{"id":301,"date":"2015-06-27T04:28:51","date_gmt":"2015-06-27T04:28:51","guid":{"rendered":"http:\/\/ciresblogs.colorado.edu\/hobitss2\/?p=301"},"modified":"2015-06-27T21:29:49","modified_gmt":"2015-06-27T21:29:49","slug":"gps-acoustic","status":"publish","type":"post","link":"https:\/\/ciresblogs.colorado.edu\/hobitss2\/2015\/06\/27\/gps-acoustic\/","title":{"rendered":"GPS-Acoustic"},"content":{"rendered":"
\"gps_a_blog\"<\/a>

The GPS acoustic system being installed on deck.<\/p><\/div>\n

Last night we towed a buoy behind the ship to\u00a0make GPS-Acoustic measurements. Here is a description of the method from Kido et al., Geophysical Research Letters, 2011:<\/p>\n

“The GPS\/acoustic technique, which was proposed and<\/p>\n

developed by the Scripps Institution of Oceanography<\/p>\n[Spiess , 1985], consists of two essential components: the<\/p>\n

kinematic GPS of a surface platform, and acoustic ranging<\/p>\n

between the surface platform and an array of seafloor<\/p>\n

transponders. As introduced by Kido et al.\u00a0 [2006], we used a<\/p>\n

towed buoy navigated near the center of the transponder<\/p>\n

array as the surface platform during a campaign (hereafter<\/p>\n

called a stationary survey). The shape of the transponder<\/p>\n

array is assumed to be rigid through repeated campaigns<\/p>\n

over the years because of its relatively short baseline. With<\/p>\n

the assumptions that sound speed in the ocean is laterally<\/p>\n

stratified and that the seafloor moves only in the horizontal<\/p>\n

direction, the horizontal position of the array and the mean<\/p>\n

sound speed from the sea-surface to the bottom can be<\/p>\n

determined with a single acoustic ping of simultaneous<\/p>\n

ranging to all the transponders [Kido et al. , 2008]. The<\/p>\n

temporal position of the array is then obtained as a time<\/p>\n

series for thousands of pings. The final position of the array<\/p>\n

in a campaign is determined by averaging the fluctuations in<\/p>\n

these time series, which are presumably due to undesired<\/p>\n

spatio-temporal variation in the sound speed beyond the<\/p>\n

stratified approximation. The resultant accuracy of array<\/p>\n

positioning in a single campaign is typically 5 cmdepending<\/p>\n

on the ocean conditions and duration of the survey.”<\/p><\/blockquote>\n

With this method we can make very precise measurements of a position on the seafloor, and by repeating measurements over several years and comparing them with sites on land, can measure the motions of the tectonic plates and motions associated with large earthquakes. Similar seafloor GPS-acoustic measurements were made before and after\u00a0the 2011 Japan Tohoku-Oki earthquake, and found displacements of the seafloor by 31 meters horizontally, which is huge.<\/p>\n

\"Conductivity<\/a>

Conductivity Temperature Depth (CTD) probe being lowered into the water. This instrument measures the electrical conductivity of the water (which is related to salinity) and the temperature of the water as a function of depth as it is lowered into the water. Both of these parameters affect sound speed in water, and need to be accounted for to accurately position the seafloor GPS array.<\/p><\/div>\n","protected":false},"excerpt":{"rendered":"

Last night we towed a buoy behind the ship to\u00a0make GPS-Acoustic measurements. Here is a description of the method from Kido et al., Geophysical Research Letters, 2011: “The GPS\/acoustic technique, which was proposed and developed by the Scripps Institution of Oceanography [Spiess , 1985], consists of two essential components: the kinematic GPS of a surface… Read More<\/a><\/p>\n","protected":false},"author":22,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-301","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_featured_media_url":"","publishpress_future_action":{"enabled":false,"date":"2026-06-06 18:30:48","action":"change-status","newStatus":"draft","terms":[],"taxonomy":"category"},"publishpress_future_workflow_manual_trigger":{"enabledWorkflows":[]},"_links":{"self":[{"href":"https:\/\/ciresblogs.colorado.edu\/hobitss2\/wp-json\/wp\/v2\/posts\/301","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ciresblogs.colorado.edu\/hobitss2\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ciresblogs.colorado.edu\/hobitss2\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ciresblogs.colorado.edu\/hobitss2\/wp-json\/wp\/v2\/users\/22"}],"replies":[{"embeddable":true,"href":"https:\/\/ciresblogs.colorado.edu\/hobitss2\/wp-json\/wp\/v2\/comments?post=301"}],"version-history":[{"count":5,"href":"https:\/\/ciresblogs.colorado.edu\/hobitss2\/wp-json\/wp\/v2\/posts\/301\/revisions"}],"predecessor-version":[{"id":311,"href":"https:\/\/ciresblogs.colorado.edu\/hobitss2\/wp-json\/wp\/v2\/posts\/301\/revisions\/311"}],"wp:attachment":[{"href":"https:\/\/ciresblogs.colorado.edu\/hobitss2\/wp-json\/wp\/v2\/media?parent=301"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ciresblogs.colorado.edu\/hobitss2\/wp-json\/wp\/v2\/categories?post=301"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ciresblogs.colorado.edu\/hobitss2\/wp-json\/wp\/v2\/tags?post=301"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}