1What is one of the main tasks in hydrographic surveying?
Depth determination\
2What must water depths be referenced to for accurate bathymetric mapping?
The reduced datum\
3What is the learning outcome of Lesson 4.2?
Computing water depth with respect to the reduced level\
4What sounding equipment may be used in shallow areas around 5 meters deep?
A graduated rod or pole\
5How is depth determined using a graduated rod or pole?
Directly from the equivalent height of the water surface\
6What equipment may be used to determine depths in areas deeper than 5 meters?
A leadline\
7What is attached to the lower end of a leadline to keep it vertical?
A weight\
8What indicates that the leadline's weight has touched the bed?
A sudden release in weight is felt\
9What reading is recorded when using a leadline?
The graduation at the water surface\
10What method is usually adopted for deeper areas such as seas and river estuaries?
Echosounding\
11What principle is used in echosounding to determine water depth?
The time interval between the transmitted pulse and the reflected pulse, together with the velocity of sound in water\
12What two quantities are used to determine depth using an echosounder?
The time interval and the velocity of sound in water\
13What is the basic formula for depth determination using an echosounder?
$h=\frac2$\
14What does $h$ represent in the echosounder depth formula?
The water depth\
15What does $v$ represent in the echosounder depth formula?
The velocity of sound\
16What does $t$ represent in the echosounder depth formula?
The time interval between transmission and reception of the signal\
17Why is the measured inclined distance different from the actual depth?
The transmitter and receiver are installed separately with a small horizontal distance\
18What is the formula for correcting the inclined distance to obtain actual depth?
$h=\sqrt