Instrumentation Flashcards
Name some technological requirements we need to consider
Why long term?
- Temporal variations / trends
- Duty cycles versus continuous?
- battery life and storage compromises?
- hard to build tech to say current weather state
What bandwidth?
- Biological receptors
- Other users (sonar)
What is the dynamic range need?
- What do you want to listen to?
- how loud or how quiet?
How good does noise performance need to be?
- How does noise effect your dynamic range?
What do you want to do with data?
- Signal processing / storage etc.
- handling data
- machine learning?
Could have
- instead of 1 system that does all
- 2 systems in parrallel?
- low energy clips high & high energy clips low with overlap
What do you do if you have a dynamic range?
Dynamic range –> to include everything then >100dB
Potential Solutions
-Band limited (avoid low and high frequencies together)
- Multi-band (different gains different bands)
- Weighted band filters - filters need to be analogue
- Matched gains to environments (dynamic gain systems)
- Logarithmic gains
- bit resolution
What is the significance of signal to noise in detection and behavioural response?
SNR
- Higher SNR means stronger clearer signal relative to background noise
- easier to detect
- more accurate perception/ interpretation/ decision making
-Lower SNR
- decreased sensitivity
- increased errors
- reduced behavioural performance
e.g. At midnight when its quiet
- a loud noise is more startling than during the day in a crowd
- not always about amplitude
What is Platform noise?
unwanted/ undesired acoustic disturbances from a physical platform
source of noise
e.g.
moored systems, flow noise, cable strum, motion due to surface waves
What is Platform noise?
unwanted/ undesired acoustic disturbances from a physical platform
source of noise
e.g.
moored systems, flow noise, cable strum, motion due to surface waves
Potential solutions to platform noise
- Surface decoupled (bottom mounted, suppression systems)
- Drifting systems / towed arrays
- Anti-strum (vortex stripping)
- Hydrodynamic shields - flow shield - sonar is at front of ship - for full effect sonar needs to be in fluid that impedance matches water
- Surface spreading
- Directional arrays
Name some measurement challenges
Harsh environments
– fast flow and tidal surges, severe wave actions …
High background noise
– high amplitude background noise (correlated to device noise)
- renewables when operating make a lot of noise
Complex acoustic propagation and ambient noise conditions
– varying bathymetry, rocky sea bed, turbulent flow, bubbles sediment
transport….
Variety of device designs and individual sources
– multiple sources, possibly widely spaced, dependent on designs
Name some methods of measuring
Boat Based
* Fairly commonly used but can suffer from parasitic noise
Autonomous recorders
* Bottom mounted / decoupled from surface
* Flow noise lower
* Good for long term deployment
Drifting buoys
* Buoy drifts with currents
* Can reduce flow noise significantly
* Repeat deployment s needed
* Not long-term deployments
* Not fixed position
What is broadside position?
main radiation lobe is directly perpendicular to array axis
maximises radiation in perpendicular direction
What is end fire position?
main radiation lobe is directed along the array axis
maximises radiation in end fire direction
