Design and test of moored optical buoy
锚泊光学浮标浮体设计及近海试验

A spar body was considered and a free-rotated saddle was used in a moored optical buoy. Theoretical results indicated that the buoy’s high initial stability enables it to be stable. Due to the centre of gravity position being lower than the buoyant centre, the rolling angle of the buoy is small, as it would result in strong ability to resist tilting and capsizing. In situ experiment results indicated that 83% of the buoy’s tilt angles are ≤10° and 54% of the buoy’s tilt angles are ≤5° under the conditions of wind speed less than 7 knots and wave height less than 3-4m, therefore the buoy performance satisfies the technical requirement for underwater light measurements. To minimize the shelf–shading effects on the light measurements, two solutions were found: First of all, stroked-out structures were used to avoid shelf-shading of buoy body, and when the solar zenith angle was 0°, the shelf-shading errors of upwelling radiance were lower than 4% and 1% for coastal and open oceans, respectively; Second, fiber spectrometer was used to avoid shelf-shading of sensors. The diameter of designed optical sensors for irradiance and radiance was 0.042m. When the beam attenuation coefficient was 0.12m-1 and the solar zenith angle was 10°, the self-shading error was 1.5% for upwelling radiance.