Crowdsourcing Urban Wind Arjan Droste, Daniel Fenner*, Bert Heusinkveld & Gert-Jan Steeneveld Meteorology & Air Quality, Wageningen University *Chair of Climatology, Technische Universität Berlin

Mea$uring the city..?

Making use of Personal Weather Stations

The Question Can we use crowdsourced wind observations for urban research? Focus on the Netatmo wind module All the same brand, easy to compare Very popular, cheap PWS... But how good is it?

Data 2.5 years of Amsterdam NetAtmo data (60 stations) 23 WUR stations Hourly averaged wind speed Test NetAtmo at WUR weather field & TU Berlin against sonic observations

The NetAtmo station – Wind Gauge Relatively new (2015); not yet validated against observations We installed one () at our weather field to compare to our own measurements

Quality Control Remove 1.0 km/h hourly averages Filter out rain & humidity Correct for systematic underestimation

Wind statistics One-to-one comparison difficult due to hyperlocality Wind (ideally) follows Weibull distribution  compare distribution fit 𝑓 𝑥 = 𝑎 𝑏 𝑥 𝑏 𝑎−1 𝑒 − ( 𝑥 𝑏 ) 𝑎 for x ≥ 0 Suboptimal for heterogeneous terrain  mixture Weibull: 2 Weibulls in 1 Weibull example Shape says something about median wind speed: high shape = higher median WS.

Time to go to the city! All data between January 2017 and July 2018 Only the inner urban stations, for fair comparison 17 AAMS; 17 Netatmo stations Step-by-step improvement through the Quality Control

The Good, the Bad... Wind in open field can be measured Quality Control reduces bias Netatmo wind distributions match reference after QC ... But contains noise & bias, suffers from moisture ... But error at low wind speeds remains ... But low wind events are still poorly captured

...and the Ugly!? All this water came out of the Netatmo sensor after being out in the field for a few months... Thanks for your attention!

Low-wind event Filtered data (left) ; filtered & bias-corrected data (right) AAMS Netatmo AAMS Netatmo Bonus slide

The NetAtmo station – Wind Gauge Specifications Height: 110 mm / Diameter: 85 mm 4 ultrasonic transducers measure wind Wind speed: Range: 0 to 45 m/s; Accuracy: 0.5 m/s Wind direction: Accuracy: 5° Records wind speed, direction & gusts https://www.netatmo.com/en-US/product/weather/weatherstation/specifications Bonus slide https://www.netatmo.com/en-US/product/weather/weatherstation/specifications