Expendable optical density profilers started from intelligent multiple shot launcher on the deep sea bottom with storage capabilities over several years

The authors developed small light weight expendable density probes with 10^-6 precision on the basis of refractometry. Since several years they tackled the very hard problems of long term stability. The decisive step to arrive at the irrevocable extremely high stability of the probe was the realization of the high pressure tolerant single block sensor head cut, ground, and polished from just one single optical glass reference material serving as index of refraction reference body and as an optical beam bulk head feed through at the same time. To ensure long term stability during storage at the sea floor the optical sensor tip is surrounded by a hermetically sealed capsule, which is completely filled with a sterile conserving liquid used also as a reference liquid against which to check the sensor stability from time to time