885

1 INTRODUCTION

In accordance with the current international

recommendations set out in the Resolution

MSC.192(79) “Adoption of the revised performance

standards for radar equipment” adopted by the

International Maritime Organisation (IMO) on 6th of

December 2004, each radar installed on or after 1st of

July 2008 on ships subject to the requirements of

SOLAS regulation V / 19 should present data from

radar tracking and on board automatic identification

system (AIS) [4]. Radar tracking aids (automatic radar

plotting aid - ARPA and automatic tracking aid -

ATA) calculate true vector, the passing distance with

detected and tracked object and time to pass it, called

respectively closest point of approach (CPA) and time

to the closest point of approach (TCPA) on the basis of

radar measurements of its distance and bearing. AIS

at given time intervals and in pulling mode

automatically transmits, receives and displays, inter

alia, indications of connected to it gyrocompass, speed

and distance measuring device and Global

Navigational Satellite System (GNSS), currently

mainly GPS, ship’s receiver. Additionally, it can

calculate and indicate CPA and TCPA on the basis of

knowledge of the geographical positions and true

motion vectors of the own ship and the opposite

vessel transmitting AIS messages. Relatively low

accuracy of radar measurements means that the data

from radar tracking can be presented with lower

accuracy than data from AIS. Due to that, when the

target data from AIS and radar tracking are both

available and the association criteria (position,

motion, etc.) are fulfilled, i.e. the AIS and radar

information is considered as concerning one physical

target, then the AIS target symbol and the

alphanumerical AIS target data should be

automatically selected and presented on the radar

display as a default condition [4].

However, the radar remains the only independent

technical source of information about surface objects

around own ship. For this reason, according to the

recommendations of the Resolution A.1106(29)

“Revised guidelines for the operational use of

shipborne automatic identification systems (AIS)”

adopted by IMO on 2nd of December 2015, the AIS

may be recommended as an anti-collision device in

due time and its introduction has not impact on the

Rule 19 “Conduct of vessels in restricted visibility” of

the International Regulations for Preventing

Collisions at Sea (COLREG) and its interpretation. The

ship’s master and watch keeping officers (OOW)

should not rely on AIS as the sole information system,

Comparative Analysis of the Usefulness of AIS and

ARPA for Anti-collision Purposes

R. Wawruch

Gdynia Maritime University, Gdynia, Poland

ABSTRACT: The article discusses the principles of presenting data available from AIS and radar tracking on

ship's radar display units and describes the results of comparative studies of the accuracy of their indications on

sea-going vessels in real meeting situations in various hydro meteorological conditions.

http://www.transnav.eu

the International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 14

Number 3

December 2020

DOI: 10.12716/1001.14.04.13

886

but should make use of all safety-relevant information

available. In general, AIS may be used to assist in

collision avoidance decision-making as an additional

source of information which supports radar and radar

tracking aids to calculate true and relative vectors of

the detected and tracked echoes on the basis of radar

measurements of their distances and bearings, by

assisting in [3,13]:

− identification of targets by name, call sign, ship

type and navigational status;

− presentation of targets heading;

− immediate identification of manoeuvres

performed by targets; and

− more accurate presentation of courses, speed over

ground and rate of turn of the targets.

IEC Standard 61993-2 presenting performance

standards for AIS required that if AIS display

equipment provides facilities for the calculation of

CPA and TCPA then these facilities should comply

with the relevant clauses of the IEC Standard 62388

“Shipborne radar - Performance requirements,

methods of testing and required test results” [1]. The

said standard specifies the minimal requirements for

radar conforming to performance standards not

inferior to those adopted by IMO in the Resolution

MSC.192(79) [2]. According to both standards,

accuracy of radar tracking shall be as presented in

Table 1 [2,4]. Mentioned in this table time of steady

state tracking means radar tracking a target in the

steady phase of movement [2,4]:

− after completion of the acquisition process; or

− without a manoeuvre of target or own ship; or

− without target swap or any disturbance.

In maritime navigation nautical miles (NM) and

knots (kn) are officially used as the units of distance

and speed. ARPA and AIS present values of distance,

CPA and speed in these units. Therefore, in this paper

they are presented in nautical miles and kilometres

and in knots and m/s (1 NM = 1852 m; 1 kn = 1 NM/h

≈ 0.514 m/s) respectively.

Resolution MSC.192(79) informs additionally that

automatic tracking accuracy [4]:

− should be achieved assuming the sensor errors

allowed by the relevant IMO performance

standards (range and bearing accuracy should be

within 50 m (or +/-1% of target range) and 2°); and

− may be significantly reduced during or shortly

after acquisition, own ship manoeuvre, a

manoeuvre of the target, or any tracking

disturbance and is also dependent on own ship’s

motion and sensor accuracy.

The testing standard should comprise detailed

target simulation tests as a means to confirm the

accuracy of targets with relative speeds of up to 100

kn. The operating instructions should contain a

qualified explanation and/or description of

information required by the user to operate the radar

system correctly, including limitations of the display

and tracking process and accuracy, including any

delays [4].

The Standard IEC 62388 requires that the tracking

accuracy be checked using simulated targets

generated by a target simulator in a noise-free and

clutter-free environment. Table 1 provides an

indication of typical tracking accuracy, averaged over

five tracking scenarios and with minimal sensor errors

as described in Annex E to that standard. The

individual scenarios are as follows [2]:

− scenario 1 applies the sensor errors as defined in

Annex E in this standard;

− scenarios 2 and 3 test own ship turns in both

directions, without sensor errors;

− scenario 4 tests for target swap, without sensor

errors; and

− scenario 5 provides 10 targets, including one

having a 50 % visibility; no sensor errors are

applied.

The test scenarios differentiate standard and high

speed craft by the parameters used. They simulate

own ship travelling at up to 30 kn (or up to 70 kn for

high speed craft), whilst tracking targets with a speed

of up to 70 kn. High rate of turn, own ship and target

manoeuvring, target swap, multiple targets on a

bearing, acceleration and fading are simulated. The

simulator assumes a 2.0° antenna (–3 dB point)

horizontal beam width, an antenna rotation rate

compatible with the category of equipment, and at a

pulse length and pulse repetition frequency as

specified by the manufacturer [2].

Additionally, the tracking system shall

demonstrate tracking capability in noisy and clutter

environments. This requirement shall be checked by

visual observation. It is fulfilled if the observer

confirms that when [2]:

− the test targets in scenario 5 are set to 10 dB above

peak noise level, they are tracked without

degradation of the tracking performance; and

− the tracking system is operated in a typical clutter

environment and using targets of opportunity

(targets of different sizes, speeds and trajectories),

continue to be tracked with minimal degradation

to tracking performance.

All of the information provided shows that

presented in Table 1 radar tracking accuracy and

accuracy of the CPA and TCPA values presented by

AIS apply only to conditions simulated in the absence

of noise and clutters. The issue requiring research is

the accuracy of the analyzed indications on seagoing

ships of different sizes in real conditions of their

exploitation and in real meeting situations.

The measurements reported in this article were

carried out to determine;

− the mean values and mean square errors of data

presented by AIS and ARPA;

− the influence of the stability of the observed and

tracked ship's motion on the accuracy of

determining its true motion vector by ARPA and

CPA by ARPA and AIS as a function of time; and

− the relationship between the accuracy of AIS and

ARPA indications and the current state of the sea.

They were carried out over several years and some

of their results have already been partly presented in

publications [12-15].

887

Table 1. Tracked target accuracy (95% probability figures) [2,4]

__________________________________________________________________________________________________

Time of steady Relative course Relative speed CPA TCPA True course True speed

state tracking

[min] [

o

] [kn / m/s] [NM / km] [min] [

o

] [kn / m/s]

__________________________________________________________________________________________________

1 min: trend 11 1.5 / 0.8 or 10% 1.0 / 1.85 - - -

(whichever is greater)

3 min: motion 3 0.8 / 0.4 or 1% 0.3 / 0.56 0.5 5 0.5 / 0.3 or 1%

(whichever is greater) (whichever is greater)

__________________________________________________________________________________________________

Table 2. Ships on which tests were carried out with the indication of their size category and on board AIS and radar

equipment [5,6,7,8,9,10,11,16,17,18]

__________________________________________________________________________________________________

Ship Used equipment / manufacturer

Size Type Gross Length Service speed Radar / ARPA AIS

tonnage [m] [kn / m/s]

__________________________________________________________________________________________________

V Bulk carrier 106884 299.9 1 5.6 / 8.0 JMA-9132-SA, JMA-9122-9XA / JRC JHS-183 / JRC

L LPG tanker 46789 226.0 16.7 / 8.6 JMA-9172-SA, JMA-9122-9XA / JRC JHS-183 / JRC

L Multipurpose ship 30469 199.8 16.8 / 8.6 Radar Vision Master FT X, S bands,

ARPA 340/25X, 340/30S / Sperry Marine Nauticast X-Pack

DS / Nauticast GmbH

M Multipurpose ship 11864 143.0 13.2 / 6.8 GR3017 (X-Band), GR3018 (S-Band), DEBEG 3400 / SAM

ARPA Multipilot 1100 / SAM Electronics GmbH

Electronics GmbH

M Liqufied gas carrier 22941 174.2 15.5 / 8.0 JMA-9932-SA, JMA-9922-6X / JRC JHS-182 / JRC

M Bulk carrier 20603 190 14.0 / 7.2 FAR-21X7(-BB) (X & S BAND), Furuno FA-150 / Furuno

M Container 16801 184.1 19.7 / 10.1 X & S Sperry Marine / Northtop R4 / SAAB

Grumman

S Bulk carrier 2735 89.4 11.0 / 5.7 FAR-28x7 model FAR-21x7 (-BB) / Furuno R4 / SAAB SAAB

Transponder Tech

AB

S Oil/chemical tanker 4667 97.4 13.6 / 6.7 Vision Master FT CAT 2 / Sperry Marine R4 / SAAB

Transponder Tech

AB

S General cargo 3443 93.42 12.0 / 6.2 Bridge Master E (S) / Sperry Marine JHS-182/ JRC

__________________________________________________________________________________________________

V- very large; L - large; M - medium; S - small

2 DESCRIPTION OF THE MEASUREMENTS

The measurements were conducted by students of the

Faculty of Navigation of the Gdynia Maritime

University as part of their engineering thesis listed in

bibliography [5,6,7,8,9,10,11,16,17,18], written under

the supervision of the author of this article. They were

done in real (not simulated) conditions during the sea

voyages of ten different ships presented in Table 2,

using AIS and radar equipment installed on these

vessels and mentioned in this table too. The division

of vessels into size categories was made

conventionally by the author of the paper. For the

analyses presented in this article, only measurement

series were selected, during which both the own ship

and the tracked vessel were proceeding with a steady

course and constant speed without performing any

manoeuvres. Any instabilities and errors of CPA and

true vector indications were therefore caused only by

inaccuracies in radar measurements and the influence

of the current hydro meteorological conditions,

mainly sea state, on the ship's movement.

Table 3 presents information on all ships tracked

during measurements, their names, type, length,

speed and distance to the own ship. They are grouped

according to the type of meeting situation with own

ship (parallel courses – overtaking, reciprocal courses

and crossing courses) and to the size of the vessel

from which the measurements were taken. The results

of measurements during which both ships (own and

observed) were at anchors are presented separately at

the end of the Table 3. The state of the sea, expressed

in degrees of the Douglas scale in the last column of

this table, describes weather conditions during the

test. Part of the measurements presented in this table

is a repetition of information presented in the earlier

publications mentioned in the bibliography [12-15].

During each test were recorded, simultaneously

every 30 seconds, following parameters of the

observed vessel indicated by AIS and ARPA: true

bearing, distance, true course, true speed, CPA and

time to reach CPA (TCPA). In order to meet the

conditions of steady state tracking set out in the IMO

resolution and the IEC standard, observed ships were

tracked by ARPAs for at least 5 minutes before the

beginning of registration and both vessels (own and

opposite) did not take any manoeuvres at this time

and later during the registration.

The terms and abbreviations used in Table 3 mean:

− Distance - distance between the ships (own and

observed) during the measurement;

− L - the length of the observed vessel presented on

the web-site;

− No/size category - consecutive number of the

measurement series / ship size category;

− T - type of the ship indicated by AIS: B - bulk

carrier, C - container vessel, CS – cargo ship, D -

dredger, F - ferry boat, FV - fishing vessel, P -

888

passenger ship, RO – ro-ro vessel, SP – special

purpose ship, T – tanker; and

− Sea state - state of the sea expressed in degrees of

the Douglas scale, sw means swell.

Table 3. Ships observed during tests divided according to the meeting situation and size category of the vessel from which

the measurements were conducted [5-18]

No/size

category

CPA (ARPA)

CPA (AIS)

Mean value

2σ

Mean value

2σ

[M / km]

Parallel courses - overtaking

1/V

0.69 / 1.28

0.04 / 0.07

0.67 / 1.24

0.04 / 0.07

2/V

4.50 / 8.33

1.74 / 3.22

4.38 / 8.11

0.74 / 1.37

3/V

0.68 / 1.26

0.02 / 0.04

0.69 / 1.28

0.04 / 0.07

4/V

17.18 / 31.82

5.20 / 9.63

15.71 / 29.09

6.12 / 11.33

5/V

2.65 / 4.91

0.14 / 0.26

2.58 / 4.78

0.12 / 0.22

6/V

11.31 / 20.95

8.68 / 16.08

9.99 / 18.50

7.04 / 13.04

7/L

6.72 / 12.45

5.82 / 10.78

7.66 / 14.19

1.60 / 2.96

8/L

9.25 / 17.13

0.06 / 0.11

9.18 / 17.00

0.06 / 0.11

893

9/L

1.64 / 3.04

0.18 / 0.33

1.45 / 2.69

0.16 / 0.30

10/L

6.27 / 11.61

2.35 / 4.35

6.33 / 11.72

0.27 / 0.50

11/L

7.79 / 14.43

3.93 / 7.28

8.38 / 15.52

0.99 / 1.83

12/L

6.01 / 11.13

5.73 / 10.62

1.38 / 2.56

0.94 / 1.74

13/M

2.11 / 3.91

0.16 / 030

2.07 / 3.83

0.18 / 0.33

14/M

2.29 / 4.24

3.04 / 5.63

2.15 / 3.98

1.42 / 2.63

15/M

1.54 / 2.85

0.24 / 0.44

1.44 / 2.67

0.42 / 0.78

16/M

1.17 / 2.17

0.20 / 0.37

1.21 / 2.24

0.20 / 0.37

17/M

2.70 / 5.00

0.42 / 0.78

2.65 / 4.91

0.36 / 0.67

18/M

1.62 / 3.00

0.48 / 0.89

1.56 / 2.89

0.56 / 1.04

19/M

2.65 / 4.91

1.20 / 2.22

2.83 / 5.24

0.70 / 1.30

20/M

11.31 / 20.95

5.24 / 9.70

11.17 / 20.69

3.94 / 7.30

21/M

15.71 / 29.09

4.64 / 8.59

15.27 / 28.28

4.52 / 8.37

22/M

2.39 / 4.43

0.64 / 1.19

2.41 / 4.46

0.28 / 0.52

23/M

6.81 / 12.61

0.22 / 0.41

6.79 / 2.58

0.16 / 0.30

24/M

4.70 / 8.70

3.42 / 6.33

4.68 / 8.67

2.54 / 4.70

25/M

8.47 / 15.69

7.52 / 13.93

9.21 / 17.06

9.32 / 17.26

26/M

0.47 / 0.87

0.82 / 1.52

0.32 / 0.59

0.34 / 0.63

27/M

1.57 / 2.91

0.63 / 1.17

1.71 / 3.17

0.31 / 0.57

28/M

12.46 / 23.08

2.19 / 4.06

11.85 / 21.95

1.68 / 3.11

29/M

3.89 / 7.20

0.68 / 1.26

3.87 / 7.17

0.28 / 0.52

30/M

8.99 / 16.65

0.75 / 1.39

8.94 / 16.56

0.61 / 1.13

31/M

0.72 / 1.33

0.02 / 0.04

0.70 / 1.30

0.06 / 0.11

32/M

0.98 / 1.81

0.05 / 0.09

0.92 / 1.70

0.10 / 0.18

33/M

0.81 / 1.50

0.18 / 0.33

0.75 / 1.40

0.21 / 0.39

34/M

0.55 / 1.02

0.21 / 0.39

0.49 / 091

0.18 / 0.33

35/M

2.46 / 4.56

1.32 / 2.44

2.38 / 4.41

1.54 / 0.79

36/M

3.44 / 6.37

0.07 / 0.13

3.34 / 6.19

0.16 / 0.30

37/M

1.84 / 3.41

0.27 / 0.50

1.90 / 3.52

0.17 / 0.31

38/M

6.22 / 11.52

7.42 / 13.74

1.86 / 3.44

2.26 / 4.19

39/M

1.68 / 3.11

2.10 / 3.89

1.81 / 3.35

2.22 / 4.11

40/M

23.84 / 44.15

0.22 / 0.41

23.90 / 44 26

0.14 / 0.26

41/M

11.13 / 20.61

1.47 / 2.72

11.25 / 20.84

0.71 / 1.32

42/S

1.94 / 3.59

0.36 / 0.67

1.90 / 3.52

0.22 / 0.41

43/S

0.46 / 0.85

0.11 / 0.20

0.45 / 0.83

0.14 / 0.30

44/S

1.11 / 2.06

0.64 / 1.19

0.63 / 1.17

0.92 / 1.70

45/S

0.53 / 0.98

0.02 / 0.04

0.80 / 1.48

0,16 / 0.30

46/S

1.08 / 2.00

1.89 / 3.50

1.36 / 2.52

0.96 / 1.78

47/S

0.85 / 1.57

1.43 / 2.65

0.92 / 1.70

1.24 / 2.30

48/S

0.77 / 1.43

0.02 / 0.04

0.80 / 1.48

0.14 / 0.26

49/S

5.65 / 10.46

0.04 / 0.07

5.66 / 10.48

0.03 / 0.06

50/S

2.37 / 4.39

2.32 / 4.30

2.77 / 5.13

1.64 / 3.04

51/S

3.72 / 6.89

0.78 / 1.45

3.64 / 6.74

0.90 / 1.67

52/S

2.66 / 4.93

0.03 /0.06

2.68 / 4.96

0.02 / 0.04

53/S

0.63 / 1.17

0.11 / 0.20

0.64 / 1.19

0.11 / 0.20

54/S

5.02 / 9.30

0.07 / 0.13

5.02 / 9.30

0.09 / 0.17

55/S

1.93 / 3.57

0.14 / 0.26

1.92 / 3.56

0.17 / 0.32

56/S

0.65 / 1.20

0.06 / 0.11

0.66 / 1.22

0.13 / 0.24

57/S

0.67 / 1.24

0.30 / 0.56

0.71 / 1.31

0.19 / 0.35

58/S

0.61 / 1.13

0.64 / 1.19

0.52 / 0.96

0.40 / 0.74

59/S

0.57 / 1.06

0.22 / 0.41

0.55 / 1.02

0.22 / 0.41

60/S

1.60 / 2.96

0.32 / 0.59

1.59 / 2.94

0.23 / 0.43

61/S

0.30 / 0.56

0.20 /0.37

0.29 / 0.54

0.16 / 0.30

Reciprocal courses

62/V

9.76 / 18.08

1.14 / 2.11

9.81 / 18.17

0.20 / 0.37

63/V

1.11 / 2.06

0.04 / 0.07

1.11 / 2.06

0.08 / 0.15

65/L

3.34 / 6.19

0.38/ 0.70

2.95 / 5.46

0.22 / 0.41

65/L

5.55 / 10.28

0.12 / 0.22

5.48 / 10.15

0.08 / 0.15

66/L

2.13 / 3.94

0.10 / 0.19

2.05 / 3.80

0.08 / 0.15

67/L

11.13 / 20.61

4.54 / 8.41

6.13 / 11.35

6.48 / 12.00

68/L

2.38 / 4.41

0.04 / 0.07

2.19 / 4.06

0.18 / 0.33

69/L

1.15 / 2.13

0.04 / 0.07

1.28 / 2.37

0.16 / 0.30

70/L

1.16 / 2.15

1.11 / 2.06

1.09 / 2.02

0.63 / 1.17

71/L

2.67 / 4.94

0.08 / 0.15

2.70 / 5.00

0.09 / 0.17

72/M

1.22 / 2.26

0.18 / 0.33

1.17 / 2.17

0.16 / 0.30

73/M

3.38 / 6.26

0.94 / 1.74

3.35 / 6.20

0.26 / 0.48

74/M

1.64 / 3.04

0.42 / 0.78

1.64 / 3.04

0.12 / 0.22

75/M

0.36 / 0.67

0.06 / 0.11

0.36 / .67

0.04 / 0.07

76/M

1.45 / 2.69

0.22 / 0.41

1.54 / 2.85

0.16 / 0.30

77/M

1.83 / 3.39

0.82 / 1.52

1.98 / 3.67

0.28 / 0.52

78/M

1.36 / 2.52

0.60 / 1.11

1.36 / 2.52

0.42 / 0.78

79/M

1.36 / 2.52

0.32 / 0.59

1.37 / 2.54

0.10 / 0.19

80/M

2.27 / 4.20

0.64 / 1.19

2.39 / 4.43

0.12 / 0.22

81/M

9.30 / 17.22

0.19 / 0.35

9.63 / 17.83

0.14 / 0.26

82/M

1.75 / 3.24

0.09 / 0.17

1.74 / 3.22

0.03 / 0.06

894

83/M

0.66 / 1.22

0.11 / 0.20

0.66 / 1.22

0.10 / 0.19

84/M

0.70 / 1.30

0.12 / 0.22

0.69 / 1.28

0.08 / 0.15

85/M

4.66 / 8.63

0.05 / 0.09

4.61 / 8.54

0.10 / 0.19

86/M

4.36 / 8.08

0.04 / 0.07

4.31 / 7.98

0.06 / 0.11

87/M

0.73 / 1.35

0.06 / 0.11

0.74 / 1.37

0.08 / 0.15

88/M

1.24 / 2.30

0.20 / 0.37

1.24 / 2.30

0.30 / 0.56

89/M

3.66 / 6.78

0.12 / 0.22

3.66 / 6.78

0.11 / 0.20

90/M

1.80 / 3.33

0.17 / 0.31

1.91 / 3.54

0.14 / 0.26

91/M

7.38 / 13.67

0.18 / 0.33

7.39 / 13.69

0.10 / 0.19

92/S

1.37 / 2.54

0.19 / 0.36

1.2 / 2.22

0.06 / 0.11

93/S

3.50 / 6.48

0.04 / 0.07

3.50 / 6.48

0.08 / 0.15

94/S

5.02/ 9.30

0.08 / 0.15

5.01 / 9.28

0.24 / 0.44

95/S

1.81 / 3.35

0.94 / 1.74

1.69 / 3.13

0.01 / 0.02

96/S

1.42 / 2.63

0.19 / 0.35

1.41 / 2.61

0.16 / 0.30

97/S

5.26 / 9.74

0.13 / 0.24

5.62 / 10.41

0.11 / 0.20

98/S

4.69 / 8.69

0.13 / 0.24

4.69 / 8.69

0.14 / 0.26

99/S

4.52 / 8.37

0.10 / 0.19

4.56/ 8.45

0.11 / 0.20

100/S

3.86 / 7.15

0.12 / 0.22

3.88 / 7.19

0.08 / 0.15

101/S

0.67 / 1.24

0.17 / 0.31

0.71 / 1.31

0.09 /0.17

102/S

0.56 / 1.04

0.24 / 0.44

0.53 / 0.98

0.14 / 0.26

103/S

0.50 / 0.93

0.26 / 0.48

0.49 / 0.91

0.05 / 0.09

104/S

1.02 / 1.89

0.38 / 0.70

1.07 / 1.98

0.06 / 0.11

105/S

1.01 / 1.87

0.28 / 0.52

0.91 / 1.69

0.13 / 0.24

106/S

0.53 / 0.98

0.25 / 0.46

0.55 / 1.11

0.05 / 0.09

107/S

0.61 / 1.13

0.12 / 0.22

0.64 / 1.19

0.07 / 0.13

108/S

1.08 / 2.00

0.26 / 0.48

1.07 / 1.98

0.27 / 0.50

Crossing courses

109/V

17.18 / 31.82

0.76 / 1.41

17.19 / 31.84

0.50 / 0.93

110/V

9.43 / 17.46

1.22 / 2.26

9.48 / 17.56

0.16 / 0.30

111/V

3.85 / 7.13

4.64 / 8.59

3.65 / 6.76

0.30 / 0.56

112/V

2.97 / 5.50

0.26 / 0.48

2.92 / 5.41

0.22 / 0.41

113/V

1.51 / 2.80

0.12 / 0.22

1.47 / 2.72

0.16 / 0.30

114/V

8.28 / 15.33

0.06 / 0.11

8.25 /15.28

0.06 / 0.11

115/L

2.60 / 4.82

0.04 / 0.07

2.54 / 4.70

0.10 / 01.9

116/L

2.90 / 5.37

0.02 / 0.04

2.79 / 5.17

0.04 / 0.07

117/L

2.84 / 5.26

0.04 / 0.07

2.70 / 5.00

0.12 / 0.22

118/L

5.92 / 10.96

0.52 / 0.96

5.30 / 9.82

0.32 / 0.59

119/L

2.05 / 3.80

0.29 / 0.54

2.06 / 3.82

0.34 / 0.63

120/L

2.17 / 4.02

1.03 / 1.91

2.27 / 4.20

0.33 / 0.61

121M

4.43 / 8.20

1.86 / 3.44

4.33 / 8.02

0.42 / 0.78

122/M

3.72 / 6.89

0.14 / 0.26

3.71 / 6.87

014 / 0.26

123/M

13.12 / 24.30

6.44 / 11.93

14.30 / 26.48

0.32 / 0.59

124/M

2.44 / 4.52

0.58 / 1.07

2.41 / 4.46

0.20 / 0.37

125/M

0.76 / 1.41

0.66 / 1.22

0.77 / 1.43

0.32 / 0.59

126/M

3.73 / 6,91

0.32 / 0.59

3.72 / 6.89

0.22 / 0.41

127/M

7.89 / 14.61

0.25 / 0.46

8.00 / 14.82

0.40 / 0.74

128/M

0.98 / 1.81

0.07 / 0.13

0.92 / 1.70

0.03 / 0.06

129/M

4.11 / 7.61

0.18 / 0.33

3.94 / 7.30

0.22 / 0.41

130/M

5.23 / 9.69

0.29 / 0.54

5.32 / 9.85

0.14 / 0.26

131/M

9.26 / 17.15

0.22 / 0.41

9.21 / 17.06

0.11 / 020

132/M

3.29 / 6.09

0.34 / 0.63

3.08 / 5.70

0.10 / 0.19

133/M

2.59 / 4.80

0.09 / 0.17

2.53 / 4.69

0.03 / 0.06

134/M

13.04 / 24.2

1,05 / 1.94

12.90 / 23.89

0.88 / 1.63

135/M

3.36 / 6.22

0.10 / 0.19

3.37 / 6.24

0.09 / 0.17

136/M

5.84 / 10.82

0.52 / 0.96

5.89 / 10.91

0.16 / 0.30

137/M

5.85 / 10.83

0.25 / 0.46

5.81 / 10.76

0.21 / 0.39

138/M

15.58 / 28.85

0.14 / 0.26

15.60 / 28.89

0.04 / 0.07

139/M

7.42 / 13.74

0.17 / 0.31

7.28 / 13.48

0.17 / 0.31

140/M

1.87 / 3.46

2.65 / 4.91

0.91 / 1.69

1.27 / 2.35

141/M

4.41 / 8.17

1.60 / 2.96

-

142/M

12.73 / 23.58

9.57 / 17.72

14.32 / 26.52

9.85 / 18.24

143/M

14.88 / 27.56

0.27 / 0.50

14.88 / 27.56

0.38 / 0.70

144/M

13.52 / 25.04

5.76 / 10.67

14.48 / 26.82

1.19 / 2.20

145/M

7.15 / 13.24

10.32 19.11

2.67 / 4.94

2.23 / 4.13

146/M

15.95 / 29.54

2.08 / 3.85

16.24 / 30.08

0.57 / 1.06

147/M

18.50 / 34.26

3.33 / 6.17

19.06 / 35.30

0.43 / 0.80

148/M

15.14 / 28.04

0.25 / 0.46

15.12 / 28.00

0.17 / 0.31

149/M

9.08 / 16.82

0.11 / 0.20

9.13 / 16.91

0.16 / 0.30

150/M

0.83 / 1.54

0.23 / 0.43

0.84 / 1.56

0.15 / 0.28

151/M

9.69 / 17.95

0.33 / 0.61

9.69 / 17.95

0.20 / 0.37

152/S

2.39 / 4.43

0.04 / 0.07

2.37 / 4.39

0.10 / 0.19

153/S

5.38 / 9.96

0.32 / 0.59

5.67 / 10.50

0.18 / 0.33

154/S

5.50 / 10.19

0.12 / 0.22

5.41 / 10.02

0.10 / 0.18

155/S

3.20 / 5.93

0.04 / 0.07

3.13 / 5.80

0.16 / 0.30

156/S

1.36 / 2.52

0.34 / 0.63

1.36 / 2.52

0.26 / 0.48

895

157/S

2.47 / 4.57

0.29 / 0.54

2.47 / 4.57

0.30 / 0.56

158/S

1.63 / 3.02

0.99 / 1.83

1.70 / 3.15

0.20 / 0.37

159/S

14.28 / 26.5

3.33 / 6.17

14.63 / 27.10

0.41 / 0.76

160/S

0.46 / 0.85

0.13 / 0.24

0.45 / 0.83

0.07 / 0.13

161/S

1.74 / 3.22

0.12 / 0.22

1.74 / 3.22

0.02 / 0.03

Both ships at anchor

162/M

0.55 / 1.02

0.58 / 1.07

0.92 / 1.70

0.56 / 1.04

163/M

1.19 / 2.20

0.96 / 1.78

0.39 / 0.72

0.56 / 1.04

164/M

0.60 / 1.11

0.62 / 1.15

0.95 / 1.80

0.26 /0.48

165/M

1.51 / 2.80

0.89 / 1.65

1.37 / 2.54

0.44 / 0.81

4 DISCUSSION OF THE TESTS RESULTS

Table 6 summarizes the information presented in

Tables 4 and 5 and shows the number of particular

types of investigated meeting situations of two ships

where errors (for 95% probability) of the presented

data were greater than their values specified in the

international standards and shown in Table 1.

Table 6. The number of meeting situations where errors of

data presented by AIS and ARPA (CPA, true course and / or

true speed) were greater than their values presented in

Table 1 (for 95% probability figures, excluding both ships at

anchor) [own study]

_______________________________________________

Data Number of meeting situations with data

errors greater than their values presented in

Table 1 / total number of meeting situation

ARPA AIS

_______________________________________________

1 2 3 All 1 2 3 All

TC 1 1 0 2 6 0 6 12

TSp 7 19 12 38 1 3 2 6

TC & TSp 2 0 6 8 1 0 0 1

CPA 9 3 3 15 23 2 9 34

CPA & TC 4 4 0 8 4 1 4 9

CPA & TSp 10 2 5 17 0 0 0 0

All data 10 3 17 30 3 0 5 8

_______________________________________________

Σ/ΣT 43/ 32/ 43/ 118/ 38/ 6/ 26/ 70/

61 47 53 161 61 47 53 161

_______________________________________________

Abbreviations used in Table 6 mean:

1 - parallel courses – overtaking;

2 - reciprocal courses;

3 - crossing courses;

All - all meeting situations;

TC - true course;

TSp - true speed; and

Σ/ΣT - number of meeting situations of a given type with

data errors greater than presented in Table 1 / total number

of all meeting situations of this type.

Table 7 presents correlation between the errors of

the results of ARPA calculation and errors of the true

course, true speed and/or CPA indications by AIS for

the same ships’ meeting situations.

The analysis of the data contained in Tables 4 and 5

shows that the differences between the average values

of the true course (ΔTC), true speed (ΔTSp) and/or

CPA (ΔCPA) indicated by the AIS and ARPA for

particular observed and tracked vessels exceeded

errors defined in the IMO Resolution MSC.192(79)

and IEC Standard 61993-2 in 40 measurement series

(24% of all of them). It should be noted that they

exceeded these errors in 29.5% of measurements for

ships overtaking on parallel courses, 24.5% for ships

at crossing courses, and 19% for vessels sailing on

reciprocal courses. Detailed information on these

meeting situations is presented in Table 8.

Table 7. Correlation between errors of the results of ARPA calculation and errors of the true course, true speed and/or CPA

indications by AIS for the same meeting situation (excluding both ships at anchor, abbreviations as in Table 7) [own study]

Data presented by

ARPA with errors

greater than

presented in Table 1

Meeting

situation

The number of meeting situations in which AIS simultaneously presented

particular data with errors greater than presented in Table 1

Type

No

TC

TSp

TC &

TSp

CPA

CPA &

TC

CPA &

TSp

All data

OK

TC

1

-

1

2

1

-

1

3

-

Σ

2

-

2

TSp

1

7

1

-

4

2

19

-

3

-

16

3

12

1

-

1

-

9

Σ

38

2

5

1

-

29

TC & TSp

1

2

-

2

-

3

6

2

1

-

2

1

Σ

8

4

1

-

2

1

CPA

1

9

1

-

6

-

2

3

-

1

-

2

3

-

1

-

2

Σ

15

1

-

8

-

6

CPA & TC

1

4

1

-

1

-

1

-

2

4

-

4

3

-

Σ

8

1

-

1

-

1

4

CPA & TSp

1

10

-

10

-

2

-

1

-

1

3

5

-

3

-

2

Σ

17

-

14

-

3

All data

1

10

-

5

3

-

2

-

896

2

3

-

1

-

2

3

17

2

-

4

-

3

4

Σ

30

2

-

9

8

-

5

6

OK

1

18

1

-

1

-

16

2

15

-

15

3

10

1

-

9

Σ

43

2

-

1

-

40

Abbreviations used in Table 7 mean:

Type 1, 2 3 - see Table 6;

OK - data presented by AIS without unacceptable errors;

TC - true course;

TSp - true speed; and

Σ - all meeting situations.

Table 8. Meeting situations in which the differences in the indications of average values of true course, true speed and CPA

by ARPA and AIS are less than the error of determining these parameters presented in the IMO Resolution MSC.192(79)

and IEC Standard 61993-2 [own study]

No

NoMS

ΔTC

ΔTSp

ΔCPA

L

D

V

Sea state

Parallel courses - overtaking

1

2V

No

Yes

289

16.8-14.5 / 31.1-26.9

0 / 0

3

2

3V

No

Yes

290

6.7-3.4 / 12.4-6.3

0 / 0

2

3

4V

Yes

No

180

19.8-19.6 / 36.7-36.3

11.1 / 5.7

4

6V

Yes

No

225

16.8-16.4 / 31.1-30.4

10.8 / 5.6

7

5

7L

Yes

No

225

14.1-13.2 / 26.1-24.4

12.0 / 6.2

3

6

9L

Yes

No

Yes

274

2.0-1.8 / 3.7-3.3

14.0 / 7.2

4

7

11L

Yes

No

295

12.5-10.6 / 23.2-19.6

11.5 / 5.9

2

8

12L

No

182

8.7-8.2 / 16.1-15.2

15.5 / 8.0

2

9

17M

No

Yes

207

18.9-15.8 / 35.0-29.3

0.5 / 0.3

1

10

21M

Yes

No

179

17.1-17.0 / 31.7-31.5

10.8 / 5.6

6

11

25M

Yes

No

185

18.7-18.4 / 34.6-34.1

11.7 / 6.0

1

12

28M

Yes

No

236

15.0-14.8 / 27.8-27.4

14.6 / 7.5

2

13

37M

No

Yes

289

9.4-3.5 / 17.4-6.5

9.0 / 4.6

5

14

38M

Yes

No

299

20.4-18.9 / 37.8-35.0

17.0 / 8.7

1

15

40M

Yes

No

Yes

261

24.4-23.8 / 45.2-44.11

8.2 / 9.4

1

16

44S

Yes

No

190

5.7-4.7 / 10.6-8.7

13.0 / 6.7

4

17

50S

Yes

No

145

4.8-4.5 / 8.9-8.3

12.2 / 6.3

3

18

60S

No

Yes

240

4.1-2.1 / 7.6-3.9

1.6 / 0.8

4

Reciprocal courses

19

64L

Yes

No

177

13.1-6.6 / 24.3-12.2

10.0 / 5.1

5

20

67L

Yes

No

333

12.5 / 23.2

14.1 / 7.3

4

21

70L

Yes

No

Yes

180

11.6-5.3 / 21.5-9.8

11.1 / 5.7

3

22

81M

Yes

No

127

14.2-10.6 / 26.3-19.6

11.3 / 5.8

3

23

89M

No

Yes

122

6.2-4.6 / 11.5-8.5

13.5 / 6.9

1

24

90M

No

Yes

115

11.0-4.2 / 20.4-7.8

9.8 / 5.0

2

25

97S

Yes

No

112

9.1-5.3 / 16.9-9.8

14.2 / 7.3

2

26

102S

Yes

No

Yes

102

6.3-1.7 / 11.7-3.1

10.2 / 5.2

4

27

105S

No

Yes

184

7.4-2.7 / 13.7-5.0

10.2 / 5.2

3

Crossing courses

28

118L

Yes

No

199

16.7-12.8 / 30.9-23.7

14.4 / 7.4

2

29

123M

Yes

No

109

17.1-16.3 / 31.7-30.2

13.4 / 6.9

5

30

138M

No

Yes

200

15.9-12.8 / 29.4-23.7

12.9 / 6.6

1

31

139M

Yes

No

Yes

254

9.5-7.5 / 17.6-13.9

7.9 / 4.1

1

32

140M

No

Yes

No

179

21.8-20.5 / 40.4-38.0

7.2 / 3.7

2

33

141M

No

Yes

No

199

6.1-5.1 / 11.3-9.4

2.2 / 1.1

7

34

142M

No

354

21.2-19.5 / 39.3-36.1

16.4 / 8.4

6

35

144M

No

Yes

No

190

18.7-15.7 34.6-29.1

10.7 / 5.5

6

36

145M

No

148

24.3-18.3 / 45.0-33.9

10.8 / 5.6

5

37

146M

Yes

No

Yes

108

18.9-15.6 / 35.0-28.9

11.3 / 5.8

5

38

147M

No

Yes

No

292

20.0-19.1 / 37.0-35.4

10.6 / 5.5

5

39

158S

No

Yes

96

2.9-2.3 / 5.4-4.3

15.6 / 8.0

3

40

159S

Yes

No

117

16.6-15.9 / 30.7-29.4

12.4 / 6.4

2

Both ships at anchor

41

162M

-

No

169

1.2 / 2.2

0/ 0

3

42

163M

-

No

183

1.7 / 3.2

0 / 0

3

43

164M

-

No

274

1.0 / 1.8

0 / 0

3

Abbreviations used in Table 8 mean:

D - the distance between the ships (own and observed) during the measurement;

L - the length of the observed vessel presented on the web-site;

No - the differences in the indications of average value are greater than errors defined in IMO resolution and IEC standard;

NoMS – number of meeting situation described in the Table 3;

Sea state – the state of the sea during the measurements expressed in degrees of the Douglas scale;

V – the mean value of the true speed of the observed ship;

Yes - the differences in the indications of average value are less than the errors defined in IMO resolution and IEC standard; and

ΔTC, ΔTSp, ΔCPA – differences in the indications of average values of true course (TC), true speed (TSp) and CPA by ARPA and

AIS.

897

The information shown in Table 8 is summarized

in Table 9.

Table 9. The number of measurement series with the

differences in the indications of the average values of

particular parameters by ARPA and AIS exceeding the error

values specified in the IMO resolution and the IEC standard

[own study]

_______________________________________________

Parameter Number of measurement series

_______________________________________________

1 2 3 ΣT

TC 5 3 1 9

TSp 2 2 2 6

TC & TSp 0 0 1 1

CPA 9 2 3 14

CPA & TC 0 0 4 4

CPA & TSp 1 2 0 3

All data 1 0 2 3

ΣT 18 9 13 40

_______________________________________________

Abbreviations used in Table 9 mean:

- 1, 2 3 see Table 6; and

- ΣT – total number of measurement series with

differences in the indications of the average values of

particular parameters by ARPA and AIS exceeding the error

values specified in the IMO resolution and the IEC

standard.

The data presented in Table 8 show the

dependence of the differences in AIS and ARPA

indications on the true speed of the observed and

tracked vessel and on the type of meeting situation.

No other correlations could be found. The next Table

10 shows the relationship between the differences in

AIS and ARPA indications and the errors in

determining the average values of individual

parameters by these devices.

Table 10. The number of measurement series in which the

average value of the true course, true speed or CPA of the

observed object indicated by ARPA and / or AIS had the

error greater than its limit defined in the IMO resolution

and IEC standard (for meeting situation in which

differences in the indications of average true course, true

speed or CPA by ARPA and AIS were greater than defined

by international regulations [own study]

_______________________________________________

The average value of the The number of measurement series

parameter presented with too in which the average value had too

great error by great error

TC TSp CPA ΣT

_______________________________________________

AIS & ARPA 9 5 21 35

ARPA 3 7 1 11

AIS 0 0 0 0

Mean value without too 5 1 2 8

great error

ΣT 17 13 24 54

_______________________________________________

Abbreviations as in the table 9.

The next table provides information on the state of

the sea during the measurement series in which errors

of the true course, true speed and / or CPA indications

by ARPA and AIS on board equipment exceeded the

values shown in Table 1.

Table 11. The state of the sea during the measurement series in which errors of the true course, true speed and / or CPA

indications by ARPA and AIS on board equipment exceeded the values shown in Table 1 (for 95% probability figures,

excluding both ships at anchor) [own study]

Data with errors exceeding the

values shown in Table 1

State of the sea expressed in degrees of the Douglas scale

Σ

1

2

3

4

5

6

7

8

ARPA indications

TC

1

-

2

TSp

4

7

13

5

7

1

38

TC & TSp

2

1

2

1

-

1

-

1

8

CPA

1

4

7

3

-

15

CPA & TC

1

2

1

2

-

8

CPA & TSp

4

5

2

1

3

-

17

All data

4

5

7

2

6

3

-

30

Σ/ΣT

17/20

25/35

33/42

14/26

16/23

8/9

4/5

1/1

118/161

AIS indications

TC

1

2

6

1

-

1

-

12

TSp

2

-

1

2

-

6

TC & TSp

-

1

-

1

CPA

5

9

5

3

-

34

CPA & TC

1

-

2

1

3

1

-

9

CPA & TSp

-

All data

-

1

2

-

8

Σ/ΣT

9/20

12/35

19/42

9/26

11/23

6/9

4/5

-/1

70/161

Collective information on the state of the sea

during particular measurement series is presented in

Table 12. Too few measurements in storm conditions

makes it impossible to draw conclusions about the

relationship between the accuracy of ARPA and AIS

indications and the state of the sea.

Table 12. State of the sea expressed in degrees of the

Douglas scale during the measurement series (including

both ships at anchor) [own study]

_______________________________________________

State of the sea 1 2 3 4 5 6 7 8

(Douglas scale)

_______________________________________________

Number of 20 35 46

x

26 23 9 5 1

measurement

series

_______________________________________________

x - including four measurement series, during which both

ships were anchored

898

5 FINAL CONCLUSIONS

Measurements described in this paper were carried

out on ten different merchant ships using popular,

often used AIS and radar on board equipment but

produced by four manufacturers only. Due to that and

due to the limited number of conducted tests (161

series of measurements while both ships are

underway and 4 when they are at anchors), it is

impossible to formulate on their basis general

conclusions about the stability and accuracy of the AIS

and ARPA indications and their dependence on hydro

meteorological conditions. Nevertheless, the

performed measurements allow for the formulation of

some remarks on these topics.

Table 6 shows that the accuracy of ARPA

indications does not depend on the type of ships’

meeting situation. ARPA presented all or part of data

with the accuracy lower than defined by international

recommendations and standard (presented in Table 1)

in 73% of the measurement series (118 out of 161). It

mainly had a problem with the accuracy of the

presentation of the true speed of the tracked vessel (in

24% of meeting situations (38 out of 161)). All ARPA

data had too great error in 19% of observations (30 out

of 161), CPA, or CPA and true course, or CPA and

true speed in 25% (40 out of 161). Generally, ARPA

reported a CPA value with an error greater than 0.3

nautical miles in 43% of meetings (70 out of 161). AIS

had problems mainly with the accurate presentation

of CPA value (in 32% of measurement series (51 out of

161)), especially in the case of overtaking ships on

parallel courses (in 49% percent of observations (30

out of 61 measurement series)).

The data presented in Table 7 show that there was

no correlation between the inaccuracies in the AIS and

ARPA indications for the same object. Out of the total

number of 30 measurement series in which ARPA

incorrectly presented all recorded data, AIS also

showed all data with too great errors in only 5 series

(in 9 series the inaccuracy was related to CPA value,

in 8 series related to CPA and true course). In 15

meeting situations where ARPA had problems with

accurately presenting only CPA values, AIS also

incorrectly showed only CPA in 8 tests. In 38 tests,

where ARPA showed insufficiently accurate

information about the true speed of the tracked vessel,

AIS had problems with the accurate presentation of its

true speed in 5 tests only and in 29 tests presented all

data of this vessel with the required accuracy.

The tests carried out have shown that both ARPA

and AIS can indicate distances between two ships at

anchors unstable and with significant inaccuracies.

A separate issue are the differences between the

AIS and ARPA indications of the average values of

the observed and tracked object true course, true

speed and CPA. In a significant number of tests (in

24% of the measurement series), they exceeded the

values of the presentation errors defined in the IMO

Resolution MSC.192(79) and IEC Standard 61993-2. It

should be noted that in all these cases, the AIS

presented the mean values of individual parameters

with acceptable errors. It is interesting that in 8 cases

of the discussed differences in the AIS and ARPA

indications, both devices showed average values of all

parameters with errors smaller than those defined in

the international regulations.

The results of the measurements presented in

Table 11 do not show a clear relationship between the

accuracy of the data presented by AIS and ARPA and

the current level of disturbances from the sea surface.

The reason for this may be the lack of a comparable

number of measurements carried out in individual sea

states expressed in the Douglas scale and too small

number of tests conducted in storm weather condition

(Table 12).

The comments presented in this article should be

taken into account when using ARPA and AIS as

technical means of observation for anti-collision

purposes. They show that the indications of both

devices in real conditions may be unstable and have

errors greater than those specified in the IMO

Resolution MSC.192(79) and IEC Standard 61993-2.

Therefore, users should not rely on the instantaneous

digital data values of the other vessel presented by

ARPA and AIS.

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