Giriş
Açıklaması şöyle
AIS is also among the types of a navigation system which helps to pinpoint the location and other navigational statistics of ships. AIS uses VHF radio channels as transmitters and receivers to send and receive messages between ships which endeavors to fulfil a lot of responsibilities.As per the regulation enforced by The International Maritime Organization (IMO), all passengers’ vessels and commercial ships over 299 Gross Tonnage (GT) sailing in the international to carry a Class A AIS transponder.
AIS Cihaz Tipleri
Class A ve Class B olarak sınıflandırılıyorlar. Açıklaması şöyle
AIS Types- Class A: Mandated for all vessels 300 GT and above engaged on international voyages as well as all passenger ships- Class B: Provides limited functionality and intended for non SOLAS vessels. Primarily used for vessels such as pleasure craftsAIS operates principally on two dedicated frequencies or VHF channels:- AIS 1: Works on 161.975 MHz- Channel 87B (Simplex, for ship to ship)- AIS 2: 162.025 MHz- Channel 88B (Duplex for ship to shore)It uses Self Organizing Time Division Multiple Access (STDMA) technology to meet the high broadcast rate. This frequency has a limitation of line of sight which is about 40 miles or so.
Class A için açıklama şöyle
Shipborne mobile equipment intended to meet the performance standards and carriage requirements adopted by IMO. Class A stations report their position (message 1/2/3) autonomously every 2-10 seconds dependent on the vessel’s speed and/or course changes (every three minutes or less when at anchor or moored); and, the vessel’s static and voyage related information (message 5) every 6 minutes. Class A stations are also capable of text messaging safety related information (message 6/8) and AIS Application Specific Messages (message 6,8,25,26), such as meteorological and hydrological data, electronic Broadcast Notice to Mariners, and other marine safety information
Class B için açıklama şöyle
Shipborne mobile equipment which is interoperable with all other AIS stations, but, does not meet all the performance standards adopted by IMO. Similar to Class A stations, they report every three minutes or less when at anchor or moored, but, their position (message 6/8) is reported less often and at a lower power. Likewise, they report the vessel’s static data (message 18/24) every 6 minutes, but, not any voyage related information. They can receive safety related text and application specific messages, but, cannot transmit them. There are two types of Class B AIS, those using carrier sense Time-Division Multiple Access (CS-TDMA) technology and those like the Class A using Self-Organizing Time-Division Multiple Access Technology (SO-TDMA). Class B/SO is generally more capable; Class B/CS is generally less expensive.
AIS Mesajları ve Zaman Damgası
AIS mesajlarında zaman damgası bulunmaz. Açıklaması şöyle.
The AIS system was initially created as a collision avoidance system, and was supposed to be used in real time, hence there was no need to transmit a timestamp.
AIS ve MEA 0183 İlişkisi
AIS mesajları binary mesajlar olmalarına rağmen, NMEA içinde gönderilebiliyorlar. AIS taşıyan iki tane mesaj var. Bunlar VDM ve VDO mesajları. Açıklaması şöyle
!AIVDM (received data from other vessels)!AIVDO (own vessel's information)
Açıklaması şöyle
!AIVDM The NMEA message type, other NMEA device messages are restricted1 Number of sentences (some messages need more than one, maximum generally is 9)1 Sentence number (1 unless it is a multi-sentence message)MsgId The blank is the sequential message ID (for multi-sentence messages)A The AIS channel (A or B), for dual channel transponders it must match the channel used14eG;... The encoded AIS data, using AIS-ASCII60* End of data, number of unused bits at end of encoded data (0-5)7D NMEA checksum (NMEA 0183 Standard CRC16)
Fragmentli Mesaj
Örnek
Şöyledir. Başka bir gemiden gelmektedir.
!AIVDM,2,1,8,A,56;OaD02B8EL990b221`P4v1T4pN0HDpN2222216HHN>B6U30A2hCDhD`888,0*4D
!AIVDM,2,2,8,A,88888888880,2*2CConsider a message sent using 2 fragments:Field 2 will be 2, the number of fragments.Field 3 will be 1 for the first fragment, and 2 for the secondField 4 can be any digit between 0 and 9, but will be common for both messages. This number is incremented for each new multi-fragment message sent by a vessel. It allows the decoding program to match together fragments that belong to the same message
AIS Taşıyan NMEA Mesajları İçin Parser
aisparser kullanılabilir.
aismessages kullanılabilir
AisLib kullanılabilir
Mesajlar
Mesaj alanları 6 bit büyüklüğünde gruplanır ve bu altı bit özel bir şekilde ASCII karakterine çevriliyor. Ancak bir alan örneğin 8 bit olabilir. Bazı mesaj açıklamaları şöyle
1. Static Information (Every 6 minutes and on request):- MMSI number- IMO number- Name and Call Sign- Length and Beam- Type of ship- Location of position fixing antenna2. Dynamic Information (Depends on speed and course alteration)- Ship’s position with accuracy indication- Position time stamp (in UTC)- Course Over Ground (COG)3. Voyage Related Information (Every 6 minutes, when data is amended, or on request)- Ship’s draught- Type of cargo- Destination and ETA- Route plan (Waypoints)4. Short safety related messagesFree format text message addressed to one or many destinations or to all stations in the area. This content could be such as buoy missing, ice berg sighting etc
Mesajlar şöyle
Message 1 Position Report
Message 2 Position Report
Message 3 Position Report
Message 4 Base Station Report
Used by fixed-location base stations to periodically report a position and time reference.
Message 5 Static and Voyage Related Data
Message has a total of 424 bits, occupying two AIVDM sentences. In practice, the information in these fields (especially ETA and destination) is not reliable, as it has to be hand-updated by humans rather than gathered automatically from sensors.
Message 6 Binary Addressed Message
An addressed point-to-point message with unspecified binary payload. The St.Lawrence Seaway AIS system and the USG PAWSS system use this payload for local extension messages. It is variable in length up to a maximum of 1008 bits (up to 5 AIVDM sentence payloads).
Message 7 Binary Acknowledgement
A receipt acknowledgement to the senders of a previous messages of type 6. Total length varies between 72 and 168 bits by 32-bit increments, depending on the number of destination MMSIs included.
Message 8 Binary Broadcast Message
Message 9 Standard SAR Aircraft Position Report
Message 10 UTC/date inquiry
Message 11 UTC/Date response
Message 12 Addressed Safety Related Message
Message 13 Safety Related Acknowledge
Message 14 Safety Related Broadcast
Message 15 Interrogation
Used by a base station to query one or two other AIS transceivers for status messages of specified types.
Message 16 Assignment mode command
Used by a base station with control authority to configure the scheduling of AIS informational messages from subordinate stations, either as a frequency per 10-minute interval or by specifying the TDMA slot(s) offset on which those messages should be transmitted.
Message 17 DGNSS Broadcast binary message
Used to broadcast differential corrections for GPS. The data in the payload is intended to be passed directly to GPS receivers capable of accepting such corrections.
Message 18 Standard Class B equipment position report
Message 19 Extended Class B Equipment Position Report
A less detailed report than types 1-3 for vessels using Class B transmitters. Omits navigational status and rate of turn.
Message 20 Data Link Management Message
This message is used to pre-allocate TDMA slots within an AIS base station network. It contains no navigational information, and is unlikely to be of interest unless you are implementing or studying an AIS base station network.
Message 21 Aids-to-Navigation Report
Identification and location message to be emitted by aids to navigation such as buoys and lighthouses.
Message 22 Channel Management
Message 23 Group Assignment
Intended to be broadcast by a competent authority (an AIS network-control base station) to set to set operational parameters for all mobile stations in an AIS coverage region
Message 25 Single slot binary message
Message 26 Multiple slot binary message with Communications State
Message 27 Position report for long range applications
İz Bilgisi Olan Mesajlar
AIS mesajlarında tekil olan alan User ID yani MMSI number. Açıklaması şöyle
Maritime Mobile Service Identity (MMSI) is a unique 9 digit number that is assigned to a (Digital Selective Calling) DSC radio or an AIS unit. Similar to a cell phone number, your MMSI number is your unique calling number for DSC radios or an AIS unit.
Bunlar şöyle
Message 1 Position Report
Message 2 Position Report
Message 3 Position Report
Message 5 Static and Voyage Related Data
Message 9 Standard SAR Aircraft Position Report
Message 18 Standard Class B equipment position report
Message 19 Extended Class B Equipment Position Report
BaseStationg Bilgisi Olan Mesajlar
Bunlar şöyle
Message 4 Base Station Report
Aids-to-navigation report Olan Mesajlar
Message 21 Aids-to-Navigation Report
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