- "Bathymetry" (as used within the
CMG InfoBank )
is the water depth relative to sea level.
- Depth values may be either negative or positive, but should all be understood to be negative.
- Elevations (topography) are the corresponding terminology for above sea level and are positive.
- For Information
Bank,
the specification of "bathymetry" also obtains "topography."
- Depths are almost always derived indirectly by measuring the time required for a signal to travel
from a transmitter, to the bottom, and back to a receiver.
- This travel time is then converted to a depth based on a variety of estimations of the signal speed
through the water column.
- This may vary based on salinity, temperature, etc.
- Unless specifically stated in the file, 1500 meters per second of time for a two-way
(surface-->bottom-->surface) travel-time is commonly used.
- Bathymetric information occurs in the
CMG InfoBank
in a variety of formats, including:
|
scattered
|
< Activity-ID
>.3## files containing time sequential information along ship tracks.
|
|
swath
|
extracted as files containing across-track depths (multiple depths at a given time).
|
|
gridded
|
evenly spaced information typically derived from the above information types
|
|
vector/polygon
|
bathymetry contours from either manual or computer interpretations of the above information types
|
|
analog
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physical records, usually electrostatic or photostatic rolls
|
|
metadata
|
information about bathymetric analog paper rolls, inventory of gear, deployment of gear, operation of gear,
magnetic tapes, and paper printer listings
|
- InfoBank bathymetric scattered data file names:
- InfoBank bathymetric metadata file names:
- The
<Activity-ID>.3## files do not include navigation.
- Navigation must be obtained from
<Activity-ID>.0## or
<Activity-ID>.6## files.
- Navigation should therefore also be extracted when you retrieve these files.
- A "time"
key is associated with each record for correlation with other scattered information datasets.
Before you can walk on water, you've got to know where the rocks are.
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