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1. Practical No. 4 Date: STUDY OF AUTOMATIC WEATHER OBSERVATORY STATION ( AWOS )   WMO defines an Automatic Weather Station ( AWS ) as a facility that automatically transmits or records observations obtained from measuring instruments. Automatic weather observation refers to the activities involved in converting measurements of meteorological elements into electrical signals through sensors , processing and transforming these signals into meteorological data, and transmitting the resulting information by wire or radio or automatically storing it on a recording medium.

2. An automatic Weather station is an automated version of traditional station either to save the human labour or to enable measurements from remote areas . The system may report in near real time via the agro System and the global Telecommunications System or save the data for later recovery. AWSs can be divided into real-time stations , which automatically transmit observed data at fixed times, and off-line stations , which record data on storage devices.

3. Real-time AWS : A station that outputs observations on a real-time basis , either regularly or upon request by the user. This type of station is used for ordinary synoptic meteorological analysis and monitoring of critical warning states such as storms and river or tide levels. It must be able to transmit observations to a network. Off-line AWS : A station that records observations on storage devices . This type of station is used for climatological analysis or as an auxiliary facility to manual observations.

4. The data obtained and stored by an off-line AWS need to be transmitted to the user at regular intervals. Visual observation elements including visibility, cloud cover, cloud type and present/past weather are not recorded by AWSs or monitored by a human observer who transmits the results.

5. Fig.: Automatic weather observing instrument

6. AWS consists of four units Data logger Data logger terminal Data storage system Personal computer

7. Data logger : It is the heart of the AWS. The data logger is usually kept in a nearby room attached to different sensors for weather data collection. It can also be left in the field . The unit has 8 to 12 analog channels, four digital inputs, two pulse counters and one frequency sensing channel. All the sensors for recording different parameters are connected to appropriate channels of the field unit. The field unit converts the raw data into practical units of the scientific measures with a data logger. The main functions are as below.

8. The main functions of data logger are as below Measurement – It collects the information from every sensor and archives it Calculation – it process the most of the meteorological data for the users ( Avr . Mini. Maxi .) Data storage – saves all the data either on its own memory or on USD cards Power supply – Manage the power supply to AWS using solar panel for instance Communication – Manages the communication protocols with the remote server. The different protocols are usually GSM, GPRS, RTC, WIFI, USD

9. b) Data logger terminal: The terminal is used to signify the field unit which sensor to use, what channels these sensors are connected to, when to store data and how to label and organize the data. Thus, all the instructions to field unit are given through the terminal. It also has the facility to display the data when required. It is connected to field unit for its working. c) Data storage system: It is used to store the tabulated data in the practical units of scientific measure. It is connected to data logger field unit for unloading the stored data. The unload data can then be transferred to a personal computer disk for permanent record and for further use and analysis.

10. Sensors : Temperature sensor Relative humidity sensor Wind direction sensor Wind speed sensor Rainfall sensor Radiation sensor Storage Module : It provides the user with a method of transporting data from field to the computer. They are packed in stainless steel canisters. The module storage capacity varies from 192,896 to 716,672 bytes.

11. Advantages of an automated weather observing systems: Compact modular design Standardization of network observations, both in time and quality Real-time continuous measuring of parameters on a 24/7 basis More reliable, accuracy Provides higher data resolution Collection of data in a greater volume Adjustable sampling interval for different parameters Generally free of reading errors and free from subjectivity Automatic message generation and transmission Access to archived data locally or remotely Data collection in harsh climates Low power consumption, Easy installation and Low maintenance

12. Disadvantages of automated observations: Limited area representation (about 3-5 km around the sensor site ) It is not possible to observe all parameters automatically as are done through a manual approach like cloud coverage and cloud types Periodic testing and calibration Well trained technicians and specialists and Higher cost of instrumentation and operation