A new optical disdrometer has been developed that is optimized for use in high wind speeds, for example, on board ships. The minimal detectable size of droplets is 0.35 mm. Each drop is measured separately with regard to its size and residence time within the sensitive volume. From the available information, the drop size distribution can be calculated with a resolution of 0.05 mm in diameter either by evaluation of the residence time of drops or by drop counting knowing the local wind. Experience shows that using the residence time leads to better results. Rain rates can be determined from the droplet spectra by assuming terminal fall velocity of the drops according to their size. Numerical modeling of disdrometer measurements has been performed, allowing the study of the effect of multiple occupancy of the sensitive volume and grazing incidences on disdrometer measurements. Based on these studies an iterative procedure has been developed to eliminate the impact of these effects on the calculated drop size distributions. This technique may also be applied to any other kind of disdrometer. Long-term simultaneous measurements of the disdrometer and a conventional rain gauge have been used to validate this procedure.

A ship rain gauge has been developed that can be used under high wind speeds such as those experienced by ships at sea. The instrument has an improved aerodynamic design and an additional lateral collecting surface, which is effective especially with high wind speeds. The ship rain gauge has been calibrated at sea against a specially designed optical disdrometer. An accuracy of 2%-3% has been obtained for 6-hourly sums. The ship rain gauge has also successfully been tested at a test site of the German Weather Service and presently is used on research vessels and voluntary observing ship.

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