Weather Station Firmware & Calculations

Some weather variables need to be recorded live as an integral function of the weather station, and other calculations can be done in post analysis - but are much more convenient to have in the same data set as your original data.

Sometimes you may need to trigger an SMS or email alert on the calculated value - such as the peak wind gust when monitoring for OH&S, or the heat stress values for either workers or livestock.

Environdata has a range of specialised firmware and calculations that can be built into the weather station, to provide you with advanced weather data as virtual sensors - built into the same databases as the weather data itself.

 

Wind Movement & Analysis Firmware

Recording a constant wind speed and direction can be done accurately by almost any weather station. However, accurate recording while the wind is varying in speed, direction or both, is far more difficult.

As an example, using the standard scalar values, which are a simple average of the direction over time:  half a minute of wind from the East and half a minute from the North would be reported as a wind direction from the North-East.  However, if the Easterly wind blows at a speed of 5m/s, the effect of a Northerly wind at 20m/s would be to blow airborne particles much more South than West.  This shows the importance of combining the wind speed with the wind direction data, known as Vector wind speed and vector wind direction.

Environdata’s AirData firmware in our Weather Maestro or WeatherMaster 3000 weather stations calculates the net effect of wind speed and direction, the vector wind speed and direction for each reporting period.

The weather stations:

  1. Continuously average wind speed each second
  2. Continuously average wind direction each second and detects and corrects for a transition through the NORTH point during the second
  3. Calculates & records NORTH/SOUTH component
  4. Calculates & records EAST/WEST component
  5. Records the Vector angle (Vector wind direction)
  6. Records the Vector magnitude (Vector Wind Speed)

In all of the above, the wind movement is normally treated as a wind speed, but can be treated as a wind run. For example, if the period of time for the scenario illustrated in Figure 1 and 2 was one hour, then the particles would have actually travelled 5.68 kilometres at an angle of 63º. 

 

Peak Wind Gust & Sigma Theta

Sigma Theta

Once the net movement of the centre of the airborne particles has been determined, the spread of the particles might be required. This is normally calculated from Sigma Theta, the standard deviation of the wind direction.

The Sigma Theta calculation has been developed by Maritimo, Williams et al. It uses the sum of sines and sum of cosines collected over the period.

The Environdata Weather Maestro weather stations can provide this Sigma Theta calculation as a standard firmware output.  This is usually required as part of an Australian Standard (AS3580.14:2014) Weather Station, with the wind sensors at 10 metres above ground on a tilt-able ten metre mast.

Peak Wind Gust

The AirData firmware can measure the highest wind gust for any given period. The “gust” is the highest consecutive 3 seconds of wind speed during a reporting interval.  If we look at our typical current readings interval of 60 seconds, then the AirData firmware will calculate the total wind speed for seconds 1, 2 & 3, then seconds 2, 3 & 4, then 3 , 4 & 5 and so on.  There are 60 x 3 second samples in any 60 second period. 

The highest consecutive 3 seconds is saved as the peak wind gust in that minute, ten minute (for example), hourly or daily intervals. be saved in the weather station memories.

In detail, the AirData firmware:

  • Monitors every consecutive 3 seconds of wind speed, as a rolling 3 second window.
  • Records the highest 3 second sample as the peak wind gust for each respective reporting interval

Evapotranspiration / Evaporation Rate

Environdata’s Weather Stations can provide a Penman FAO56 Evaporation calculation as a standard output (from a “virtual” sensor) if the appropriate actual sensors are connected: namely, relative humidity, air temperature, wind speed and solar radiation.

The calculation used is the hourly equation from the most recent Irrigation and drainage paper (FAO56) entitled Crop Evapotranspiration. The FAO56 calculation has been recognised by researchers and managers as the most accurate way to determine evapotranspiration in crops.  However it has also proved to be a reliable and accurate way to calculate evaporation from open bodies of water such as dams or reservoirs.

However, the calculations rely on accurate data from an onsite weather station, calculated hourly, the weather station will need to have Air temperature, relative humidity, wind speed and solar radiation (or net radiation) sensors.

Output: Evaporation Rate in mm per hour & total evaporation per day in mm 

Traditional Method - Class A Pan

The calculation of evaporation has been traditionally done by meteorologists using an “A” class pan – a 120.7mm diameter pan filled with 20cm of water, with measurements taken every morning at 9am to determine the change in water level from evaporation.   

This method is more expensive, and requires a higher level of maintenance to ensure the Pan is operating correctly.  While the Class A Pan is often no longer used, utilising the Evaporation rate firmware instead, they are stil required for empirical studies and monitoring.  Environdata can provide you with a class A Pan, in easy to maintain polished marine grade stainless steel, with bird guard, Automatic refill kit & water level sensor.

Thermal Work Limit (TWL)

Heat stress occurs when the body’s metabolic heat production exceeds the individual’s ability to dissipate the heat produced by exercise (work).

To help mitigate risk of heat stress on workers in risky environments, work sites need to monitor the weather.  The Thermal Work Limit is the best practice method to monitor for conditions that may lead to heat stress.  Developed by researchers at Curtin University, TWL calculates the ability of an acclimatized worker to safely dissipate heat generated by their metabolic activity, or work level.

Environdata has incorporated the TWL firmware into their Weather Stations, as long as you have the correct sensors attached, Air Temperature, Relative Humidity, Wind Speed and Black Globe Temperature. The traditional heat stress measurement of Wet Bulb Globe Temperature (WBGT) is also a standard output from the TWL firmware.

Heat Load Index & Accumulated Heat Load Units

Otherwise known as HLI & AHLU, Heat Load Index and Accumulated Heat Load Units are extremely important measures of cattle heat stress, typically in feedlot conditions.  Environdata's Weather Maestro Weather Stations calculate HLI & AHLU - including Multiple AHLU in our latest models.  You will need the correct sensors; Black Globe Temperature, Relative Humidity & Wind Speed.

Calculated every hour using the official MLA HLI and AHLU Calculations, with your own weather station onsite to monitor the heat stress conditions, you have the ability to implement management plans to avoid the worst effects of heat stress.

Environdata are Australia’s weather station specialists since 1982, so please contact us for advice on your weather monitoring requirements, positioning on your site, and general advice on all things weather station related.

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