19 - Transmission Loss and Prop Loss Curves

Question 1

Composition of Transmission Loss

3 types

Answer 1

• Spreading
• Scattering
• Absorption

Question 2

What is Passive SONAR?

Answer 2

The target puts out a specific amount of sound

Suffers one-way transmission loss; Source of sound = target’s noise

Transmission Loss (TL) = One way

Question 3

What is Active SONAR

Answer 3

SONAR transducer puts out a specific amount of sound

Suffers two-way TL; Source of sound = searching unit’s active SONAR

TL = Two-way; Multiply equation by 2 (send and receive)

Question 4

TL Equation for Spreading

Answer 4

• Sound spreads out
• Assume
• 2000m deep ocean
• Sensor @ 1000m depth

Two types:
- Spherical = 20logR; R < 1000m
- Cylindrical = 10logR + 30; R > 1000m

Two types: Spherical and Cylindrical

Question 5

TL Equation for Absorption

Answer 5

Process of converting acoustic energy into heat

May assume alpha (absorption coefficient) = 0 when f < 3kHz

Question 6

TL Equation for Scattering

Answer 6

• Sound reflects off foreign bodies in the water

Represented by Transmission Loss Anomaly (A)

Direction of propagation changes because of velocity change