1. Sound Transmission Signal degradation in frequency and time domains Boundary effects and density gradients Noise Ranging Signal optimization

2. Time-frequency perception Animal ears set the threshold frequency at which sounds are perceived in the time or frequency domain In each domain, transmission distortion can result from attenuation, loss of pattern and masking by noise Time domainFrequency domain Modulating frequency

3. Absorbtion depends on medium Absorbtion values: water = 0.008 dB / 100 m air = 1.2 dB / 100 m ground = 6 dB / cm

4. Absorbtion depends on frequency

5. Absorbtion depends on humidity

6. Scattering leads to frequency filtering

7. Frequency modulation resists distortion by scattering

8. Frequency transmission problem Varied thrushes produce tonal songs in mature oak forests. If the diameter of the trees is 1 m, which frequency will exhibit the greatest attenuation? 0.34 kHz or 3.4 kHz or 34 kHz Wavelengths = 1 m; 0.1 m; 0.01 m

9. Signal propagation near boundaries Boundary waves can occur if the signal is absorbed and reradiated by the second medium or a surface wave propagates. This only occurs when impedance of medium 2 > impedance of medium 1

10. Boundary effects

11. Transfer functions f d = the minimum frequency where direct and reflected waves cancel at receiver Reflected waves cancel direct waves when the reflection is out of phase Notch ranges from 300-800 Hz. Few ground animals use it.

12. Temperature gradients cause refraction Sound velocity increases with temperature High to low temperature gradients bend sound back toward low temperatures and v.v. ForestDesert

13. Wind can refract sound Winds can alter sound velocities by 5-10%

14. Density gradients in water from temperature, pressure, or salinity cause refraction Ocean SummerWinter

15. Background noise can mask sounds Forest Open ocean Pasture Coastal ocean

16. Vegetation causes scattering Low AM rates (below 10 Hz) resist reverberation in forests

17. Signal design is important for long range communication

18. Range of detection Detection range depends on amplitude at source and frequency If range information is needed, signals should incorporate features that degrade predictably with distance, i.e. wide bandwidth

19. Signal design and transmission distance

20. Signal design parameters Bandwidth Frequency Duration Modulation type and rate Location of sender and receiver Transmission medium

21. Optimal Signal Design

22. Adaptive signal design?

23. Sound transmission varies with habitat Sound travels further in water than air than ground FM signals resist degradation and can be detected in noise Lower frequencies travel farther Tonal signals travel farther because more energy is concentrated in one bandwidth AM signals are better in open environments