{"id":41,"date":"2015-12-08T06:00:41","date_gmt":"2015-12-08T06:00:41","guid":{"rendered":"http:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/?p=41"},"modified":"2015-12-12T07:05:58","modified_gmt":"2015-12-12T07:05:58","slug":"multibeam-mapping","status":"publish","type":"post","link":"https:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/2015\/12\/08\/multibeam-mapping\/","title":{"rendered":"MULTIBEAM MAPPING"},"content":{"rendered":"<ul>\n<li>or &#8216;How we map, part I&#8217;<\/li>\n<\/ul>\n<p style=\"text-align: justify\">Water absorbs electromagnetic waves. That&#8217;s why we know so little about the 70\u00a0% of Earth&#8217;s surface that are covered by water.<\/p>\n<p style=\"text-align: justify\">So mapping the oceans relies on acoustic waves. Echosounder systems emit an acoustic signal and measure the time, untill the reflection of the wave from the seafloor is received. Knowing the sound speed of water, the measured time interval can be converted into distance. Similar to light, sound reflections are caused by density changes. This can be, for example, the water-rock or water-sediment boundary (commonly known as seafloor), or gas bubbles in the water column (e.g. in hydrothermal plumes).<\/p>\n<p style=\"text-align: justify\">Primitive echosounders were used prior to the first world war, initially for communication, and eventually for detecting icebergs (spurred on by the Titanic disaster). During the second world war, echosounders were further developed to help search for submarines using a single beam (like in the movie \u201eDas Boot\u201c). Today, although some single-beam echosounders are still used, many mapping echosounders use a fan-shaped array of many acoustic beams directed downwards to detect the seafloor. The system onboard Kilo Moana (a Kongsberg EM122) is capable of recording a set of up to 432 depth measurements at a time, and can make two such measurement sets simultaneously. When operated in water depths of ca. 5000\u00a0m, one so-called &#8216;swath&#8217; covers about 15\u00a0km of seafloor in an across-ship-track orientation.<\/p>\n<p style=\"text-align: justify\">&#8212;<\/p>\n<ul style=\"text-align: justify\">\n<li>oder &#8220;Wie wird kartiert, Teil I&#8221;<\/li>\n<\/ul>\n<p style=\"text-align: justify\">Wasser absorbiert elektromagnetische Wellen. Aus diesem Grund wissen wir nur sehr wenig \u00fcber die 70% Erdoberfl\u00e4che, die von Wasser bedeckt sind.<\/p>\n<p style=\"text-align: justify\">Die Kartierung der Ozeane basiert deshalb auf akustischen Wellen. Echolot-Systeme erzeugen ein akustisches Signal und messen die Zeit, bis der vom Meeresboden reflektierte Schall wieder empfangen wird. Mit dem Wissen um die Schallgeschwindigkeit in Wasser, kann aus dem Zeitinterval die Distanz berechnet werden. \u00c4hnlich wie beim Licht, verursachen Dichte\u00e4nderungen die Reflexion des Schalls. Eine solche Dichte\u00e4nderung findet sich zum Beispiel an der Wasser-Gesteins- bzw. der Wasser-Sediment-Grenze (gemeinhin als Meeresboden bekannt), oder auch in Gasblasen in der Wassers\u00e4ule (wie sie unter anderem in Hydrothermalen Plumes vorkommen).<\/p>\n<p style=\"text-align: justify\">Die ersten Echolote wurden schon vor dem Ersten Weltkrieg genutzt, urspr\u00fcnglich zur Kommunikation, sp\u00e4ter auch zum Detektieren von Eisbergen (gef\u00f6rdert durch das Titanic-Ungl\u00fcck). W\u00e4hrend des Zweiten Weltkriegs wurden die Echolote dann weiter entwickelt, um die Suche nach U-Booten zu unterst\u00fctzen, wobei immer nur ein Schallsignal ausgesendet wurde (siehe im Film \u201eDas Boot\u201c). Heutzutage sind zwar noch einige einfache Echolote im Einsatz, zum Kartieren jedoch werden \u00fcberwiegend F\u00e4cherecholote genutzt, die, wie der Name schon sagt, einen F\u00e4cher an Schallwellen vertikal nach unten aussenden und so einen ganzen Streifen Meeresboden vermessen. Das System an Bord der Kilo Moana (ein Kongsberg EM122) kann \u00fcber den F\u00e4cher verteilt bis zu 432 Tiefenmessungen durchf\u00fchren, wobei jeweils zwei dieser F\u00e4cher zeitgleich gemessen werden. In <\/p>\n","protected":false},"excerpt":{"rendered":"<p>or &#8216;How we map, part I&#8217; Water absorbs electromagnetic waves. That&#8217;s why we know so little about the 70\u00a0% of Earth&#8217;s surface that are covered by water. So mapping the oceans relies on acoustic waves. Echosounder systems emit an acoustic signal and measure the time, untill the reflection of the wave from the seafloor is [&hellip;]<\/p>\n","protected":false},"author":160,"featured_media":42,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-41","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorised"],"_links":{"self":[{"href":"https:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/wp-json\/wp\/v2\/posts\/41","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/wp-json\/wp\/v2\/users\/160"}],"replies":[{"embeddable":true,"href":"https:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/wp-json\/wp\/v2\/comments?post=41"}],"version-history":[{"count":4,"href":"https:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/wp-json\/wp\/v2\/posts\/41\/revisions"}],"predecessor-version":[{"id":67,"href":"https:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/wp-json\/wp\/v2\/posts\/41\/revisions\/67"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/wp-json\/wp\/v2\/media\/42"}],"wp:attachment":[{"href":"https:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/wp-json\/wp\/v2\/media?parent=41"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/wp-json\/wp\/v2\/categories?post=41"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.oceanblogs.org\/mappingtheoceanfloor\/wp-json\/wp\/v2\/tags?post=41"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}