Anatomy of the Weather Station

• The Davis Vantage Pro2 Plus Weather Station

  The Davis Vantage Pro2 Plus weather stations are typically mounted on the south side of school roofs so that the solar powered unit (shown here) receives unobstructed sunlight. The weather stations transmit data to a monitor located in the school and a small 3 Volt Lithium CR123A battery provides a backup power source for the unit. The weather station measures temperature, humidity, rain amount & rate, solar radiation, UV index, wind speed and wind direction. See our information page for a brief description of these weather variables and for a table showing the sensor specifications & accuracy.

• The Monitor

  A small portable display monitor is located in each school, typically in the school library, main office or computer lab. The display unit is hooked up to the computer we provide and this is connected to the school network. Data is then sent once a minute to our central server located at the University of Victoria and this data is made available through our website. Most of the display monitors have been set to display wind speed (in kilometers per hour), temperature and wind chill (in degrees Celcius), UV index, Daily rain (in mm), solar radiation (in Watts per square metre) and air pressure (in millibars) like the unit shown here. These settings can be changed by referring to either the complete manual or to the quick reference guide. Air pressure is measured within the display monitor and is corrected to sea level. This means that we need to accuracy know the elevation of where we install the display monitor.

• Measuring Wind

  The wind speed is measured by a simple Cup Anemometer. The wind speed is determined by measuring how many times the cups (seen in the photo) turn full circle in a second. A Weather Vane is also attached to the unit. It points towards (and then reports) the direction from which the wind is blowing. At each school, the arm holding the anemometer and weather vane always points northward (and the solar panel is always facing the south). The picture to the right shows wind coming from the south (southerly wind).

• Measuring Rain

  The amount of rain is measured using a Tipping Bucket rain gauge (shown here). Rain falls into the black cylinder (seen from above in the top photo on the right) which acts as a funnel and channels the water through a small hole in the base of the cylinder. The water then falls into one of two collectors which are balanced on a pivot (seen in the bottom photo on the right). Every time 0.254 mm (0.01 inch) of rain falls, the collector fill up and tips, thereby sending an electric signal to the receiving unit. By measuring the time between tips, the rain rate can be measured. The black cylinder is not heated so that when it snows, the snow will accumulate until such time as conditions allow it to melt. Melting snow will then fill the collecters with water causing them to tip. As a consequence, a snow fall will be recorded as a rain event once the snow has melted.

• Measuring Solar Radiation & the UV Index

  The weather station has a Solar Radiation Sensor (a silicon photodiode detector) that measures the solar radiation with wavelengths between 300 and 1100 nanometers. It is the small white disk located in the top left of the picture below. The weather station also has a Ultraviolet Radiation (UV) Sensor that measures the UV radiation with wavelengths between 290 and 390 nanometers. It is the small white disk located in the bottom left of the picture below. An interpretation of the UV index is given in the table on the right.

  UV Index Description Recomended Protection 0-2 Low danger to the average person Wear sunglasses; wear sunscreen if there is snow on the ground, which reflects UV radiation, or if you have particularly fair skin. 3-5 Moderate risk of harm from unprotected sun exposure Wear sunglasses and sunscreen, cover the body with clothing and a hat, and seek shade around midday when the sun is most intense. 6-7 High risk of harm from unprotected sun exposure Wear sunglasses and sunscreen having SPF 15 or higher, cover the body with clothing and a wide-brim hat, and reduce time in the sun from two hours before to three hours after solar noon. 8-10 Very high risk of harm from unprotected sun exposure Same precautions as above, but take extra care - unprotected skin can burn quickly. 11+ Extreme risk of harm from unprotected sun exposure Take all precautions, including: wear sunglasses and sunscreen, cover the body with a long-sleeve shirt and pants, wear a broad hat, and avoid the sun from two hours before to three hours after solar noon. Source: http://epa.gov/sunwise/uviscale.html.

• Measuring Temperature and Humidity

  The temperature and humidity sensor is found within the white radiation shield attached to the bottom of the weather station (shown to the right). This radiation shield protects the sensor from direct sunlight in the day and reduces radiative heat loss at night. It allows the temperature and humidity sensor to better measure the actual air temperature. In the three photos below, the radiation shield has been dismantled to show where the temperature and humidity sensor is located.

• Inside the radiation shield

  Top View

  Dismantled Radiation Shield

  Temperature/Humidity Sensor