Basic Concepts of GMDSS

Full implementation of GMDSS regulations was effected on 1 Feb 1999 , applying to all cargo ships 300 Gross tons & above & to all Passenger Ships, Regardless of size on International Voyages.
Before GMDSS was implemented, a radio watch was kept on the Distress Frequencies by a dedicated Ofiicer using Headphones or Loudspeakers.
In the GMDSS, the DSC - Digital Selective Calling Equipment keeps Watch automatically.

Before GMDSS , a vessel in Distress relied primarily on another vessel for assistance.

The GMDSS emphasizes the ability to alert SAR - Search & Rescue , authorities ashore as well as shipping in the to achieve a co-ordinated response to Distress situations.




GMDSS involves Terrestrial as well as Satellite Communications System.
DSC is a terrestrial system available in the MF / HF / VHF frequency bands.
Characteristics of the Earth / Sea / like Terrain / Surface, Weather Conditions, day night times affect the Propogation of these signals.
Shore stations used in terrestrial communications are called CRS - Coast Radio Stations.

Note- not all CRS are equipped with DSC facilities.

Satellite communications in the GMDSS involves the INMARSAT - Inmarsat Satellites systems for Distress & Routine communications and the COSPAS SARSAT systems for distress purposes only.
Shore stations in the INNARSAT systems are known as LES - Land Earth Stations.
 Shore Stations in the COSPAS SARSAT system are called LUT - Local User Terminal 
 


 DSC is a calling system, not a working system - it is a means of establishing contact , requiring receiving stations to watch on an appropriate frequency to receive the rest of the information sent by non DCS means on non DSC frequencies.

The DSC Equipments has the MMSI - Maritime Mobile Service Identity number of the vessel programmed into itself, it is also interfaced with the GPS onboard , which means that the DSC equipment knows who its is and where it is



This makes it possible to use DSC to automatically address information, attract the attention of all stations , an individual station , a group of ships, within A Defined Geographical Area .


GMDSS Sea Areas ;-


A1 - area within the Radiotelephone coverage of at least one VHF Coast station in which continuous DSC alerting is available. Such an area could extend about 20- 50 Miles Offshore.


A2 - Area , excluding Sea area A1, within the Radiotelephone coverage of at least one MF Coast Station in which Continuous DSC alerting is available. Such an area could extent about 150 - 250 Miles Offshore.


A3 - Area excluding Sea area A1 & A2 , within coverage of Inmarsat Geo-stationary Satellite in which continuous alerting is available. area lies between about Latitudes 70 Degree North & South.


A4 - Area outside Sea Areas A1, A2, A3 ( Polar Regions )








1 comment: