Turtle Posted August 7, 2008 Report Share Posted August 7, 2008 OK. Here's the other shoe; you can all breath now. :hyper: What happens to the heat from the submarine volcanos under the Artic ice? What does the heat plume look like as a gradient in waters over active submarine volcanos, and how does it affect the ice overhead? This article makes no mention of it, and I can find no graphs elsewhere. :eek_big: >> Fire Under Arctic Ice: Volcanoes Have Been Blowing Their Tops In The Deep Ocean freeztar 1 Quote Link to comment Share on other sites More sharing options...
Overdog Posted August 7, 2008 Report Share Posted August 7, 2008 Hmmm, I finally managed to find some recent material related to this. XBT's (Expendable BatheyThermograph) are the temperature probes I dropped when in the Navy... globeandmail.com: Ocean warming understated, scientists say Quote Link to comment Share on other sites More sharing options...
Turtle Posted August 7, 2008 Report Share Posted August 7, 2008 Hmmm, I finally managed to find some recent material related to this. XBT's (Expendable BatheyThermograph) are the temperature probes I dropped when in the Navy... globeandmail.com: Ocean warming understated, scientists say ..."If you miscalculate how quickly the instrument falls through the water column, you miscalculate the depth and therefore the temperature at that depth and that's the prime source of error," Dr. Church said. ... Does this mean they aren't actually measuring the temperature, but rather calculating it based on the measured depth of the probe? :eek_big: Quote Link to comment Share on other sites More sharing options...
Overdog Posted August 7, 2008 Report Share Posted August 7, 2008 Does this mean they aren't actually measuring the temperature, but rather calculating it based on the measured depth of the probe? :eek_big: No, the probes actually measure the temperature, but the temperature chart of Temp/Depth printed out is based on an assumed speed that the probe falls through the water. So if that speed assumption was off, it would show the thermocline and temperatures at incorrect depths. Quote Link to comment Share on other sites More sharing options...
Turtle Posted August 7, 2008 Report Share Posted August 7, 2008 No, the probes actually measure the temperature, but the temperature chart of Temp/Depth printed out is based on an assumed speed that the probe falls through the water. So if that speed assumption was off, it would show the thermocline and temperatures at incorrect depths. Ahhh. Roger. Thnx. :eek_big: Quote Link to comment Share on other sites More sharing options...
freeztar Posted August 7, 2008 Report Share Posted August 7, 2008 No, the probes actually measure the temperature, but the temperature chart of Temp/Depth printed out is based on an assumed speed that the probe falls through the water. So if that speed assumption was off, it would show the thermocline and temperatures at incorrect depths. Why not use sonar to track the depth? No assumptions needed. Quote Link to comment Share on other sites More sharing options...
Overdog Posted August 7, 2008 Report Share Posted August 7, 2008 Why not use sonar to track the depth? No assumptions needed. Actually, the temperature profile is used to calibrate the sonar, as the temperature profile profoundly affects how the sound pulse propagates through the water. Standard operating procedure was to drop an XBT every four hours, everywhere we went. I once read somewhere that the Navy was authorized to launch up to 44,000 XBT's per day. But this was during the good ol' days of the cold war. A sound pulse from a hull-mounted sonar will actually bounce off that sharp temperature change where the thermocline begins. Also, above 2000 feet, temperature is the controlling factor. Since sound travels perpendicular to the wave front, if the top of the sound wave is in warmer water, the sound pulse will bend downward, as though it were a sound beam. So if the thermocline is right up near the surface, the sonar pulse will bend sharply down toward the bottom... Temperature also affects the speed of the sound pulse, as does salinity and depth. So, unless you have configured your sonar with accurate temperature information, your sonar will not be accurate. modest 1 Quote Link to comment Share on other sites More sharing options...
Overdog Posted August 8, 2008 Report Share Posted August 8, 2008 I guess what the study about the XBT inaccuracies is telling us, in addition to underestimating the mixing of warm and cold seawater, is that if the cold war had actually gone hot, the aiming of our anti-submarine weapons would also have been off target to some extent.:eek_big: Quote Link to comment Share on other sites More sharing options...
freeztar Posted August 8, 2008 Report Share Posted August 8, 2008 Actually, the temperature profile is used to calibrate the sonar, as the temperature profile profoundly affects how the sound pulse propagates through the water. Standard operating procedure was to drop an XBT every four hours, everywhere we went. I once read somewhere that the Navy was authorized to launch up to 44,000 XBT's per day. But this was during the good ol' days of the cold war. A sound pulse from a hull-mounted sonar will actually bounce off that sharp temperature change where the thermocline begins. Also, above 2000 feet, temperature is the controlling factor. Since sound travels perpendicular to the wave front, if the top of the sound wave is in warmer water, the sound pulse will bend downward, as though it were a sound beam. So if the thermocline is right up near the surface, the sonar pulse will bend sharply down toward the bottom... Temperature also affects the speed of the sound pulse, as does salinity and depth. So, unless you have configured your sonar with accurate temperature information, your sonar will not be accurate. Thanks for that OverD! That makes much more sense now. :eek_big: This topic, while not off-topic to this thread, would certainly make a good thread on its own. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.