Popular Science QA——Hydrographic Survey

1. What is hydrographic survey?

Hydrographic survey is the science of measurement and supervision of marine waters and subaqueous relief for the purpose of safe navigation of vessels and marine conservation. It applies to survey of marine waters, as well as that of lakes and rivers, which is collectively referred to as hydrographic survey or waterway survey by several nations. Measurement of the conducted water regions can be compiled into navigation chart. Initiated from hydrographic surveying, marine survey extends itself to the aspects of marine geodetic survey, submarine topography survey and other marine special survey.

In China, hydrographic survey and chart cartographic are collectively known as “Marine Surveying and Mapping”.


2. What hydrographic survey does? What are its apparatus?

Hydrographic survey deals with a wide variety of subjects, of which strong emphasis is placed on positioning survey, bathymetric survey, sweeping survey and tide survey, as well as bottom characteristics sampling.


(1) Positioning apparatus: Satellite Positioning System (GPS/Beidou navigation and positioning/GLONASS), Theodolite and Total Station;

(2) Bathymetric apparatus: Single-Beam Bathymeter, Double Frequency Detector, Multi-Beam Bathymeter;

(3) Sweeping survey: Side Scan Sonar System,(flexible/fixed) Sweeping System at definite depth;

(4) Tide survey: Water Gauge, Pressure Tide Gauge, Float Tide Gauge, Floating Tidal Current Meter, Doppler Tidal Current Meter;

(5) Bottom Characteristics Sampling: Bottom Sampler.


3. How to conduct bathymetric survey?

Traditionally, survey of bathymetry is made directly with a sounding rod or a hand lead. Modern bathymetric survey is generated to measure the depth with the principle of echo: sounding apparatus transmits and receives acoustic wave, then the distance between a transducer of sounding apparatus and water bottom can be calculated by dividing the result of a time difference between a timing of radiating a sound wave and a timing of receiving the sound wave multiples the velocity of an acoustic wave in water by 2; the velocity of an acoustic wave in water is about 1500 meters/second which may alters with the differences of temperature, water salinity and depth, resulting the necessity of determination of sound speed in the measurement region. Airborne Laser Bathymetry can be conducted in a relative clear water region.

The information of chart water depth refers to the vertical distance between a certain point in the water and sounding datum. As a result, besides field survey, water depth can be figured out until the completion of acoustic wave velocity correction, location and slant distance rectification and draft amendment.


4. How to detect submerged obstructions?

Submerged obstruction refers to various objects that affect maritime navigation which typically indicates wreck or man-made sinker. Such shallow water spots or regions as reefs under water or shoals are referred to as shoal zones or shoal waters.

The most frequently used apparatus to detect submerged obstructions is side scan sonar which is a strip map overlap survey method, generally through the method of capping by lateral line strip by strip and gradually approaching obstructions; once the suspected obstruction is discovered, Multi-Beam Bathy meter will accurately measure it, if necessary, divers or Autonomous Underwater Vehicles will submerge to survey it.


5. What is Autonomous Underwater Vehicles (AUV)? What does it comprise?

The scientific name for Autonomous Underwater Vehicles (AUV) is Remotely Operated Vehicle (ROV), which is a type of robot for hazardous environment, having the ability to dive under water as human’s replacement to complete certain operation, known as submersible. AUV have extended to be a major tool to explore marine, as a result of the harsh and dangerous underwater environment and human being’s limited ability to dive. AUV consists of two major types, Remotely Operated Vehicle (ROV) and Underwater Unmanned Vehicle (UUV), the former one has three types including underwater self-propelled type, towing type and crawling type on the submarine structure.

Remotely Controlled Vehicle is composed of surface facilities and submarine facilities (the former one includes operation console, cable winch, dipping equipment and power supply system, and the latter one includes repeater and the main body of submersible). The main body of submersible (see Figure) moves under water by propeller which is equiped with various items of eclipse equipment (video, camera and spot light) and operation apparatus (manipulator, cutter and washer).


6. What is chart? And what is navigation chart?

Chart, a type of map, is used to demonstrate charting phenomenon in marine regions. It is typically divided into general chart and special chart:

1) General chart tends to be rapidly developed which involves chorography of marine area and relief map of the ocean.

2) Special chart contains military area map, submarine map and yacht map.

Navigation chart belongs to special chart. As a major chart constantly and widely-used type, however, it is listed as a separate category customarily. In a narrow sense, chart refers to navigation chart.


7. What is the Electronic Charts (EC)?

The definition of Electronic Charts (EC) is relatively complicated. Electronic Charts (EC) contains electronic display and applied chart system.

Electronic Charts (EC) officially refers to Electronic Chart Display and Information System (ECDIS), including applied system of EC and Electronic Navigation Charts (ENC). Both hardware and software of ECDIS shall comply with relevant international standards. ENC, an equivalent of paper chart, shall be certified by national organization.

A simplified ECS, also called EC, has the basic functions of ECDIS and is used as the auxiliary system in navigation, though hasn’t been certified so far.

The charts, which haven’t been certified by national organization or been used in navigation, can only been regarded as digital chart.


8. How to correct the charts and electronic charts?

Since the changeable navigation environment, widening channel, movements of navigation mark, appearances of obstructions, regional alternation as well as above-water and underwater activities need to be manifested on the charts, the chart publication and distribution departments, such as China MSA and maritime department of navigation and safety, shall periodically release announcements including corrected charts and data. On the receipt of such announcements, the corresponding paper charts must be labeled accordingly, and the electronic chart will be corrected automatically by ECDIS.


9. What is the earliest chart in the world?

Charts are used to direct the eastern and western navigators to explore the new world, and become more scientific and reasonable through navigating practices. These valuable charts have been preserved until now so that people in modern times are fortunately granted a glimpse of them. However, only some of these charts are recorded by words and most of them disappeared throughout the course of history.

1)The most ancient world map

Babylon Map carved on the ground

It is known as the most ancient world map and was found in the 7th B.C, reflecting Babylonians’ imagination and horizon of the world. Babylon is located in the center of world with the Euphrates and the Tigris passing through and flowing into the Persian Gulf. The surroundings are covered with miseries symbolized by curves. The small rings on the inner circle represent the cities and regions, and the three triangles on the ex-circle represent the ocean island on which creatures once lived according to the legend.

2)The most earliest coastline map in China

Tomb map in Han Dynasty in Mawangdui

Excavated from Mawangdui Tomb in Hunan province, the tomb map in Han Dynasty in Mawangdui, also called topographic map, was painted by several colors on silks in 168 B.C. With south at the top, north at the bottom, east at the left and west at the right, the map manifested the south gulf of the estuary of Pearl River, which is known as the earliest coastline map in China.

3)The largest and most ancient world map in China

Universal Map of Great Ming Dynasty

Some parts of China land were painted on the foundation of Zhu Siben’s map, while the

African, European and South-east Asian parts were finished according to Li Zeming’s map. India and other regions may take other geographic references as an example.

4)The largest navigation chart in the Middle Ages

Mauro Map

Mauro, the Venetian map maker, painted this circular world navigation chart on the ship’s skin in 1459 A.C., among which the information about Asia came from Travels of Marco Polo. Equipped with this map, the Portuguese navigators had courage to circumvent the Africa.

5)The earliest map directing independently navigation in China

Zheng He’s Nautical Chart

Zheng He’s Nautical Chart, adopting China traditional painting style, were labeled seven navigating routes during Zheng He’s voyage to the west. The landmarks, including mountains, islands, bridges, temples and cites, were painted vividly. The major countries, states and counties were marked by red boxes. This map recorded about 530 places and over 50 navigating routes of the fleet.


10. What is the future of hydrographic surveying and chart mapping?

In the information age, hydrographic surveying and chart mapping present new characteristics: from manual and mechanical operation to digitization and automation, from paper publication and post circulation to network services.

With the advent of E-navigation times, traditional hydrographic surveying will turn into a way to collect and determine all the elements concerning the navigating security, while chart mapping will provide all the navigating information through various channels and forms.