Traditional surveys utilise the principles of triangulation, so that when the position and distance of two points are known, the position of the third point can be found by angular measurements. The position of the first point is established by using the existing datum from earlier surveys or by astronomical observations. In the case of Hong Kong, the datum point is at North Point. To set up a triangle, distances previously measured by metallic tapes had given way to modern electronic equipment which was easier to use and delivered more accurate returns.
To exemplify these advances made in survey hardware, one need to look no further than the innovative installations and instruments put aboard HMS Dampier during her years in Asia.
One of the earliest examples of post-war equipment on HMS Dampier was the Taut Wire Measuring Gear for Beacon-laying, which was installed in 1954 (before the advent of the electronic “hydrodist” in the 1980s, which could even more accurately measure distances).
In 1953, Dampier started using portable echo-sounding equipment in her survey work. The ship was also fitted with an underwater Asdic transducer under her hull to monitor underwater relief features.
Sonar equipment was employed to measure the depth of waters, especially near shallow shoals and sandbars, to ensure that there were no obstructions to shipping. Sonar could usually detect such hidden hazards with great accuracy.
To protect equipment and survey records, Dampier was fitted with an air conditioning unit in its survey chartroom in 1954, an uncommon fitting in those days.
During its survey of North Borneo (now Sabah) in 1956, Dampier started using a new Decca Chain and Track Plotter for distance and sounding measurements. The result of the survey was so successful that it established that the shorter route from Tawau to ports on the north-east coast could be taken safely. This route greatly benefitted log carriers loading timber from this area.
In 1957, two Range Decca Navigational Aids were installed to improve the accuracy of the position-fixing of survey datum points. With the new equipment, Dampier re-surveyed the Hong Kong harbour approaches in a series of exercises under the command of R.A.G. Nesbitt.
In 1960, Dampier was again in dock for refitting. New equipment included the installation of a new Survey Radar and Tellurometer equipment, which was developed in South Africa for the precise measurement of distances for surveying purposes.
Apart from the above-mentioned advances, after the Second World War, a radio position-finding system operating on hyperbolic principles, with transmitter stations onshore and receiving equipment onboard ships, was developed to track the position of a ship. This Decca Navigator System was also used on survey ships to easily fix positions of the survey area and its objects. The Decca equipment was later superseded by a Hifix system using portable radar equipment, which enabled a network of radio position lines over the survey area to be established to enhance efficiency and accuracy.[34]
When modern Global Positioning Systems, which allow satellites to accurately pinpoint positions on earth, and other advanced electronic hardware and software were available, most of the less sophisticated equipment became obsolete. When the Hydrographic Office was established in Hong Kong, a decision was made to leapfrog into the latest electronic technology by buying the most modern and cutting-edge instruments.
Notes:
- [34]Lt. Cdr. Geoffrey B. Mason: “Hydrographic work up to the 1980’s”, http://www.naval-history.net/xGM-Tech-HydrographicSurvey.htm, accessed 07/2012; George Stephen Ritchie, Challenger: the life of a survey ship, (New York: Abelard-Schuman), 1958.
Part 2 Chapter 4.6 - Advancement in hardware and progress of surveying techniques
