Evaluation of a Low-Cost Optical Rain Sensor

Abstract. Rain gauges play a vital role in weather monitoring, irrigation and drainage water management, and hydrologic studies. The need exists for an accurate, low-cost, and yet robust recording rain gauge not subject to plugging. The objective of this study was to compare an optical rain sensor with manual and tipping bucket rain gauges in field settings and to perform laboratory calibrations of the optical sensor. Optical, manual, and tipping bucket rain gauges were installed adjacent to one another, on a single adjustable stand, at field locations near Wyndmere, Fargo, and Grand Forks in eastern North Dakota for portions of the growing season in 2013; field data in this paper focuses on the data from Wyndmere. Laboratory testing of the optical sensor included calibration of the sensor using equipment and procedures employed for tipping bucket rain gauges. At the Wyndmere site in 2013, the optical sensor tended to overestimate large rainfall events and underestimate smaller rainfall events. Linear regression of manual vs. optical sensors produced an R² of 0.75. The average percent deviation and the average absolute percent deviation of the optical sensor from a manual rain gauge at Wyndmere in 2013 were 55.0% and 86.9%, respectively. Laboratory testing indicated that the optical sensor is not a promising candidate to replace the water measurement mechanism in a tipping bucket rain gauge. Analyses of the data from Fargo and Grand Forks remains to be done. Additional field testing is planned for 2014.