Northeast Fisheries Science Center
Oceanography Branch

Drifters: Design, Construction, Use...

(last modified Sep 2009)


Contents:

General Mission/Goals

History of our drifter production

In 2004, we were funded by NOAA's Northeast Consortium to develop student-built, satellite-tracked, lobstermen-deployed drifters. This was the fourth phase of the Environmental Monitors on Lobster Traps project (see Manning and Pelletier, 2009 and  emolt.org).  Funded parties including the Gulf of Maine Lobster Foundation, the Southern Maine Community College (SMCC), and NOAA's Northeast Fisheries Science Center were interested in tracking the potential transport of early-staged larvae along the coast of Maine. In subsequent years, we were primarily funded by McGillicuddy et al in another NOAA funded project (GOMTOX) to track the advection of HABs (Manning et al, 2009).   Another big boost to the project occurred in the summer of August 2009 when we hosted a NSF-funded workshop to teach a few dozen educators from around the country (from the Marine Advanced Technology Education (MATE) consortium). Several other investigations are documented elsewhere. Applications funded to date include:

One of the primary motivations for drifter deployments is to help validate the many numerical circulation models as well as the growing network of CODAR systems.
Given multiple years with multiple fundings, the dataset to conduct such statistics is rapidly growing.
drifter archive

eMOLT "Rachel" Drifter vs Davis "CODE" Drifter 

Most surface drifters in use today are the "Davis CODE" design first described decades ago by Davis (1985) for the Coastal Ocean Dynamics Experiment. There are specifications and pictures of this type of drifter in each of the manufacturer's web sites below (Table 1).  However, since they are often fitted with costly  (~$2K) GPS electronics, we found, in our case of very limited budget, it was unwise to use them  along the coast of New England  due to the high risk of running aground and being picked up by curious lobstermen and pleasure boaters.

Table 1.  Some existing surface drifters that have performed well over the last decade or two
type manufacturer web site location
Davis-X-shaped CODE Brightwaters http://www.brightwaters.com Stonybrook Univ, Long Island

MetOcean http://www.metocean.com England

ClearWater  http://www.clearwater-inst.com/docs/b_CS1.htm Waltham, Mass.

Technocean http://www.technocean.com/DOCS/argodrifter.htm Fort Myers, Florida
Tri-Star scaled down PacificGyre http://www.pacificgyre.com Santa Barabara, Calif.
Seimac C-AST Barrel Seimac http://www.seimac.com Halifax, Nova Scotia

drifter

Having eliminated the costly electronics within the housing unit, we simply mount a relatively inexpensive GPS transmitter (similar to those used by the trucking industry on the highway) on a smaller  (~2 inch) diameter foam-filled PVC pipe (ballasted appropriately).  Since it is built by students at the Southern Maine Community College and originally funded by the Environmental Monitors on Lobster Trap project, we  call it the eMOLT SMCC "Rachel" Model  (drifter models are named after the new students who spent the most time on design and construction).  From our experience in using hundreds of these drifters since 2004, we can reduce the cost GPS drifters 3 times. While these homemade rigs typically survive several months, they do not survive nearly as long as the commercial products noted above. Nevertheless, they have so far logged hundreds of thousands of kilometers of ocean.  While they are designed to be expendable for the most part, with some effort and ship time, of course, they are reusable.  Batteries are good for several months with near-hourly samples.  See more on "survival statistics" below.

How the system works and who is involved

There are six institutions/companies currently involved:

Interested scientist and educators communicate with:
It is best to copy all three parties in your email communications.


Assembling Standard "Rachel" drifter 

This requires about 15 minutes per unit.   A flathead screw driver & pliers needed.

  1. insert the four fiberglass rods matching plastic hose bushings to PVC w/longer ones on top
  2. hose clamp the rods so they remain symetrically in place
  3. slip on the four sails (~19" by 36")
  4. put 4 cotter pins on the outside end of sails at top
  5. slip on 4 stainless washers
  6. slip on 4 floats
  7. repeat 5 and then 4 to secure the floats

GPS Transmitter Setup   Putting units to sleep
Documenting deployments and recoveries

In an attempt to automate the operation, users are asked to enter their deployment and recovery information on a web based forms.
While the complete system is not operational at the time of this writing (Sep 2009), the plan is to serve data and googlemap plots without further human intervention.



Tracking Units on the Web
Other Drifter Configurations
"Kathleen" bucket drifter for very-near surface work

This model was originally designed for UMASS's Dan McDonald to look at the top 30cm of the Merrimack River Plume in the Fall of 2009.
It is simply an inverted plastic bucket that is properly ballast to float just below the surface. The transmitter is mounted a few inches above the seasurface.
"Super buckets" were also deployed with strobe lights (>4 mile visibility) and internally recording:
  1.  temperature (multiple depths)
  2.  salinity (StarOddi DST-CT)
  3.  more frequent positions (Garmin units)

ID Convention

         EXAMPLE: 098430702 is the 2nd drifter dropped in August 2009 at approximately 43N and 070W

References


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