The most important influence on in-situ absorption measurements is turbidity. Turbidity due to
suspended substance causes light scattering, shading and thus influences absorption over the entire
spectrum, whereas other interfering substances absorb light only in a limited wavelength region. It
is well known that the spectral shape caused by suspended solids depends upon the wavelength with
a factor l
x
, where x depends on the particle diameter. Therefore for turbidity compensation a
mathematical equation was developed which describes the relationship between scattering intensity
and wavelength as a function of the particle diameter based on the basic relationships given by
Huber and Frost (1998). The turbidity compensation feature uses the original spectrum and
estimates two parameters of the turbidity function. Turbidity compensation has two tasks: the
measurement of turbidity/suspended solid and baseline compensation for the measurement of
dissolved substances. The results of the turbidity compensation showed to be very sensitive to the
initial values of these parameters.