Evaluation and improvement of an iterative scattering correction scheme for in situ absorption and attenuation measurements

The performance of several scattering correction schemes for reflecting-tube absorption and beam attenuation measurements is evaluated with data collected in European shelf seas. Standard scattering correction procedures for absorption measurements perform poorly because of nonzero absorption in the near infrared and wavelength-dependent scattering phase functions. A previously described iterative correction procedure based on Monte Carlo simulations of the Western Environmental Technologies Laboratories (WET Labs) ac-9 and independent estimates of particle backscattering initially performs poorly, but is greatly improved when realistic losses at flow-tube walls are incorporated into the model. The updated Monte Carlo scattering correction provides excellent agreement with independent absorption and attenuation measurements made with a point-source integrating-cavity absorption meter (PSICAM) and a Laser In Situ Scattering and Transmissometer (LISST, Sequoia Scientific), respectively. Implications for historic datasets and requirements for application to future datasets are discussed.