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 ARGOS 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
• 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 the rainfall 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 (say fog patches) remain unobserved.

The first AWS's were often placed where electricity and communication lines were available. Nowadays, the solar panel, wind-generator and cellphone technology have made wireless AWS's easier to place.

Contents 1 Oberservation times 2 Configuration of an AWS 2.1 Enclosures 2.2 Station solar panel 2.3 Masts

[edit] Oberservation times

Historically readings were taken by weather observers who were typically not paid and performed the duty as part of their permanent job (i.e. Postal master). 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 of an AWS

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 generator;
• Mast;

[edit] Enclosures

Enclosures used with automatic weather stations are typically weather proof fiberglass, ABS or stainless steel.

1. The ABS plastic enclosures are light weight and inexpensive. They are commonly used in mass-produced AWS's but are less secure and rugged then the 2 alternatives.
2. The fiberglass enclosure is used when chemical resistivity including corrosion from water is required. These enclosures are middle of the range and are subject to fiberglass deterioration.
3. The stainless steel enclosures are the optimum choice and typically come in either 316 s/s or 304 s/s. They are rugged, vandal proof 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 a solar panel connected in parallel with a solar regulator and re-chargeable battery. As a rule of thumb, solar ouput is at its optimum for only 5hrs 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 panels output.

Panel output in full sun @ 12VDC(approx.)

• 5W = 400mA/hr
• 10W = 800mA/hr
• 20W = 1.6A/hr
• 40W = 3.3A/hr

[edit] Masts

A number of sized masts are used with automatic weather stations:2M(6'),3M(10'),10M(33'),30M(100'). Other sizes are avaliable on request but typically these sizes have been used as standards for differing applications.

• The 2M(6') mast is used for the measurement of parameters that effect a human subject. The mast height is referenced to head height.
• The 3M(10') mast is used for the measurement of parameters that effect crops (such as wheat, sugar cain etc). The mast height is referenced to crop top.
• The 10M(33') 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 30M(100') 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 30M(100') at 10M(33') and at 2M(6'). Other sensors are mounted around the 2M or lower height.