Rainfall estimation using moving cars as rain gauges – laboratory experiments

Abstract

Abstract. The spatial assessment of short time-step precipitation is a challenging task. Low density of observation networks, as well as the bias in radar rainfall estimation motivated the new idea of exploiting cars as moving rain gauges with windshield wipers or optical sensors as measurement devices. In a preliminary study, this idea has been tested with computer experiments (Haberlandt and Sester, 2010). The results have shown that a high number of possibly inaccurate measurement devices (moving cars) provide more reliable areal rainfall estimations than a lower number of precise measurement devices (stationary gauges). Instead of assuming a relationship between wiper frequency (W ) and rainfall intensity (R) with an arbitrary error, the main objective of this study is to derive valid W -R relationships between sensor readings and rainfall intensity by laboratory experiments. Sensor readings involve the wiper speed, as well as optical sensors which can be placed on cars and are usually made for automating wiper activities. A rain simulator with the capability of producing a wide range of rainfall intensities is designed and constructed. The wiper speed and two optical sensors are used in the laboratory to measure rainfall intensities, and compare it with tipping bucket readings as reference. Furthermore, the effect of the car speed on the estimation of rainfall using a car speed simulator device is investigated. The results show that the sensor readings, which are observed from manual wiper speed adjustment according to the front visibility, can be considered as a strong indicator for rainfall intensity, while the automatic wiper adjustment show weaker performance. Also the sensor readings from optical sensors showed promising results toward measuring rainfall rate. It is observed that the car speed has a significant effect on the rainfall measurement. This effect is highly dependent on the rain type as well as the windshield angle.

Areal rainfall estimation using moving cars – computer experiments including hydrological modeling

“…Rabiei et al (2013) proposed to use a linear relationship for taking the effect of the car speed for RainCars into consideration. A similar approach could be applied for compensating the effect of wind speed, knowing the wind direction.…”

“…The results are compared with what occurs in practice, i.e., using only the rain gauge network. The uncertainties for the rainfall measurement by RCs are taken from the results of the laboratory experiments (Rabiei et al, 2013). For a more general conclusion, larger uncertainties are also investigated.…”

“…This is more important for high temporal resolution data when the spatial variability of rainfall becomes larger. Rabiei et al (2013) investigated the possibility of using RCs for rainfall estimation with laboratory experiments. A strong relationship between rainfall intensity and the wiper speed, adjusted with front visibility, was observed.…”

“…Is the accuracy of optical sensors investigated by Rabiei et al (2013) sufficient for areal rainfall estimation as well as discharge simulation?…”

“…As a result, several new ideas have emerged to help estimating areal rainfall with higher temporal and spatial resolution. Rabiei et al (2013) observed that moving cars, called RainCars (RCs), can potentially be a new source of data for measuring rain rate. The optical sensors used in that study are designed for operating the windscreen wipers and showed promising results for rainfall measurement purposes.…”