This scenario is to evaluate to compare ship's position response between AIS and ARPA illustrated as Fig.6.
Investigation of scenario-5 was executed and we got that swapping was caused in approaching close the breakwater in a distance approx. 200 meters.
This scenario is to evaluate to compare ship's position response between AIS and ARPA in a case of U-turn illustrated as Fig 7.
Investigation of scenario-6 was executed and we got the results that there was little difference between AIS and ARPA in case of small U-turn.
This scenario is to evaluate to compare ship's position response between AIS and ARPA in a case of sailing among anchored barges illustrated as Fig.7.
Investigation of scenario-7 was executed and we got the results that it is not possible to plot in ARPA due to swapping, on the other hand the AIS data was stable.
This scenario is to evaluate to compare ship's position response between AIS and ARPA in a case of crossing illustrated as Fig.8 and passing each other.
Investigation of scenario-8 was executed and we got the results that it is stable in ARPA and AIS in case of crossing (CPA approx. 50 meters), but it is not to plot in case of passing (CPA 20 -> 30 meters).
This scenario is to evaluate to compare ship's position response between AIS and ARPA in case of leaving or approaching illustrated as Fig. 10 with speed 5 knots, 12 knots and 14 knots.
Fig. 10 Scenario-9
Investigation of scenario-8 was executed and we got the results that it is stable in ARPA and AIS in case of leaving, but it is not to plot and caused to swap in case of approaching with head-on obstructs.
2.3 Conclusion of investigation
Hereby the results of investigation are concluded as follows.
(1) Refresh rate of data
In case of short range such as 3 nm., it is cleared that the timing of data readout is different, so it is necessary to use dead reckoning by AIS data.
In case of closing target ships it is not able to read the ship's name on the display due to the overlay the readouts, so it will be effective to enlarge partially or to make ON-OFF function of ship's name.
(3) Utility of AIS to support ARPA
In case of demerits of ARPA, it is confirmed to be able to use AIS by this investigation. According to apply AIS function, it is necessary to improve the guideline on the display of RADAR.
3. FUSION OF AIS AND ARPA DISPLAY
3.1 Difference between AIS and ARPA
It is said that ARPA and AIS should be same system to display and present information on RADAR display and/or ECDIS for taking the targets movements, but the distinguish differences exist and we surveyed using sea experiences and simulator.
After experiences, it is evident that the performance difference between ARPA and AIS as follows;
(a) The coverage of AIS is greater than that of RADAR.
(b) The response is different between ARPA and AIS.
(c) It is disadvantage of ARPA against AIS in case of identification target ships.
In (a), in case of ARPA it is able to work only during the reception of RADAR echoes, but AIS function is able to work within the VHF-band radio-wave coverage and even in the blind sector of RADAR such as that RADAR echoes do not return from the target ships behind the islands or mountains.
In (b), in case of ARPA its update time is constant and approximately 2.5 seconds (due to the rotation speed of RADAR scanner is 24 rpm) because of plotting RADAR echoes, but in case of AIS its update time is different according to Ship's speed and ROT (Rate of Turn). For example, within the ship's speed 10 knots it is 10 seconds, and with over 24 knots it is 2 seconds.
In (c), it was evident that the "SWAP" phenomena caused when large course changing was in confused water. In case of AIS, she transmitted the target ship's position fixed with GPS, so no "SWAP" phenomena should cause.
When ARPA data and AIS data are superimposed on ECDIS or RARAR display, APRA symbol and AIS symbol will be displayed approximately at same position, and then it is difficult to identify each other, although the displayed symbols are different.
3.2 Proposal fusion of AIS and ARPA
Hereby we propose the fusion of AIS and ARPA Display easy to distinguish the target identification in case of superimposing ARPA data and AIS data on the display EGDIS or RADAR display.
It is necessary to judge that the target ship's information from ARPA and AIS should be sent from the same ship or not. The conditions required judging, the differences of following parameters should be less than constances.
(a) Distance between AIS target ship's position and ARPA one.
(b) Difference of distance between AIS distance and ARPA one from own ship.
(c) Difference of bearing between AIS bearing and ARPA one from own ship.
(d) Difference of ship's speed between AIS ship's speed and ARPA one.
(e) Difference between ship's course between AIS data and ARPA data.
When these two symbols are judged as the same target ship, then the target symbols are defined as the same ship and it is able to display the fusion target symbols and easy to observe the display.
When it is able to judge that the data of AIS target and ARPA target are sent from same ship, then it shall be useful as ship maneuvering supporting system because it would be easy to identify targets according to application of the fusion display on ECDIS or RADAR superimposing ARPA and AIS target. It is not so easy to set the conditions to judge as the same ship, it should be used to judge using soft-computing such as "Fuzzy theory", etc. and then we can apply the fusion display using the intelligent method just like human judgment system.
In case of using RADAR with a short range such as 3 nm range, because of the difference of update time between ARPA and AIS, the display difference between ARPA and AIS on the display should be caused. According to this reason, it should be necessary to interpolate the speed and course of AIS using dead reckoning in using a RADAR short range.
Though AIS is very valid system to avoid collisions, it is expected not for AIS to be popular to all kinds of ships. According to this reason, the use of AIS and/or ARPA is effective for safe navigation. If there is no ARPA data then use AIS data, for ships uninstalled AIS it would be useful using ARPA. We confirm that the adoption with both data AIS and/or ARPA would be valid for the supporting system for safety navigation.
 ITU Recommendation ITU-R M. 1371-1
[21 MSC.74 (69) Annex 3
Takehiro Yamashita was born in Ehime, Japan. He received the B.E. degree in electrical engineering from Ehime University, Ehime, Japan in 1990. He is currently with Furuno Electric Co., Ltd. He is developing AIS transponder.