🕑 Reading time: 1 minuteIn hydrographic surveying, sounding is the measurement of depth below the water surface. Sounding is most important for any water body to improve its navigable properties, to know about silting and scouring etc. Hydrographic surveying is branch of surveying which deals with the measurements of hydrographic bodies or water bodies.
Methods of Locating Soundings in Hydrographic SurveyingThe soundings are located by the observations made from the boat or from the shore or from both. There are four methods are there to locate the soundings by:
- Conning the survey vessel
- Observations with theodolite or sextant
- Theodolite angles and EDM distances from the shore
- Microwave systems
Sounding by Conning the Survey VesselIn this method, conning means keeping the boat at known course. This method is suitable for rivers, open sea up to 5 km off shore. The markers are fixed on the shore called as ranges along which vessel or boat is run. This method is again sub divided into two types as follows.
- Location by cross rope
- Location by range and time interval
Location by Cross RopeIn this method, a wire or rope with markings or tags at known distances is stretched across the channel. The starting point of rope at the shore is marked as reference point. Then using boat, the sounding at different distances of wire are determined by weighted pole. This method is more accurate. This is most suitable for rivers, narrow lakes and for harbors. This is also suitable for knowing the amount of material removed by dredging.
Location by Range and Time IntervalIn this method, the boat is positioned in range with two signals provided on the shore. Then, the boat is rowed at constant speed and time required to reach the instant of sounding is measured which gives the distance of total point along the range. This method is more suitable for less width channels or rivers. It is not so much accurate.
Sounding by Observations with Theodolite or SextantTheodolite or sextant is used to measure angles in surveying. In this method, the sounding is located by measuring angles. Here also, there are a lot of subdivided methods are there to locate sounding. They are
- By range and one angle from the shore
- By range and one angle from the boat
- By two angles form the shore
- By two angles from the boat
- By one angle from the shore and one angle from boat
- By intersecting angles
- By tachometry