What is bathymetry?
Bathymetry is the science of measuring the depth of water
in ocean, riverine or lake environments.
What kind of information can you get from bathymetry?
Just like the surface of the land isn't always completely flat.
The surface of the sea floor is full of various features like reefs,
ripples, mountainous ridges, deep canyons and even shipwrecks.
The bottom of the ocean is also very dynamic, meaning it's constantly changing
Bathymetry data provide scientists not only with a depth measurement,
but also a picture of what the sea floor looks like.
This can provide information about current and past conditions,
what kind of substrate or the material that exists,
and if there are any hazards for vessel navigation, among other things.
How do you collect bathymetry data?
Measuring water depth is not
a new concept, but the way we do it has evolved over time.
Historically, scientists would lower a lead weight attached to a rope over
the side of a vessel to record the depth of water.
Today we use active sonar
or sound navigation and ranging.
A transducer emits a pulse of sound into the water column,
which then bounces off the sea floor
and then returns to the transducer just like an echo.
The time it takes for the sound to travel through the water column is recorded
and then calculated to provide a depth measurement.
Scientists at the US Geological Survey St Petersburg Coastal & Marine
Science Center primarily use two types of sonar transducers
single beam echo sounders and multi-beam echo sounders.
A single beam transducer repeatedly emits
a single pulse of sound directly beneath the vessel,
providing a single depth measurement along the traveled track line.
A multi-beam transducer
repeatedly emits hundreds of pulses of sound
in a fan-like fashion beneath the vessel, providing a large swath
of depth measurements perpendicular to the vessel's track.
How do you analyze or interpret what bathymetry data means?
After the survey vessels return to the dock,
the data acquired is imported into a suite of special computer programs
which allow scientists to analyze and interpret the data.
These programs perform all the necessary calculations to assign each pulse of sound
emitted from the transducer a depth measurement or sounding.
These soundings can represent the seafloor, a feature
on or above the sea floor, or anything within the water column
that may have blocked the sound from reaching the bottom.
When all the soundings are put together, scientists can begin
to see what the sea floor and associated environment looks like
many times, with the use of high resolution multi-beam data,
The picture that is developed can even provide insight
into habitat types, such as seagrass beds or reef structures.
So why is this work important?
Our oceans, rivers, lakes and waterways
make up a large portion of the Earth's surface, but
only a small portion has been mapped with enough detail to be useful.
Vessels of all sizes need to know the water depth of the areas
where they're navigating so that they can travel safely from port to port.
Fisheries industries and fisheries managers need to know
where specific habitats are located, which harbor certain species
and renewable energy sources such as offshore wind infrastructure,
need to ensure that they can establish systems safely and securely
Here at the USGS St Petersburg Coastal & Marine Science Center,
We are using bathymetry data to map
changes in barrier islands and nearshore environments.
This allows our scientists to better understand the seafloor
and the associated environment, recognized changes
and provide predictions about how the seafloor,
coastal environments, and coastal hazards may change in the future.