Automatic Weather Station
Weather station
Definition of weather station
An automatic weather station (AWS) is defined as a “meteorological station at
which observations are made and transmitted automatically”(WMO).
It is a building or unit or integrated system for taking, recording, reporting and sometimes transmit metrological observation. It accommodated with instruments and equipments for weather forecasts and to study the weather and climate.
Advantages of AWS
Some advantages of Automatic weather stations over the conventional one are:
Data quality is independent from the observer.
The data is taken & transmitted at the same time.
The real time data is available which can be used forweather forecasting purpose / Disaster management etc.
The frequency of the data can be increased as per the need of the user
The data is available after the normal working hours also or any time.
Operational costs reduces by reducing the number of observers.
The stations can be established in the remote locations.
Disadvantages of AWS
Some of the disadvantages are:
- The loss of the data due to theft of solar panel, Battery etc.
- The loss of the data due to some of the meteorological parameters like suddenly occurred cloud, sudden formation of the weather etc.
Key features of AWS
Automated weather stations measure and record meteorological variables over extended periods without the need for human intervention rather than stations that require manual intervention.
Rugged design, low power requirements, and long-distance communications methods allow automatic weather stations to operate remotely for long periods without the need for human intervention.
It collects, processes and stores the data from all sensors and moreover manages the communication protocols with remote servers.
AWS used to save human labour by enabling measurements from remote areas.
Components of AWS
AWS consists of a weather proof enclosure which contains the data logger, rechargeable battery, telemetry (optional) and the meteorological sensors work on energy obtained from solar panel or wind turbine.
General requirement of all the components of the AWS is, they must be rugged enough to operate in tropical environment. The general conditions are :
Operating Temperature range: -40°C to 40°C (hills) and 20°C to 60°C
Weather Condition: All weather including heavy rain & wind upto 60 m/s.
Data logger
It is the heart and brain of AWS. The quality & life of the AWS station is wholly dependent upon the data logger. Main functions of data logger are,
Measurement: It collects the information from every sensor and measure.
Calculation: Average, minimum, maximum etc, values of the meteorological data can processes for the users.
Data storage: It saves all the data either on its own memory or on SDcard.
Power supply: the data-logger manages the power supply of the Automatic Weather Station.
Communication: the data-logger manages the communication protocols with the remote server. Satellite communications or GSM and GPRS network used for communication with remote server.
Battery
Batteries store the energy generated by the solar panels or wind turbines and ensure functioning. The battery must be maintenance free and storage must be of such that it will run AWS uninterrupted even when solar or wind energy is not available for at least 30 days.
Sensors
According to usefulness of AWS various sensors attached. Main perameter recorded by AWS are : Atmospheric pressure, Rainfall, Relative humidity, Wind speed, Wind direction, Air temperature. As per requirement other parameters like Visibility, Soil moisture & temperature, Solar radiation, Snow depth, Snow fall, Leaf wetness etc can be measured by AWS. The quality of the AWS data is solely dependent upon the quality of the sensors in all weather conditions. Various sensors are,
Thermometer : Thermometers are typically used to measure the temperature of the photovoltaic panels. Thermometer ensures that the temperature of the PV panels is recorded.
Anemometer : Anemometers are used to measure the velocity of winds. Cup type anemometers are most commonly used.
Wind vane : It shows the direction from which wind flows.
Hygrometer : A hygrometer is a device which is used to measure humidity or moisture content in the air.
Barometer : Barometers are used to measure the atmospheric pressure at the given location.
Rain Gauge : The rain gauge is used to find out the rainfall at the given location.
Pyrometer : Pyrometers are used to measure the solar radiation at the given location.
Transmitting antenna
In case of satellite based AWS, this is a directional antenna which transmits the signal to the Satellite. In case of GSM/GPRS AWS, this is an omni directional antenna which transmits the signal to GSM/GPRS network.
Telemetry (optional)
Telemetry equipment is used to send the recorded data to the desired locations at the desired frequency.
Considerations while choosing and setting up an AWS.
Following thoughts we have to kept in mind while choosing and setting up an AWS,
AWS site must be free from obstructions like tall buildings, trees, etc.
The site should preferably be located on the same level as the roadway of the station.
The site must be selected in such a way that the distance between the fencing of the site and the proposed AWS mast should be at least 3 meters. This distance is recommended to minimize the effect of the fence on the sensors readings especially when weeds and/or debris on the fence act as a horizontal obstruction.
Following conditions to be avoided:
Obstructions like tall buildings, trees etc.
Location of the site on the edge of a slope, hillocks, cliff or inside a valley.
Large industrial heat sources.
Locations near high-tension power lines.
Low places holding standing water after rains.
Underground obstructions like buried cables or conduits.
Pollution influence from surrounding farms and towns
To choose an AWS the first thing is to design the exact configuration (i.e. the type of sensors, amount of memory of the data-logger, power required, etc.).
The main characteristics should be considered while choosing and setting up an AWS are: Reliability, toughness, Simple operation, Reduced level of maintenance, Installation of few sensors and estimation of other parameters.
Kind of sensor we have to use so it gives the exact value of parameter we require.
Position of sensor i.e. the height and location of sensor shall be properly defined. So it give the accurate reading.
Site should be such that there is possibility to add another sensor as and when we require.
Robust data loggers and communication devices are required which can work in extreme environments e.g., temperature and prolonged time with high humidity values.
In extreme weather areas waterproof AWS enclosure should be rust proof and salt resistant.
In remote regions security of AWS equipment has become a major concern. It is quite common that there are many thefts of solar panels and batteries from the AWS sites.
The installation near military camps or police stations is often adopted as a suitable site.
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