A sensor system comprised of a diffuse light source and a sensor mounted
on a transparent layer of material that is adjacent to a fluid. The
refractive index of the transparent layer is greater than the refractive
index of the fluid, causing a portion of the diffuse light source to be
reflected from the interface of the transparent layer and the adjacent
fluid. A sensor is placed at a location to intercept the reflected light.
The diffuse light source and the sensor are optically coupled to the
transparent layer with a transparent material wit a refractive index
greater than that of the fluid. A light absorbing coating is placed ante
surface of the transparent layer in order to absorb extraneous light from
internal scattering of light from the fluid and light external to the
sensor system.