2. Measurements and Methods
Our field program included the
collection of data in June-August of 1998, 1999, and 2000 during three Arctic
cruises on the R/V
Oceania operated by the Institute
of Oceanology, Polish Academy of Sciences. The high-latitude study area
extended from about 70 to 80o N within the meridional zone between 1
and 20o E . This area includes the north polar waters of the
In situ optical measurements - In situ optical measurements were made down to a depth of 100 - 200 m in close proximity (time and space) to water samples collected from discrete depths. We used two in situ optical packages:
1) SeaWiFS Profiling Multichannel Radiometer (SPMR, Satlantic, Inc.) for measuring downwelling irradiance Ed and upwelling radiance Lu at 13 spectral wavebands in freefall mode away from ship perturbations. The instrument is equipped with a set of filters matching the SeaWiFS/MODIS bands, in addition to wavelengths which are not included in the current satellite ocean color sensors (for example, in the UV range).
2) Multisensor Datalogger System (MDS) for measuring vertical profiles of the physical and optical properties of seawater. The system includes SeaBird Sealogger 25 (SBE25) with temperature, conductivity, and pressure sensors, two single-wavelength (488 and 660 nm) c-Star beam transmissometers (WetLabs, Inc.), WetStar chlorophyll fluorometer (Wet Labs, Inc.), and PAR sensor (Biospherical Instruments, Inc). Hydroscat-6 sensor (HobiLabs, Inc.) providing measurement of light backscattering at six wavelengths in the visible spectral region is also integrated with the system.
Analysis of water samples - Water samples from discrete depths were used to measure particulate absorption spectra, ap(l) from 380 to 750 nm by means of a filter-pad technique. These measurements were made with a dual-beam bench-top spectrophotometer equipped with an integrating sphere (UV4-100, Unicam, Ltd.). Samples for chlorophyll-a concentration were also collected. Chlorophyll-a was typically determined with a spectrophotometric method using ethanol extracts. On the 1999 cruise additional samples were analyzed with HPLC and fluorometric methods (for details on chlorophyll methods see Chl-a methods ). The analyses of water samples were carried out in collaboration with Polish bio-optical team (Dr. R. Hapter, Mr. S. Kaczmarek, and Ms. J. Ston).
Other Observations- A number of observations and analyses were carried out as part of the Polish research program. Profiles of water temperature and conductivity were measured with the SeaBird CTD probe and ocean currents with ADCP (Prof. J. Piechura and Dr. W. Walczowski, hydrography team). Meteorological/air-sea interaction observations included wind speed and direction, air pressure, air temperature, air humidity, marine aerosol concentration and size distribution (Dr. T. Petelski, air-sea interaction team). Sky, sea surface state, and sea ice conditions were also recorded on a digital camera. Air bubbles in the near surface layers of ocean were measured with the acoustic technique (Dr. J. Tegowski, marine acoustics team). These ancillary observations are relevant to our project because, for example, the ocean reflectance depends on whitecaps and submerged bubble clouds.