Thursday, August 27, 2009

Heezen Tharp Map in Google Earth!

Finally something that I have been waiting for for a long time. Back
when I was an undergrad, one of the projects I worked on was to gather
maps and measurements of the barrier islands of the biggie
small islands from the ENTIRE globe! Mind you these were in the days
before Google Earth so we had to use REAL maps. In order to do the
project I spent several weeks camped out at the Library of Congress
Maps Division, *side note: you owe it to yourself to check this place
out some time*. Unlike other libraries at the LoC you don't just
wander through the stacks looking for the material you are after oh no
only the librarians do that so instead you have to present them with
lists of the material you want. At the time the best available global
coverage high resolution maps were 1:20,000 maps from WWII they were
called JOGs for Joint Operation Graphics they also had another
"recently" acquired (thank you end of the Cold War) global map set
from the Russians. The Russian maps were in Cyrillic but since I
wasn't interested in place names just islands these were fine. After
several days of drawing maps from various different map sets, one of
the very helpful librarians pulled me aside to give me a glimpse of
the back room- first to impress upon me the yeoman's task that I had
been asking them to do- you see they were having to pull maps from
opposite corners of their mapping space and they have literally acres
of space down there. The second thing the librarian did was to ask
"You're an Oceanographer right?" One always wonders what is coming
next with a question like that but I said "Well yes I'm studying to be
one". The librarian then asked if I knew who Bruce Heezen and Marie
Tharp were. Know who they are well of course every Oceanography,
Geology, and Geography department in the planet used to have a copy of
their maps of the seafloor on the walls. Turns out the LoC had
recently acquired a vast collection of the maps and the precursor
mylars that went into making those maps. I was quickly showed to an
area in the back room where tables and boxes where piled in a chaotic
fashion, a huge mish mash of maps and books and correspondence all
related to this mammoth work. This experience kicked off a long
standing interest in both the maps and the map makers that continues
to this day. I later went to visit the archives of the Smithsonian
where they had some 60+ boxes of archive material for Heezen, one of
the founding titans in modern geological oceanography.

Years later first when playing with Fledermaus and then again in
Google Earth I had this notion that wouldn't it be great to bring the
old Heezen Tharp map into one of these visualization systems and
compare the maps of today with what Heezen and Tharp produced- they
had in comparison a very limited and scant data set from which to
build their extrapolated map. Well it seems others had the same idea
too as I just found this layer in Google Earth that includes the
Heezen Tharp map. What a great teaching resource! What a marvelous
piece of mapping history.

USCG Healy expedition in Google Earth and on NOAA OER

Kudos to Kurt for getting the Healy post now live on Google Earth
under the Ocean Layer. Click on "Expeditions" and fly up to the arctic
for a peak. If you click on the expedition icon you'll see the latest
image from the aloft camera on the Healy. Keep tuning in for more
updates as the Healy working with the Louis S. St Laurent push north.

There is also an expedition summary on the NOAA Ocean Exploration and
Research, Exploration page

Tuesday, August 25, 2009

In Search of the Asian Clam...

Researchers at the UC Davis Tahoe Environmental Research Center invited Gavia operators from the University of British Columbia, University of New Hampshire, and University of Delaware to Lake Tahoe in search of the invasive Asian clam that is becoming more prevalent in these waters. In a true collaborative effort between UBC and UDel/UNH AUV teams, the Gavia was run with the UBC control, props, and nose module and the UDel/UNH positioning system and Geoswath, with the battery modules of each being swapped in to extend run time. Due to the transparency of lake waters of up to 70m, our primary objective was to photograph the lake bed to determine clam distributions. The clams threaten the clarity of the lake by increasing nutrient levels in the lake, encouraging a thick algae growth to carpet the bottom. Consequently we also collected water quality measurements including CDOM, backscatter, chlorophyll concentration, and CTD during these missions.

The Gavia ready for night swimming in the quiet waters of Lake Tahoe, is trimmed with incompressible foam needed to provide lift at the nose in the freshwater.

Working on the boat from dusk until dawn had its rewards: beautiful sunrises on the lake!

Our first week of missions entailed circumnavigating the lake along the 5m contour at an altitude of 2.5m. In order to optimize the clam detection algorithm we wrote, which targets the white color of dead clams, we ran missions at night to avoid sunlight reflections on the bottom, which would be classified as clams. We also avoided boat traffic by executing missions at night. Night work in clear water made tracking the Gavia easy, as we just followed the strobe/tower lights. This also allowed us to precisely time when the camera card was full by having a stopwatch that started when the strobe started and stopped when it turned off. We captured 2 hours of photos before pulling the Gavia back aboard and transferring the photos to the Toughbook via LAN.

An image of the bed reveals sandy sediments with an abundance of clams and algal growth.
Our image-processing algorithm is shown below with the original image in the top right, initial clam detections in the top left, and advanced clam detection in the bottom right.
Mission planning was the most challenging task as the perimeter of the lake is full of erratics. Our most successful technique for mission planning included using Fledermaus to locate waypoints on the 5m contour from the multibeam data Mayer et al. published, Control Center to plot the points, and GoogleEarth to check for erratics. Though tedious this has allowed us to run 2-hour missions (to fill the camera card) without having to stop and restart due to obstacles. This afforded us time to watch the amazing Perseid meteor showers.

A glance at the Lake Tahoe shoreline by day reveals the dangers of flying the Gavia through shallow waters!
At the end of the first battery pack our team transformed from Gavia-/star- gazers to a professional pit-crew able to download data, change the Gavia battery (which entailed removing a CTD, buoyant trim, cleaning o-rings, and carefully aligning the modules) with great efficiency.

The circumnavigation was completed by the start of our second week and yielded important information on clam presence around the lake. The remainder of our missions was spent surveying areas with high clam concentrations using two strategies: 1. Contour following at 10-15m depth intervals by running shorter survey lines parallel to contours as in the circumnavigation. 2. Running survey lines perpendicular to contours from about 5m to 70 m depth or to the edge of the shelf break. Bottom-tracking proved difficult during these missions, the Gavia would often abort missions because she was unable to reach a waypoint in time. Another difficulty was maximizing the number of useable images we could collect in missions that cut across contours. Flying across contours was challenging because the Gavia has trouble bottom-tracking along steep areas, which are prevalent along the basin walls. Slopes of greater than 10 to 15 degrees were common and because of this we ran more, shorter missions. We would send Gavia perpendicular to the contours at 1.5 m altitude and then make the return leg constant depth of 2 m to avoid ploughing the AUV into the steep slopes. Because of the many sites of interest and the relatively time-consuming nature of this mode of operation, we ran about 2-4 lines per site.

Project PI, Marion Wittmann, and boat captain, Brant Allen of UC Davis enjoying the night on Tahoe.
Throughout our two weeks the Gavia covered more ground than on any previous research trip. We found clams at greater depths (80 m) than previously discovered and also imaged algal mats and the pond liner used to control clam populations along the south shore. The only disappointment is that we did not have the time to run survey lines with sufficient overlap to obtain quality Geoswath data. Leaving Tahoe with the knowledge that Gavia has collected an abundance of data and successfully contour-followed and run across steep contours, two seemingly impossible survey goals, is extremely rewarding. This was a spectacular end to the Gavia’s and my first full field season with Team CSHEL!Andrew, me, and Alex keeping warm in the cold dawn hours on Lake Tahoe.

Monday, August 10, 2009

Bottom mount is home again!

Some photos courtesy Co-PI Doug Miller after recovery of the ADCP
bottom mount aboard the RV Captain White.
Thanks to all involved.

Tuesday, August 4, 2009