Visualizing the Field of Bathymetry

Intro:

Soooo...Over the course of quarantine I've been getting really into fish. As well as anything that has been lurking in our oceans. I thought a good intro topic to the oceans, would be to cover the physics of our ocean floor. There are currently a lot of really cool techniques that are being used to visualize underwater surfaces. So Let's dive in, and learn how the 3D world is helping improve deep sea mapping.

What is Bathymetry?

Bathymetry is the measurement of the depth of water in oceans, rivers, or lakes. This is a pretty historical topic as well, as scientists have been trying to map the oceans for thousands of years. It often involves the use of maps, so scientists can clearly see what is happening below bodies of water. It also involves studying a large amount of terrain.

These maps are called bathymetric maps, and they look pretty similar to topographic maps. Topographic maps are used on land masses, and use lines and scales to show the shape and elevation of a particular area. There are differences between these maps. Lines on Topographic maps represent equal points in elevation, where on bathymetric maps the lines represent equal depths in the ocean. They also contain circular shapes that represent trenches in the Earth's crust. Bathymetric maps also illustrate false colors as well. These false colors are used to illustrate different aquatic depths in bodies of water.

The first attempts at determining the depths of the ocean were done by dropping a rope in the water, and measuring how far down it went.  However these attempts were very inaccurate. But it wasn't until the 15th century that noise started to be used as a measurement tool. Leonardo da Vinci discovered that ship noise could be heard underwater, and that their sound waves also travel underwater. This methodology would be carried by scientists into our current era of scientific understanding. This technique also got further developed in World War 2 to locate enemy submarines, and in 1985 when Jean-Louis Michel and Robert Ballard searched for the Titanic.

Today, these echo sounders are used to create precise measurements of water bodies. Echo sounders usually dragged behind research vessels. They are designed to create a pulsing sound that creates echoing waves, that then bounce off the ocean floor and back to the boat. The time it takes for the wave to travel to and from the boat determines how deep the seabed is.

Because the oceans cover 71% of the Earth, it is pretty important to understand what is underneath all that water, and how it's topology will change in the future.  Currently, only 5% of the global oceans have been mapped by modern day sonar systems. This unfortunately leaves a lot of unknowns in our future when it comes to the oceans.

Bathymetric Surveys 

Bathymetric surveys involve the use of the technology we have previously mentioned. However, it involves more than just echo sounders to gather data. However, before we dive into that, we should probably mention the types of echo sounders that are used to map seabeds.

One type of echo sounder that is used is called a Multi-beam echo sounder. This sound tool provides a huge amount of angular resolution detail in its data. Angular resolution gives scientists the ability to measure different angles and points of views of an object. This a great thing to have when searching for shipwrecks or underwater mountain ranges. Multi-beam sounders also account for the movement of the boat it is attached to , and map the ocean floor better than a single-beam sounder. Another cool feature of Multi-sounders is that they determine if something on the ocean floor is hard or soft. The stronger it's signal is, the harder the object. 

Single Beam Echo sounders (SBESs) are the smaller and simpler version of a MultiBeam sounder. They operate in the same way, and are made out of piezoelectric crystal- or ceramic-based transducers to create sound.

On top of echo sounders, Light Detection and Ranging (LIDAR) is also used. This technique uses laser beams that are projected from an aerial vehicle, and measures how long it takes for them to travel back to the aircraft. It works in the same principle with echo sounders, but just with lasers.

Bathymetric surveys also employ the use of ADCPs, sub-bottom profilers, and Autonomous Underwater Vehicles to visualize the ocean floor.

A lot of scientific discoveries have been made with bathymetric surveys. For example, without these surveys we would not have known about the underwater seamounts off the coast of Hawaii. These seamounts are called the Hawaii-Emperor Seamount Chain, and they rise for over 1,000 meters above the seafloor. They are ancient volcanoes that have been dormant for thousands of years.

Government organizations also research the seafloor to gather coastline data. The US National Geophysical Data Center (NGDC) and the International Hydrographic Organization (IHO) also gather bathymetric data to protect traveling sea vessels and marine environments. The NGDC also creates digital elevation models out of it's surveys to simulate how tsunamis might affect cities or countries around the globe. It also provides a worldwide data bank for countries to use to study ocean biometrics. Bathymetry data is highly important because we need it to keep people safe while they are traveling overseas, and while navigating the unknown. 

This data can also help us map and reduce sediment pollutants. These sediments can be introduced into water systems via storms and waste management systems. These sediments can be classified as grass clippings, human waste, leaves, oils, micro-beads, and much more. Pond and wetland reduction can be directly linked to sedimentation in the environment.  As well as causing a reduction in fish populations. The sediment can clog fish gills, add toxic levels of nitrogen and phosphorus into the waters, and allow weed build up in waterways. It also clogs drainage pathways, so during large storms a body of water will have no other option than to overflow.

Also, according to the United Nations Sustainable Development Goals it is mandatory for us to map the oceans. There are UN goals that require all of us globally to try and conserve and sustainable use the oceans, seas, and other marine environments. We can only do this by understanding what lies beneath these bodies of water. Science has only mapped 5% of our water bodies with sonar, we unfortunately have to rely off of satellite data.  Satellites can be great at mapping shallow bodies of water, but they can be a bit questionable with calculating ocean ranges at large depths. Most of these satellites collect data in multiple spectral bands and infrared light. This data only provides rough estimates of what the bottom of the ocean might accurately look like.

One of the main difficulties of achieving this UN goal is that most of the ocean lies in international waters. This means they lie beyond international jurisdiction. So no one country has control over them. This means it's often hard to get research permits for those area.

VFX and Further Development

So after researching and reading about all these techniques around mapping terrain, I started to think about how houdini VFX software could help this field. The first thing that popped into my mind were Houdini's terrain tools.

Houdini terrain tools are vast, and allow for the user to have control over adjustments for multiple height fields, and parameters. There are already presets for certain environments you can build with height fields inside the software, but often you can just layer them on your own. Some of the other height field SOPs also allow you implement false colors across your 3D terrain, and control the placement of elevation around the scene. It also allows you to add mask fields to control center areas of your terrain, and soften certain areas. There are also height field noise options for you to add more detail into the ground of your terrain, and quick shade option to add realistic textures. This could be a great advantage of the software when considering angular resolution in bathymetric data.

So already these tools sound like a great way to plug in bathymetric data, and create realistic models of the ocean floor, and other bodies of water. We already know that Houdini is being used to create marine simulations of the oceans, so this idea is not too far fetched.  But where could you find data for a project like this?

Well you can check out Gridded Bathymetry Data HERE.

This site has open source data that anyone can contribute to, and download. They can downloadable maps of the ocean floor, bodies of water, and other terrain. All their data is based around global elevation models, and contains any data they can find on a worldwide level.

References:


Bathymetric Data Viewer: https://maps.ngdc.noaa.gov/viewers/bathymetry/

Visualizing Bathymetric Data Using the Esri Ocean Basemap: https://www.esri.com/news/arcwatch/1012/visualizing-bathymetric-data-using-the-esri-ocean-basemap.html

How Much of the Seafloor Is Left to Explore?: https://oceanexplorer.noaa.gov/world-oceans-day-2015/how-much-of-the-seafloor-is-left-to-explore.html

Bathymetric Surveys: https://www.usgs.gov/centers/oki-water/science/bathymetric-surveys?qt-science_center_objects=0#qt-science_center_objects

Seafloor Mapping – The Challenge of a Truly Global Ocean Bathymetry: https://www.frontiersin.org/articles/10.3389/fmars.2019.00283/full

Interactive 3-D Visualization: A tool for seafloor navigation, exploration, and engineering: https://scholars.unh.edu/cgi/viewcontent.cgi?article=1207&context=ccom

Haptic visualization of bathymetric data: https://ieeexplore.ieee.org/document/6183815

What is bathymetry?: https://oceanservice.noaa.gov/facts/bathymetry.html

Bathymetry: https://www.nationalgeographic.org/encyclopedia/bathymetry/

Bathymetry Post-Processing Guide: https://2ughld46m1gt1arvat2ix2d8-wpengine.netdna-ssl.com/wp-content/uploads/pdf/BathymetryPostprocessingGuide.pdf

The Art of Bathymetry: https://www.hydro-international.com/content/article/the-art-of-bathymetry

Lake Mapping Services: https://www.solitudelakemanagement.com/lake-mapping-services-bathymetry-gps-surface-mapping-and-more

The Importance of Lake Mapping and Bathymetry: https://www.solitudelakemanagement.com/the-importance-of-lake-mapping-and-bathymetry

An overview of the Bathymetry toolbox: https://desktop.arcgis.com/en/arcmap/10.3/tools/bathymetry-toolbox/an-overview-of-the-bathymetry-toolbox.htm

CONDUCT SOPHISTICATED SEAFLOOR ANALYSIS IN REAL-TIME WITH SONARWIZ BATHYMETRY: https://chesapeaketech.com/products/bathymetry/

HYPACK® FOR HYDROGRAPHIC SURVEYING: https://www.hypack.com/applications/hydrographic

GEBCO 2020 Gridded Bathymetry Data Download: https://download.gebco.net/

 

Global ocean & land terrain models: https://www.gebco.net/data_and_products/gridded_bathymetry_data/

 

Seafloor Mapping | Software/Utilities: https://dawn.science.oregonstate.edu/sf_soft