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An Electronic Discriminator to Eliminate the Problem of Horizontal Raindrop Drift¹

ABSTRACT

Raindrops falling through still air drift randomly causing difficulty in collecting uniform soil splash samples from single-drop detachment studies. We developed a simple electronic discriminator to eliminate this problem that can be used easily with any single drop rainfall tower. The main detector of the discriminator consists of two optical light source-sensors positioned at right angles in a horizontal plane. These sensors detect and select for use only those drops falling within a 6.4 mm square target window. Labor and materials for constructing the discriminator cost about $400. Two experiments were conducted to test the performance of the discriminator. One study analyzed drop masses collected both with and without use of the discriminator, and compared these quantities with drops collected directly from the drop former. No significant difference in mass between drops collected with the device and those collected directly from the drop former was found. A significant (P<0.01) decrease in drop mass was found without use of the device. The discriminator also decreased drop mass variance about six times. The second experiment measured soil splash from uniformly packed cores of Norbourne fine-sandy loam (Typic Argiudolls) packed at an average bulk density of 1.35 Mg m^–3 and equilibrated to –2 kPa soil water potential. Results show an average splash increase of about 46% (4.2 mg) with use of this device versus without it. Soil splash variance was also reduced by 19%, further confirming that use of the discriminator significantly reduces alterations in drop characteristics, thus insuring against biasing of raindrop kinetic energy versus soil splash relationships.

¹ Contribution from the Missouri Experiment Station Journal Series no. 9493. Univ. of Missouri, Columbia, MO 65211. This work was supported by Missouri Agric. Exp. Station Project 396, and University of Missouri/ARS Cooperative Agreement no. 58-519B-3-1235.

² Assistant Professor of Agronomy, Univ. of Missouri, Columbia, MO 65211. Soil Scientist, USDA-ARS Watershed Research Unit, Columbia, MO 65203 and Electronics Technician, Office of Research, Univ. of Missouri, Columbia, MO 65211.

Received for publication March 9, 1984. Accepted for publication August 10, 1984.