قياس الأعماق

قياس الأعماق Bathymetry، هي دراسة عمق مياه البحيرات أو قاع المحيطاتand μέτρον (metron), "measure"] تُرسم مخططات قياس الأعماض to support safety of surface or sub-surface navigation, and usually show seafloor relief or terrain as contour lines (called depth contours or isobaths) and selected depths (soundings), and typically also provide surface navigational information. Bathymetric maps (a more general term where navigational safety is not a concern) may also use a Digital Terrain Model and artificial illumination techniques to illustrate the depths being portrayed. Paleobathymetry is the study of past underwater depths.

 

 

في الأصل، يختص قياس الأعماق بقياس عمق المحيط عن طريق رصد العمق. استخدمت التقنيات المبكرة الحبال أو الكابلات الثقيلة المتدلية على جانب السفينة. تقيس هذه التقنية عمق نقطة واحدة فقط في وقت القياس، ولهذا فهي غير مفيدة. كما أنها تعتمد على حركات السفينة والتيارات التي تحرك الحبل أو الكابل وبالتالي فهي غير دقيقة.

 

 

خريطة قياس أعماق البحر المتوسط. تجمع البيانات المستخدمة لرسم خرائط قياس الأعماق عن طريق سونار يثبت أسفل أو على جانب قارب، pinging" a beam of sound downward at the seafloor or from remote sensing LIDAR or LADAR ]

The amount of time it takes for the sound or light to travel through the water, bounce off the seafloor, and return to the sounder tells the equipment what the distance to the seafloor is. LIDAR/LADAR surveys are usually conducted by airborne systems.

 

 

طبوغرافية قاع المحيط بالقرب من خندق پورتو ريكو. Starting in the early 1930s, single-beam sounders were used to make bathymetry maps. Today, multibeam echosounders (MBES) are typically used, which use hundreds of very narrow adjacent beams arranged in a fan-like swath of typically 90 to 170 degrees across. The tightly packed array of narrow individual beams provides very high angular resolution and accuracy. In general a wide swath, which is depth dependent, allows a boat to map more seafloor in less time than a single-beam echosounder by making fewer passes. The beams update many times per second (typically 0.1-50 Hz depending on water depth), allowing faster boat speed while maintaining 100% coverage of the seafloor. Attitude sensors allow for the correction of the boat's roll, pitch and yaw on the ocean surface, and a gyrocompass provides accurate heading information to correct for vessel yaw. (Most modern MBES systems use an integrated motion-sensor and position system that measures yaw as well as the other dynamics and position.) A boat-mounted Global Positioning System (GPS) (or other Global Navigation Satellite System (GNSS)) positions the soundings with respect to the surface of the earth. Sound speed profiles (speed of sound in water as a function of depth) of the water column correct for refraction or "ray-bending" of the sound waves owing to non-uniform water column characteristics such as temperature, conductivity, and pressure. A computer system processes all the data, correcting for all of the above factors as well as for the angle of each individual beam. The resulting sounding measurements are then processed either manually, semi-automatically or automatically (in limited circumstances) to produce a map of the area. في 2010 a number of different outputs are generated, including a sub-set of the original measurements that satisfy some conditions (e.g., most representative likely soundings, shallowest in a region, etc.) or integrated Digital Terrain Models (DTM) (e.g., a regular or irregular grid of points connected into a surface). Historically, selection of measurements was more common in hydrographic applications while DTM construction was used for engineering surveys, geology, flow modeling, etc. Since ca. 2003-2005, DTMs have become more accepted in hydrographic practice.

Satellites are also used to measure bathymetry. Satellite radar maps deep-sea topography by detecting the subtle variations in sea level caused by the gravitational pull of undersea mountains, ridges, and other masses. On average, sea level is higher over mountains and ridges than over abyssal plains and trenches.[4]

في الولايات المتحدة يقوم مهندسو البحرية العسكرية الأمريكية معظم مسوحات القنوات المائية، بينما تقوم الادارة الوطنية للمحيطات والغلاف الجوي (NOAA) بنفس المهمة فيما يخص قاع المحيط. بيانات قياس الأعماق متوفرة لدى مركز البيانات الجيوفيزيائية الوطني (NGDC) التابع للادارة الوطنية للمحيطات والغلاف الجوي .[5] Bathymetric data is usually referenced to tidal vertical datums.[6]لقياس أعماق مياه المحيط this is typically Mean Sea Level (MSL), but most data used for nautical charting is referenced to Mean Lower Low Water (MLLW) in American surveys, and Lowest Astronomical Tide (LAT) in other countries. Many other datums are used in practice, depending on the locality and tidal regime.

Occupations or careers related to bathymetry include the study of oceans and rocks and minerals on the ocean floor, and the study of underwater earthquakes or volcanoes. The taking and analysis of bathymetric measurements is one of the core areas of modern hydrography, and a fundamental component in ensuring the safe transport of goods worldwide.