How the Weather System Works

The weather system has two parts: a solar-powered Frost Alarm/Weather Station and the Harvest database with its web server. In the field, the weather station regularly records weather data (temperature, wind, rainfall, etc.). Every hour during normal conditions or every minute under frost conditions, the system sends its new data via a GPRS cellular link to the central Harvest database. Our database processes, records, and then stores your weather data.

On the website you can view current graphs as well all your weather history, and you can configure your alarms and password.

Temperature

Temperature is measured with up to six digital sensors (2 x wired and 4 x wireless) which can be placed anywhere near the weather station.

Rainfall

Rainfall is measured with a tipping-bucket rain gauge.We can supply the low cost Pronamic gauge (1mm per tip), higher cost Davis gauge (0.25mm per tip) or you can supply your own rain gauge.

Wind

Wind is measured using a Davis Instruments anemometer, usually mounted directly on top of the weather station. These sensors are rated from 4–280km/h and have an accuracy of 5%.

Humidity

Humidity is measured using a Honeywell HIH-3610 sensor, which has a range of 0–90% and an accuracy of 5%. After the humidity data has been temperature-compensated, the dewpoint temperature is calculated from the humidity and the air temperature.

Soil Moisture

Soil Moisture is measured using either a Decagon EC-20 or EC-5 probe. The newer Decagon EC-5 sensor has an accuracy of ±3% across all soil types. More info on both sensors can be found on the Decagon website.

Other Sensors

Other sensors are available, such as leaf wetness, solar radiation, flow meters, float switches and pressure sensors. We can monitor analog and digital inputs of various kinds, such as battery voltage and contact inputs.

Alarms

Every weather system can be configured with frost and heat alarms. If frost alarms are turned on and the temperature goes below the set frost alarm temperature, a text message (or voice message or email) is sent to the user. Frost alarms are useful for crop growers, among other things—they alert the owner to the danger so action can be taken before crops are damaged, and they only operate during a given growing season. Heat alarms are useful wherever over-heating is a problem: an alarm message is sent when the temperature exceeds the set heat alarm temperature.

Each sensor can have both a frost alarm and a heat alarm, and each alarm is specified with two alarm levels and a reset level. For a frost alarm, a paging message is sent when the temperature crosses below each of the two alarm levels. No more alarms are sent until the temperature has crossed back above the reset level, at which time the weather system goes back into "wait for alarms" state. Heat alarms work the same way, but the temperature must cross above the given temperatures for an alarm, and back below the reset level to reset.

Alarms can be configured on almost any input: digital inputs, analog sensors, battery voltages, high wind speed, etc.

Growing Degree Days (GDD)

Growing degree days are used to estimate the maturity of crops during a growing season. We calculate GDD10 values (GDD50 for Fahrenheit), which means that the average daily temperature is accumulated only if it is above 10°C (50°F). More specifically, we use the standard GDD formula:

GDD10 = max(0, Tavg−10)
GDD50 = max(0, Tavg−50)

where Tavg is a day's mean temperature. Each day's GDD value is then added to the current total for the period, and this summed result is displayed on the web page.

Richardson Chill Units (RCU)

Plants need a certain amount of cold weather during the winter in order to mature properly later on. Straight chill units simply count the number of hours below 7°C, but we use the Richardson Chill Units to provide a more accurate model for orchards and vineyards. First we calculate the average temperature for each hour, and then use the table below to accumulate the RCU: