Dispatches from Sea >>
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| March 2007 |  Laura Preston, educator, UNH/Salem High School, Salem, NH. |
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| April 2007 | |||||||
April 17, 2007
Keep your thinking caps on for our discussion here on “ground-truthing.” This has been a huge part of our work for the past three weeks.
In the classroom lab (or in life) we ask a question, create a hypothesis, do some testing (collecting and analyzing data) of the hypothesis, and conclude with a report on what we found to be the answer to our original question. Sometimes we need to revise our hypothesis or rethink the testing component.
The scientists at sea are using this very process! They have a couple of hypotheses for their original question (How do the seafloor geology and lava and vent chemistry reflect the underlying subsurface distribution of melt?). They are testing their hypotheses here at sea by collecting samples and analyzing them (some here at sea and some back in the lab at home), and they will conclude and report their findings to their scientific community over the next two years.
The Pacific Ocean is the world’s largest and deepest ocean. It is difficult to study something that is more than two miles deep in places. In the past, mariners, the military, and scientists have collected data of the ocean’s floor remotely. For example, echo sounding, emitting a signal from a ship and recording the time it takes to bounce off the seafloor and come back to the ship (and using the time to calculate depth), and satellites for collecting sea surface elevations (which follow the trend of the seafloor topography), have been used in this area. During this cruise DSL-120A sonar (using acoustic signals to interpret surface features) has be used as well. There is some detail in the sonar record produced, but not enough detail to truly see what is on the ocean floor (its kind of like taking a photograph of a city skyline: you see there are buildings of different shapes and sizes, but can’t quite make out what the buildings are made of, although you can make educated guesses).
In-situ (at the site) studies are also being conducted on this cruise to verify the scientists’ interpretation of the remote sensing data. The features that have been studied and sampled are all the things we have seen on the seafloor with the Jason II ROV, the Towcam imaging device, and the rock corer. So, things like pillow lavas, lava buds, fissures and so on are overlain on the basemap so that patterns can be determined for the entire area. And that is the idea behind ground truthing, taking what you know about the area remotely, and testing that knowledge at the ground level.
 An example of our remote sensing dataset from the DSL – 120A side scan sonar. A typical fissure and pillow lava are circled. |
 A typical fissure appears black on the map and is circled in red. |
 Pillow lava is circled in yellow. |
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 An example of our ground – truthing dataset of the same area. Pillows and fissures position are plotted using shapes. |
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And….finally, we seem to have a sunset photo contest going on now. Here is the first entry, Scott White’s real sunset image! Sorry Jess, he wins!
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