HTB weather and precipitation sensors Mesoscale Atmospheric Network Workshop University of Helsinki, 12 February 2007 Heikki Turtiainen

©Vaisala | date | Ref. code | Page 2 Contents WXT510 Weather Transmitter WXT network implementation VRG101 Weighing Precipitation Gauge

©Vaisala | date | Ref. code | Page 3 WXT510 Weather Transmitter Compact (only 9.5” / 24 cm tall) No moving parts - durable and requires minimum maintenance Optimal life time cost Easy to use purchase, install and use 6 MEASUREMENTS IN 1 INSTRUMENT 1. temperature 2. relative humidity 3. rain fall 4. wind speed 5. wind direction 6. barometric pressure

©Vaisala | date | Ref. code | Page 4 WXT510 Weather Transmitter CPU board Pressure, temperature and humidity module Screw terminal Ultrasonic wind sensor Piezoelectric rain sensor

©Vaisala | date | Ref. code | Page 5 Weather Transmitter WXT510 - Basic Specs Relative Humidity Range: 0…100% Accuracy: ± 3% (0-90%) ± 5% (90-100%) Air Temperature Range: -52…+60°C (-60…+140°F) Accuracy* (at 20°C): ± 0.3°C (0.5°F) Barometric Pressure Range: 600…1100 hPa Accuracy: ± 0.5 hPa (0…30°C) ± 1.0 hPa (-52…+60°C) Wind Speed Range: 0…60 m/s Accuracy: m/s ± 0.3m/s or ± 3%, whichever is greater m/s ± 5% Wind Direction Range: 0…360° Accuracy: ± 3° Liquid Precipitation Accumulation Accuracy: 5%** Intensity Range: 0…200 mm/h * for sensor element ** Due to the nature of the phenomenon, deviations caused by spatial variations may exist in precip. readings, especially in short time scale. The accuracy specified does not include possible wind induced error

©Vaisala | date | Ref. code | Page 6 Windcap - ultrasonic wind sensor Durable and maintenance free Zero starting thresholds or distance constants virtually zero. No moving parts - thus sensor performance doesn’t degrade with wear nor is affected by natural contaminants such as salt, dust or sand. Vaisala’s proprietary equilateral triangle design solves the turbulence problem. (1 redundant measurement path)

©Vaisala | date | Ref. code | Page 7 Equilateral triangle design vs. orthogonal design Reliable measuring paths Unreliable measuring path Wind direction Turbulence Unreliable measuring path Reliable measuring paths Vaisala proprietary equilateral triangle design Orthogonal design Turbulence Wind direction

©Vaisala | date | Ref. code | Page 8 RAINCAP  measuring principle A raindrop hitting the piezoelectric detector generates a voltage pulse U i, whose amplitude is a function of the drop volume V i. Consequently, drop size can be estimated from the measured voltage: V i = f(U i ) Accumulated rainfall is sum of the individual drops R [mm] = Σ f(U i )

©Vaisala | date | Ref. code | Page 9 RAINCAP  calibration Type calibration is based on comparison with accurate reference instruments under different field conditions: light and moderate rain in Finland moderate and heavy rain in Malaysia Individual production calibration using highly repeatable laser pulse equipment Rainfall R = Σ f(U i )

©Vaisala | date | Ref. code | Page 10 Helsinki Testbed Weather Transmitter network Currently 62 stations with 112 WXT510 weather transmitters. Average distance < 10 km. Data interval 5 min.

©Vaisala | date | Ref. code | Page 11 Cell phone base station masts utilized as meteorological towers Upper Weather Transmitter h = m Lower Weather Transmitter h = 2 m GPRS communications unit Middle level Weather Transmitters h = m

©Vaisala | date | Ref. code | Page 12 Installation examples Temporary battery operated WXT station near Hietaniemi Beach.

©Vaisala | date | Ref. code | Page 13 All-weather Precipitation gauges Weighing rain gauges 5 pcs VRG101 all-weather precipitation gauges –Lahti –Nummi-Pusula, Loukku –Vihti, Maasoja –Nurmijärvi, Röykkä –Helsinki, Malmi Airport measure both liquid and solid precipitation heated rim Tretyakov-type wind shield communications: GPRS Lahti

©Vaisala | date | Ref. code | Page 14 VRG101 - Vaisala All Weather Precipitation Gauge FEATURES Weighing principle applying high accuracy, temperature compensated load cell Simple, robust design All weather operation with heating option High capacity up to 650 mm (25”) Large collecting area to enhance performance in light rain and snow Selection of optional features for enhanced performance and extended service interval Field-removable measurement unit, enabling use of pre-calibrated measurement units. Field check with dedicated weight.

©Vaisala | date | Ref. code | Page 15 VRG101 Components 1=Lock 2=Collecting funnel 3=Side guide plate 4=Container (volume 30 liters) 5=Faucet 6=Collector tray 7=Spirit level 8=Load cell and electronics 9=Base plate 10=Rim 11=Top cone 12=Enclosure

©Vaisala | date | Ref. code | Page 16 Specifications of VRG101 Capacity650 mm (25 in) without automatic draining pump antifreeze charge included Collecting area400 cm 2 (62 in 2 ) Resolution0.1 mm (0.005 in) Accuracy± 0.2 mm (± 0.01 in) of measured amount during a rain event > 0.5 mm Temperature range °C ( °F) Output Serial RS485/RS232 Pulse (tipping bucket emulation) Power Consumption< 30 mW (without heating)

©Vaisala | date | Ref. code | Page 17 Problems with Liquid Precipitation: Evaporation Error Evaporation of collected water Problem: Evaporation from the container

©Vaisala | date | Ref. code | Page 18 VRG101 Solution: Evaporation Error VRG101 software filters out “negative rainfall” due to evaporation Use of anti-evaporation oil is not required uncorrected corrected time rainfall mm

©Vaisala | date | Ref. code | Page 19 Problems with Liquid Precipitation: Wetting Loss... evaporate and are never measured Problem: Wetting loss on the gauge inlet Raindrops sticking on the inlet tube...

©Vaisala | date | Ref. code | Page 20 VRG101 Solution: Wetting Loss The orifice/inlet geometry minimizes wetting loss: Funnel shaped inner orifice element is resting on the collector container so that it’s mass is measured together with the container. Water sticking on the funnel surface will be measured and included in the cumulative rainfall before it evaporates.

©Vaisala | date | Ref. code | Page 21 VRG101 Solutions for Solid Precipitation Solution: The mass of the funnel element is also measured. Snow accumulation on the funnel surfaces does not introduce error. Problem 1: Uneven snow distribution in the container Solution: The load cell technology used measures only forces along the vertical axis. Eccentric snow accumulation is not a problem. Problem 2: Snow deposit on the inlet funnel surface

©Vaisala | date | Ref. code | Page 22 VRG101 Solutions for Solid Precipitation Solution: Intelligent heating control by software Heating is applied only when necessary, using control algorithm based on air temperature and precipitation amount. Evaporation loss caused by heating is minimized. Compared to continuous heating, power consumption on a typical winter day is decresed from over 2 kWh to kWh. Problem 4: Evaporation error caused by heating Problem 5: Large heating power consumption Problem 3: Outblowing of snow Solution: Optimized gauge geometry for solid precipitation. Deep container and funnel-shaped inlet orifice minimize outblowing of snow.

©Vaisala | date | Ref. code | Page 23 VRG101 Wind Shields XRS111 / XRS121 / XRS131 Stabilizes the wind conditions over the gauge

©Vaisala | date | Ref. code | Page 24 Installation examples WXT + VRG101 weighing precipitation gauge at Malmi Airport