Preparing the buoy for transport to the harbor

Deployment of the Ozone Instrument on a Buoy

Our new ozone instrument was integrated onto a 3-m diameter discus buoy, along with aerosol and iron/rainwater instruments from Ed Sholkovitz (link to SEA-AER page). The complete package also included meteorological instruments to measure temperature, relative humidity, wind, and rain, a central computer to coordinate all the instruments, and a line-of-sight RF modem for communication with the shore. The buoy was trucked to the Woods Hole dock, placed in the water, towed by R/V Asterias to a mooring off the WHOI Quissett campus on October 22, and anchored. The ozone instrument turned on properly and recorded data for the next few days. On October 25, because of failures of electrical components on other instruments, the buoy was towed back to the Woods Hole dock for changes to all the motor controllers. We took this opportunity to download all the data, and insulate the ozone detection cell. Ozone was then measured over the next week, with the buoy anchored in Woods Hole harbor. The data showed that everything was working on the instrument, but that of the two channels to measure ozone, channel B was noisier than channel A. In the laboratory, both channels had low noise. We attempted to remedy this problem by strengthening the plate holding the detector electronics to the cell. We then measured ozone for another week on the buoy in Woods Hole harbor. All systems worked well, though by this time our inlet tubing had been damaged by all the unplanned foot traffic on the buoy(!) which reduced the flow through the instrument. Following recovery of the buoy, we changed the flow conditions, added further insulation to the cell, and ran the complete package of buoy instruments outside at the WHOI Quissett campus for another week.

Final prep work at the WHOI dock. Mike Purcell makes some adjustments
on top while we hold the buoy steady.

Towing the buoy out of the harbor

Preparing the mooring

The buoy moored in Vineyard Sound

Results

All in all, it was a very successful engineering test - all the equipment functioned, and several problems were identified and fixed. In particular, there were no water leaks in any of the components, the inlet and outlet worked properly, the power supply and controller worked, there were no software problems, and serial data output was transferred to the controller and the RF modem link. Within the instrument, the computer, lamp, heaters, pump, and power supplies all worked properly. The 4-port valve worked flawlessly over hundreds of hours of operation on the buoy. The only problems were the added noise that appeared on channel B, and as expected, the high rate of power usage (typically 2 to 2.5 A at 27 V). However, there are several changes to the electrical system which can improve this. First, the cell heaters ran more than necessary. Better insulation will easily remedy this. For deployments in cold conditions, the heater setpoint of 33 C could be reduced as well. In the laboratory, we found that the air flow through the instrument was much larger than necessary. The pump can be run at a lower voltage to reduce flow, extending its life and reducing power consumption. However, the biggest improvements will have to come from the computer, which now accounts for over half the power consumption. Expertise developed at WHOI on low-power data systems will be used to tackle this problem.

Future work

We are now analyzing the data from the buoy test, and planning the next set of experiments. In the summer of 2002, we intend to deploy the ozone instrument at the Martha's Vineyard Coastal Observatory, for a combination of further engineering tests and science. We hope to have our first open-ocean buoy experiment in 2003.

Atmospheric ozone measured from the buoy on October 22, 2001

A short section of data from the same day, showing ozone fluctuations with timescales of a few minutes