Lecture_12

# Lecture_12 - Speed of Sound in the Sea NS 212 Shep y Basics...

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Speed of Sound in the Sea NS 212 Shep

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Basics – back to first principles: It is accepted that we use acoustics (changes in pressure) as a primary sensor system undersea What’s wrong with other methods? Light? Excessive attenuation Radar? Excessive attenuation (The gradual loss in intensity of any kind of flux through a medium) There’s another method used as a localization tool called magnetic anomaly detection (MAD) which we will discuss later
Basics – back to first principles: Acoustic energy also travels in wave form as a pressure wave H L H L H L

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Principles: Equivalent mathematical relationships to EM energy: and where This is different! P is a function not only of time, but also of distance from the source! r = distance from source, t = amount of time since
Principles: P measures the maximum amplitude of the sine wave Which represents the maximum pressure excursion above and below the static/hydrostatic pressure that exists in the fluid at the location of the wave train

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Measurement units Note that we are now using pressure (Pa) instead of electric field strength (W) A sonar system’s “receiver” is thus physically measuring pressure Instead of using the “peak” value of pressure, however, the system processes the average value as compared to the ambient pressure level Mathematically, we express the average value as the root mean square (RMS) for a periodic function (in reality, electronics--radar systems-- also are using “average” power values though we have up until now ignored this distinction)
Measurement units

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• Spring '14
• Sonar, sound speed profiles

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