Effects Of Sensor Characteristics On The Inferred Vertical Structure Of The Diffuse Attenuation Coefficient Spectrum

A series of model calculations illustrate how the spectral characteristics of an irradiance sensor can affect estimates of the vertical structure of the diffuse attenuation coefficient for downwelling irradiance (K(z,λ)). The effect of a finite spectral response function is observed in regions of the spectrum where large dispersive changes exist in the optical properties. For open ocean environments, this occurs in the orange-red region of the spectrum (λ550nm). Four model calculations are made using different spectral response functions (h(λ)) to determine the effects on the inferred K(z,625nm) profiles related to: 1) a finite bandpass, 2) the "leakage" of a finite amount of blue-green light, 3) spectral tails, and 4) a spectral response function measured with a spectroradiometer. The results of these model calculations indicate that the background irradiance (or equivalently- the blocking level) sampled by the spectroradiometer must be less than 10-6% (or 8 orders of magnitude) of the irradiance of interest for an accurate estimate of K(z,x). Also, the half power bandwidth of h(λ) should he lOnm or less. The model results are compared to observed vertical profiles of K(z,λ) sampled from the R/P FLIP in the North Pacific Ocean during the Optical Dynamics Experiment (ODEX). These calculations illustrate the possible implications of inappropriate sensor design on the interpretation of observed K(z,λ) profiles.