Hydrographic surveying deals with mapping the configuration and features of water bodies like oceans, lakes, and rivers. Modern hydrographic surveying utilizes various technologies to map depths, shorelines, tides, currents, and other physical properties. This data is used to create navigational charts and for coastal engineering projects. Key equipment includes multibeam echosounders, lidar, and autonomous underwater vehicles to efficiently collect substantial bathymetric data, which then undergoes extensive post-processing and correction before being compiled into navigational charts and maps.

2.  Hydrographic surveying deals with the configuration of the bottom
and adjacent land areas of oceans, lakes, rivers, harbors and other
water forms on Earth.
 In strict sense, it is defined merely as the surveying of a water area;
however, in modern usage it may include a wide variety of other
objectives.
- such as measurements of tides, current, gravity, earth magnetism,
and determinations of the physical and chemical properties of water.
(tides: periodic rise and fall of the sea level)
 The principal objective of most hydrographic survey, is to obtain
basic data for the compilation of nautical charts with emphasis on the
features that may affect safe navigation. (nautical – Relating to
shipping)
 Also used for acquiring the information necessary for related marine
navigational products and for coastal zone management, engineering,
and science.
(coast - shore of a sea or ocean)

3. Importance of Hydrographic Surveying:
Uses of hydrographic surveying are given below:
1. Depth of the bed can be determined
2. Shore lines can be determined
3. Navigation Chart Preparation
4. Locating mean sea level
5. Scouring, silting and irregularities of the bed can be
identified
6. Tide measurement
7. River and stream discharge measurement
8. Massive structures like bridges, dams harbors are
planned.

7. The applications of hydrographic surveying:
1. Dock and Harbor Engineering
2. Irrigation
3. River Works
4. Land reclamation ( is the process of creating
new land from oceans, seas, riverbeds or lake beds)
5. Water Power
6. Flood Control
7. Sewage Disposal

8. Hydrographic Surveyor Job
 Hydrographic survivor’s daily job is basically to check the
depths of the harbor and ensure the declared depths (the
minimum declared depths are depths safe for shipping). He
then produces charts for the pilots to bring the shipping in
to the harbor.
 The information obtained from hydrographic surveying is
required to bring up nautical charts which involve:
1. Available depths.
2. Improved Channels.
3. Breakwaters (a barrier built out into the sea to protect a
coast or harbour from the force of waves).
4. Piers.
5. The aids to navigation harbor facility.

9. Steps involved in starting a hydrographic survey
 Reconnaissance
 Locate Horizontal Control
 Locate vertical Control

12. Modern method:

13. Sounding technique for hydrographic survey:
 The measurements of depths below the water surface are called Soundings.
 Old technique but still in use
 The objective of making soundings is to determine the configuration (or relief) of
the bottom of the body of water.
 This is done by measuring from a boat the depths of water at various points.
 This operation of sounding is most commonly required in hydrographic surveying
and is similar to that of levelling.
 Soundings are required for
(i) the preparation of charts for navigation,
(ii) the determination of the quantity of the material dredged, and of the area where
the material is to be dredged or where the dredged material may be dumped and
(iii) the design of works such as break waters, sea walls, wharves etc.
 Since the elevation of the water surface which is taken as level surface of reference
is continually varying in tidal waters, it is necessary to ascertain the water level at
the time each sounding is made by taking tide gauge readings at regular intervals of
time during the period of soundings so that the observed sounding can be reduced to
the datum.

14. Equipment required for Sounding:
Sounding boat
Sounding rods/poles
Lead lines
Sounding chain, sounding lead
Sounding machine
Fathometer/ Eco sounding device

25. Modern Devices used in hydrographic survey:

27. Altimetry satellites basically determine the distance from the satellite to a target surface by
measuring the satellite-to-surface round-trip time of a radar pulse. However, this is not the only
measurement made in the process, and a lot of other information can be extracted from altimetry.
The magnitude and shape of the echoes (or waveforms) also contain information about the
characteristics of the surface which caused the reflection. The best results are obtained over the
ocean, which is spatially homogeneous, and has a surface which conforms with known statistics.
Surfaces which are not homogeneous, which contain discontinuities or significant slopes, such as
some ice, rivers or land surfaces, make accurate interpretation more difficult.

28. And bathymetric chart is a type of isarithmic map (An isarithmic map is a type of
Thematic map that represents a continuous field using line and/or region symbols to connect
places of similar value. It is sometimes called a heat map) that depicts the submerged
topography and physiographic features of ocean and sea bottoms. Their primary
purpose is to
1. Provide detailed depth contours of ocean topography
2. Provide the size, shape and distribution of underwater features
3. Provide details about temperatures, elevations, rainfalls, barometric pressures,
depth to bedrocks and other topographic characteristics.
Bathymetry: is the study of underwater depth of lake or ocean floors.

30. Modern survey cont. (Summary):
 In suitable shallow-water areas lidar (light detection and ranging) may be used.
Equipment can be installed on inflatable craft, such as Zodiacs, small
craft, autonomous underwater vehicles (AUVs), unmanned underwater
vehicles (UUVs) or large ships, and can include side-scan, single-beam
and multibeam equipment (see figures in next slides). At one time different data
collection methods and standards were used in collecting hydrographic data for
maritime safety and for scientific or engineering bathymetric charts, but
increasingly, with the aid of improved collection techniques and computer
processing, the data is collected under one standard and extracted for specific use.
 After data is collected, it has to undergo post-processing. A massive amount of
data is collected during the typical hydrographic survey, often several soundings
per square foot. Depending on the final use intended for the data (for
example, navigation charts, Digital Terrain Model, volume calculation
for dredging, topography, or bathymetry) this data must be thinned out. It must
also be corrected for errors (i.e., bad soundings,) and for the effects
of tides, waves/heave, water level and thermoclines (water temperature
differences). Usually the surveyor has additional data collection equipment on site
to record the data required for correcting the soundings. The final output of charts
can be created with a combination of specialty charting software or a computer-
aided design (CAD) package, usually Autocad or arcGIS.

36. Bathymetric map for a bridge over a river

37. Bathymetric map preparation: ArcGIS is best software for such maps