Abnormal ship identification method based on AIS VHF signal

Abstract

The present invention relates to the technical field of abnormal ship positioning, and in particular to an abnormal ship identification method based on AIS very high frequency signals, comprising: obtaining current ship messages and historical ship messages sent by a ship to be detected, obtaining a monitoring base station and the current ship message position according to the current ship message, and determining the actual number of message receptions of the ship to be detected within a unit time according to the historical ship message; obtaining the positions of all base stations, and judging whether the ship to be detected meets the ship detection prerequisite; when it is determined that the ship to be detected meets the ship detection prerequisite, obtaining the actual number of receiving base stations that actually receive the current ship message, and the number of out-of-range base stations located outside a preset range in the actual receiving base stations; when the number of base stations within the determined range is not 0, continuously monitoring the ship to be detected through the monitoring base station to obtain multiple ship messages, and judging whether the ship to be detected is an abnormal ship. The abnormal ship identification method is simple, efficient, and has a high accuracy rate.

Description

Technical Field

[0001] The invention relates to the technical field of abnormal ship positioning, and in particular to an abnormal ship identification method based on AIS very high frequency signals. Background Art

[0002] With the rapid development of the maritime shipping industry, AIS (Automatic Identification System) has become an important means to ensure the safety of ship navigation, protect the marine environment, and improve traffic efficiency. At present, my country has built an AIS shore-based network system to achieve full-time and all-weather monitoring of coastal and inland ships.

[0003] Abnormal AIS signals may not only cause other ships to be unable to accurately judge the dynamics of ships in nearby waters, thereby increasing the risk of ship collisions; but also interfere with normal maritime traffic management and affect the maritime department's monitoring and scheduling of ship traffic flows. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an abnormal ship identification method based on AIS very high frequency signals.

[0005] To solve the above problems, the technical solution adopted by the present invention is:

[0006] A method for identifying abnormal ships based on AIS very high frequency signals, the method comprising:

[0007] Step 1: obtaining the current ship message and the historical ship message sent by the ship to be detected, obtaining the monitoring base station and the current ship message position according to the current ship message, and obtaining the actual number of message receptions of the ship to be detected within a unit time according to the historical ship message;

[0008] Step 2: Obtain the positions of all base stations and determine whether the ship to be detected meets the ship detection prerequisite, wherein the ship detection prerequisite includes: (1) the actual number of message receptions per unit time reaches a preset unit reception number; (2) the number of theoretical receiving base stations within a preset range with a radius R centered on the current ship message position reaches a base station number threshold;

[0009] Step 3: when it is determined that the ship to be detected meets the prerequisite for ship detection, the number of actual receiving base stations that actually receive the current ship message and the number of out-of-range base stations that are outside the preset range among the actual receiving base stations are obtained;

[0010] Step 4. When it is determined that the number of base stations within the range is not zero, the monitoring base station continuously monitors the ship to be detected to obtain multiple ship messages, and based on the theoretical number of receiving base stations, the actual number of receiving base stations, the current ship message, and the signal-distance correspondence relationship, the multiple ship messages determine whether the ship to be detected is an abnormal ship.

[0011] As an implementation mode of the invention, step 4 includes:

[0012] Step S401: Use the following formula to obtain the base station ratio of the current ship message: P : P=n / N ;

[0013] in, n is the actual number of receiving base stations, N is the theoretical number of receiving base stations;

[0014] Step S402: if P≥20%, the ship to be detected is marked, and abnormal ship verification is performed based on the signal-distance correspondence relationship. If the verification is successful, the ship to be detected is determined to be an abnormal ship; if the verification is not successful, the ship to be detected is determined to be a normal ship;

[0015] If P<20%, the ship to be detected is verified as an abnormal ship based on the signal-distance correspondence. If the verification is successful, the ship to be detected is determined to be an abnormal ship. If the verification is not successful, the n value in step S401 is increased by one, and the P value is calculated again. If P>20%, the ship to be detected is determined to be a normal ship, otherwise, the ship to be detected is determined to be an abnormal ship.

[0016] As an implementation mode of the invention, the abnormal ship verification is performed on the ship to be detected based on the signal-distance correspondence relationship in the following manner:

[0017] (1) obtaining a current distance and a current received signal level obtained by parsing the current ship message by the monitoring base station, and determining whether the current received signal level meets the signal theoretical value range; the current distance is the distance between the current ship message position and the monitoring base station;

[0018] (2) obtaining the monitoring distance and the monitoring signal level obtained by parsing each of the ship messages by the monitoring base station, so as to determine whether the average monitoring signal level difference within a preset distance range from the monitoring base station during the movement of the ship to be detected meets the signal difference theoretical value range; wherein a monitoring signal level difference is obtained by subtracting a monitoring signal level from a current receiving signal level;

[0019] (3) When it is determined that the current received signal level does not meet the signal theoretical value range; and / or during the movement of the ship to be detected, the average monitoring signal level difference within the preset distance range from the monitoring base station does not meet the signal difference theoretical value range, it is determined that the abnormal ship verification is established.

[0020] As an implementation method of the invention, in step (1), the current distance x The current signal reception level y The theoretical signal value range is as follows:

[0021] Relation 1: 0 ≤ x <20 km, [-60+(- z )] ≤ y ≤ -60 dBm;

[0022] Relation 2: 20 ≤ x <40 km, [-72+(- z )] ≤ y ≤ -72 dBm;

[0023] Relation 3: 40 ≤ x <60 km, [-76+(- z )] ≤ y ≤ -76 dBm;

[0024] Relation 4: 60 ≤ x <80 km, [-79+(- z )] ≤ y ≤ -79 dBm;

[0025] Relation 5: 80 ≤ x <100 km, [-82+(- z )] ≤ y ≤ -82 dBm;

[0026] Relation 6: 100 ≤ x <120 km, [-84+(- z )] ≤ y ≤ -84 dBm;

[0027] Relation 7: 120 ≤ x <140 km, [-85+(- z )] ≤ y ≤ -85 dBm;

[0028] Relation 8: 140 ≤ x <160 km, [-86+(- z )] ≤ y ≤ -86 dBm;

[0029] Relation 9: 160 ≤ x <180 km, [-87+(- z )] ≤ y ≤ -87 dBm;

[0030] Relation 10: 180 ≤ x <200 km, [-88+(- z )] ≤ y ≤ -88 dBm;

[0031] Relation 11: 200 ≤ x <220 km, [-89+(- z )] ≤ y ≤ -89 dBm;

[0032] Relation 12: 220 ≤ x <240 km, [-90+(- z )] ≤ y ≤ -90 dBm;

[0033] Relation 13: 240 ≤ x <260 km, [-90.6+(- z )] ≤ y ≤ -90.6 dBm;

[0034] Relation 14: 260 ≤ x <280 km, [-91+(- z )] ≤ y ≤ -91 dBm;

[0035] Relation 15: 280 ≤ x <300 km, [-92+(- z )] ≤ y ≤ -92 dBm;

[0036] Relation 16: 300 ≤ x <320 km, [-92.5+(- z )] ≤ y ≤ -92.5 dBm;

[0037] Relation 17: 320 ≤ x <340 km, [-93+(- z )] ≤ y ≤ -93 dBm;

[0038] Relation 18: 340 ≤ x<360 km, [-93.5+(- z )] ≤ y ≤ -93.5 dBm;

[0039] Relation 19: 360 ≤ x <380 km, [-94+(- z )] ≤ y ≤ -94 dBm;

[0040] Relation 20: 380 ≤ x <400 km, [-94.5+(- z )] ≤ y ≤ -94.5 dBm;

[0041] Relationship 21: x ≥ 400 km, [-95+(- z )]≤ y ≤ -95 dBm;

[0042] in, z is a constant whose value range is [2,6].

[0043] As an embodiment of the invention, in step (2), the monitoring distance x' Difference from average monitoring signal level y' The theoretical range of signal difference is as follows:

[0044] Range 1: 0 ≤ x' <40 km, [-12+(- a )] ≤ y' ≤ [-12+ a ]dBm;

[0045] Range 2: 20 ≤ x' <60 km, [-4+(- a )] ≤ y' ≤ [-4+ a ]dBm;

[0046] Range 3: 40 ≤ x' <80 km, [-3+(- a )] ≤ y' ≤ [-3+ a ]dBm;

[0047] Range 4: 60 ≤ x' <100 km, [-3+(- a )] ≤ y' ≤ [-3+ a ]dBm;

[0048] Range 5: 80 ≤ x' <120 km, [-2+(- a )] ≤ y' ≤ [-2+ a ]dBm;

[0049] Range 6: 100 ≤ x' <140 km, [-1+(- a )]≤ y' ≤ [-1+ a ]dBm;

[0050] Range 7: 120 ≤ x' <160 km, [-1+(- a )] ≤ y' ≤ [-1+ a ]dBm;

[0051] Range 8: 140 ≤ x' <180 km, [-1+(- a )] ≤ y' ≤ [-1+ a ]dBm;

[0052] Range 9: 160 ≤ x' <200 km, [-1+(- a )] ≤ y' ≤ [-1+ a ]dBm;

[0053] Range 10: 180 ≤ x' <220 km, [-1+(- a )] ≤ y' ≤ [-1+ a ]dBm;

[0054] Range 11: 200 ≤ x' <240 km, [-1+(- a )] ≤ y' ≤ [-1+ a ] dBm;

[0055] Range 12: 220 ≤ x' <260 km, [-0.6+(- a )] ≤ y' ≤ [-0.6+ a ]dBm;

[0056] Range 13: 240 ≤ x' <280 km, [-0.4+(- a )] ≤y' ≤ [-0.4+ a ]dBm;

[0057] Range 14: 260 ≤ x' <300 km, [-1+(- a )] ≤ y' ≤ [-1+ a ]dBm;

[0058] Range 15: 280 ≤ x' <320 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ]dBm;

[0059] Range 16: 300 ≤ x' <340 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ]dBm;

[0060] Range 17: 320 ≤ x' <360 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ]dBm;

[0061] Range 18: 340 ≤ x' <380 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ]dBm;

[0062] Range 19: 360 ≤ x' <400 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ]dBm;

[0063] in, a is a constant whose value range is [0.2,1].

[0064] As an implementation mode of the invention, in step 1, the monitoring base station and the current ship message location are obtained according to the current ship message in the following manner:

[0065] The received signal level after parsing of each base station that receives the current ship message is obtained, the base station with the highest received signal level is used as a monitoring base station, and the position parsed by the monitoring base station is used as the current ship message position.

[0066] As an implementation mode of the invention, in step 2, the method for determining the number of preset unit receiving units includes:

[0067] Based on the current ship message, a message broadcasting interval is obtained, and according to the broadcasting interval, a theoretical number of received messages per unit time is obtained. S 理论 , and use the following formula to get the preset unit receiving quantity S 预设 : S 预设 = 20%× S 理论 .

[0068] As an implementation method of the invention, in step 2, the value range of R is 200 ≤ R <300 km, the base station number threshold range is [2,4].

[0069] The beneficial effects of adopting the above technical solution are:

[0070] The abnormal ship identification method based on AIS very high frequency signal provided by the present invention first obtains the current ship message and the historical ship message sent by the ship to be detected, and then obtains the monitoring base station, the current ship message position and the actual message reception number per unit time; then, based on the above data, it is judged whether the ship to be detected meets the ship detection prerequisite, and when it is determined that the ship detection prerequisite is met, the actual number of receiving base stations that actually receive the current ship message and the number of out-of-range base stations located outside the preset range among the actual receiving base stations are obtained; finally, when it is determined that the number of base stations within the range is not 0, the ship to be detected is continuously monitored by the monitoring base station to obtain multiple ship messages, and based on the theoretical number of receiving base stations, the actual number of receiving base stations, the current ship message, the multiple ship messages, and the signal-distance correspondence relationship, it is judged whether the ship to be detected is an abnormal ship, that is, it is only necessary to receive the message and parse the message through the base station to realize the identification of the abnormal ship. The abnormal ship identification method is simple and efficient, reduces the risk of ship collision, and facilitates the monitoring and scheduling of ship traffic flow by the maritime department.

[0071] In addition, the present invention takes into account that for abnormal ships, the mismatch between distance and signal strength is its most obvious feature. Therefore, by judging the relationship between signal level and signal receiving distance, the abnormal ship can be accurately judged with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 This is a graph showing the relationship between the signal reception level and the theoretical value of the transmission distance.

[0073] Figure 2 It is a theoretical step diagram of signal reception level and transmission distance.

[0074] Figure 3 It is the simulation result of the virtual ship.

[0075] Figure 4 It is the simulation result of the real ship.

[0076] Figure 5 The present invention provides a flowchart of an abnormal ship identification method based on AIS very high frequency signals. DETAILED DESCRIPTION

[0077] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is clearly and completely described below in conjunction with specific embodiments.

[0078] The present invention realizes abnormal ship identification based on AIS very high frequency signals, and specifically, abnormal ships are identified by signal levels, which is explained below.

[0079] AIS signals operate at the VHF stage, with signal frequencies of 161.975MHz and 162.025MHz. The attenuation of VHF radio signals in free space is mainly affected by the following factors:

[0080] (1) Distance attenuation: As radio signals propagate in free space, signal strength attenuates as distance increases. According to the free space propagation model, signal strength is inversely proportional to the square of the distance, that is, the relationship between signal strength P and distance d is:

[0081] ;

[0082] This means that the greater the distance, the weaker the received signal strength.

[0083] (2) Frequency influence: The higher the frequency of the radio signal, the more significant the attenuation is. This is because high-frequency signals are usually subject to more scattering and absorption in free space. This phenomenon is particularly evident in the very high frequency (VHF) and ultra-high frequency (UHF) ranges.

[0084] 2. The relationship between the transmission distance of the AIS (Automatic Identification System) signal and the received signal level can be derived using the free space propagation model. The following are the basic steps and formulas for the derivation process.

[0085] (1) Basic concepts:

[0086] Transmitted power (Pt): The power output by the transmitter, usually measured in watts (W).

[0087] Received Power (Pr): The signal power received by the receiver.

[0088] Distance (d): The straight-line distance between the transmitter and the receiver, measured in meters (m).

[0089] Antenna Gain (Gt and Gr): The gain of the transmitting and receiving antennas, expressed in dimensionless units (relative to the gain of an ideal antenna).

[0090] (2) Free Space Path Loss (FSPL) formula

[0091] In free space, the path loss of a signal can be calculated using the following formula:

[0092] L=20log 10 (d)+20log 10 (f)+32.44;

[0093] in:

[0094] L is the path loss in decibels (dB).

[0095] d is the distance in kilometers (km).

[0096] 32.44 is a constant used to convert the result of the formula to dB (applicable for distances in kilometers and frequencies in MHz).

[0097] f is the signal frequency in MHz. In the AIS system, the signal frequency is 161.975MHz or 162.025MHz.

[0098] (3) Antenna gain

[0099] In AIS (Automatic Identification System) shipboard equipment, the gain of the transmitting antenna and the receiving antenna generally varies according to the specific equipment and system design. Usually, the gain values ​​are as follows:

[0100] Transmit antenna gain: Generally between 3dBi and 6dBi, depending on the type and design of the antenna.

[0101] Receiving antenna gain: Usually between 3dBi and 6dBi. Some high-performance receiving antennas may have higher gains.

[0102] Pr = Pt-L+Gt+Gr;

[0103] When high power transmission is used, Pt is 12.5W, and the corresponding signal level is 40.97dBm.

[0104] Therefore, after considering the receiving and transmitting antennas, the relationship between the signal receiving level and the theoretical transmission distance (the distance between the base station and the ship) can be calculated according to the above formula, as shown in Figure 1Based on the above theoretical values ​​and taking into account the numerical fluctuations, the theoretical step diagram of signal reception level and transmission distance is obtained, as shown in Figure 2 The simulation results are shown in Figure 3 As shown (each color in the figure corresponds to the simulation result of a ship).

[0105] However, since the actual position of the abnormal ship transmitting the signal often deviates from the position carried in the message by a long distance, and it uses fixed equipment to continuously transmit at a certain position, the signal of the abnormal ship has the following characteristics: First, the base station that actually receives the signal is far away from the position of the ship carried in the ship message, that is, it exceeds the coverage range of the actual signal of the base station; second, since the position of the transmitting signal is fixed, no matter how far the base station receiving the signal is from the ship, the level of the received signal does not change with the change of distance. The simulation results of the virtual ship are as follows: Figure 4 As shown (each color in the figure corresponds to a simulation result of a ship). Based on the above characteristics, an embodiment of the present invention provides an abnormal ship identification method based on AIS very high frequency signals to perform the following detection on abnormal ships.

[0106] The embodiment of the present invention provides a method for identifying abnormal ships based on AIS very high frequency signals, such as Figure 5 As shown, the method includes:

[0107] Step 1: obtaining the current ship message and the historical ship message sent by the ship to be detected, obtaining the monitoring base station and the current ship message position according to the current ship message, and obtaining the actual number of message receptions of the ship to be detected within a unit time according to the historical ship message;

[0108] The message sent by the ship can be received by the base station in the coverage area, and the coverage range of the base station overlaps, so the current ship message may be received by one base station, or by 2, 3 or even more base stations (this step can be implemented based on the MMSI code of the message). Therefore, in order to ensure that the current ship message location is unique and to carry out subsequent steps, the following method is used to obtain the monitoring base station and the current ship message location according to the current ship message:

[0109] Obtain the received signal level of each base station that receives the current ship message after parsing the current ship message, take the base station with the highest received signal level as the monitoring base station, and take the position parsed by the monitoring base station as the current ship message position. In the present invention, the position generally refers to the position coordinates.

[0110] For historical messages, in order to avoid dropping messages and thus affecting the number of messages received per unit time, the actual number of messages received by the ship to be detected per unit time is obtained as follows:

[0111] S101. For any base station, obtain all ship messages corresponding to the MMSI code carried in the current ship message, and obtain the actual number of message receptions per unit time according to all the ship messages;

[0112] S102: taking the number of received messages with the largest value as the actual number of received messages of the ship to be detected within a unit time.

[0113] The aforementioned unit time is obtained according to the message broadcasting interval of the ship to be detected, which can be 1 minute or 1 hour. Different ships correspond to different message broadcasting intervals, as shown in Tables 1 and 2. It can be seen from Table 1 that when it is a "ship anchored or berthed and moving at a speed exceeding 3 kn", its corresponding message broadcasting interval is 10s, and the unit time can be set to 1 minute; when it is a "ship anchored or berthed and moving at a speed not exceeding 3 kn", its corresponding message broadcasting interval is 3 minutes, so the unit time can be set to 1 hour.

[0114] Table 1 Reporting intervals for Class A shipborne stations

[0115]

[0116] Table 2 Class B “SO” shipborne station reporting interval

[0117]

[0118] In addition, in order to improve accuracy, each base station can obtain the actual number of message receptions within multiple unit times, and then obtain the final actual number of message receptions within a unit time by comparing all the actual number of message receptions obtained by multiple base stations.

[0119] Step 2: Obtain the positions of all base stations and determine whether the ship to be detected meets the ship detection prerequisite, wherein the ship detection prerequisite includes: (1) the actual number of message receptions per unit time reaches a preset unit reception number; (2) the number of theoretical receiving base stations within a preset range with a radius R centered on the current ship message position reaches a base station number threshold;

[0120] In condition (1), the method for determining the preset unit reception quantity includes: obtaining the message broadcasting interval based on the current ship message, and obtaining the theoretical number of message receptions per unit time according to the broadcasting interval. S 理论 , and use the following formula to get the preset unit receiving quantity S 预设 : S 预设 = 20%× S 理论 .

[0121] For example: When the message broadcast interval is 3 minutes / time, the theoretical number of messages received per hour is S 理论 is 60 / 3=20, then the preset unit receiving quantity is S 预设 = 20%×20=4. Therefore, when the number of messages received per hour is ≥4, it is determined that the prerequisite (1) is met.

[0122] In condition (2), the value range of R is 200 ≤ R <300 km, the base station number threshold range is [2,4].

[0123] The positions of all base stations are obtained in advance. For any base station, whether it is a theoretical receiving base station is determined by judging whether the distance between the base station and the ship message position is less than or equal to R.

[0124] Step three: when it is determined that the ship to be detected meets the prerequisite for ship detection, the number of actual receiving base stations that actually receive the current ship message and the number m of out-of-range base stations among the actual receiving base stations that are outside the preset range are obtained.

[0125] The number of all actual receiving base stations can be obtained through step one, and then whether they are within the preset range is determined based on the relationship between the distance between each actual receiving base station and the current ship message and R, thereby obtaining the number m of out-of-range base stations among the actual receiving base stations that are outside the preset range.

[0126] Step 4. When it is determined that the number m of base stations within the range is not 0, the monitoring base station continuously monitors the ship to be detected to obtain multiple ship messages, and determines whether the ship to be detected is an abnormal ship based on the theoretical number of receiving base stations, the actual number of receiving base stations, the current ship message, multiple ship messages, and the signal-distance correspondence.

[0127] This step specifically includes:

[0128] Step S401: Use the following formula to obtain the base station ratio of the current ship message: P : P=n / N ;

[0129] in, n is the actual number of receiving base stations, N is the theoretical number of receiving base stations;

[0130] Step S402: if P≥20%, the ship to be detected is marked, and abnormal ship verification is performed based on the signal-distance correspondence relationship. If the verification is successful, the ship to be detected is determined to be an abnormal ship; if the verification is not successful, the ship to be detected is determined to be a normal ship;

[0131] If P<20%, then the ship to be detected is verified as an abnormal ship based on the signal-distance correspondence relationship. If the verification is successful, the ship to be detected is determined to be an abnormal ship; if the verification is not successful, the n value in step S401 is increased by one, and the P value is calculated again. If P>20%, the ship to be detected is determined to be a normal ship, otherwise, the ship to be detected is determined to be an abnormal ship;

[0132] The following method is used to verify the abnormal ship based on the signal-distance correspondence relationship:

[0133] (1) obtaining a current distance and a current received signal level obtained by parsing the current ship message by the monitoring base station, and determining whether the current received signal level meets the signal theoretical value range; the current distance is the distance between the current ship message position and the monitoring base station;

[0134] Among them, the front distance x The current signal reception level y The theoretical relationship can be obtained by Figure 2 Get, as follows:

[0135] Relation 1: 0 ≤ x <20 km, [-60+(- z )] ≤ y ≤ -60 dBm;

[0136] Relation 2: 20 ≤ x <40 km, [-72+(- z )] ≤ y ≤ -72 dBm;

[0137] Relation 3: 40 ≤ x <60 km, [-76+(- z )] ≤ y ≤ -76 dBm;

[0138] Relation 4: 60 ≤ x <80 km, [-79+(- z )] ≤ y ≤ -79 dBm;

[0139] Relation 5: 80 ≤ x <100 km, [-82+(- z)] ≤ y ≤ -82 dBm;

[0140] Relation 6: 100 ≤ x <120 km, [-84+(- z )] ≤ y ≤ -84 dBm;

[0141] Relation 7: 120 ≤ x <140 km, [-85+(- z )] ≤ y ≤ -85 dBm;

[0142] Relation 8: 140 ≤ x <160 km, [-86+(- z )] ≤ y ≤ -86 dBm;

[0143] Relation 9: 160 ≤ x <180 km, [-87+(- z )] ≤ y ≤ -87 dBm;

[0144] Relation 10: 180 ≤ x <200 km, [-88+(- z )] ≤ y ≤ -88 dBm;

[0145] Relation 11: 200 ≤ x <220 km, [-89+(- z )] ≤ y ≤ -89 dBm;

[0146] Relation 12: 220 ≤ x <240 km, [-90+(- z )] ≤ y ≤ -90 dBm;

[0147] Relation 13: 240 ≤ x <260 km, [-90.6+(- z )] ≤ y ≤ -90.6 dBm;

[0148] Relation 14: 260 ≤ x <280 km, [-91+(- z )] ≤ y ≤ -91 dBm;

[0149] Relation 15: 280 ≤x <300 km, [-92+(- z )] ≤ y ≤ -92 dBm;

[0150] Relation 16: 300 ≤ x <320 km, [-92.5+(- z )] ≤ y ≤ -92.5 dBm;

[0151] Relation 17: 320 ≤ x <340 km, [-93+(- z )] ≤ y ≤ -93 dBm;

[0152] Relation 18: 340 ≤ x <360 km, [-93.5+(- z )] ≤ y ≤ -93.5 dBm;

[0153] Relation 19: 360 ≤ x <380 km, [-94+(- z )] ≤ y ≤ -94 dBm;

[0154] Relation 20: 380 ≤ x <400 km, [-94.5+(- z )] ≤ y ≤ -94.5 dBm;

[0155] Relationship 21: x ≥ 400 km, [-95+(- z )]≤ y ≤ -95 dBm;

[0156] in, z is a constant whose value range is [2,6].

[0157] For example, when z is 3 and the current distance is 30 km, it must comply with relation 2, that is, the corresponding level theoretical value range is -75 ≤ y ≤ -72 dBm, and then determine whether the current received signal level is within the theoretical value range.

[0158] (2) obtaining the monitoring distance and the monitoring signal level obtained by parsing each of the ship messages by the monitoring base station, so as to determine whether the average monitoring signal level difference within a preset distance range from the monitoring base station during the movement of the ship to be detected meets the signal difference theoretical value range; wherein one of the monitoring signal level differences is obtained by subtracting a monitoring signal level from a current receiving signal level;

[0159] Monitoring distance x' Difference from average monitoring signal level y' The theoretical range of signal difference is as follows:

[0160] Range 1: 0 ≤ x' <40 km, [-12+(- a )] ≤ y' ≤ [-12+ a ]dBm;

[0161] Range 2: 20 ≤ x' <60 km, [-4+(- a )] ≤ y' ≤ [-4+ a ]dBm;

[0162] Range 3: 40 ≤ x' <80 km, [-3+(- a )] ≤ y' ≤ [-3+ a ]dBm;

[0163] Range 4: 60 ≤ x' <100 km, [-3+(- a )] ≤ y' ≤ [-3+ a ]dBm;

[0164] Range 5: 80 ≤ x' <120 km, [-2+(- a )] ≤ y' ≤ [-2+ a ]dBm;

[0165] Range 6: 100 ≤ x' <140 km, [-1+(- a )]≤ y' ≤ [-1+ a ]dBm;

[0166] Range 7: 120 ≤ x' <160 km, [-1+(- a )] ≤ y' ≤ [-1+a ]dBm;

[0167] Range 8: 140 ≤ x' <180 km, [-1+(- a )] ≤ y' ≤ [-1+ a ]dBm;

[0168] Range 9: 160 ≤ x' <200 km, [-1+(- a )] ≤ y' ≤ [-1+ a ]dBm;

[0169] Range 10: 180 ≤ x' <220 km, [-1+(- a )] ≤ y' ≤ [-1+ a ]dBm;

[0170] Range 11: 200 ≤ x' <240 km, [-1+(- a )] ≤ y' ≤ [-1+ a ]dBm;

[0171] Range 12: 220 ≤ x' <260 km, [-0.6+(- a )] ≤ y' ≤ [-0.6+ a ]dBm;

[0172] Range 13: 240 ≤ x' <280 km, [-0.4+(- a )] ≤ y' ≤ [-0.4+ a ]dBm;

[0173] Range 14: 260 ≤ x' <300 km, [-1+(- a )] ≤ y' ≤ [-1+ a ]dBm;

[0174] Range 15: 280 ≤ x' <320 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ]dBm;

[0175] Range 16: 300 ≤x' <340 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ]dBm;

[0176] Range 17: 320 ≤ x' <360 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ]dBm;

[0177] Range 18: 340 ≤ x' <380 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ]dBm;

[0178] Range 19: 360 ≤ x' <400 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ]dBm;

[0179] in, a is a constant whose value range is [0.2,1].

[0180] (3) When it is determined that the current received signal level does not meet the signal theoretical value range; and / or during the movement of the ship to be detected, the average monitoring signal level difference within the preset distance range from the monitoring base station does not meet the signal difference theoretical value range, it is determined that the abnormal ship verification is established.

[0181] The abnormal ship identification method based on AIS very high frequency signal provided by the present invention first obtains the current ship message and the historical ship message sent by the ship to be detected, and then obtains the monitoring base station, the current ship message position and the actual number of message receptions per unit time; then, based on the above data, it is judged whether the ship to be detected meets the ship detection prerequisite, and when it is determined that the ship detection prerequisite is met, the actual number of receiving base stations that actually receive the current ship message and the number of out-of-range base stations located outside the preset range among the actual receiving base stations are obtained; finally, when it is determined that the number of base stations within the range is not 0, the ship to be detected is continuously monitored by the monitoring base station to obtain multiple ship messages, and based on the theoretical number of receiving base stations, the actual number of receiving base stations, the current ship message, the multiple ship messages, and the signal-distance correspondence relationship, it is judged whether the ship to be detected is an abnormal ship, that is, it is only necessary to receive the message and parse the message through the base station to realize the identification of the abnormal ship. The abnormal ship identification method is simple and efficient, reduces the risk of ship collision, and facilitates the monitoring and scheduling of ship traffic flow by the maritime department.

[0182] In addition, the present invention takes into account that for abnormal ships, the mismatch between distance and signal strength is its most obvious feature. Therefore, by judging the relationship between the signal level and the signal receiving distance, the abnormal ship can be accurately judged with high accuracy.

Claims

1. A method for identifying abnormal ships based on AIS very high frequency signals, characterized in that: The method comprises: Step 1: obtaining the current ship message and the historical ship message sent by the ship to be detected, obtaining the monitoring base station and the current ship message position according to the current ship message, and obtaining the actual number of message receptions of the ship to be detected within a unit time according to the historical ship message; Step 2: Obtain the positions of all base stations and determine whether the ship to be detected meets the ship detection prerequisite, wherein the ship detection prerequisite includes: (1) the actual number of message receptions per unit time reaches a preset unit reception number; (2) the number of theoretical receiving base stations within a preset range with a radius R centered on the current ship message position reaches a base station number threshold; Step 3: when it is determined that the ship to be detected meets the prerequisite for ship detection, the number of actual receiving base stations that actually receive the current ship message and the number of out-of-range base stations that are outside the preset range among the actual receiving base stations are obtained; Step 4: when it is determined that the number of base stations within the range is not zero, the monitoring base station continuously monitors the ship to be detected to obtain multiple ship messages, and determines whether the ship to be detected is an abnormal ship based on the theoretical number of receiving base stations, the actual number of receiving base stations, the current ship message, the multiple ship messages, and the signal-distance correspondence relationship; Step 4 includes: Step S401: Use the following formula to obtain the base station ratio of the current ship message: P : P=n / N ; in, n is the actual number of receiving base stations, N is the theoretical number of receiving base stations; Step S402: if P≥20%, the ship to be detected is marked, and abnormal ship verification is performed based on the signal-distance correspondence relationship. If the verification is successful, the ship to be detected is determined to be an abnormal ship; if the verification is not successful, the ship to be detected is determined to be a normal ship; If P<20%, the ship to be detected is verified as an abnormal ship based on the signal-distance correspondence relationship. If the verification is successful, the ship to be detected is determined to be an abnormal ship; if the verification is not successful, the n value in step S401 is increased by one, and the P value is calculated again. If P>20%, the ship to be detected is determined to be a normal ship, otherwise, the ship to be detected is determined to be an abnormal ship; the ship to be detected is verified as an abnormal ship based on the signal-distance correspondence relationship in the following manner: (1) obtaining a current distance and a current received signal level obtained by parsing the current ship message by the monitoring base station, and determining whether the current received signal level meets the signal theoretical value range; the current distance is the distance between the current ship message position and the monitoring base station; (2) obtaining the monitoring distance and the monitoring signal level obtained by parsing each of the ship messages by the monitoring base station, so as to determine whether the average monitoring signal level difference within a preset distance range from the monitoring base station during the movement of the ship to be detected meets the signal difference theoretical value range; wherein a monitoring signal level difference is obtained by subtracting a monitoring signal level from a current receiving signal level; (3) When it is determined that the current received signal level does not meet the signal theoretical value range; and / or during the movement of the ship to be detected, the average monitoring signal level difference within the preset distance range from the monitoring base station does not meet the signal difference theoretical value range, it is determined that the abnormal ship verification is established.

2. The method for identifying abnormal ships based on AIS very high frequency signals according to claim 1, characterized in that: In step (1), the current distance x The current signal reception level y The theoretical signal value range is as follows: Relation 1: 0 ≤ x <20 km, [-60+(- z )] ≤ y ≤ -60 dBm; Relation 2: 20 ≤ x < 40 km, [-72+(- z )] ≤ y ≤ -72 dBm; Relation 3: 40 ≤ x < 60 km, [-76+(- z )] ≤ y ≤ -76 dBm; Relation 4: 60 ≤ x < 80 km, [-79+(- z )] ≤ y ≤ -79 dBm; Relation 5: 80 ≤ x < 100 km, [-82+(- z )] ≤ y ≤ -82 dBm; Relation 6: 100 ≤ x < 120 km, [-84+(- z )] ≤ y ≤ -84 dBm; Relation 7: 120 ≤ x < 140 km, [-85+(- z )] ≤ y ≤ -85 dBm; Relation 8: 140 ≤ x < 160 km, [-86+(- z )] ≤ y ≤ -86 dBm; Relation 9: 160 ≤ x < 180 km, [-87+(- z )] ≤ y ≤ -87 dBm; Relation 10: 180 ≤ x < 200 km, [-88+(- z )] ≤ y ≤ -88 dBm; Relation 11: 200 ≤ x < 220 km, [-89+(- z )] ≤ y ≤ -89 dBm; Relation 12: 220 ≤ x < 240 km, [-90+(- z )] ≤ y ≤ -90 dBm; Relation 13: 240 ≤ x < 260 km, [-90.6+(- z )] ≤ y ≤ -90.6 dBm; Relation 14: 260 ≤ x < 280 km, [-91+(- z )] ≤ y ≤ -91 dBm; Relation 15: 280 ≤ x < 300 km, [-92+(- z )] ≤ y ≤ -92 dBm; Relation 16: 300 ≤ x < 320 km, [-92.5+(- z )] ≤ y ≤ -92.5 dBm; Relation 17: 320 ≤ x < 340 km, [-93+(- z )] ≤ y ≤ -93 dBm; Relation 18: 340 ≤ x < 360 km, [-93.5+(- z )] ≤ y ≤ -93.5 dBm; Relation 19: 360 ≤ x < 380 km, [-94+(- z )] ≤ y ≤ -94 dBm; Relation 20: 380 ≤ x < 400 km, [-94.5+(- z )] ≤ y ≤ -94.5 dBm; Relationship 21: x ≥ 400 km, [-95+(- z )] ≤ y ≤ -95 dBm; in, z is a constant whose value range is [2,6].

3. The abnormal ship identification method based on AIS very high frequency signal according to claim 1 is characterized in that: In step (2), the monitoring distance x' Difference from average monitoring signal level y' The theoretical range of signal difference is as follows: Range 1: 0 ≤ x' < 40 km, [-12+(- a )] ≤ y' ≤ [-12+ a ] dBm; Range 2: 20 ≤ x' < 60 km, [-4+(- a )] ≤ y' ≤ [-4+ a ] dBm; Range 3: 40 ≤ x' < 80 km, [-3+(- a )] ≤ y' ≤ [-3+ a ] dBm; Range 4: 60 ≤ x' < 100 km, [-3+(- a )] ≤ y' ≤ [-3+ a ] dBm; Range 5: 80 ≤ x' < 120 km, [-2+(- a )] ≤ y' ≤ [-2+ a ] dBm; Range 6: 100 ≤ x' < 140 km, [-1+(- a )]≤ y' ≤ [-1+ a ] dBm; Range 7: 120 ≤ x' < 160 km, [-1+(- a )] ≤ y' ≤ [-1+ a ] dBm; Range 8: 140 ≤ x' < 180 km, [-1+(- a )] ≤ y' ≤ [-1+ a ] dBm; Range 9: 160 ≤ x' < 200 km, [-1+(- a )] ≤ y' ≤ [-1+ a ] dBm; Range 10: 180 ≤ x' < 220 km, [-1+(- a )] ≤ y' ≤ [-1+ a ] dBm; Range 11: 200 ≤ x' < 240 km, [-1+(- a )] ≤ y' ≤ [-1+ a ] dBm; Range 12: 220 ≤ x' < 260 km, [-0.6+(- a )] ≤ y' ≤ [-0.6+ a ] dBm; Range 13: 240 ≤ x' < 280 km, [-0.4+(- a )] ≤ y' ≤ [-0.4+ a ] dBm; Range 14: 260 ≤ x' < 300 km, [-1+(- a )] ≤ y' ≤ [-1+ a ] dBm; Range 15: 280 ≤ x' < 320 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ] dBm; Range 16: 300 ≤ x' < 340 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ] dBm; Range 17: 320 ≤ x' < 360 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ] dBm; Range 18: 340 ≤ x' < 380 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ] dBm; Range 19: 360 ≤ x' < 400 km, [-0.5+(- a )] ≤ y' ≤ [-0.5+ a ] dBm; in, a is a constant whose value range is [0.2,1].

4. The method for identifying abnormal ships based on AIS very high frequency signals according to claim 1, characterized in that: In step 1, the monitoring base station and the current ship message location are obtained according to the current ship message in the following manner: The received signal level after parsing of each base station that receives the current ship message is obtained, the base station with the highest received signal level is used as a monitoring base station, and the position parsed by the monitoring base station is used as the current ship message position.

5. The abnormal ship identification method based on AIS very high frequency signal according to claim 1 is characterized in that: In step 2, the method for determining the number of preset units to be received includes: Based on the current ship message, a message broadcasting interval is obtained, and according to the broadcasting interval, a theoretical number of received messages per unit time is obtained. S 理论 , and use the following formula to get the preset unit receiving quantity S 预设 : S 预设 = 20%× S 理论 .

6. The method for identifying abnormal ships based on AIS very high frequency signals according to claim 1, characterized in that: In step 2, the value range of R is 200 ≤ R < 300 km, the base station number threshold range is [2,4].

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