|The observing system is deployed on the P.T. Barnum, the newest vessel of the Bridgeport Port Jefferson Steamboat Company's fleet of three ferries. The schematic diagram above shows the general placement of the different environmental sensors. In general, the system consists of one set of instruments to measure near-surface meteorological properties (upper diagram), one set of instruments to measure surface water properties and current profiles below the ship (lower diagram), and additional equipment to log, display and transmit the data. Measurements of the near-surface water properties are based on sampling water from a sea-water intake system. Measured quantities include sea surface temperature (SST), salinity, chlorophyll-a, and dissolved oxygen. In general, the meteorological sensors are placed on either the roof of the upper deck or on masts fixed to the two bridge wings. In this case, measured quantities include wind speed and direction, temperature, relative humidity, pressure, incoming solar and infrared radiation, and precipitation. The system also includes a Global Positioning System (GPS) to provide position information for the data samples. In addition, a compass provides orientation information for the vessel. This, along with the GPS position, provides the information necessary for correcting the wind observations for the movement and orientation of the vessel.
Apart from providing basic meteorological and hydrographic information for the central Long Island Sound, the above set of meteorological measurements, in conjunction with the SST data, provide the necessary information to compute robust estimates of the exchanges of heat, momentum and freshwater across the air-sea interaface (see Objective 2). Specifically, this involves the four main components of the surface heat flux (i.e., net solar and infrared radiative fluxes, latent and sensible fluxes), the surface wind stress, and the surface freshwater flux.
The instrument packages relay their measurements to a computer housed on the vessel. This computer stores the data internally as well as transfers the data in "real-time" (about every 15 minutes) to the Marine Sciences Research Center at Stony Brook University where it is displayed on the world wide web, disseminated to the local National Weather Service office as well as analyzed in the context of the project's Scientific Objectives. The computer also displays the data on board the vessel itself to provide the observed information to the passengers and crew.
The P.T. Barnum traverses the central Long Island Sound approximately eleven times every day of the year during the hours of about 7am to 9pm, except for short intervals (~days) when it is dockside for periodic maintenance. For the most part, this sampling scheme will provide the means to measure and document seasonal variations, synoptic weather variations, and some aspects of the diurnal cycle as well as the cross-Sound variability that might be present in the quantities discussed above.