Automatic weather station
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An automatic weather station (AWS) is an automated version of the traditional weather station, either to save human labour or to enable measurements from remote areas. The system may report in near real time via the Argos System and the Global Telecommunications System, or save the data for later recovery.
Most automatic weather stations have
- Thermometer for measuring temperature
- Anemometer for measuring wind speed
- Hygrometer for measuring humidity
- Barometer for measuring pressure
Some of them even have
- Ceilometer for measuring cloud height
- Rain gauge for measuring rainfall
- Present weather sensor and/or visibility sensor
Unlike manual weather stations, automatic weather stations cannot report the class and amount of clouds. Also, precipitation measurements are a bit problematic, especially for snow, as the gauge must empty itself between observations. For present weather, all phenomena which do not touch the sensor, such as fog patches, remain unobserved.
The first automatic weather stations were often placed where electricity and communication lines were available. Nowadays, the solar panel, wind turbine and mobile phone technology have made it possible to have wireless AWSs that are not connected to the electrical grid or telecommunications network.
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[edit] Observation times
Historically readings were taken by weather observers who were typically not paid and performed the duty as part of their permanent job, such as a postmaster. These weather readings were taken from 9am one day to 9am the next as unpaid observers were unwilling to take readings from midnight to midnight. Since the advent of automatic weather stations, these time intervals remained, more as a part of tradition.
[edit] Configuration
The configuration of an AWS may vary due to the purpose of the system but typically consists of:
- A weather-proof enclosure containing the data logger, rechargeable battery and telemetry (optional)
- Meteorological sensors
- Solar panel or wind turbine
- Mast
[edit] Enclosures
Enclosures used with automatic weather stations are typically weather proof fiberglass, ABS or stainless steel.
- ABS plastic enclosures are light weight and inexpensive. They are commonly used in mass-produced AWS's but are less secure and rugged than fiberglass or stainless steel.
- Fiberglass enclosures are used when chemical resistivity including corrosion from water is required. These enclosures are middle of the range and are subject to fiberglass deterioration.
- Stainless steel enclosures are the optimum choice and typically come in either 316 s/s or 304 s/s. They are rugged, vandal resistant and corrosion/chemically resistant. These enclosures are also expensive and can typically cost more than double the same sized fiberglass enclosure.
[edit] Station solar panel
The main power source for an automatic weather station is usually one or more solar panels connected in parallel with a regulator and one or more rechargeable batteries. As a rule of thumb, solar output is at its optimum for only 5 hours each day. As such, mounting angle and position are vital. In the Northern Hemisphere the solar panel would be mounted facing south vice versa for the Southern Hemisphere. The angle of the panel differs from place to place but it should never be mounted with an angle of 5 deg as dust build up will dramatically decrease the panel's output.
Approximate solar panel output in full sun at 12 volts of direct current
- 5W = 400mA/hr
- 10W = 800mA/hr
- 20W = 1.6A/hr
- 40W = 3.3A/hr
[edit] Mast
The standard mast heights used with automatic weather stations are 2, 3, 10 and 30 meters. Other sizes are available on request but typically these sizes have been used as standards for differing applications.
- The 2 meter (6.6 feet) mast is used for the measurement of parameters that effect a human subject. The mast height is referenced to head height.
- The 3 meter (9.8 feet) mast is used for the measurement of parameters that effect crops (such as wheat, sugar cane etc). The mast height is referenced to crop top.
- The 10 meter (32.8 feet) mast is used for the measurement of parameters without interference from objects such as trees, buildings or other obstructions. Typically the most important weather parameter measured at this height is wind speed and direction.
- The 30 meter (98.4 feet) mast is used for the measurement of parameters over stratified distances for the purposes of data modelling. A common application is to take measurements of wind, humidity and temperature at 30, 10, and 2 meters. Other sensors are mounted around the 2 meter or lower height.
[edit] See also
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