January 9 lecture Flashcards
What is the First reason why the ocean is difficult to study?
“Seeing”
Water is a more efficient absorber of electromagnetic radiation than the atmosphere, meaning that we cannot see most of the ocean Optically
Is radar and other oceanography instruments effected by the oceans ability to absorb electromagnetic radiation?
Yes, Radar and Sonar still use portions of the electromagnetic spectrum to examine the ocean.
What is the second reason why the ocean is difficult to study? ( 3 things included )
“Inaccessibility”
- We can’t breathe water
- The ocean is very deep with the avarge depth being almost 4km
- Most of the ocean is remote from the sea surface
Why is it hard to sample deep ocean water?
In order to take a sample of deep ocean water you must lower an instermant on a wire to reach the depth, and this can take hours.
Why are Ships a reason why studying the ocean is difficult?
Sea ships are slow, moving around 20km/hr, meaning that it takes long periods of time to reach distant parts of the ocean.
What is the cost of one day of operation for a Deep ocean ship?
$40,000
What is the third reason why it is difficult to study the ocean?
“Pressure”
- Ocean pressure incenses by 1-atm every 10m you descend
What would the atmospheric pressure be at 110m depth?
12x the pressure than at sea level.
Why are submersible instruments a reason for why it is difficult to study the ocean?
They need to be disgined to survive great amounts of pressure, thus meaning that they cost lots of money.
What is the Fourth reason for why it is difficult to study the ocean? ( kinda three things in one )
Conductivity/Corrosion/Fouling
How does conductivity affect how difficult it is to study the ocean?
Because sea water conducts electricity, it can cause short circuits to electrical equipment, meaning we need special water tight electrical items
how does corrosion affect how difficult it is to study the ocean?
Seawater is corrosive, Meaning that special metals must be used so that they do not rust or corrode.
What is fouling? and how dose it affect how hard it is to study the ocean?
It is when sea creatures grow on equipment.
This casuses difficulties for instruments with moving parts
What is the 5th reason why it is difficult to study the ocean?
“Wave motion”
The dynamic movement of the oceans surface.
How does wave motion affect how difficult it is to study the ocean? ( three things )
It causes problems with working on moving ships:
- Seasickness
- Deploying instruments
- Rapidly changing conditions
What was the original method for measuring Bathymetry?
You would let out rope with a weight on the end until it hit the bottom.
It was called Sounding
What unit was originally used to measure depth when sounding?
they used Fathoms = the length on a sailors outstretched arms defined as 6ft
shown with a tied knot every six feet to measure it
How was sounding adapted over time? What changes did they make?
The rope was later changed to piano wire with a weight at the end, deployed with a wench
What is the biggest problem with measuring bathynetry?
Determining when the weight hit the bottom.
Why is it hard to determine when the weight hit the bottom? ( two things )
- It can take multiple Km of line, and it can continue to pull after it has struck bottom.
- Currents can cause the weight to drift sideways increasing the measured distance.
What is echo sounding?
It is a method of measuring Bathymtery where you transmit bursts of 10-30 kHz of sound and listen for the echo of the sea floor.
How do you measure distance using Echo sounding?
2 x Distance = Velocity x time
What are the limitations of Echo sounding?
- Tracks are not well distributed
- Arvarges over some region of the ocean
Why is data collected from Echo Sounding usually inaccurate?
The sound cone spreads out the deeper it gets, and if the sea floor is uneven it will measure the average depth, thus making accurate readings unattainable.
What is Multibeam Echo sounding?
A modern Bathymetry measuring method, using multiple simultaneous sound frequencies to more accurately measure sea depth.
What is seabeam?
It is the first Multibeam Echo Sounder
maps sea floor strips of up to 60km wide.
What is Side Scan Sonar?
A device that can be towed behind a boat, that accurately measures bathymetric data
How can we use satellites to measure the seas topography?
The satellite measures the sea surface topography, can measure the hight of the sea surface up to 3- 6 cm accuracy.
how can satellites tell if there is an under sea mountain or crevasse.
Since rock is denser than water and heavier it has a higher gravitational attraction, the sea surface is slightly higher over these spots.
What is the reason behind how water is higher about undersea mountains
The undersea mountain is pulling water towards it, making it pile up over it, rising the sea surface.
