Main methods of elevation control survey

The survey methods of elevation control include leveling, trigonometric leveling, barometric leveling and GPS leveling.

Elevation control survey is the control survey work of establishing elevation control network. Its task is to accurately measure the elevation of a series of ground control points with a unified elevation datum in the survey area, and provide elevation control basis for topographic mapping and engineering survey.

job description

Obtain the control survey of unified elevation in the whole country or a certain area. Mainly through the leveling network composed of leveling routes (that is, elevation control network) to reflect. China's national elevation control survey is divided into first, second, third and fourth leveling surveys. The first-class leveling is the backbone of the national elevation control network and the basis for studying vertical crustal movement and related scientific problems. The second-class leveling is attached to the first-class leveling ring, which is the comprehensive basis of national elevation control.

Third-and fourth-class leveling is to directly obtain the elevation of plane control points, which is used for topographic mapping and elevation needs of various engineering construction. The elevation of plane control points can also be determined by trigonometric leveling. In the elevation control survey of hydropower projects, in order to control the development and management of the whole river basin or river (reach), the horizontal route along the river or the ring network is generally adopted, and it is jointly measured with the national leveling points.

Measurement method

(1) height system in the survey area shall adopt the national elevation datum. When surveying in areas with existing elevation control network, the original height system can be used. When it is difficult to connect small measuring areas, the assumed height system can also be used.

(2) The methods of elevation measurement include leveling method, electromagnetic wave ranging trigonometric leveling method, etc. Common leveling methods.

Leveling method

Level markers shall be buried at all levels of leveling points. Benchmarks should be selected in places with hard soil to facilitate long-term maintenance and use. Wall leveling points should be selected on stable buildings, and the points should be easy to find and conform to the regulations.

In leveling, the smoothest and shortest connection holes should be selected to meet the requirements of less stations, fast observation and high accuracy. There should be no less than two leveling points buried in each hole, and it is advisable to place a level for joint measurement. When the hole spacing at both ends is greater than 1km, temporary leveling points should be added in the middle.