PnB_PRR_Calibration

The accuracy of the upper ocean apparent optical properties (AOPs) of the Santa Barbara Channel ultimately depends on precise and consistent radiometric calibrations.

Our profiling reflectance radiometer is calibrated twice each year and, for the most part, this instrument has been stable for the entirety of the project. As a result, we have been able to rely on the use of coefficients that have been interpolated between scheduled calibrations.

Below are plots of the calibration history:

The PRR-600 is a hand-lowered profiling reflectance radiometer designed to measure downwelling irradiance, upwelling irradiance, and reflectance in the SeaWiFS wavelength bands. The instrument measures seven channels each of downwelling irradiance and upwelling radiance (412, 443, 490, 510, 555, 665 nm, and PAR (400-700 nm)). Temperature and depth/pressure transducers operate to 200 m. Tilt and roll sensors are also included.

The PRR incorporates a free-fall design that allows it to drop away from the ship and avoid ship-shadow. Filter photodetectors in the head of the unit are specified to 10 nm FWHM +/- 1 nm with center wavelengths designed to hit the SeaWiFS bands while taking into account details such as the viewing geometry of the system. Both the irradiance and radiance detector geometries have been designed to limit the solid angle to 10o, and the filter design has been specified to compensate for this solid angle in arriving at the center wavelengths and bandwidths in the assembled instrument. The PRR-600 irradiance collector is Teflon®, backed with quartz, optimized for excellent cosine response in water.