Types of hydrographic soundings

1. Hydrographic surveying is branch
of surveying which deals with the
measurements of hydrographic
bodies or water bodies.

2. Sounding
• Sounding in hydrography are similar to reduced level in
topography
• Provides necessary data to represent underwater surface
conventionally on plan or chart
• Defined as depth measured below the water surface of water
body.

3. Range :
• A range or range line is the line
along which soundings are made
• These are usually fixed
perpendicular to the shore line
• And parallel to each other
Shore signal:
• Each range line is marked with
two signals
• The signals are usually wooden
tripods with a white and
coloured flag on top

4. Equipments Soundings
The following equipments are used for measurement of
sounding
• Sounding boat
• Sounding rods or poles
• Lead Lines and sounding chains
• Sounding Machine
• Fathometer

5. • It should be stable
• Should have sufficient space to accommodate 3 persons
• The motor should have adequate control both for low speed
and rough waters
Sounding boat

7. Sounding rods or poles
• Usually 25-75 mm in diameter
• 3-5 meter long timber rods are used for shallow waters
• To facilitate plunging, the rod is weighted with lead at the base
• The rod should be light but stiff enough to prevent bending

8. Lead lines
• It consists of a graduated line or
chain to which a lead is attached
• Made with cotton or hemp
• Under ordinary tension and when
wet should not change in length

9. Echo Sounding Machine
• Also known as fathometer.
• Used when depth of water is too
much
• It measures the depth below the
boat on which it is installed
• It works on echo property of sound
• The sound waves emitted at the
surface of water are recorded back
after these return from the under
water surface
2D =Vt Where,
V= velocity of
sound waves in
water
t= time of travel

10. Methods of Locating Soundings in
Hydrographic Surveying
• The 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:
1. Conning the survey vessel
2. Observations with theodolite or sextant
3. Theodolite angles and EDM distances from the shore
4. Microwave systems

11. 1. Sounding by Conning the Survey Vessel
• 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

12. Location by Cross Rope
• A single wire or rope stretched b/w
2 supports A & B on opposite banks
• The width is divided into number of
segments
• And tags are attached at division
points
• Distances are marked from a
reference tag, called 0 tag.
• The boat is rowed to a point a1
below the tag no.1 and sounding is
taken
• Similarly other points are located
Suitable in narrow river and narrow lakes
and harbours.

13. Location by Range and Time Interval
• The sounding boat is rowed from the
shore near point A and rowed along
the range line
• After some time the boat attains
constant speed from a
• A sounding is taken at point a1, and
the time of observation is noted
• Knowing the speed of boat and time
interval distance aa1 is calculated
• Likewise, soundings are taken at points
a2, a3 etc.
• And time of observations are noted
• Thus distances of the various sounding
points a2, a3, etc. are determined

14. 2. Observations with Theodolite or Sextant
• Theodolite or sextant is used to measure angles in surveying.
• In this method, the sounding is located by measuring angles.
• These are the following methods for locating sounding
• 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

15. Location by Range and One Angle from the shore

16. • There are four range lines AAI, BBI, CCI and DDI.
• The theodolite is set up at the station BI for locating points on
the range line AAI.
• The theodolite is oriented along BIAI.
• Let x1 be the perpendicular distances of the point B from A.
• The sounding boat is rowed along the line AAI.
• The first sounding is taken at a1 and the corresponding angle is
measured as α1
Tan α1 = AIa1/x1
AIa1 =x1(Tan α1)

17. Continue..
• Like wise, the other points a2,a3 etc. are located on the range
line AAI.
• Now, the instrument is shifted to the station CI.
• The boat is rowed from a3 to point b3.
• The horizontal angles of the points b3,b2,b1 from C are
measured.
• Thus the points are located.
• This method is quite accurate and convenient.
• It is mostly used in practice.

18. By Range and One Angle
from the boat
• For locating sounding points on the
range line AAI, a signal is fixed at point
B on the range line BBI.
• The sounding boat is rowed along the
range line AAI to the sounding point
a1 and the angle Aa1B =α1 is
measured with nautical sextant
mounted on the boat
The distance Aa1 is given by,
Tan α1=d/Aa1
Aa1= d/Tan α1
Likewise the points a2,a3 etc. are located
Now the signal is fixed at point C, the
boat is rowed along range line BBI and
the sounding points b1,b2,b3 are
located.

19. Location by Two Angles form the Shore
• This method is used when it is not possible to keep the
sounding boat on a fixed range line.
• The method requires 2 theodolites
• The instruments are setup at two known stations A and B
on the shore line

20. Location by Two Angles
form the Shore
• When the sounding boat is at P1, whose
location is required, horizontal angles at
both the instruments measured as α1
and α2.
• The time at which the sounding is taken
should be noted.
• The distance d between A and B is also
measured.
• The co-ordinates of point P1 may be
computed from the relations:
• X = d Tan α2/(Tan α1 + Tan α2)
• Y= d Tan α1.Tan α2/(Tan α1+ Tan α2)

21. Location by two angles
from boat
• In this method the location of
sounding is made by measuring
two angles α1and α2
simultaneously with a sextant from
the sounding boat at P to 3
prominent signals A, B and C.
• The precision is poor when the
point P is near the circumference
of the circle passing through A, B
and C.
• If stations A, B and C are on a
straight line or if point B is nearer
to the boat P than points A and C,
the location of P is accurate.

22. Location by One
Angle from the
Shore and One
Angle from Boat

23. Continue..
• In this method, two points A and B are selected on the shore.
• The point A is the instrument station and point B is the shore signal
point.
• P is the sounding point which is to be located.
• When the boat is at P, the angle α is measured with the theodolite
at A and angle β is measured at the boat with a nautical sextant.
• Knowing the distance d between A and B the position of P can be
determined from its coordinates x and y.
• X=[ d sin (α + β)/sin β ].cos α
• Y=[d sin (α + β)/sin β ].sin α

24. Location by
Intersecting ranges
• Two sets of intersecting ranges are
shown one set perpendicular to
the shore and the other set
inclined to the shore.
• To locate the sounding point a1,
row the boat to the point where
the ranges AAI and CBI intersect.
• The signals are fixed at points B,
BI,C, CI etc.so that the points of
intersection can be located by
sighting.

25. Location by Tacheometry

26. • The method is very much useful in smooth waters.
• Three lines AAI, BBI, and CCI are shown.
• The Tacheometer is setup at station AI and oriented along AAI.
• A levelling staff is held vertically on the bottom of the sounding
boat.
• The boatman rows the boat along the range line from shore to
a1.
• When the boat reaches the point a1, a stadia reading is taken
on the staff and a sounding is also taken.
• The horizontal distance between the instrument station and the
boat is calculated by

27. D=(f/I) S+(f + d)
S = staff intercept
I= stadia interval
f= focal length of objective
d= distance of vertical axis from optical centre of objective

28. 3. Locating Sounding by theodolite and
EDM Distances from Shore
• In this method, EDM and Theodolite are placed on
the shore in fixed positions.
• From this set up, the reflector placed on the boat
is targeted and point of sounding is located.
• This method is more accurate when the water is
still.
• This is one of the modern methods of fixing
sounding vessel.

29. 4. Location of Sounding by Microwave Systems
• In this method, a device called Tellurometer is used which
contains three units’ namely master unit, remote unit and
master antenna.
• Master unit is fixed to the boat and other two units are located
on the shore at two shore stations.
• The distances are measured from boat to the shore stations
using micro waves produced by tellurometer.
• Now from all these known distances the antenna produces the
two sets of range information. Tellurometer is useful for
distances up to 100km from the shore.