Aquaculture Engineering

Levelling - Methods of levelling

Unit 1- Surveying

Levelling

Methods of levelling
There are three methods of levelling.

• Barometric levelling
• Trignometric levelling
• Spirit levelling

Barometric levelling
Barometric levelling makes use of the phenomenon that the difference in elevation between two points is proportional to the difference in atmospheric pressure at these points. At a given point, the atmospheric pressure does not remain constant in the course of the day, even in the course of an hour. This method is therefore relatively in accurate.

Trignometric levelling
(Indirect levelling): Trignometric levelling is the process of levelling in which the elevation of points are computed from the vertical angles and horizontal distances measured in the field.

Spirit levelling or Direct levelling
It is the branch of levelling in which vertical distances with respect to a horizontal line may be used to determine the relative difference in elevation between two adjacent points.