Investigation of Passing Ships in Inaccessible Areas Using Satellite-based Automatic Identification System (S-AIS) Data

Abstract

Shipping of North Korea is not yet publicly well documented. Taedong River, the most important sea route of North Korea, is selected as a model study area to show how effectively a remote place can be investigated through the application of satellite-based Automatic Identification System (S-AIS) for understanding shipping and tracks of vessels which passed the lock gate in the Taedong River and visited the nearby ports on its track. S-AIS data of the year 2014 were analyzed on the basis of various time periods, country of registry and category of ships. A total of 325 vessels were observed. The ships under the flags of North Korea, Cambodia and Sierra Leone were found to be dominant in frequencies which accounted for 43.08%, 16.00%, and 8.92%, respectively. Trajectories of the 325 ships in the Yellow Sea were also checked according to the flags. It is concluded that some ships under the flags of Cambodia, Sierra Leone, Mongolia, Panama and Kiribati are regarded as flags of convenience, and ships without flag and ship type codes also comprised a remarkable portion out of the total ships.

1. Introduction

Automatic Identification System (AIS) is a shipboard broadcast system which transmits ship’s various information like vessel identity, position, type, speed, course, destination etc. in between ships and land-based onshore AIS receiving station in real-time through the use of Very High Frequency (VHF) radio wave. The transmitted AIS data is usually used for automatic ship tracking, thus convenient for mutual navigation safety and security implementation. In order to ensure the safety of navigation, AIS is made mandatory for almost all new building vessels since 2002 by the amendments of the International Convention for the Safety of Life at Sea (SOLAS), 1974 endorsed by the International Maritime Organization (IMO). SOLAS 1974 demands all ships of 300 gross tonnage or above international voyages and domestic cargo ships of 500 gross tonnage or above to be fitted with an AIS. As most categories of ships must be equipped with AIS, it becomes an opportunity for monitoring and surveillance of vessels in a wide range.

In general, the typical coverage of land-based AIS system is around 20 nautical miles which is a limitation of the system, but significantly differs according to the VHF propagation conditions and sensors height (Vespe et al., 2008; Yang et al., 2012). Kim et al. (2016) installed the AIS at Socheongcho Ocean Research Station (SORS) located at the relatively open sa ad tested the observation range performance. In this test, the effective propagation range was calculated as about 25.2 nautical miles. Therefore, the land-based AIS system can be used for monitoring of only limited area like harbor or coastal region. To expand the coverage for monitoring EEZ or sea lanes, some specialized low earth orbit satellites are recently launched which can receive the AIS message in a wider range over the coastal area coverage through the use of terrestrial standard AIS receiver, thus can be beneficial to overcome this limitation. Even the existing land-based AIS can also be used in conjugation with the satellite-based AIS (S-AIS) for the same purpose. According to the report of Hoye et al.(2008), a satellite at 1,000 km altitude solely can handle up to 900 vessels’ messages with over 99% detection probability within 6 seconds of reporting interval during the satellite pass.

Ground observation AIS is limited to the observation range depending on the radio wave arrival distance, surrounding obstacles and weather conditions. Although efforts have been made to expand the range of observation by installing AIS at maritime observation stations located in the offshore area (Hong and Yang, 2014; Kim et al., 2016), it is impossible to collect ship information in areas that are physically difficult to access. The greatest advantage of the wide range of vessel monitoring by S-AIS is that information on a ship engaged in international navigation can be explored easily. Using this advantage the present study is aimed to check the feasibility of using S-AIS data for analyzing various shipping information of such a remote area which is difficult or not allowed to access physically. Therefore, some North Korean ports in the Yellow Sea were selected as the study area with the target of finding out shipping-related various information. North Korea is a socialist developing country, and weakness of the whole transport system is considered as one of the major causes of its hindered development (Ducruet and Jo, 2008). Detailed data regarding ports and maritime transportation of that country is not yet much available as well as not justified enough. For instance, Ducruet and Jo (2008) collected different estimations about ports of that country from various sources which were neither to be found well-matched nor possible to verify due to various restrictions.

In this study, we use the S-AIS information to identify vessels operating in areas where difficult physical access, and to analyze the operating characteristics using navigation and national information. In particular, the present study is designed to understand shipping and tracks of those vessels which entered the Taedong River in North Korea through the Yellow Sea and visited one or more from the ports of Nampo, Taean, Songnim or Pyeongyang on that river. The S-AIS messages of those ships were analyzed according to registry of nation, ship type, frequency and temporal positions in the area. The routes of those ships were also identified through analysis of the movement path in the Yellow Sea which also facilitates hypothetically examining flag of convenience (FOC) of those vessels.

2. Data and Methods

In this study, S-AIS data obtained from ExactEarth Company between 1st  January to 31st December 2014 for the Yellow Sea are used. The exactEarth Company (https://www.exactearth.com/) was established for providing the high-quality ship information from S-AIS to the customers (Chen, 2014). AIS data is composed of 27 messages (International Telecommunication Union, 2014), and among those 5 dynamic messages (messages 1, 2, 3, 18, 19) and 2 static messages (messages 5, 24) were used for the acquisition of required information. The detail description for those messages described in Hong and Yang (2014). Brief description and total number of each type of AIS messages of the year 2014 are shown in Table 1. All messages contain Maritime Mobile Service Identity (MMSI) data that is composed of 9 digit number as their own identification. According to Recommendation ITU-R M.1371-5 (International Telecommunication Union, 2014), MMSI format is M₁I₂D₃X₄X₅X₆X₇X₈X₉, where the first three digits is designated as MID and X is for any figure from 0 to 9. MID denotes the administration (country) within the range from 201 to 705. It is implied that there is no way to know the flag of ship that has MID less than 201 or more than 705. The X represents the type of Inmarsat. For example, if the ship has an Inmarsat C, then the MMSI could have the number of ‘0’ on the end.

Table 1. Brief description of AIS messages acquired from 1st January to 31st December 2014 for the target ships in the Yellow Sea

Fig. 1 shows the research area in the Yellow Sea where the large rectangular box (black)specifies S-AIS data acquired area for this study. The red and blue small boxes show the regions of interest (ROIs) around major ports in North Korea and South Korea, respectively. N1 includes many ports on the Taedong River such as the ports of Nampo, Taean, Songnim and Pyeongyang in North Korea, and S1, S2, and S3 indicate Incheon-Pyeongtaek-Anseong, Gunsan, and Mokpo ports, respectively in South Korea. The black and white triangles that are located in northwestern and southwestern parts of North Korea indicate position of Sinuiju and Haeju port, respectively.

Fig. 1. Research area in the Yellow Sea where the large black box represents the region for acquired S-AIS data, and red and blue boxes show areas around main ports in North Korea and South Korea, respectively. The black and white triangles indicate Sinuiju and Haeju ports of North Korea, respectively.

Among the five dynamic AIS messages used for this study, messages 1, 2, and 3 are for those ships equipped with Class A type AIS, and messages 18 and 19 are for those ships equipped with Class B type AIS. Although each message includes different parameters, all messages have MMSI and geographic location data (longitude and latitude) in common. The ships which entered the N1 area (in Fig. 1) are considered as the main target of this study since those ships are under the control of North Korea or related to North Korea in terms of international trade. The Nampo Port in the N1 area is considered as a major trading port and the gateway of North Korea because of its position on the Taedong River, only around 17 km away from the West Sea Lock Gate (Jo and Ducruet, 2006). Therefore, AIS data of all the ships which entered the N1 area were extracted first. Then the usage of ports of other countries and moving route about all main targets were investigated by extracting the position information in Yellow Sea.

3. Results and Discussions

1) Investigation of Shipping on the Taedong River

Fig. 2 is a satellite image of the N1 area showing the positions of ships for the whole of study period classified by flags extracted from S-AIS. This is a natural color composite image of Landsat 8 satellite comprised of Band 4 (0.64 – 0.67μm), Band 3 (0.53 – 0.59μm), and Band 2 (0.45 – 0.51μm) corresponding to the visible red, green, and blue, respectively, with a spatial resolution of 30 m for the date of 24th May 2015. Landsat 8 data was acquired from Earth Resource Observation and Science (EROS) website (https://glovis.usgs.gov/). In Fig. 2, it is clearly depicted that all the ships which entered the West Sea Lock Gate, passed along the Taedong River and visited Nampo, Songnim or Taean which are the main ports on that river. Some of the ships which existed in the northern region of Taean are regarded as ships coming to or going from Pyeongyang. A total of 325 ships under the flags of 16 countries or without nationality information are identified and marked as colored dots in this image.

Fig. 2. Position of ships superimposed on Landsat 8 satellite image for the whole of study period. The dot marks of each color represent corresponding flag of ships.

Fig. 3 shows the number of ships according to daily and monthly observation extracted from the N1 area. The average number of daily existence of ships is 17 with a standard deviation of 8 ships. Fig. 3(b) shows the number of monthly existence of ships by white, red, blue, and yellow bars representing ships by total number, under the flag of North Korea, other flags, and flags without nationality information, respectively. The result shows that North Korean ships accounts for more than 40% of the total ships. The largest number of ships’ existence is 803 accounted for the month of December, followed by 752 numbers for the month of January. On the contrary, the smallest number for the existence of ships was only 322 accounted for the month of September. The result shows that the number of ships in winter season is larger than those in summer season, and it is contrary to commonly expectation since frozen condition of the Taedong River makes trouble of shipping. Therefore, identifying the number of moving ships is also important to reveal the cause of this contradictory finding.

Fig. 3. The number of (a) daily and (b) monthly existence of ships in the N1 area. In figure (b), white, red, blue, and yellow bars represent total number, under the flag of North Korea, other flags, and flags without nationality information, respectively.

The speed over ground (SOG) of ships was also investigated to find out moving ships. Ships with nonzero SOG are the ships in motion; thereby SOGs were extracted first in order to determine the moving ships(Fig. 4(a)) out of all existed ships. Surprisingly it is evident from Fig. 4(a) that more ships are found to be as moving ships in the winter season than in summer season. However, the ratio of moving ships to all ships is larger in summer season than in winter season which indicates that there are many ships which stayed at the berth in winter which might be the cause of larger number of ships in the winter.

Fig. 4. The number of (a) moving ships and (b) ratio of moving ships to allships.

Fig. 5 show the number of ships in the N1 area according to their flags. It shows that the ships under the flag of North Korea (43.08%) is dominant in number followed by ships under the flags of Cambodia (16.00%), without nationality information (9.54%), Sierra Leone (8.92%), Panama (7.08%), Mongolia (4.92%), and Kiribati (4.31%). The results show the North Korean ships ranked the first in frequency as expected. However, it is necessary to identify that the ships of other countries since some nations,Cambodia, Sierra Leone, Mongolia, Kiribati, and Panama, have unfavorable condition of seaborne trade because of landlocked country and/or far from maritime trade.

Fig. 5. Bar graph of the number of ships according to the flags which visited the N1 area in 2014. The x-axis represents the national information from S-AIS data. Unknown in the x-axis means that there is no information for the nationality.

The N1 area includes three ports of Nampo, Songnim, and Taean. As it mentioned above, Nampo port has a capability of the trade port for the handling of raw material and products as a major trading port of North Korea, and Songnim port is for Yellow Steel which is the largest steel mill of North Korea as a function of auxiliary port of Nampo port. The ships accessed to three ports were classified according to ship type using AIS. Table 2 shows the number of ships according to their type in three ports and others indicating the other ports except Nampo, Songnim, and Taean or the ships without destination information. There are largest number of ships in Nampo port especially cargo ship and it is inferred that the Nampo and Songnim ports have a landing and loading facilities for tanker.

Table 2. The number of ships in three ports according to their types

2) Trajectories in the Yellow Sea for Ships Visited the Taedong River

A ship in operation has to be registered in the national register of any particular country, thereby flies the flag of that country. However, flagging out from one national flag to a FOC is also being practiced for some ships in order to gain advantages like reducing operating costs, more relaxed crewing requirements and less vigorous regulation etc. (Gianni, 2008). The tracks for the ships that entered the N1 area were investigated in the Yellow Sea (Fig. 6)to check whether or not some flags are representing as major trading partner of North Korea. In Fig. 6, ship trajectories of 16 countries and unknown flags are shown from the top left for North Korea to the bottom right for Togo depending on the frequency as explained in Fig. 5.

Fig. 6. Ships trajectories according to the flags in the Yellow Sea for all the ships which entered the N1 area in 2014.

As for the ship tracks of North Korea, it is found that almost all the ships under the flag of North Korea navigated between North Korea and China in the Yellow Sea. Some of the North Korean ships entered Sinuiju and Haeju ports of North Korea as marked in Fig. 1. In addition, there are two ships that existed in territorial waters of South Korea near the S3 area which is marked in Fig. 1. It is identified that the names of those two ships are the Nam San 8 and the Woory Star, and their types are tanker and cargo, respectively. They have only one position information in territorial waters of South Korea. It might be the limitation of observation time of S-AIS, but there is a high probability that they did not transmit AIS signal normally. South Korea promulgated the ‘May 24th Measures’ after sinking of ROKS Cheonan and it include a ban on North Korean ships in the territorial waters of South Korea (Korea Herald, 2010).

Fig. 6 also shows that many ships under the flags of Cambodia, Sierra Leone, Panama, Mongolia, and Kiribati including the ships without flag information have similar tracks with that of North Korea. For quantitative interpretation of a trajectory similarity, Jaccard index (Jaccard similarity coefficient, J)(Jaccard, 1912) was used and shown in Equation (1).

\(\mathrm{J}=\frac{N K_{p} \cap N_{p}}{N K_{p} \cup N_{p}}\)       (1)

In this equation, NK_p and N_p are the positions of North Korean ships and ships of each nation including unknown flag respectively, and ∩ and ∪ are itersection and union, respectively. Using this equation, the similarity of trajectories between North Korean ships and other countries listed in Fig. 5 were computed individually. For the comparison of positions, the position information of longitude and latitude were rounded to two decimal places, and it means that if the differences of longitude and latitude between two ships were smaller than 0.01°, the two ships were regarded as existed at the same position. The results are shown in Table 3. The value of J is expressed between 0 and 1 where the value 1 expresses the maximal similarity. The values are less than 0.2, and it is judged that the low value of J is natural since the routes have the least possibility to match with another one. Nevertheless, ships under the flag of Cambodia have a relatively higher value followed by Sierra Leone, Mongolia, Kiribati, Panama, and the ships without nationality information. It infers that a portion of North Korean ships probably used FOC by flying the flags of these countries to trade with other nations. In 2015, the United Nations Security Council (S/2015/131) has announced the list of 15 North Korean ships as a FOC in 2014.

Table 3. The position similarity to North Korean ships for other ships entered the N1 area in 2014

3) Ships Entered the Ports of both North Korea and South Korea

The ships under the flag of Cambodia, Sierra Leone, Mongolia, Kiribati, and Panama, and without nationality information were regarded as the countries of FOC shipping of North Korea through the confirmation of trajectory of ship in the Yellow Sea and the route similarity to North Korean ships. Unfortunately over the past several decades the rate of FOC for the world’s merchant fleets has continuously increased (Gianni, 2008). Due to various immerging problematic issues like providing cover for illegal, unreported and unregulated fishing (Gianni and Simpson, 2005), oil pollution (Payne, 1980), terrorist and criminal activities (Gianni, 2008), worldwide concerns are also increasing on FOC shipping (Lillie, 2004). As an example, 16 North Korean crews were found to be on board in the freighter named Grand Fortune 1 of under Mongolian flag which sank 74 kilometers south of Geomun Island?in South Korea on 4th April 2014 (Jeong, 2014). To confirm the entry of North Korea-related ships into South Korea, the ships that entered both the Taedong River (N1 area) and the ports of South Korea (S1, S2, and S3 areas) were extracted. A total of 15 ships are found to navigate both territorial waters of North Korea and South Korea, and information of these ships is shown in Table 4. Out of those 15 ships, 14 were cargo and 1 was tanker, and ships under the flag of Cambodia were dominant followed by Panama, Niue, and China. There are 13 ships located in the S1 area, 9 ships in the S2 area, and 3 ships in the S3 area. It is apparent that the management at least for the S1 area is required since most North Korean ships entered the South Korea through this area.

Table 4. The list of ships that passed round major ports of South Korea as well as entered the N1 area in 2014

The positions of 15 ships listed in Table 4 were also analyzed in order to ensure whether those are FOC shipping of North Korea. In Fig. 7, the locations of each ship in the Yellow Sea are marked as colored dots. Through the investigation on trajectories of those vessels, it is confirmed that there is no ship moved between the N1 area and the S1, S2, or S3 areas directly. However, it cannot be ensured solely from this study since there is no way to confirm for the ships that do not have position information in Yellow sea such as the An Da No. 66, Petrel 1, and Rich Land 58 ships. The Dong Feng 6 ship under the flag of Niue shows the direct trajectory between the S1 area and Sinuiju port of North Korea. The Sun Crystal and Ming Yue ships under the flag of Sierra Leone and Cambodia respectively also had a similar route with the Dong Feng 6 ship even though some positions are missing in territorial waters in South Korea. It is also confirmed that the Gold Meiship under the flag of Cambodia and the Feng An ship without any nationality information show the most similar trajectory with ships under the flag of North Korea as shown in Fig. 6. It is judged that the ships that entered the North Korea have to be considered as North Korean related ships as FOC, and these ships hve to be managed though the continuous monitoring in the future in case of entering South Korea.

Fig. 7. Position of specific ships that entered both territorial waters of North Korea and South Korea.

4. Conclusions

The information of ships that entered the Taedong River from 1st January to 31st December 2014 was obtained from S-AIS, and a total of 325 ships were found to navigate on the Taedong River. The ships flied the flag of North Korea were dominant, and there are ships under the flags of 15 countries and without nationality information. Some ships under the flags of Cambodia, Sierra Leone, Mongolia, Kiribati, and Panama suspected as FOC shipping from an analysis of trajectory similarity in the Yellow Sea. There are also a lot of ships without nationality information which have similar trajectory with North Korean ships. One of the reasons of FOC usage for North Korea might be avoidance of surveillance, which possibly allows those ships to navigate in territorial waters of South Korea. It is identified that 15 ships related with North Korea entered the ports of South Korea, and two ships of those directly navigated between North Korea and South Korea ports. From this study, the ships that existed in the region where entry is not allowed physically were identified using S-AIS, and it shows the usefulness of S-AIS in respect of safety and security by extracting ship’s information that is hard to obtained solely from a land-based AIS for large area.