Complete AIS Message JSON Documentation
AIS decoding
AIS-catcher can print AIS messages in JSON. The output format is specified with the -o switch. As an example to show a full decoding of JSON messages use -o 5:
echo '!AIVDM,1,1,,B,3776k`5000a3SLPEKnDQQWpH0000,0*78' | AIS-catcher -r txt . -o 5
{"class":"AIS","device":"AIS-catcher","scaled":true,"channel":"B","nmea":["!AIVDM,1,1,,B,3776k`5000a3SLPEKnDQQWpH0000,0*78"],"type":3,"repeat":0,"mmsi":477213600,"status":5,"status_text":"Moored","turn":0,"speed":0.000000,"accuracy":true,"lon":126.605469,"lat":37.460617,"course":39.000000,"heading":252,"second":12,"maneuver":0,"raim":false,"radio":0}
Below documents the JSON format used for decoding AIS messages. Depending on the settings for JSON decoding fields may or may not be included in the outcome.
With format JSON_NMEA only the common fields will be included in the JSON package. The AIS message details are still included in the NMEA array embedded in the JSON. With format JSON_FULL the program will perform a full decoding of the AIS messages and include in the JSON. The output format is largely compatible with gpsdecode.
Common Fields
These fields are present in all AIS messages:
| Field |
Type |
Description |
Example |
| class |
String |
Always "AIS" |
"AIS" |
| device |
String |
Always "AIS-catcher" |
"AIS-catcher" |
| type |
Integer |
Message type number |
1 |
| scaled |
Boolean |
Values scaled to real units |
true |
| channel |
String |
AIS channel |
"A" |
| nmea |
String |
Original NMEA sentence |
"!AIVDM,1,1,,A,13..." |
| mmsi |
Integer |
MMSI number |
123456789 |
Optional configuration-dependent fields:
| Field |
Type |
Description |
| version |
String |
Software version |
| driver |
Integer |
Driver identifier |
| hardware |
String |
Hardware identifier |
| signal_power |
Float |
Signal strength in dB |
| ppm |
Float |
Frequency error in ppm |
| rxtime |
String |
Reception timestamp |
| country |
String |
Country name from MMSI |
| country_code |
String |
Two-letter country code |
Type 1, 2, 3: Position Report Class A
| Field |
Type |
Range/Units |
Description |
| status |
Integer |
0-15 |
Navigation status |
| status_text |
String |
See note 1 |
Navigation status description |
| turn |
Float |
±720°/min |
Rate of turn |
| turn_unscaled |
Integer |
Raw |
Unscaled turn value |
| speed |
Float |
0-102.2 knots |
Speed over ground |
| accuracy |
Boolean |
- |
Position accuracy flag |
| lon |
Float |
±180° |
Longitude |
| lat |
Float |
±90° |
Latitude |
| course |
Float |
0-359.9° |
Course over ground |
| heading |
Integer |
0-359° |
True heading |
| second |
Integer |
0-59 |
Second of timestamp |
| maneuver |
Integer |
0-2 |
Maneuver indicator |
| raim |
Boolean |
- |
RAIM flag |
| radio |
Integer |
- |
Radio status |
Type 4: Base Station Report
| Field |
Type |
Range |
Description |
| year |
Integer |
YYYY |
UTC year |
| month |
Integer |
1-12 |
UTC month |
| day |
Integer |
1-31 |
UTC day |
| hour |
Integer |
0-23 |
UTC hour |
| minute |
Integer |
0-59 |
UTC minute |
| second |
Integer |
0-59 |
UTC second |
| accuracy |
Boolean |
- |
Position accuracy flag |
| lon |
Float |
±180° |
Longitude |
| lat |
Float |
±90° |
Latitude |
| epfd |
Integer |
0-8 |
EPFD type |
| epfd_text |
String |
See note 2 |
EPFD description |
| raim |
Boolean |
- |
RAIM flag |
| radio |
Integer |
- |
Radio status |
| Field |
Type |
Range |
Description |
| ais_version |
Integer |
0-3 |
AIS version |
| imo |
Integer |
1-999999999 |
IMO number |
| callsign |
String |
7 chars |
Radio callsign |
| shipname |
String |
20 chars |
Vessel name |
| shiptype |
Integer |
0-99 |
Ship type code |
| shiptype_text |
String |
See note 3 |
Ship type description |
| to_bow |
Integer |
0-511m |
Dimension to bow |
| to_stern |
Integer |
0-511m |
Dimension to stern |
| to_port |
Integer |
0-63m |
Dimension to port |
| to_starboard |
Integer |
0-63m |
Dimension to starboard |
| epfd |
Integer |
0-8 |
EPFD type |
| epfd_text |
String |
See note 2 |
EPFD description |
| eta |
String |
ISO8601 |
Estimated time of arrival |
| draught |
Float |
0-25.5m |
Draft in meters |
| destination |
String |
20 chars |
Destination port |
| dte |
Boolean |
- |
Data terminal flag |
Type 6: Binary Addressed Message
| Field |
Type |
Range |
Description |
| seqno |
Integer |
0-3 |
Sequence number |
| dest_mmsi |
Integer |
9 digits |
Destination MMSI |
| retransmit |
Boolean |
- |
Retransmit flag |
| dac |
Integer |
- |
Designated Area Code |
| fid |
Integer |
- |
Function ID |
| data |
String |
- |
Binary data |
Type 7: Binary Acknowledge
| Field |
Type |
Range |
Description |
| mmsi1 |
Integer |
9 digits |
MMSI number 1 |
| mmsiseq1 |
Integer |
0-3 |
Sequence for MMSI 1 |
| mmsi2 |
Integer |
9 digits |
MMSI number 2 |
| mmsiseq2 |
Integer |
0-3 |
Sequence for MMSI 2 |
| mmsi3 |
Integer |
9 digits |
MMSI number 3 |
| mmsiseq3 |
Integer |
0-3 |
Sequence for MMSI 3 |
| mmsi4 |
Integer |
9 digits |
MMSI number 4 |
| mmsiseq4 |
Integer |
0-3 |
Sequence for MMSI 4 |
Type 8: Binary Broadcast Message
| Field |
Type |
Range |
Description |
| dac |
Integer |
- |
Designated Area Code |
| fid |
Integer |
- |
Function ID |
| data |
String |
- |
Binary data |
Type 9: Standard SAR Aircraft Position Report
| Field |
Type |
Range |
Description |
| alt |
Integer |
0-4095 |
Altitude in meters |
| speed |
Integer |
0-1023 |
Speed over ground |
| accuracy |
Boolean |
- |
Position accuracy |
| lon |
Float |
±180° |
Longitude |
| lat |
Float |
±90° |
Latitude |
| course |
Float |
0-359.9° |
Course over ground |
| second |
Integer |
0-59 |
UTC second |
| regional |
Integer |
- |
Regional reserved |
| dte |
Boolean |
- |
DTE flag |
| assigned |
Boolean |
- |
Assigned mode flag |
| raim |
Boolean |
- |
RAIM flag |
| radio |
Integer |
- |
Radio status |
Type 10: UTC/Date Inquiry
| Field |
Type |
Range |
Description |
| dest_mmsi |
Integer |
9 digits |
Destination MMSI |
Type 11: UTC/Date Response
Same fields as Type 4
| Field |
Type |
Range |
Description |
| seqno |
Integer |
0-3 |
Sequence number |
| dest_mmsi |
Integer |
9 digits |
Destination MMSI |
| retransmit |
Boolean |
- |
Retransmit flag |
| text |
String |
- |
Safety related text |
Same fields as Type 7
| Field |
Type |
Range |
Description |
| text |
String |
- |
Safety related text |
Type 15: Interrogation
| Field |
Type |
Range |
Description |
| mmsi1 |
Integer |
9 digits |
Interrogated MMSI 1 |
| type1_1 |
Integer |
1-27 |
First message type |
| offset1_1 |
Integer |
- |
First slot offset |
| type1_2 |
Integer |
1-27 |
Second message type |
| offset1_2 |
Integer |
- |
Second slot offset |
| mmsi2 |
Integer |
9 digits |
Interrogated MMSI 2 |
| type2_1 |
Integer |
1-27 |
First message type |
| offset2_1 |
Integer |
- |
First slot offset |
Type 16: Assignment Mode Command
| Field |
Type |
Range |
Description |
| mmsi1 |
Integer |
9 digits |
First MMSI |
| offset1 |
Integer |
- |
First offset |
| increment1 |
Integer |
- |
First increment |
| mmsi2 |
Integer |
9 digits |
Second MMSI |
| offset2 |
Integer |
- |
Second offset |
| increment2 |
Integer |
- |
Second increment |
Type 17: DGNSS Binary Broadcast Message
| Field |
Type |
Range |
Description |
| lon |
Float |
±180° |
Longitude |
| lat |
Float |
±90° |
Latitude |
| data |
String |
- |
DGNSS data |
Type 18: Standard Class B CS Position Report
| Field |
Type |
Range |
Description |
| reserved |
Integer |
- |
Reserved |
| speed |
Float |
0-102.2 knots |
Speed over ground |
| accuracy |
Boolean |
- |
Position accuracy |
| lon |
Float |
±180° |
Longitude |
| lat |
Float |
±90° |
Latitude |
| course |
Float |
0-359.9° |
Course over ground |
| heading |
Integer |
0-359° |
True heading |
| second |
Integer |
0-59 |
UTC second |
| regional |
Integer |
- |
Regional reserved |
| cs |
Boolean |
- |
Carrier sense unit flag |
| display |
Boolean |
- |
Display flag |
| dsc |
Boolean |
- |
DSC flag |
| band |
Boolean |
- |
Band flag |
| msg22 |
Boolean |
- |
Message 22 flag |
| assigned |
Boolean |
- |
Assigned mode flag |
| raim |
Boolean |
- |
RAIM flag |
| radio |
Integer |
- |
Radio status |
Type 19: Extended Class B CS Position Report
| Field |
Type |
Range |
Description |
| reserved |
Integer |
- |
Reserved |
| speed |
Float |
0-102.2 knots |
Speed over ground |
| accuracy |
Boolean |
- |
Position accuracy |
| lon |
Float |
±180° |
Longitude |
| lat |
Float |
±90° |
Latitude |
| course |
Float |
0-359.9° |
Course over ground |
| heading |
Integer |
0-359° |
True heading |
| second |
Integer |
0-59 |
UTC second |
| regional |
Integer |
- |
Regional reserved |
| shipname |
String |
20 chars |
Vessel name |
| shiptype |
Integer |
0-99 |
Ship type code |
| shiptype_text |
String |
See note 3 |
Ship type description |
| to_bow |
Integer |
0-511m |
Dimension to bow |
| to_stern |
Integer |
0-511m |
Dimension to stern |
| to_port |
Integer |
0-63m |
Dimension to port |
| to_starboard |
Integer |
0-63m |
Dimension to starboard |
| epfd |
Integer |
0-8 |
EPFD type |
| epfd_text |
String |
See note 2 |
EPFD description |
| raim |
Boolean |
- |
RAIM flag |
| dte |
Boolean |
- |
DTE flag |
| assigned |
Boolean |
- |
Assigned mode flag |
Type 20: Data Link Management
| Field |
Type |
Range |
Description |
| offset1 |
Integer |
- |
Offset number 1 |
| number1 |
Integer |
- |
Reserved slots 1 |
| timeout1 |
Integer |
- |
Timeout 1 |
| increment1 |
Integer |
- |
Increment 1 |
| offset2 |
Integer |
- |
Offset number 2 |
| number2 |
Integer |
- |
Reserved slots 2 |
| timeout2 |
Integer |
- |
Timeout 2 |
| increment2 |
Integer |
- |
Increment 2 |
| offset3 |
Integer |
- |
Offset number 3 |
| number3 |
Integer |
- |
Reserved slots 3 |
| timeout3 |
Integer |
- |
Timeout 3 |
| increment3 |
Integer |
- |
Increment 3 |
| offset4 |
Integer |
- |
Offset number 4 |
| number4 |
Integer |
- |
Reserved slots 4 |
| timeout4 |
Integer |
- |
Timeout 4 |
| increment4 |
Integer |
- |
Increment 4 |
Type 21: Aid-to-Navigation Report
| Field |
Type |
Range |
Description |
| aid_type |
Integer |
0-31 |
Aid type |
| aid_type_text |
String |
See note 4 |
Aid type description |
| name |
String |
20 chars |
Name of aid |
| accuracy |
Boolean |
- |
Position accuracy |
| lon |
Float |
±180° |
Longitude |
| lat |
Float |
±90° |
Latitude |
| to_bow |
Integer |
0-511m |
Dimension to bow |
| to_stern |
Integer |
0-511m |
Dimension to stern |
| to_port |
Integer |
0-63m |
Dimension to port |
| to_starboard |
Integer |
0-63m |
Dimension to starboard |
| epfd |
Integer |
0-8 |
EPFD type |
| epfd_text |
String |
See note 2 |
EPFD description |
| second |
Integer |
0-59 |
UTC second |
| off_position |
Boolean |
- |
Off position indicator |
| regional |
Integer |
- |
Regional reserved |
| raim |
Boolean |
- |
RAIM flag |
| virtual_aid |
Boolean |
- |
Virtual aid flag |
| assigned |
Boolean |
- |
Assigned mode flag |
Type 22: Channel Management
| Field |
Type |
Range |
Description |
| channel_a |
Integer |
- |
Channel A number |
| channel_b |
Integer |
- |
Channel B number |
| txrx |
Integer |
- |
Tx/Rx mode |
| power |
Boolean |
- |
Power level |
| addressed |
Boolean |
- |
Addressed flag |
| band_a |
Boolean |
- |
Channel A band |
| band_b |
Boolean |
- |
Channel B band |
| zonesize |
Integer |
- |
Zone size |
| If addressed = true: |
|
|
|
| dest1 |
Integer |
9 digits |
Destination MMSI 1 |
| dest2 |
Integer |
9 digits |
Destination MMSI 2 |
| If addressed = false: |
|
|
|
| ne_lon |
Float |
±180° |
NE longitude |
| ne_lat |
Float |
±90° |
NE latitude |
| sw_lon |
Float |
±180° |
SW longitude |
| sw_lat |
Float |
±90° |
SW latitude |
Type 23: Group Assignment Command
| Field |
Type |
Range |
Description |
| ne_lon |
Float |
±180° |
NE longitude |
| ne_lat |
Float |
±90° |
NE latitude |
| sw_lon |
Float |
±180° |
SW longitude |
| sw_lat |
Float |
±90° |
SW latitude |
| station_type |
Integer |
- |
Station type |
| ship_type |
Integer |
- |
Ship type |
| txrx |
Integer |
- |
Tx/Rx mode |
| interval |
Integer |
- |
Reporting interval |
| quiet |
Integer |
- |
Quiet time |
Type 24: Static Data Report
Message Type 24 Part A Fields
| Field |
Type |
Range |
Description |
| partno |
Integer |
0 |
Part number, always 0 for Part A |
| shipname |
String |
20 chars |
Name of the vessel |
Message Type 24 Part B Fields
| Field |
Type |
Range |
Description |
| partno |
Integer |
1 |
Part number, always 1 for Part B |
| callsign |
String |
7 chars |
Vessel radio callsign |
| shiptype |
Integer |
0-99 |
Type of ship and cargo |
| shiptype_text |
String |
See note 1 |
Description of ship type |
| vendorid |
String |
3 chars |
Manufacturer's ID |
| model |
Integer |
0-15 |
Equipment model code |
| serial |
Integer |
0-999999 |
Unit serial number |
| to_bow |
Integer |
0-511 |
Distance from GPS to bow in meters |
| to_stern |
Integer |
0-511 |
Distance from GPS to stern in meters |
| to_port |
Integer |
0-63 |
Distance from GPS to port in meters |
| to_starboard |
Integer |
0-63 |
Distance from GPS to starboard in meters |
| mothership_mmsi |
Integer |
9 digits |
MMSI of mothership for auxiliary craft |
Message Type 25 Fields
| Field |
Type |
Range |
Description |
| addressed |
Boolean |
true/false |
Message has specific destination |
| structured |
Boolean |
true/false |
Message contains structured data |
| dest_mmsi |
Integer |
9 digits |
Destination MMSI if addressed |
| data |
String |
- |
Binary payload data |
Message Type 26 Fields
| Field |
Type |
Range |
Description |
| addressed |
Boolean |
true/false |
Message has specific destination |
| structured |
Boolean |
true/false |
Message contains structured data |
| dest_mmsi |
Integer |
9 digits |
Destination MMSI if addressed |
| radio |
Integer |
0-3 |
Radio status |
| data |
String |
- |
Binary payload data |
Message Type 27 Fields
| Field |
Type |
Range |
Description |
| accuracy |
Boolean |
true/false |
Position accuracy: true if < 10m |
| raim |
Boolean |
true/false |
RAIM flag: Receiver Autonomous Integrity Monitoring |
| status |
Integer |
0-15 |
Navigation status |
| status_text |
String |
See note 1 |
Navigation status description |
| lon |
Float |
±180° |
Longitude in decimal degrees |
| lat |
Float |
±90° |
Latitude in decimal degrees |
| speed |
Integer |
0-62 |
Speed over ground in knots |
| course |
Integer |
0-359 |
Course over ground in degrees |
| gnss |
Boolean |
true/false |
GNSS position status |
Notes
Navigation Status Values:
| Value |
Description |
| 0 |
Under way using engine |
| 1 |
At anchor |
| 2 |
Not under command |
| 3 |
Restricted manoeuverability |
| 4 |
Constrained by draught |
| 5 |
Moored |
| 6 |
Aground |
| 7 |
Engaged in fishing |
| 8 |
Under way sailing |
| 9 |
Reserved for HSC |
| 10 |
Reserved for WIG |
| 11-13 |
Reserved |
| 14 |
AIS-SART is active |
| 15 |
Not defined |