| Did you know that land surveyors are also | | | | of a ship to measure the depth at that point. |
| responsible for surveying water, including the | | | | Because this allows the measuring of only one |
| depths of the oceans? These types of surveys | | | | point at a time, it is quite inefficient. Since the |
| are called hydrographic and bathymetric surveys. | | | | boat is constantly moving, this method is also not |
| The data collected during a hydrographic survey | | | | very accurate. |
| includes water depth, contours along the bottom, | | | | Today, these high-tech surveys are actually |
| the direction of the current, high water marks, | | | | conducted using GPS, sonar, and LIDAR or |
| and any underwater landmarks or even shore | | | | LADAR systems. These processes measure the |
| landmarks that may aid in navigating the | | | | time it takes for a sound or light to travel through |
| waterway. | | | | the water, bounce off the sea floor, and return |
| A bathymetric survey is a specific type of water | | | | to the sounding equipment. They can take |
| survey dealing exclusively with the underwater | | | | hundreds of measurements in a single pass, and |
| land and the mapping of the seabed. There are | | | | store the depth, the exact location (using GPS |
| other specific types of surveys dealing with | | | | technology), and other survey information. Some |
| water, like basin or interior hydrography, which is | | | | of these processes are conducted by airplanes, |
| specifically for rivers and bodies of potable | | | | while other surveying equipment may be carried |
| (drinkable) water. | | | | by boats. Modern hydrographic and bathymetric |
| These surveys may be conducted for many | | | | surveys use multiple beams arranged to cover a |
| different reasons, including the planning of | | | | swath of 90 to 170 degrees, producing a very |
| hydropower plants, the locating of mineral | | | | accurate map with much fewer passes over the |
| resources, especially oil or gas, planning | | | | seafloor than are required with single beam |
| navigational routes, or marine exploration. A | | | | equipment. |
| hydrographic survey may also be necessary | | | | Today's surveying equipment produces several |
| when planning buildings or other improvements to | | | | soundings for every square foot of the water's |
| the waterway or the land adjacent to the water. | | | | surface. Once the readings have been received, |
| These surveys may even be used for | | | | they are processed by sophisticated computer |
| paleobathymetry, which is the study of | | | | equipment to account for many variables, such as |
| underwater depth changes over time, or by | | | | the bending of sound waves due to water |
| treasure hunters searching for shipwrecks. | | | | qualities like temperature and pressure, which |
| Unlike most land surveys conducted on dry land, | | | | vary as the beam travels through the depth of |
| hydrographic and bathymetric surveys cannot | | | | the water. The end result includes a |
| usually be conducted by physically visiting and | | | | computer-generated visual image of the seabed |
| measuring the area in question. Surveying of | | | | (known as a digital terrain model) along with other |
| bodies of water has been around in at least a | | | | details. A bathymetric chart produced in this |
| rudimentary form for centuries; the practice | | | | manner usually shows contour lines (known as |
| began long ago as a navigational aid for sailors. | | | | depth contours or isobaths) at selected depths, |
| The first bathymetric surveys were conducted | | | | similar to what might be found on a contour map |
| using heavy rope or cable lowered over the side | | | | of dry land. |