Quality control methodology for temperature data of Automatic Weather Stations with non-wooden radiation shield Eng. Nuwan Kumarasinghe Chief Electronics Engineer Department of Meteorology, Sri Lanka nuwan1960@gmail.com
Capital city Sri Jayawardenapura Kotte Commercial City - Colombo Land Area - 65,525 Sq km Population 22 Million Due to the location of Sri Lanka, within the tropics between 5 55' to 9 51' North latitude and between 79 42' to 81 53' East longitude, the climate of the island could be characterized as tropical.
Highlands of Sri Lanka
Golden Beaches..
Historical monuments
Wild Life in Sri Lanka
The mean annual temperature varies from 27 C in the coastal lowlands to 16 C in the central highlands (1900m above mean sea level). This relatively unique feature manifesting as sunny beaches to rain forests inland is a tourist attraction
Though the Department of Meteorology was established on 1st October 1948, meteorological observations in Sri Lanka have a long history dating back to around 1850 Conventional meteorological instruments are used since its inception
38 AWS have been installed during 2007-2009 under JICA Project. AWS Network 9.50 3.00 to 3.00 38 AWS Stations 9.00 8.50 8.00 7.50 7.00 6.50 6.00 80.00 80.50 81.00 81.50
Different sensors used in AWS Network Ogasawarakeiki TS 801C Vaisala PTB 330 Vaisala HUMICAP HMT 330 Vaisala WMT 700 Ogasawarakeiki RS 102 EKO MS-402
Placement of conventional Meteorological Instruments Wooden Stevenson Screen WMO International Conference on Automatic Weather Stations, 24-26 October 2017, Offenbach, Germany
Placement of temperature sensor of AWS Metallic Radiation Shield
Hygrometer Data logger Thermometer Barometer Wind sensor Pyranometer Rain gauge
Main Objective of the Study To verify the behavior of the Pt-100 sensor In this study 2 AWS locations were selected. Colombo Head Office and Kandy (Katugastota) in the central part of the country. Temperature data from 3rd December 2009 to 6th December 2009 between manual thermometer and AWS sensor has been compared
Inter comparison of Temperature Sensors Manual Vs. AWS at Colombo Comparision of AWS and Manual Temperature Data during 3-6 December, 2009 at Colombo 35.00 30.00 25.00 20.00 15.00 AWS 10.00 5.00 Dec/03/02:30 Dec/03/05:30 Dec/03/08:30 Dec/03/11:30 Dec/03/14:30 Dec/03/17:30 Dec/03/20:30 Dec/03/23:30 Dec/04/02:30 Dec/04/05:30 Dec/04/08:30 Dec/04/11:30 Dec/04/14:30 Dec/04/17:30 Dec/04/20:30 Dec/04/23:30 Dec/05/02:30 Dec/05/05:30 Dec/05/08:30 Dec/05/11:30 Dec/05/14:30 Dec/05/17:30 Dec/05/20:30 Dec/05/23:30 Dec/06/02:30 Dec/06/05:30 Dec/06/08:30 Dec/06/11:30 Dec/06/14:30 Dec/06/17:30 Dec/06/20:30 Dec/06/23:30 Temperature ( C 0 ) Manual Date /Time WMO International Conference on Automatic Weather Stations, 24-26 October 2017, Offenbach, Germany
Inter Comparison of Temperature Sensors Manual Vs. AWS at Kandy Comparision of AWS and Manual Temperature Data during 3-6 December, 2009 at Katugastota,Kandy 35.00 30.00 25.00 20.00 15.00 AWS 10.00 Manual 5.00 Dec/03/02:30 Dec/03/05:30 Dec/03/08:30 Dec/03/11:30 Dec/03/14:30 Dec/03/17:30 Dec/03/20:30 Dec/03/23:30 Dec/04/02:30 Dec/04/05:30 Dec/04/08:30 Dec/04/11:30 Dec/04/14:30 Dec/04/17:30 Dec/04/20:30 Dec/04/23:30 Dec/05/02:30 Dec/05/05:30 Dec/05/08:30 Dec/05/11:30 Dec/05/14:30 Dec/05/17:30 Dec/05/20:30 Dec/05/23:30 Dec/06/02:30 Dec/06/05:30 Dec/06/08:30 Dec/06/11:30 Dec/06/14:30 Dec/06/17:30 Dec/06/20:30 Dec/06/23:30 Date/Time Temperature (C 0 )
Properties of Meteorological Sensors Sensitivity The change in the response of a measuring instrument divided by the corresponding change in the stimulus Resolution A quantitative expression of the ability of an indicating device to distinguish meaningfully between closely adjacent values of the quantity indicated. It is the smallest change the device can detect Hysteresis The property of a measuring instrument whereby its response to a given stimulus depends on the sequence of preceding stimuli Drift The slow variation with time of a metrological characteristic of a measuring instrument Response time Time interval between the instant when a stimulus is subjected to a specified abrupt change and the instant when the response reaches and remains within specified limits around its final steady value. Normally defined as the time the sensor takes to measure 63% of the change
Possible Reasons Where; y is the change after elapsed time t; A is the amplitude of the step change applied; t is the elapsed time from the step change; and τ is a characteristic variable of the system having the dimension of time Response Time of Thermometer > Response Time of Pt-100 Introduction of wooden enclosure for Pt-100
Some other factors can be influenced Metallic reflectors / objects such as solar panels in the vicinity Wind speed and direction Rainfall Cloud coverage Study has to be further carried out, accordingly develop some correction factors for AWS readings in the future.
In day time (7AM to 16PM), temperature of AWS is higher. Conclusions In night time (16PM to 7AM), conventional thermometer is higher. This difference is due to response time for sensor device and/or heat capacity for radiation shield and Stevenson screen. It is noted that metallic radiation shield absorb solar energy during the day time and remained inside more time than the wooden screen. This may lead Pt-100 temperature sensor to response fast as compared with the mercury thermometer which is in the wooden screen. This can be improved by introducing Wooden Enclosure for Temperature Sensor
Reference 1. Amudha B1., Anjan A., Ranalkar M., Vashistha R.D., and Rudra Pratap. Effect of non wooden radiation shield on measurements of air temperature and humidity in Automatic Weather Stations at climatologically different Indian stations Pune and Mumbai, WMO TECO 2008. 2. Guide to Meteorological Instruments and Methods of Observation WMO No. 8. Acknowledgement Mr. K.H.M.S. Premalal, Director General of Meteorology, Sri Lanka Mr. Ananda Jayasinghearchchi, Director, DoM, Sri Lanka Ms. S.N. Jayanath, Technical Officer DoM, Sri Lanka Mr. Krunoslav Premec, Scientific officer, Instruments and Methods of Observation-WMO and his Staff
Thank you.. Acknowledgement Director General of Meteorology, Sri Lanka Mr. K.H.M.S. Premalal Director Mr. D.A. Jayasinghearachchi Technical Officer Ms. S.N. Jayanath Mr. Krunoslav Premec and WMO Staff