India has long coastline of 7517 kms with 12 major ports and 187 minor & intermediary ports. Major ports all together handled 423 million tones traffic & non-major ports all together handled 519 million tones traffic during the year 2006-07. Traffic at Indian ports has been growing at the rate of over 11% during last 5 years and with continuing rapid growth in trade, port traffic is expected to grow further. Lack of port infrastructure has been one of the major problems (i.e. low draught & inadequate back up services) in our maritime development. Shippers prefer shipments by large size & deeper draughts vessels, which is more economical in cost of operation. So, to accommodate such bigger vessels, the required depths should be available. Accordingly there is huge demand for dredging & quality hydrographic services at the Indian Ports as the channels to be widened & deepened to accommodate bigger vessels. Almost all the major ports in India have plans to widening & deepening their approach channels in order to accommodate bigger ships. Further, the maintenance-dredging requirement of ports is substantial considering the siltation problem at the ports.

A completely new situation has risen after the total revision of chapter V of the annex to SOLAS that maintains that hydrographic services are binding to Governments under international law. - For the first time, international law makes it mandatory to operate hydrographic services. This obligation applies to all states that are parties to SOLAS.

IHO published the 4th edition of special publication No.44 in April 1998 of IHO standards for hydrographic surveys. The principal aim of this publication is to specify minimum standards for hydrographic surveys in order that hydrographic data collected according to these standards is sufficiently accurate and that the certainty of data has to be adequately quantified to be safely used by mariners.

The new edition of IHO standards for hydrographic surveys describes a very important change. The accuracy of a survey is no longer dependent on the scale of the analogue chart. The accuracy as well as resolution of a survey depends on the type of the area to be surveyed. The preface of IHO standards recognises that hydrographic data is alsoimportant for coastal zone management, environment monitoring, resource development, legal and jurisdictional issues and coastal engineering works etc.

1. To calculate the error limits for depth accuracy the corresponding values of 'a' and 'b' listed in above table to be introduced into the formula
   
   With 'a' = constant depth error,
   i.e. the sum of all constant depth error
   'b*d ' = depth dependent error, i.e. the sum of all depth
   dependent errors
   ' b' = factor of depth dependent error
   ' d' = depth
2. For safety of navigation purposes, the use of an accurately specified mechanical sweep to guarantee a minimum safe clearance depth throughout an area may be considered sufficient for above order surveys.
3. The value of 40 m has been chosen considering the maximum expected draught of vessels.
4. The line spacing can be expanded if procedures for ensuring an adequate sounding density are used.

For ports & harbours, and especially for those where the underkeel clearance is small, 100 % coverage of the seafloor is required during the sounding process in order to make sure that all potential hazards are mapped. It is not possible by single beam echosounder alone. So alternative technologies available are as follows:

• Mechanical sweeping is best but time consuming and therefore expensive.
• Towing side scan sonar is often impractical in confined areas such as ports.
• Compact high frequency multibeam echosounders, probably most viable alternative for the future, which can comply with the requirement of SP-44.