The shortest definition for hydrographic survey is surveying water bodies. It deals with the measurement of physical characteristics of surface and subsurface water bodies, i.e. boundaries (X, Y coordinates) depth (Z coordinate), surface level (Z coordinate) as well as other measurements like flow velocity, sampling of river bed and suspended sediment materials. As it is important to be aware of the fact that, the quality of any study is only as good as the quality of the information gained through the data collected, and the influence of any error incurred during the measurements leads to limiting the accuracy of the study, a highly trained researchers and technicians equipped by up to date surveying equipments are responsible for the data collection. HRI developed surveying system that proofed high quality performance.
In the design phase, maps, aerial photographs and other pieces of information (e.g. results of previous campaigns) are used to define where and how the measurements will take place. It is always useful to have an inspection of the area to have the most up-to-date insight into the circumstances, to minimise the unforeseeable difficulties. The output of this phase is a measurement plan in forms of charts, time planning, personnel and budget estimates.
During the field work, the following measurements are taken and documented:
* positioning of surface objects (edge of water, pillars of bridges etc.; X, Y and Z coordinates);
*positioning of subsurface (under-water) objects (X,Y and Z coordinates) – water depth measurements;
*recording flow velocities.
The output of a fieldwork is the measurement data set, usually stored in digital format. It is frequently referred to as raw data.
After the data has been collected from the site the data processing stage then started to produce a day by day dataset in the form of:
1- A reference point data which is the raw data of the GPS units that fixed on the reference Bench Mark point.
2- A Bench marks data which is the raw data of the Fixed GPS units that identifying the position of these Bench Marks
3- Topographic data which is the raw data of the Rover GPS units that leveling the banks, the islands and the water-line.
4- Bathymetric data which is the raw data of the Rover GPS unit that equipped on the boat to identify the coordinates of bathymetric pass and the water depths data that collected from the echo-sounder during this pass.