LESOs – the critical link in GMDSS

Their critical role in providing maritime safety

This article explains the importance of the Land Earth Stations (LESs) in the critical path between a vessel in distress and the maritime rescue co-ordination centres (MRCCs).

Many ships that ply the seas and oceans of the world today have at least one Inmarsat satellite communications terminal fitted as standard.

However, every ship that is subject to the International Maritime Organisation (IMO) Safety of Life at Sea (SOLAS) Convention and the Global Maritime Distress and Safety System (GMDSS), and which travel outside of coastal Navtex coverage, must have Inmarsat C equipment fitted.

Increasing regulation of the fisheries industry now means also that increasing numbers of fishing vessels are being fitted with Inmarsat equipment, to allow for mandatory vessel position monitoring.

Ocean-going yachts and many other types of vessel, realising the vital part that Inmarsat can play in ensuring their safety, also fit Inmarsat equipment on a voluntary basis.

Mariners trust Inmarsat with their lives and often do not stop to think of just how their call for help will be handled in an emergency – they just accept the fact that their distress call will get through and that they will get a response.

There are currently three Inmarsat two-way communications equipments that are approved for use within the GMDSS – Inmarsat B, Inmarsat C and Inmarsat Fleet F77.

Distress messages can be sent or received on all three, with distress alerts capable of being sent at the touch of a button. All three of these GMDSS services operate through the Inmarsat constellation of geo-synchronous satellites and through the Inmarsat land earth stations (LESs).

From the Inmarsat perspective it could be said therefore that there are four principal, key components in the maritime safety chain from a ship in distress. These are:

• the GMDSS mobile earth station (MES)
• the Inmarsat satellite
• the Inmarsat land earth station
• and the maritime rescue coordination centre (MRCC)

The Inmarsat system provides three of these vital ingredients; the MES, the satellite and the LES.  Combined, they provide a robust and reliable means of communication between the ship in distress and the MRCC and is always be available on demand.

The IMO requires that the Inmarsat system must be available for ship-shore distress priority alert calls for a minimum of 99.9% of the time.

The key partnership between Inmarsat and the highly qualified land earth station managers and operations co-ordinators ensures system availability to this very high standard. This close working relationship is in evidence throughout every day of every year, around the clock and around the world.

GMDSS provision via Inmarsat maritime safety services is depicted in the diagram shown.

Although some rescue coordination centres have Inmarsat maritime terminals fitted amongst their communications equipment, the primary means of distress alerting ship-shore will always be via an Inmarsat land earth station.

Each land earth station operates and maintains transmission, reception, satellite dish and switching equipment to track and communicate through the Inmarsat satellites. Highly skilled LES operations personnel are key elements in the dedicated provision of safety services to the international maritime community.

Although the Inmarsat distress alerting system is largely automated, manual intervention is always available instantly in the event of a misconnection between the MES, the LES to the MRCC.

Distress alerts give audible and visual indication when they are received at an LES. Under normal circumstances the alert is delivered automatically to the associated MRCC and no action is required at the LES.

However, if this delivery fails for any reason, LES personnel that are on duty around the clock are alerted to the failure. They immediately assume manual control of the distress and ensure that the alert is delivered to the associated MRCC by the quickest means that remain available – which may be voice, fax or telex. They then monitor and maintain open the communications link between the ship and the RCC.

Unsung heroes of many rescues, these LES operations personnel deserve special mention. Without them, who knows how many lives could have been lost?

Many LESs have multiple antennae and can ‘see’ more than one satellite ocean region. It has been said that seafarers trust Inmarsat with their lives.

It must be remembered that it is the Inmarsat system, including the vital Inmarsat land earth stations, that provides the service.