Shearing Stress Meter

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  • a Air Force Cambridge Research Laboratories, Bedford, Mass. 01730
  • | b Division of Environmental Mechanics, CSIRO, Canberra, Australia
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Abstract

An improved shearing stress meter (drag plate) of 6 ft (183 cm) diameter has been constructed for micro-meteorological work. This size should enable representative sampling of rough surfaces and is intended particularly for farmland experimental sites where, after harvesting, the ground is either left to grain stubble or ploughed.The sensors are inductive proximity probes, whose advantages of robustness and stability enable the instrument to be handled without undue precautions against damage and to withstand gusts of over 20 dyn cm−2 while achieving a resolution of 0.01 dyn cm−2.Comparison experiments involving two drag plates installed in a ploughed field with a sonic anemometer mounted nearby indicate good agreement in stress measurement among all three instruments.

Abstract

An improved shearing stress meter (drag plate) of 6 ft (183 cm) diameter has been constructed for micro-meteorological work. This size should enable representative sampling of rough surfaces and is intended particularly for farmland experimental sites where, after harvesting, the ground is either left to grain stubble or ploughed.The sensors are inductive proximity probes, whose advantages of robustness and stability enable the instrument to be handled without undue precautions against damage and to withstand gusts of over 20 dyn cm−2 while achieving a resolution of 0.01 dyn cm−2.Comparison experiments involving two drag plates installed in a ploughed field with a sonic anemometer mounted nearby indicate good agreement in stress measurement among all three instruments.

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