Frequently Asked Questions

• What is GDD (Growing Degree Days)?

  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), and below 30°C (86°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.

   

  Click link to see Harvest sensor used to measure GDD: Temperature sensor 

  Click on this link to see Harvest Systems that can be used to remotely display this data: Harvest Data Loggers

   

   

• What are Richardson Chill Units?

  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:

  Temperature (°C)	Temperature (°F)	RCU (per hour)
  T < 1.5	T < 34.7	0.0
  1.5 ≤ T < 2.5	34.7 ≤ T < 36.5	+0.5
  2.5 ≤ T < 9.2	36.5 ≤ T < 48.6	+1.0
  9.2 ≤ T < 12.5	48.6 ≤ T < 54.5	+0.5
  12.5 ≤ T < 16.0	54.5 ≤ T < 60.8	0.0
  16.0 ≤ T < 18.0	60.8 ≤ T < 64.4	−0.5
  T ≥ 18.0	T ≥ 64.4	−1.0

  Click link to see Harvest sensor used to measure RCU: Temperature sensor 

  Click on this link to see Harvest systems that can be used to remotely display this data: Harvest Data Loggers

   

• What is Dew Point?

  Dew Point

  The Dew Point is the temperature at which a pocket of air (in this case around the temperature/humidity sensor) would form dew.

  To calculate the Dew Point temperature, the unit requires a temperature and humidity sensor to be attached.

  The Dew Point temperature is directly related to the temperature of the air in a given humidity. If the humidity is 100% then the Dew Point temperature will be equal to the temperature of the air. As the humidity decreases, so does the Dew Point temperature.

  The Dew Point is helpful for predicting if and when dew will form on the vines. It is also important to note that if the Dew Point falls below freezing (0°c) then it is known as the frost point. This is a good indication that any dew forming will instead be in the form of a frost. On a cloudless night with no wind the sunset dew point temperature is a rough indication of the overnight low if no clouds form or no wind commences.

  Click link to see Harvest sensor used to measure dew point:  Temperature/Humidity Sensor 

  Click on this link to see Harvest Systems that can be used to remotely display this data: Harvest Data Loggers

   

   

   

• What is Wet Bulb Temperature?

  Wet Bulb Temperature

  Wet bulb is a calculation that refers to the lowest temperature on the leaves that will be experienced by the evaporation of water alone.

  To calculate the Wet Bulb temperature, the unit needs to have a humidity and temperature sensor attached.

  Using the air temperature and the dew point (calculated with humidity and air temperature), the Wet Bulb temperature is able to be calculated.

  The application of the Wet Bulb temperature is primarily in regards to frost protection.

  Always make sure your water frost protection turns on before the wet bulb temp gets near zero as the leaves will suddenly drop from air temp to wet bulb temp which can be 2-3 degrees lower than air temp

  Don't use an uncovered temp sensor to make decisions about frost fighting as an uncovered sensor could be either wet or dry and give different temp readings based on those two conditions. You know that a covered sensor will always be dry

  Click link to see Harvest sensor used to measure Wet Bulb temperature:  Temperature/Humidity Sensor 

  Click on this link to see Harvest Systems that can be used to remotely display this data: Harvest Data Loggers

   

   

   

• What is Wind Chill?

  Wind Chill

  Wind chill is the lowering of the body temperature due to the passing flow of lower temperature air. This is because the wind strips away the thin layer of warm air above your skin. The stronger the wind, the more heat lost from your body, and the colder it will feel. When the winds are light, it will feel closer to the actual air temperature.

  Wind Chill Temperature is only defined for temperatures at or below 10°C and wind speeds above 4.8 kph. 

  The equation specifically is:

  Wind Chill (°F) = 35.74 + 0.6215T - 35.75(V0.16) + 0.4275T(V0.16)

  Where T= Air Temperature (°F) and V= Wind Speed (mph)

  We can then display this data in either °F or °C with our built in converters

  Click links to see Harvest sensors used to measure Wind Chill: Temperature Sensor  Wind Speed/Direction Sensor

  Click on this link to see Harvest Systems that can be used to remotely display this data: Harvest Data Loggers

   

   

   

• What is Feels Like?

   

   Feels Like (Australian Apparent Temperature)

  The Australian Bureau of Meteorology, using a model developed by the US Navy, researched and then developed their own formula, the Australian Apparent Temperature.

  The apparent temperature, invented in the late 1970's, was designed to measure thermal sensation in indoor conditions. It was extended in the early 1980's to include the effect of sun and wind. 

  The formula is:

  

  where:

  • T_a = dry bulb temperature (°C)
  • e = water vapour pressure (hPa)
  • v = wind speed (m/s) at an elevation of 10 m

  The vapour pressure can be calculated from the temperature and relative humidity using the equation:

  

  The Australian formula includes the important factor of humidity and is somewhat more involved than the simpler North American model. The North American formula was designed to be applied at low temperatures (as low as −46 °C), when humidity levels are also low.

  Click link to see Harvest sensor used:  Temperature/Humidity Sensor 

  Click on this link to see Harvest Systems that can be used to remotely display this data: Harvest Data Loggers

   

   

   

   

   

• What is Potential Evapotranspiration (PET)?

  Potential Evapotranspiration (PET) 

  Evapotranspiration is a term that describes the amount of water that travels to the air from sources of evaporation, such as water bodies, soil, and vine/tree canopies, and water lost through plant transpiration. 

  Potential Evapotranspiration (PET) is defined as the amount of evaporation that would occur if a sufficient water source were available.

  To calculate the Potential Evapotranspiration we require the weather station to have a temperature and humidity sensor, wind speed and direction sensor, and a solar radiation sensor. 

  Data from the sensors are fed into a calculation based on an article (see the article here) by Jay Ham, Professor, Department of Agronomy, Kansas State University. The calculated value is recorded in mm/hr as well as total Evapotranspiration, in mm, experienced over the time period being viewed. 

  By knowing how much water has been lost due to Evapotranspiration, a grower is able to confidently know how much irrigation will be needed to replace the water lost. 

  Required Sensors:

  Click links to see sensors required  Temperature/Humidity Sensor,  Wind Speed/Direction Sensor,  Solar Radiation Sensor 

  Click on this link to see Harvest Systems that can be used to remotely display this data: Harvest Data Loggers

   

   

• How do you measure Sunshine Hours?

  Sunshine Hours

  Sunshine hours or sunshine duration is a climatological indicator, measuring the duration of sunshine in a given period, usually over a day or a year for a given location on Earth. The number of sunshine hours achieved over a period can be considered as an indicator for the cloudiness of a location. 

  To calculate sunshine hours for a given location with a Solar Radiation sensor (instead of an expensive pyrheliometer which would use the standard threshold of 120 Watts/m²), Harvest utilises a formula developed by Campbell Scientific. This formula uses the definition of sunshine hours as being "when the measured global radiation is greater than 0.4 times the potential solar radiation outside the earth’s atmosphere on a horizontal surface".

  The Technical Note released by Campbell scientific can be viewed here.

  Click on this link to see required sensor: Solar Radiation Sensor 

  Click on this link to see Harvest Systems that can be used to remotely display this data: Harvest Data Loggers

   

   

   

• What is the Topp soil moisture equation?

  Soil Moisture Measurement using the Topp Equation

  In June of 1980, G. Clarke Topp and his team members, J.L Davis and P. Annan, published a watershed paper which included what would come to be known as the Topp equation. The equation is so commonly used that some people don’t even know they’re using it. The Topp Equation makes it possible for us to measure an electrical property of the soil (the dielectric permittivity) and correlate that electrical property with the water content in the soil. 

  It has been shown that the relationship between volumetric water content (θ) and dielectric water constant (Ka - the ratio of the absolute permittivity of a substance to the absolute permittivity of free space.) is essentially independent of soil texture, porosity, and salt content. The equation below was developed by Topp et al. (1980) for conversion of Ka to volumetric water content:

  θ = -5.3 x 10-2 + 2.92 x 10-2 Ka – 5.5 x 10-4 Ka2 + 4.3 x 10-6Ka3

  True Time Domain probes like the Acclima measure dielectric permittivity and report that value as well as calculating and reporting the Volumetric Water Content (VWC) using the Topp equation.

  Click on this link to see Acclima True TDR sensors: Acclima TDR

  Click on this link to see Harvest Systems that can be used to remotely display this data: Harvest Data Loggers

  
   

   

• What is the Bacchus Botrytis Disease Model?

   Bacchus Botrytis Disease Model

  Botrytis cinerea is a disease that affects soft fruits, mainly wine grapes, usually affecting vines that experience constant wet or humid conditions, or over irrigation. It can lead to the loss of produce.

  To detect Botrytis risk we monitor leaf wetness using the Decagon leaf wetness sensor. For best results the sensor is recommended to be placed NEAR the crop but not in it to avoid it being sprayed. It is also recommended that the sensor be mounted at a 10 degree angle so it is almost horizontal. This will give the best data results.

  By measuring the duration that leaves have been wet, and utilizing a temperature sensor we can apply these to the Botrytis disease risk model and provide an output in the form of an infection index value. When this index reaches 1.0 there is a high probability of infection and crops should be sprayed or irrigation reduced or stopped.

  Data from the leaf wetness sensor is fed into a model developed in New Zealand by Dr Balasubramaniam (Bala).

  The equation specifically is:

  I= 84.37 - 7.238T + 0.1856T2

  Where I is risk index and T is the mean air temperature during a wet hour. The I values were summed for the duration of each wet period. After four hours of "dry" the risk index is reset.

  

  Click on the links to see required sensors: Temperature Sensor  Leaf Wetness Sensor 
  

  Click on this link to see Harvest Systems that can be used to remotely display this data: Harvest Data Loggers

   

   

• What is the Downey Mildew Disease model?

  Downy Mildew

  Downy mildew is driven by the weather. The disease can devastate individual properties and in some seasons, affect production from the regions. It occurs sporadically according to the suitability of conditions for infection. Periods of high risk from Downy can be determined by monitoring the properties micro climate for factors such as temperature, rainfall, relative humidity (RH) and leaf wetness.

  The rule of thumb for the primary infection of Downy Mildew is 10:10:24 which gives a guide to the conditions in which infection might occur, i.e. at least 10mm rainfall is needed while temperatures are at least 10ºC during a 24 hour period.

  We have taken this rule of thumb and applied it to the weather station data to give a risk period for the primary infection of the disease.

  Click on the links to see required sensors: Temperature/Humidity Sensor  Rain Gauge  Leaf Wetness 
  

  Click on this link to see Harvest Systems that can be used to remotely display this data: Harvest Data Loggers

• What is the Powdery Mildew Disease Model?

  Powdery Mildew (Gubler Model)

  Powdery mildew is a fungal disease that affects many different plants. The damage is caused to both the leaves and fruit, and if left unchecked, will result in total crop loss as well as the potential death of the plant.

  The calculation we use is based on the Conidial infections model developed by Doug Gubler from the University of California. It is an extremely complex calculation based upon the temperature we read from the desired sensor.

  The optimal temperatures for Powdery Mildew Conidial development is between 21°C and 32°C. The greater the number of hours during the day that the temperature is within this range, the higher the risk for Powdery Mildew. 

  • Risk increases: With every day with equal or more than 6 hours of 21°C <= Temperature < 32°C ==> +20 Points
  • Risk decreases: With every day when temperature is 32°C or above or when 6 hours of at least 21°C are not reached ==> -10 Points

  If the Powdery Mildew risk is less than 20 points the spraying interval can be extended. With 20 to 60 points the normal spraying interval is valid. If the risk is more than 60 points you should shorten the spraying interval.

  You can read more about the control of Powdery Mildew using this model here.

  Click link to see required sensor: Temperature Sensor 
  

  Click on this link to see Harvest Systems that can be used to remotely display this data: Harvest Data Loggers

• How is Rainfall Measured?

  How is rainfall most accurately measured?

   The World Meteorological Society recommends that weather stations are placed at a distance away from any nearby obstacles that is at least six times the height of the obstacles as the most optimal way to ensure accurate readings, this can prove impossible on a lot of orchards and farms due to space requirements so some compromise may be required.

   The rain gauge needs to be level to operates accurately. There is a bubble level built into the base of your rain gauge you can use this to help with leveling.

  Also see info on rain gauge choice

  Which rain gauge should I choose?

  Davis - The Davis rain gauge is our entry level offering. The gauge uses a self-emptying tipping spoon type mechanism with a clip in filter to reduce blockages and provision for optional bird spikes 

  Hyquest TB7 - The TB7 is our mid range offering, it is based off the industrial TB6 design at a more affordable price point due to it's plastic construction. It also has provision for bird spikes. We recommend this rain gauge for most weather monitoring systems.

  Hyquest TB6 - The TB6 is designed for industrial/meteorological purposes where a very high accuracy of measurement is required.

  How often should I clean my rain gauge?

  Your rain gauge should be cleared of debris at least every 6 months and vegetation or other obstructing objects kept at a reasonable distance. Clean cobwebs and insects from inside the bucket, clean the tipping bucket and check that it tips freely with very little force i.e. you should be able to blow on it to make it tip.

  We have found that placing a Harvest insect repellent inside of the rain gauge can help prevent insects living inside the rain gauge. 

  Why is my neighbours rain gauge reading different to mine?

  Rain gauges a even few metres apart at a similar level can differ by 10 percent as the capture area of a rain gauge is not large enough to cope with the statistical variation of rainfall. To try and overcome this variation very accurate scientific rain gauges have been made that have a capture diameter of one metre which is impractical for normal use. It is also important to note that the higher the rain gauge is mounted off the ground the less rain it will read due to be affected by wind.

• What are the Technical Requirements to view data?

  Technical Requirements

  Mobile or Tablet

  As we cannot feasibly test all combinations of device, operating system, and application we cannot guarantee you will be able use your device to view the data.

  For best results we would recommend:

  • Device that is no more than 2 - 3 years old
  • Up to date operating system
  • Up to date browser (e.g. Safari, Chrome, or Android Web Browser)
  • Enabling cookies for the website - this is required for any login
  • Internet connection with at least 2Mbps download speed and the ability to access external websites - recommend Wi-Fi, or cellular connection on 3G or better

  Computer

  Minimum requirements for a computer:

  • Up to date modern browser: Chrome, Microsoft Edge, Safari, or Firefox
  •  You may find you can use other browsers (including Internet Explorer 9+), however the above will give best results and cannot guarantee all functionality will be available
  • Operating system and computer hardware as recommended to run these browsers
  • Internet connection with at least 2Mbps download speed and the ability to access external websites