Draft,construction and operation of a sequential rain sampler

Sequential sampling of rain on a volume basis presents fewer problems than sampling on a time basis. The optimum diameter of the collector opening depends on the rainfall statistics, the size of the sample needed for chemical analysis and the total number of samples that has to be collected. The sampler described here consists of a square polyethylene funnel of 0.64 m² and a fraction collector with 250 polypropylene tubes of 39 ml, which is activated by a rain detector. Each fraction corresponds to about 0.05 mm of rainfall. The funnel is covered by a roller blind that automatically rolls up when it starts to rain. Evaluation of the system leads to the conclusion that the collector opening can be made smaller (by 0.20 m²), that the measured rainfall rate depends on the averaging time, and that all other surfaces of the sampling set-up should be covered with inert material.