<title>Monte Carlo modeling of the light field in reflective-tube-type absorption meters</title>

The light field in reflective tube type absorption meters was modeled with Monte Carlo methods. The entrance light field was varied and the systems geometry was varied together with the inherent properties of a test medium. This enabled us to calculate the radiance attenuation as a function of the field of view for several variants of a reflective tube absorption meter. It was found that an instrument with a Lambertian entrance light field and a small field of view measures the sum of absorption and backscattering with an error less than 2 - 5%. This result is independent of the shape of volume scatter functions for surface water. For small fields of view the reflectivity of the cylinder was found not to be critical.