Expendable high precision micro optical sensors to be used in automated concerted profilings for large area density contouring of the deep sea

This paper deals with a newly developed miniature optical density probe of better than ppm precision on the basis of the measurement of the angle of refraction of a tiny collimated light beam when passing through the interface plane between the sea water under test and an optical index of refraction standard reference material. For the first time the problems of designing and building of an extremely stable optical bulk head in combination with a particularly compact micro optical bench module were solved. These findings were the prerequisites to achieve the required high stability of the instrument. The central opto-electronical parts are few and consist mainly of a well defined single mode laser diode as a light source and a high precision lateral effect photo diode as beam position measuring device of the goniometer. The realized prototypes measure in all Neptunian waters down to 6000 meters. These high precision micro optical density measuring devices for buoyancy driven expendable pop-up profilers are to be released in concerted actions from numerous bottom stationed autonomous multiple shot releasers properly distributed over a large area in the deep sea in order to observe the variability of the density field in space and time with high precision.