THE Marine Department has set up a Hydrographic Office, the first for Hong Kong. It will chart Hong Kong waters and publish charts, notices to mariners and other nautical publications. The office is headed by Nick Emerson, who has been conducting applied hydrographic and oceanographic studies for 25 years. He comes from Irish Hydrodata, which provides hydrographic services to the Irish Government. He is assisted by hydrographers T.C. Sin and W.L. Tang and 10 technical staff. The office will gradually replace the services now provided to the shipping community by the British Admiralty. By 1997, the office will employ 105 staff with two fully equipped survey launches. Although there are sounding charts of Hong Kong waters dating back to at least 1759, it was arguably the Royal Navy chart of 1841, surveyed by Captain Sir Edward Belcher that set the standard. The charts' accuracy and detail have been followed and even included in the many versions of Admiralty charts that have been issued over the following years. But the Royal Navy survey ships have not been to Hong Kong since 1972, with recent publications supplemented by surveys carried out by the Civil Engineering Division. A study by management consultants Price Waterhouse recommended that a fully functional hydrographic office be set up in the Marine Department to fill the obvious gap to be left when the Admiralty's obligation would cease on June 30, 1997. Mr Emerson said the technologies used by his office will be quite different from Capt Belcher's days when wooden sailing ships conducted surveys using sextants, compasses and individual lead-line soundings. Then painstaking manual engraving of every detail was accomplished in reverse on copper plates before printing, he said. The hydrographic office will be equipped with fast, stable, purpose-built survey launches using echo-sounding equipment which can provide seabed depth information over a 100-metre area width in a single pass travelling at 10 knots. A satellite network in conjunction with a shore-based reference station will give accuracies of a few centimetres. With computer logging of all data, interactive post-processing ashore on high-speed workstations means that virtually no manual drafting will be necessary before a digital chart is ready for printing. ''These techniques should ensure that new chart versions, necessary because of the continual coastline changes and port developments, will be ready to print almost on demand,'' he said. They also could lead to ancillary publications for the fishing and leisure boating communities.