Bathymetry is the part of hydrology that is performed to measure and obtain depth values for the depth of water (from the surface to the bottom).
A hydrological survey is a survey to obtain water parameters, and this activity includes measurement, mapping, and visualization.
The results of the hydrographic survey can be used for various needs, including:
- Navigation and navigation safety.
- Determination of territorial boundaries or areas at sea.
- Laying of submarine cables and pipelines, as well as.
- Study of coastal dynamics and marine resource management.
Hydrographic Survey Configuration consists of:
- Positioning at sea and use of the reference system.
- Depth measurement.
- Tidal observations and binding to BM.
- Detailed measurement of the situation and coastline (for coastal mapping).
- Reference system.
Things that affect bathymetric measurements
To get the true depth value, many corrections must be considered. Each correction entered will have its effect on the depth value. Which affects the depth value:
The tidal phenomenon is a dynamic rise and fall of sea level. In this case, during the survey activity, the depth value recorded on the tool is not the actual depth value, but the depth value which is still affected by the tidal phenomenon. To get the true depth value, the generalization results must be corrected with tidal data.
- Static draft
The static draft is a measure of how deep the transducer is “submerged” in a body of water. The depth reading value obtained using the echosounder is the depth value from the transducer surface to the bottom of the water, therefore it is necessary to add a draft value.
- Dynamic Draft
Throughout the survey, with the condition of the moving vessel, the draft will vary
The burden of both goods on board and personnel onboard greatly affects the transmitter (sounder) attached to the ship. The more the load on the ship, the more the sounder will sink. The draft of this ship must be taken into account and can vary throughout the survey so that the depth value is calculated from the surface of the water to the bottom of the water.
We often see when the ship is traveling at high speed the bow (front) will be lifted more than the stern (back), this will affect the position of the sounder to be not perpendicular to the bottom of the water.
3. Vessel movement (Heave, Pitch, Roll)
Other factors such as weather will affect the movement of the ship during the sounding. The presence of waves and wind creates a dynamic draft and the position of the transducer changes.
4. Sound Velocity
Sound Velocity (SV) is how fast the acoustic wave propagates in the medium. In this case, the medium in question is water. The SV data is required in correction to get the true depth value.