Cousin Island is on the World Geodetic System


“On behalf of MLUH, Survey Division, I would like to extend our sincere gratitude for your help and support in the Geodetic Control Survey. It was through your effort in assisting us that we achieved our objectives well on time,” Mr Hendrick Youpa from the Survey Division at the Ministry of Land Use and Housing (MLUH) said in a communique to Nature Seychelles after a team from the department recently completed their work on Cousin Island Special Reserve.

Geodesy is the science of accurately measuring and understanding three important properties of the Earth: geometric shape, orientation in space, and gravity field - as well as the changes of these with time.

 Cousin Island - view from up top photo by Martjin Hammers

Countries and organizations use geodesy to map the shoreline, determine land boundaries, and improve transportation and navigation safety. To measure points on the earth’s surface, surveyors assign coordinates (similar to a unique address) to points all over the earth. In the past, surveyors determined the coordinates of points by using earth-based surveying tools to measure the distances between points. Today, geodesists use space-based tools like the Global Positioning System (GPS) to measure points on the earth’s surface.

MLUH carries out these surveys in order to link Seychelles’ results to the global networks, World Geodetic System and International Terrestrial Reference Frame. Additionally, these local control points are important in current as well as future analysis. In other countries, such surveys are crucial for monitoring plate tectonic movements (shifts in the earth’s crust).

“We had a previous schedule of eight days in total to conduct the work. However, we managed to have other surveyors on board which meant extra equipment, therefore reducing our work to three days with a total of eighteen people scattered on different islands,” says Mr James Mainga, a Land Surveyor with MLUH.

 Cousin Island was a key point in the survey

Apart from Cousin Island, the MLUH team also conducted surveys on La Digue, Praslin, Curieuse, Round Island and Félicité.

“While designing the network for observation, the geometry for the field work observations was a significant factor,” Mainga explains. “Considering the geographic location of Cousin Island, it played a key role in enhancing the geometry on the western side of Praslin Island. As a result this will improve the accuracy of the results obtained.”

This is not the first time such a survey has been conducted on Cousin, according to MLUH records a survey was carried out in September 1975. Such surveys can be done every three to five years and sometimes even up to ten years. This varies from country to country with some countries actually needing to carry out such surveys monthly or annually if they have greater plate tectonic movements. Wear and tear of control points is also a key factor in determining how often surveys are done, as they require regular monitoring and maintenance.

“Although we are a small NGO we are always happy to work together with government departments in such work where the information is pertinent not only to Seychelles’ but actually, as in this case, the global data base,” says Dr Nirmal Shah, Nature Seychelles’ CEO.

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