A large number of images of the sea-surface have been taken during recent UK-SOLAS funded cruises in the North Atlantic and Norwegian Sea. The RRS Discovery cruises DOGEE and SEASAW have provided approximately 60 days of whitecap images (over 60,000 images) in open ocean conditions. Since September 2006 images are continually being recorded from the weather ship M/V Polarfront located at Station Mike (66N, 2E). This is believed to be the largest collection of open ocean whitecap images, with associated surface meteorological and wave measurements, ever assembled. It will form an invaluable data set for future investigation of air-sea exchanges of CO2, moisture and heat, marine aerosol production and validation of satellite derived foam coverage.

Digital images taken from the bridge of the RRS Discovery and M/V Polarfront were converted to a greyscale image. A manually selected threshold value was used to identify the total whitecap fraction from the background sea surface. Images contaminated by sun-glint and sky reflection were manually removed from the analysis. To reduce the processing time automatic methods to select the threshold value are being explored.

Initial results show an increase in whitecap fraction with wind speed, which is similar to the open ocean measurements of Monahan and O'Muircheartaigh (1980). Further analysis of the images from Polarfront will provide whitecap data at mean wind speeds of up to 28 m/s. When complete, the whitecap data from these UK-SOLAS cruises will be used to investigate parameterizations of whitecap coverage in terms of mean meteorological variables and sea state.