On Feb. 10, 1999, the Executive Yuan published 22 base points and the baselines (marked with red line) of territorial sea (the first issue) around Taiwan Island and the islands at its vicinity. It covers the islands of Penghu, Little Ryuku, Green Island, Orchid Island, Turtle Island and Pengchiayu. The area between red line and yellow one with the extension outward from the red line with the distance of 12 nautical miles is the territorial sea (as indicated with yellow line), and 12 more nautical miles outward is the contiguous area (shown with blue line). The Exclusive Economic Zone (EEZ) of our nation as claimed internationally by maritime countries covers the area with 200 nautical miles from the base points.
The land in Taiwan area has been surveyed and made into photo base maps yearly in accordance with the mid-term program. The basic charts of territorial sea and the contiguous areas offer the basic data with the aspects of ocean physics, ocean chemistry, and ocean biology for researches.
Hydrographic survey is primarily conducted with sonar device, which transmits and receives reflected sound echo reflected from the bottom of waters. From the time delay between transmission and reflection, the detection and location of submerged objects or measurement of the depth can be obtained for any investigations of marine information. Thus, on-vessel echo sounders and positioning device such as gyroscope, GPS receiver are basically used in survey. Other methods and instruments are used for advanced investigations and analyses over ocean current, salinity, nutrients, and even aquatic species at fixed points for a long period of time. The data obtained from the hydrographic survey can be used for sailing, dredging of sea-route, coastal protection, port engineering, sea territory claim, anti-smuggling crimes, protection of fishery, and development of fishing ground. Salinity and temperature analysis can also be used for researches of sea level and weather prediction, seabed heat and volcano researches, disaster protection planning and so on. Recently, after the opening of seashores, the maritime entertainment activities has become developed, the relevant facilities to support its development depend upon the information gathered from surveying. In the recent years, more international attentions have paid to focus on the topic of continental shelf, especially, the extraction and exploration over the mineral resources such as methane hydrate and others has brought a new concept of economic protection.
1. Law on the Territorial Sea and Contiguous Zone of the Republic of China
2. Law on the Exclusive Economic Zone and Continental Shelf of the Republic of China
III. Navigation Chart and Base Chart of Marine Area：
1. Charts ：
Chart, different from land map, is traditionally used for sailing with the lowest tide height as the beginning of water depth for safety consideration. Generally, the contents in chart include water depth, seabed, current velocity and blocks (wrecked ships, reefs), with sea-route pole (flags) lantern, compass, coastal type, dyke, island, submarine cables (pipes), fishery zone marks (anchor, hazard or warnings) and others.
Currently, the charts (sea-route chart) scaled of 1/50,000, 1/150,000 published by Navy, or even the smaller ones of 1/1,000,000 or 1/4,000,000 that can cover larger sea area, are mainly used for sailing
With a certain overlap between adjacent map sheets, the map sheets are horizontally or vertically designed to meet the convenient uses of practical area situation. The existing used charts around Taiwan island are shown 1:50,000 with yellow frames, while 1:150,000 with purple frame.
2.Base Charts of Marine Areas：
The base charts cover the marine areas of the territorial sea and the contiguous zone. They mainly contain the basic information of administrative boundaries, seabed terrain, sentiment properties, ocean currents, seabed texture and so on. The final goal of base charts production is to offer overall platform for the purpose of verification of national maritime territory, exploring marine resources, everlastingly planning and managing under a integrated coordinate system among the information both on land and marine areas. In Taiwan Strait area, the water depth is shallower than 100 meters on average. For overall planning and seashore engineering, the currently used charts with the scale of 1:50,000 are obviously inadequate. Therefore, base charts are planned with two scales to produce. Generally, those areas with the water depth of 30 meter or shallower or 6 nautical miles seaward are produced with 1:5,000, and others are with 1:50,000 to meet the various needs.
3.Littoral Zone Mapping：
ational land consists of sea territory, land, and littoral zone. Land and sea territories have been mapped with serial projects. The littoral zone, located between them, is still limited by the traditional surveying technique so that little information has been mapped. During flood tide, shipboard bathymetric instruments is in a quandary at the shallow water, while during the ebb tide, mud and soft sand sentiment hinder the surveying work from land. Constantly, scattered sites have been surveyed according to specific purposes with small area. As a result that there is a gap with no information to connect the land and sea territory.
Airborne LiDAR (Light Detecting and Ranging) technology equipped with IMU (Inertial Measurement Unit) and GPS (Globe Positioning System) can obtain 3D terrain relief information quickly and make the establishment of littoral zone possible. A pilot plan of mapping basic littoral landform with LiDAR technology along west shore in the north part of Chang-hua county has been performed in 94 fiscal year.
IV. Hydrographic Survey Equipment：
Surveying and investigation are the two main works to obtain oceanic information. Surveying work includes water depth, seabed terrain, and hydrometric measurement. GPS, onshore microwave positioning system, LiDAR, heave compensator, motion sensor, gyro compass, side scan sonar, hydrometry meter, and others are used. Investigation data contain seabed characters, hydrologic features, sea state conditions, salinity, and temperature etc. with grab, dredge sampler, various corers, weather station, tide station, tide gauge, data collection buoy, and others.
In the past years, benefited the development of telecommunication and computer technology combined with GPS, maritime information for vessels have not been limited only the paper charts which were produced basing on the information of survey and investigation in the past tens years. The economic and safe navigation route choice can be flexibly made with the latest real time practical information. A flexible and real time update oceanic database has become essential for supporting maritime positioning, disaster simulation analysis, marine right and navigation safety ensuring, variety and prosperity of marine organism keeping, rational exploitation of fishery and recreation activities, and contiguously promotion of ocean science studies.