%% date:: [[2024-05-24]] parent:: %% # [[Bathymetry]] ![[Bathymetry.svg]] Bathymetry is the science of measuring the oceanbed, and comes from the words *bathús* (Greek for "deep") and *métron* (Greek for "measure"). Bathymetry is determining how deep the oceans are as well as mapping out the seabed topography. Bathymetry is difficult for the following reasons: - *Water pressure*: The farther down you go, the higher the atmospheric pressure, so it's difficult for both people and machines - *Communication:* The sheer distances involved mean it can be difficult to transmit messages to the surface. - *Light:* No light reaches the deepest parts of the ocean floor, so other alternative senses need to be used ot observe them - *Temperature:* Hydrothermal vents along the floor can cause temperatures to be about 226 degrees Celsius (438 degrees Fahrenheit) [^pbs] Some bathymetry techniques could have significant applications in the study of other hostile environments, such as other planets like [[Mars]]. ## Methods ### Depth sounding Depth sounding is the oldest form of bathymetry and involves dropping a line, weighed down by lead, [^sounding] into the sea and measuring the distance that the line sank. This distance was often measured in *fathoms*. ![[bathymetry-depth-sounding.png]] *Drawing of a ship and her crew doing depth sounding* [^sounding] Depth sounding was initially done for safety and navigation. Knowing how deep the water was helped the crew understand which areas were too dangerous for the ship to traverse. Eventually, it also became useful in the exploration of the oceanbed itself. ### Echo sounding Eventually, depth sounding was mechanised and *echo sounding* replaced it. Echo sounding is electronic depth sounding by way of emitting a noise and then measuring the echo. With the speed of sound in water being known, the depth of the ocean can be calculated. This is also called [[Sonar]]. Sonar can be carried out as a single beam or a multibeam of sound/vibrations. ![[bathymetry-echo-sounding.png]] *Echo sounding map* [^wiki] ### Aerial imaging [[Lidar]] is like sonar but with light instead of sound. In a way, it can be thought of as a type of "light sounding". It can use different types of light, including ultraviolet and visible light, and is useful in contexts other than for mapping the ocean floor. It's usually done from the air. ### Satellite imaging Satellites have also been used for imaging in a similar way to aerial imaging. ![[bathymetry-satellite-imaging.png]] *Satellite-derived bathymetry of the Midway Islands in the US* [^satellite] The main advantage of satellite-derived bathymetry compared to other methods is being able to observe the depths of an ocean from a distance. ### Buoys [^wiki]: Wikipedia. *Bathymetry.* https://en.wikipedia.org/wiki/Bathymetry [^sounding]: Wikipedia. *Depth sounding.* https://en.wikipedia.org/wiki/Depth_sounding [^satellite]: Wikipedia. *Satellite-derived bathymetry.* https://en.wikipedia.org/wiki/Satellite-derived_bathymetry [^pbs]: Jacboson, R. (2015). See the strange creatures NOAA found at the bottom of the sea. https://www.pbs.org/newshour/science/coral-forests-rare-sea-stars-inhabit-unseen-ocean-floor %% # Text Elements # Drawing ```json { "type": "excalidraw", "version": 2, "source": "https://github.com/zsviczian/obsidian-excalidraw-plugin/releases/tag/2.1.4", "elements": [ { "id": "4y8R7iOA", "type": "text", "x": 118.49495565891266, "y": -333.44393157958984, "width": 3.8599853515625, "height": 24, "angle": 0, "strokeColor": "#1e1e1e", "backgroundColor": "transparent", "fillStyle": "solid", "strokeWidth": 2, "strokeStyle": "solid", "roughness": 1, "opacity": 100, "groupIds": [], "frameId": null, "roundness": null, "seed": 967149026, "version": 2, "versionNonce": 939059582, "isDeleted": true, "boundElements": null, "updated": 1713723615080, "link": null, "locked": false, "text": "", "rawText": "", "fontSize": 20, "fontFamily": 4, "textAlign": "left", "verticalAlign": "top", "containerId": null, "originalText": "", "lineHeight": 1.2 } ], "appState": { "theme": "dark", "viewBackgroundColor": "#ffffff", "currentItemStrokeColor": "#1e1e1e", "currentItemBackgroundColor": "transparent", "currentItemFillStyle": "solid", "currentItemStrokeWidth": 2, "currentItemStrokeStyle": "solid", "currentItemRoughness": 1, "currentItemOpacity": 100, "currentItemFontFamily": 4, "currentItemFontSize": 20, "currentItemTextAlign": "left", "currentItemStartArrowhead": null, "currentItemEndArrowhead": "arrow", "scrollX": 583.2388916015625, "scrollY": 573.6323852539062, "zoom": { "value": 1 }, "currentItemRoundness": "round", "gridSize": null, "gridColor": { "Bold": "#C9C9C9FF", "Regular": "#EDEDEDFF" }, "currentStrokeOptions": null, "previousGridSize": null, "frameRendering": { "enabled": true, "clip": true, "name": true, "outline": true } }, "files": {} } ``` %%