Weather Equipment Siting
by Dennis Sleighter
Many folks keep track of weather conditions at their home or business. Reasons may include agricultural interests, needs for their particular company’s operations, or just a general, or robust, interest in weather conditions. Most people who fall into this category have a basic discount store style thermometer and/or rain gage. Others have various higher levels of quality of equipment, up to the degree of having a multi-array of weather sensors tied into a computer for local data archiving and/or transmission over the Internet for others to view. However, no matter what type or assortment of equipment you may have, where this equipment is located will play a huge role in the accuracy of the measurements.
I’ve listed below the optimal locations for the placement of temperature sensors (or thermometers), rain gages, and anemometers (wind speed and direction equipment). Of course the key word here is “optimal”. More than likely, the area you have available for your weather equipment will have some “problem” about it that will prevent you from obtaining these “optimal” conditions. But if you are able to obtain the standards listed below for placement, then you should have a high level of confidence that the measurements taken are as accurate as the quality of precision the particular piece of equipment you have allows.
- Additional sources of heat and lack of air flow decrease accuracy.
- Should be mounted 4 to 6 feet above a grassy surface.
- Should be mounted in a location free of direct sunlight.
- Should be mounted at least 100 feet away from any paved surface.
- Should be mounted in a location that allows for the instrument to receive a good, free flow of air.
- Should be mounted no closer than 4 times the height of any obstruction (ex: a 40 foot tree, 80 feet away is too close. At least 160 feet would be needed.)
- A greater flow of air over and around the gage will decrease accuracy.
- Should be located so that it has uniform obstruction of wind on all sides of it.
- Surrounding objects will be no closer than a distance equal to two times their height above the top of the gage (ex: a gage located within a grove of 30 foot trees, should not be less than 60 feet from any one of the trees)
- Should not be located near an isolated obstruction.
- Should not be located in a completely open area.
- Avoid locating the gage over a hard surface (prevents the effects of splashing of water back into small gages)
- A turbulent and/or obstructed flow of air will decrease accuracy.
- Should be located 10 meters (33 feet) above the average height of the ground within 500 feet of the instrument
- The upper limit of 33 feet should be exceeded to a height equal to 15 feet higher than any obstruction within 500 feet of the instrument. (an “obstruction” is any object that has its top higher than 10 degrees above the angle formed between the standard 33 foot location of the sensor and the top of the object in question)
- Should be oriented with respect to “true” north, not magnetic north.