opportunity vessels according to claim 3, characterized in that, The superposition calculation is achieved through the following formula: RSSI d (x,y,t)=RSSI t (x,y)+ΔRSSI'(x,y,t); Among them: RSSI d (x,y,t) is the final dynamic prediction signal strength at time t and location (x,y); RSSI t (x,y) is the static reference signal strength of the target AIS entity beacon at the center point (x,y) of the grid cell; ΔRSSI'(x,y,t) is the environmental calibration factor of the center point (x, y) of the grid cell obtained by spatial interpolation.

5. The method for real-time dynamic evaluation of the effective range of AIS physical navigation marks based on opportunity vessels according to claim 3, characterized in that, The static reference signal strength RSSI t The calculation of (x,y) is as follows: ； Among them, P tx This refers to the ship's nominal transmission power. G tx Standard gain for shipboard AIS transmitting antennas; G rx The receiving antenna gain of the target AIS beacon in the corresponding ship direction; L misc It is the sum of inherent feeder and connector losses; d is the distance between the transmitter and receiver; h t Indicates the height of the transmitting antenna; h r This indicates the height of the receiving antenna.

6. The method for real-time dynamic evaluation of the effective range of AIS physical navigation marks based on opportunity vessels according to claim 1, characterized in that, The method further includes step E after step D: in the real-time dynamic range map, the dynamic range boundary of the target AIS entity beacon in the current marine environment is drawn according to a preset signal strength threshold and then visualized.

7. The method for real-time dynamic evaluation of the effective range of AIS physical navigation marks based on opportunity vessels according to claim 1, characterized in that, When the dynamic range of action is less than the preset service distance, an early warning message will be automatically sent to the VTS or navigation mark maintenance system.

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