The International Maritime Organization (IMO), known as the Inter-Governmental Maritime Consultative Organ-ization (IMCO) until 1982, was established in Geneva in 1948 and came into force ten years later, meeting for the first time in 1959 [Weblink 2015c].
Headquartered in London, United Kingdom, the IMO is a specialized agency of the United Nations with 171 Member States and three Associate Members. The IMO’s primary purpose is to develop and maintain a compre-hensive regulatory framework for shipping, and its remit today includes safety, environmental concerns, legal matters, technical co-operation, maritime security and the efficiency of shipping. IMO is governed by an assem-bly of members and is financially administered by a council of members elected from the assemassem-bly. The work of IMO is conducted through five committees and these are supported by technical subcommittees. Member organi-zations of the UN organizational family may observe the proceedings of the IMO. Observer status is granted to qualified non-governmental organizations.
IMO is supported by a permanent secretariate of employees who are representative of the organization’s mem-bers. The secretariate is composed of a Secretary-General who is periodically elected by the assembly, and various divisions such as those for marine safety, environmental protection and a conference section [Weblink 2015c].
This section derives and defines a requirement baseline based on publications from the IMO. The IMO ran through a development of their operational requirements since 1983. Since then, IMO initiated a study into a world-wide satellite position-fixing system for safety of navigation and a report – Study of a world-wide radio navigation system – was adopted by the IMO Assembly in 1989. IMO resolutions have been published by the IMO since then. It is noted that there are obviously two independent developments (here also called “families”) for the operational requirements within the IMO – on the one hand for worldwide radio navigation systems and on the other hand for a future GNSS. Both points of view are deemed relevant and will therefore be discussed.
According to the understanding of the author the link between these two “families” is missing.
First, accuracy standards for navigation are described and assessed “for position-fixing systems, in particular radio navigation systems, including satellite systems” in the IMO Resolution A.529(13) [IMO 1983]. The IMO Resolution A.577(14) [IMO 1985] stated some basic recommendations on the operational status of electronic position-fixing systems such as “the authorities or companies responsible for the operation of a selected system,
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or of any of its constituent parts, should at all times make available to navigators appropriate information on the operational status of such systems or parts thereof”.
The diagram in Figure 4-1 depicts the chronicle evolution of the respective IMO resolutions on navigation related issues (“Family 1”). The upper layers revoke the latter layer respectively which means that resolution A.1046(27) [IMO 2011] contains the actual operational requirements.
Figure 4-1: Chronicle evolution of respective IMO resolutions on navigation related issues („Family 1“)
The IMO resolution A.666(16) from 1989 [IMO 1989] for the first time expresses the “need for a world-wide radio navigation system to provide ships with navigational position-fixing throughout the world”. Different relevant systems (GPS, Differential Omega, Loran-C, etc.) are listed and detailed with respect to their technical and operational aspects. It is also noted that “GPS would be suitable for use as it is expected to be operational in the early 1990s”. Resolution A.815(19) [IMO 1995] recalls and revokes Resolution A.666(16) [IMO 1989] by which it adopted some studies of a wide radio navigation system. Operational requirements for a world-wide radio navigation system are expressed here for different phases of operation.
Resolution A.953(23) [IMO 2003] updates resolution A.815(19) [IMO 1995] by which it adopted the report on the study of a world-wide radio navigation system which is annexed to that resolution. The resolution A.1046(27) [IMO 2011] recollects and revokes resolution A.953(23) [IMO 2003] and expresses the actual opera-tional requirements on worldwide radio navigation systems that are summarized in Table 4-1.
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Table 4-1: Summary of operational requirements for a worldwide radionavigation system according to resolution A.1046(27) published by the IMO [IMO 2011]
*: the period of time of 30d is taken from the previous resolution A.953 as there is no actual value in the resolu-tion A.1046(27) [IMO 2011].
It is noted that the operational requirements expressed in Table 4-1 do not consider a need for integrity. The operational requirements according to the IMO resolutions which are associated to “family 2” differ from those derived from the resolutions of “family 1”. The relation between the IMO resolutions of “family 2” is depicted in Figure 4-2 showing the chronicle evolution of the respective IMO resolutions on navigation related issues (“Family 2”). The upper layers revoke the latter layer respectively which means that resolution A.915(22) [IMO 2002] contains the actual operational demands.
A.915(22) (2002)
A.860(20)
(1997) A.880(21)
(1999)
Figure 4-2: Chronicle evolution of respective IMO resolutions on navigation related issues („Family 2“)
The actual resolution A.915(22) [IMO 2002] revokes resolution A.860(20) [IMO 1997] and recognizes “the need for a future civil and internationally-controlled global navigation satellite system (GNSS) to contribute to the provision of navigational position-fixing for maritime purposes throughout the world for general navigation, including navigation in harbour entrances and approaches and other waters in which navigation is restricted”
[IMO 2002]. The maritime requirements for a future GNSS are described in the resolution and are depicted in Table 4-2. Resolution A.880(20) [IMO 1999] does not contain any operational requirements for GNSS but deals with the implementation of the International Safety Management (ISM) Code.
Horizontal 95%
Update Rate of Computed/Display
ed Position Data Integrity Time-To-Alarm
[sec] Continuity Availability
Ocean Waters 100m <2s N/A ASAP N/A 0.998 over
30d * Harbour
Entrances, Harbour Approaches and Coastal Waters
10m <2s N/A 10s ≥0.9997 over
a period of 15min
0.998 over 30d *
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Table 4-2: Summary of operational requirements for a worldwide radionavigation system according to resolution A.915(22) published by the IMO
*: global coverage; **: regional; ***: local
It is noted that no specifications are defined for the vertical component. The fix interval is required to be 1s for all phases of operation. More stringent demands may be necessary for ships operating above 30 knots.
Currently the IMO resolutions A.1046(27) and A.915(22) form the backbone of IMO’s requirements for maritime radio navigation systems. The first “family” with A.1046(27) depicts operational needs for a worldwide radio navigation system including systems other than GNSS as well. It does not claim any need for integrity but for coarse positioning accuracy. The second “family” represented by A.915(22) exclusively focuses on GNSS. At first sight, these requirements seem to be very challenging as there are specifications for integrity and continuity defined over a period of time of 3 hours.
Comparing both “families”, it turns out that the demands from the first “family” are quite lax compared to the second “family”. Basically, both sets of operational requirements derived in this section could be associated to GNSS as it is a worldwide radio navigation system. As mentioned earlier, the first “family” is not only related to GNSS but also to other systems such as LORAN-C, for example. The specifications from the second “family” are specified for a GNSS exclusively. A.915(22) must be viewed as a ‘positioning’ document related to requirements for future developments of GNSS to be considered within the framework of A.1046(27).
Because continuity over an exposure period of 3 hours seems to be very demanding with respect to compliance of the system design, an exposure period of 15 minutes (according to the requirement from A.1046(27)) shall be assumed in parallel to the analysis performed in this document. In doing so, the impact on performance shall be assessed considering the two different exposure periods.
Operation Abs. Accuracy Alert Limit Hor.[m] Hor.
[m] TTA
[sec] Integrity Risk
(per 3 hours) Availability [%]
per 30 days Continuity [%]
over 3 hours
Ocean* 10 25 10 1.E-05 99.8 N/A
Coastal* 10 25 10 1.E-05 99.8 N/A
Port approach and restricted waters**
10 25 10 1.E-05 99.8 99.97
Port*** 1 2.5 10 1.E-05 99.8 99.97
Inland
waterways* 10 25 10 1.E-05 99.8 99.97
System Level Parameters Service Level Parameters Integrity
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