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Intro to Hydro survey part 2.pptx
- 1. Speed of Sound •Speed of sound – Factors affecting speed of sound through water. – Sound Velocity Profile • Reflection • Transmission loss 1 Hydrography Branch National Mapping and Resource Information Authority LTJG KERWIN C FERRER ENS DIONESIO C GATO JR Hydrographic Survey Officers
- 2. Depth = (T)(c)/2 Tis sound wave travel time. C is the speed of sound. 2 Hydrography Branch National Mapping and Resource Information Authority
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- 7. Speed of Sound •Sound propagation through the water column is affected by: – Density – Pressure • Density is affected by: – Water salinity – Temperature 7 Hydrography Branch National Mapping and Resource Information Authority LTJG KERWIN C FERRER ENS DIONESIO C GATO JR Hydrographic Survey Officers
- 8. Speed of Sound •Pressure = Speed • Salinity = Speed • Temp. = Speed Sound Velocity Profile
- 10. Sound propagation inhomogenous water
- 11. Sound propagation invarying water column
- 12. Measured depth Actual depth Result isan error in measured depth!
- 13. Solution for BathymetricSurveys • To obtain the actual depth of the seabed, bathymetric system must know the speed of sound propagation for each water column in the survey area. • Actual Sound Velocity Profile of the survey area must be determined. 13 Hydrography Branch National Mapping and Resource Information Authority LTJG KERWIN C FERRER ENS DIONESIO C GATO JR Hydrographic Survey Officers
- 14. Solution for BathymetricSurveys • Surface layers – water temperature is the dominant component in SV • Deep-sea layers – pressure dominates. 14 Hydrography Branch National Mapping and Resource Information Authority LTJG KERWIN C FERRER ENS DIONESIO C GATO JR Hydrographic Survey Officers
- 15. Acquiring SVP • Conductivity, Temperature,Depth (CTD) sensors. • Expendable BathyTermograph (XBT) 15 Hydrography Branch National Mapping and Resource Information Authority LTJG KERWIN C FERRER ENS DIONESIO C GATO JR Hydrographic Survey Officers
- 16. • Conductivity, Temperature, andDepth (CTD) Sensor • It measures conductivity, temperature and depth. • May contain additional sensors (i.e. light sensor, water sampling).
- 17. CTD sensors are cast downwhen the vessel is stationary.
- 18. CTD cast maylast an hour or more depending on depth.
- 19. CTD cast for depthof 2 km is about 1.5 hours.
- 20. CTD casts are conducted dependingon the nature of survey area.
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- 22. • Uses time-of-flightsound velocimeter. • Also measures pressure. • Can only acquire data when vessel is stationary. • Usually used for determining SVP of shallow areas. Smart SV&P
- 23. • Expendable BathyTermograph (XBT). •For determining SVP of water surface. • Not accurate for areas with high variation of salinity.
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- 26. Reflection of soundfrom the seabed transmit return backscatter Echo
- 27. • Composition of seabedaffects the strength of returning sound waves. • Major factor is the grain size. NOS Hydro Manual, 1981
- 28. Reflection of soundfrom the seabed transmit return backscatter
- 29. Reflection of soundfrom the seabed transmit Concrete backscatter return
- 30. Transmission Loss • SoundEnergy is transformed into heat while travelling through the water column. This phenomenon is called ATTENUATION.
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- 33. 2/12/2024 From Dr. LarryMayer, CCOM-UNH High frequency multibeam sonar Deep sea
- 34. Take into considerationsound frequency when planning for a survey.
- 35. High Frequency MultibeamSonar • 40 to 200 kHz • Experience high attenuation (energy loss) in the water. • Suitable for shallow areas that requires detailed image of the seabed.
- 36. 2/12/2024 From Dr. LarryMayer, CCOM-UNH High frequency multibeam sonar Shallow sea
- 37. Low Frequency Sonar Whalestake advantage of low frequency waves for: - Locating food - Communicating with other whales over long distances.
- 38. Low Frequency MultibeamSonar • 3.5 to 12 kHz • Low attenuation (energy loss) in the water. • Suitable to use when surveying deep areas. • Less detailed as compared with high frequency sonars.