Hydrographic Measurements

Question 1

What environments can you map?

Answer 1

Intertidal
Coastal
Deep water

Question 2

What are the type of exploration techniques?

Answer 2

Light - LIDAR, video and photography and photogrammetry
Sound - Echo sounding - single beam, multi beam, interferometric sonar
Side scan sonar
Sub bottom profiling and seismic
Magnetics

Question 3

What geophysical characteristics can you measure?

Answer 3

Morphology - bathymetry
Sediment
Physical and chemical parameters
Habitats
Feature locations
Derived variables - slope, aspect, seabed rugosity, habitat patchiness

Question 4

What is the reason for mapping?

Answer 4

Industry survey
Exploration
Research question

Question 5

What affects mapping?

Answer 5

Budget
Time
Scale
Resolution

Question 6

Optical approaches?

Answer 6

Behaviour and properties of light
Light is an em wave
Depth limited
Only useful for seasurface measurements/shallow waters/instruments close to the seabed

Question 7

What is LIDAR?

Answer 7

Light imaging, detection and ranging
Measures distances to objects using reflections
Difference in laser return time and wavelengths are out together to produce a 3D image
Depth limited by water clarity

Question 8

Seabed imagery and Video?

Answer 8

Lens and sensor to translate light to images
Stills and video cameras deployed on frames
Need lights
Build up a sequence of images

Question 9

What is photogrammetry?

Answer 9

Build up a 3D image

Question 10

Acoustic approaches?

Answer 10

Send out pulses of sand and use the time it takes to travel back to calculate the distance and build up an image

Question 11

Sound sources and receivers?

Answer 11

Made for piezoelectric ceramic materials
Convert electrical energy into mechanical energy
Seismic sources and receivers vary

Question 12

Single beam?

Answer 12

Producer + receiver

High res depth measurements

Question 13

Multibeam?

Answer 13

More complete image
Mounted to surface vessels
Measure in swath
Right angles to direction of motion

Question 14

SideScan sonar?

Answer 14

Two beams either side of a tow fish
Sound reflects back and the intensity of the return is recorded
Harder surfaces - light areas strong return
Backscatter
Low frequency - low res - distance the energy travels is improved

Question 15

Sub bottom profilings?

Answer 15

Low frequency 
Aggregate surveys
Route planning
Glacial history
Hydrocarbon exploration

Question 16

Magnetics?

Answer 16

Measures magnetic field strength

Unoxidised iron - increases magnetisation