The Design, Installation and Operation of a Fully Computerized, Automatic Weather Station for High Quality Meteorological Measurements

THE DESIGN, INSTALLATION AND OPERATION OF A FULLY COMPUTERIZED, AUTOMATIC WEATHER STATION FOR HIGH QUALITY METEOROLOGICAL MEASUREMENTS

Haralambos S. Bagiorgas1*, Margarita N. Assimakopoulos2, Argiro Patentalaki1, Nikolaos Konofaos3, Demetrios P. Matthopoulos1 and Giouli Mihalakakou1

1 University of Ioannina, Department of Environmental and Natural Resources Management, 2 G. Sepheri Str., 30100 Agrinio, Greece. 2 University of Athens, Department of Physics, Division of Applied Physics, Laboratory of Meteorology, University Campus, Build. Phys V, 15784 Athens, Greece. 3 University of Patras, Computer Engineering and Informatics Department, 26500 Rio Patras, Greece.

SUMMARY

The design, installation and operation of an Automatic cause the data obtained from the device should be both ac- Weather Station (AWS) are described and analysed in the curate and compatible with the World Meteorological Or- present paper. This station of high endurance is easy to be ganization (WMO) standards. Moreover, the station’s main- installed and capable for long-time operation without sig- tenance is a hard process, time consuming and of high cost. nificant problems. The metadata of the station which are the characteristics of the instruments, electronic logic con- In general, AWS contains sensor-based equipment. Its trol and datalogging systems are described in detail, ac- sensors contain a conventional cup anemometer, wind vane, cording to the Guides of the World Meteorological Or- miniature temperature screen with wet and dry bulb plati- ganization (WMO). Moreover, a computer controlled envi- num resistance thermometers, solarimeter, net radiometer ronment is designed and implemented, with capabilities of and tipping bucket raingauge. Many researchers have dealt data acquisition and control with flexible and high perform- with this matter and a great improvement has been achieved ing software and hardware capabilities. The AWS can easily in accomplishing the technical characteristics of the mete- communicate, so directly as remotely, with some modifi- orological instruments [1-10] as well as in the communica- cations and both possibilities are examined in detail. Fi- tion part of the AWS and the data acquisition and process- nally, an evaluation procedure is presented and analyzed, ing [11-13]. Βesides, so far, significant new developments while the obtained results are used for testing the system. and operational experiences together with new observation The evaluation depicted the unique and well established technology have been presented. Today, as AWS are com- characteristics of the system and proved its potential ap- pletely automated, AWS may record weather conditions al- plication to meteorological data collection and calcula- most everywhere on the globe, even under extremely hard tion. conditions [14-16], hence, AWS networks of completely automated weather stations have been adopted [17-20].

There are many advantages of using AWS’s systems KEYWORDS: Automatic weather station, real-time communication data link, con- instead of customary stations, but the main are: monitoring trol software, direct communication, remote station. of data in sparse areas where human observations are not practical, continuously flux of data at frequent intervals and for any observation time, increase of coverage, elimination of the subjectivity in observations, cost reduction [10] etc. Of course, there are many difficulties in AWS’s operation, INTRODUCTION as the disagreement between the professional meteorological observer and the automated observations [21-23], espe- Real-time meteorological and environmental obser- cially in the type and the intensity of precipitation [24,25], vations can be provided by Automatic Weather Stations the inabilities in guaranteeing the renewal of the spare parts, (AWS), gathering data from a network through various a wear of the material, the lack of flexibility, an aging sys- communication channels. The design, installation and op- tem of transmission of the data, etc. [10] but these prob- eration of well-functional AWS is a challenging task be- lems decrease day by day.

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Our AWS has been established in Western Greece, in The present paper has as main objective to emerge in- the center of the prefecture of Aitoloakarnania, in the city formation and guidance on the design, installation and op- of Agrinio, an urban area of about 100,000 habitants, which eration of an, easy to install and maintain, fully computer- is characterized by a rather complicated topography. In ized, automatic weather station for high quality meteoro- Western Greece the climate has the basic features of Greek logical measurements in an urban area. It also demonstrates climate (a typical Mediterranean climate): mild and rainy the “flexibility” and propriety of this station both for near, as winters, relatively warm and dry summers and, generally, well as for remote applications, with some appropriate modi- extended periods of sunshine throughout most of the year fications each time. Moreover, this paper presents a pro- [26]. Moreover, due to the influence of topography (great cedure for the validation of the station, so in case of direct mountain chains along the central part and other mountain- communication as in case of the remote station too, which ous bodies) on the air masses coming from the moisture had been achieved by comparison of the AWS’s data with sources of the central Mediterranean Sea, Western Greece these of a thermograph, barograph and other conventional has a more wet climate comparatively to the dry climate of recording devices of the Greek Meteorological Agency’s Attiki (Athens’ greater area) and East Greece in general, in- (EMY) station in Agrinio. This comparison verified both cluding sometimes some harsh phenomena (storms, floods, accuracy and reliability of the AWS. Finally, the present etc.) [27]. Despite of the particular climatological charac- paper depicts the general difficulties that erase in the estab- teristics of Agrinio area (such as Western Greece), there was lishment of an urban meteorological station, concerning the sparse meteorological data coverage, which led to the im- selection of the station’s position and the settlement of the perative need for an AWS that could monitor continuously sensors, for the station to be well representative for urban - and on regularly selected time steps - basic meteorologi- sites and in accordance to the WMO guidelines at the same cal parameters in order to provide a weather identification time. and determination as similar to a human observer as possible, ultimately replacing the observer. AWS FOR DIRECT COMMUNICATION The descriptions in this paper AWS should be used for energy, environmental, agricultural and meteorological ap- Description of the equipment, plications, such as the estimation of the wind and solar communications link and power supply energy potential of the area, the investigation of urban heat Equipment: In planning a new AWS, the selection of island effect (in Agrinio region, which is recently highly equipment depends on the nature of the regular data that developed and urbanized), the calculation of the area’s are to be measured and on the site location. Consideration potential in ground cooling applications, etc. should also be given to whether the versatility of the sys- The wind energy potential in Western Greece was tem might be enhanced by future addition of further sen- evaluated from measurements of wind speed and direction sors. The range of sensors offered and similar equipment at four weather stations. Weibull parameters estimated by is wide and the selection of a well established set guaran- three different methods were used to estimate wind power tees trouble-free performance in the future. potential in this area [28]. Additionally, analysis of the “unit energy cost”, being the specific cost per kilowatt-hour ob- The various instruments making up the station involve tained for several wind turbines, at different hub heights, a datalogger, a temperature and humidity probe, a wind- has been carried out for every station [29]. sonic 2D anemometer, a tipping bucket raingauge, a barometric pressure sensor, a pyranometer, a soil temperature An aluminium nocturnal radiator, painted with appro- probe, a soil moisture probe, a pyrgeometer and a sunshine priate white paint, was established on the roof of the De- duration meter. Table 1 summarizes the instruments and partment of Environmental and Natural Resources Man- their specifications and characteristics, while technical de- agement in Agrinio, in Western Greece [30]. A both sim- tails, specifications, operation ranges and other special in- ple and accurate model for the prediction of the radiator formation for the instruments can be found in data sheets heat exchange performance was presented. The model, using available1 [31]. as input data some meteorological parameters from our AWS measurements, calculated with appropriate algorithms Communications Link: AWSs report observations by a the outlet temperature of the radiator. variety of formats, including telephone lines, radio modems, mobile phone networks and satellite networks. The The station ought to serve in educational purposes as communications between the AWS and the data collection well, without compromising the systems integrity. More- agency should be: reliable, inexpensive (satellite telephone over, it ought to communicate easily, either directly for can be expensive) and in accordance to standard protocols. short distances, as remote for long, with the necessary modifications. The system needs to be economically viable There are several ways to communicate with the data- and maintainable on a long-term basis and the data collected logger in order to retrieve data. The most commonly rec- should be accurate and physically accepted while extra care should be taken in eliminating any possible reasons for ob- 1 http://www.campbellsci.co.uk/ (Campbell Scientific, 2004), taining poor quality data. http://www.munro-group.co.uk, www.druckinc.com, www.kippzonen.com

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TABLE 1 - WMO recommendations.

Instrument Description General description - Characteristics Maximum rate of program execution: 64 times per second Maximum rate of single input measured: 750 samples per second Data and programs storing: non-volatile Flash memory or battery-backed SRAM Standard memory storing: 62,000 data points CR10X Measurement Ports: 25-pin female; configured as DCE, 9-pin CS I/O Port male; connects to datalogger via SC12 cable and Control System Datalogger Processor: Hitachi 6303 [i,ii] Data storage: 128 Kb SRAM standard (approximately 60,000 data values - Additional 2 Mb Flash as an option Voltage: 9.6 to 16 Vdc Typical current drain:1.3 mA quiescent, 13 mA during processing, and 46 mA during analog measurement Batteries: DM12-9 (12V9Ah DiaMec) directly connected. Humidity Sensor: ROTRONIC HYGROMER C94 Temperature Sensor: Pt100RTD Humidity Measuring Range: 0...100%RH MP101A-T7-WAW Temperature Measuring Range (operating): -40 to 60oC Air temperature - temperature and Temperature Limits (storage): -50 to 70oC Air moisture humidity probe [i] Humidity Accuracy at 20oC: ±1,0%RH (factory) Temperature Accuracy at 20oC: ±0,2oC Humidity Sensor Stability: better than 1%RH over a year Response Time (without filter): 10 seconds (%RH and temperature) Measurement Units: m/s in SDI-12 mode; knots, mph, kph, ft/min also available in other communication modes Wind Speed Range: 0 to 60ms-1 (130mph) for maximum accuracy; gust survival 100ms-1 (220mph) Accuracy: ±2% Resolution: 0.01ms-1 Windsonic 2D Wind Direction Wind speed and Anemometer (Gill Range: 0 to 360° – no dead band direction Instruments) [iii] Accuracy: ±3° Resolution: 1° Environmental Operating Temperature: -35° to +70°C Operating Humidity: <5% to 100% Power Requirement: 9-30V DC at 40mA (typical) Funnel Diameter: 254mm ARG100 Tipping Overall Height: 340mm Rainfall Bucket Raingauge Output: Contact closure at tip Weight: 1.0 kg Operating Pressure Ranges: 600 to 1100 mbar absolute, Overpressure: 1.4 bar absolute Frequency Output: TTL square wave from 600 to 1100Hz Voltage Output: 0 to 2.5V (4-wire) or 0 to 5V (4-wire) Druck RPT410F [iv] Barometric pressure Accuracy (standard): ±0.5 mbar at 20oC, ±1 mbar from -10 to 50 oC, ±2 mbar from -20 to 60 oC, ±2.5 mbar from -40 to 60 oC Long Term Stability: Better than 100 ppm/year Operating Temperature Range: -40 oC to 60 oC Response time (95 %): 18 s Non stability (change/year): ± 1 % Temperature dependence of sensitivity: ± 6 % (-10 to +40 °C) Sensitivity (µV/W/m2): 10 to 35 CM3 pyranometer Short wave (solar) Level accuracy: 1° [v] radiation Operating temperature: -40 to +80 °C Spectral range (50 % points): 305 - 2800 nm Typical signal output for atmospheric applications: 0 - 50 mV Maximum irradiance : 2000 W/m2 Expected daily accuracy: ± 10 % Element: 1/3 DIN (to BS1904, IEC751, DIN43760) PT100/3 (1/3 DIN Typical PRT Element Error: <±0.15°C at -100°C, <±0.1°C at 0°C, <±0.31°C at +200°C Soil temperature PRT) Probe) (excluding datalogger and bridge resistor accuracy) Maximum temp. of standard probe: +80°C Accuracy: ±2.5% VWC using standard calibration iwith bulk electrical conductivity, < 0.5 deciSiemen m-1 (dSm-1) and bulk density, <1.55g cm-3 in measurement range 0% VWC to 50% VWC Precision (reproducibility): 0.05% VWC Resolution: Probe-to-probe variability ±0.5% VWC in typical saturated soil CS616 Water Content Soil moisture Output: ±0.7 volt square wave with frequency dependent on water content Rreflectometer [i] Typical Power Requirements: 65mA at 12V DC during measurement - 45µA quiescent Measurement Time: with Instruction 138: 0.50ms - With Instruction 27: 50ms Power Supply Voltage: 5V DC minimum, 18V DC maximum Enable Voltage: 4V DC minimum, 18V DC maximum Sensitivity (nominal): 10 µV/W/m² Spectral Range: 4.5 µm to 42 µm (50 % points) Window Heating Offset (under direct solar irradiance): 25 W/m² max. (with 1000 W/m²normal incidence solar radiation) Long wave (Infrared) Operating Temperature: -40 ºC to +80 ºC CG3 pyrgeometer [v] earth radiation Response time (63 %): <8 seconds Thermopile Output Range: -250 to +250 W/m² Temperature Dependence of Sensitivity: less than ±5 % (-10 ºC to +40 ºC) Field of View: 150 º Operating temperature: -30 °C to +70 °C Heating level 1: dew removal CSD1 Sunshine Heating level 2: ice and snow removal above -15 °C (wind speed<1 m/s) Sunshine duration duration meter [v] Output: 0 VDC or 1 VDC ±0.1 V Power requirement: without heating: 12 ±3 VDC, <10 mA, with heating level 1: 12 ±3 VDC, 1 W (nominal), with heating level 2: 12 ±3 VDC, 10 W (nominal) [i] Campbell Scientific (2004) http://www.campbellsci.co.uk/ [ii] http://www.munro-group.co.uk [iii] Stock C 2002 Ultrasonic Wind Sensor – A new approach from Gill Instruments Royal Met Society Newsletter No 19 15-17 [iv] www.druckinc.com [v] www.kippzonen.com

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ommended method is to use a direct link to a computer, a transformer and a charger. This offers a great stability to either a laptop on site, or to a desktop PC at any conven- power voltage and protects the station from abrupt network ient location using an appropriate interface package. It is voltage changes; as the station is not directly connected to more convenient to have our measurements transmitted to, the electricity network. Moreover, the battery offers a sta- and stored in a computer either for immediate viewing or ble energy supplying for a short-time period. The battery for later retrieval and manipulation. As a further option, voltage is monitored through a datalogger channel. The communication can be carried out by using a remote com- battery is a lead acid battery, non spillable sealed and re- munications package with a modem to transmit data, either chargeable and it is connected to a charging regulator. via the public telephone network or by one of the cellular As said, Figure 1 pictures clearly the battery and its networks. In that occasion we must select another appro- connection to the power supply system. priate interface. However a long connection is more vul- nerable to lightning damage, so we need to consider extra Software lightning protection measures. For distances over 15 metres A powerful and simple software, which is used to sup- we use RAD-SRM Short Range Modems in the communi- port direct communications (not remote) between CR10X cations link. datalogger and the PC is the Campbell Scientific’s PC200W Since the computer-station distance is less than 15 me- ver3.0 software2. This software, which is compatible, so tres, the simplest communication method is to use an appro- with many contemporary dataloggers (including the CR800), priate interface package; hence we use the SC32A opto- as many retired dataloggers (e.g., CR10, 21X, CR23X) can isolated interface, permanently mounted inside the enclo- support programming of the datalogger, data collection and sure together with the datalogger. The SC32A interfaces a storing in comma separated files on the PC’s hard disk, RS232 peripheral, commonly a computer or a printer, to the setting of the datalogger’s clock, access to a terminal emu- serial I/O port of the Campbell Scientific datalogger. The lation mode and display of real-time measurements. SC32A provides optical isolation between the datalogger For better data processing and display, we use a new, and the computer’s electrical system, protecting against more powerful software, called Analyzer ver4.5 (Scientific ground loops, normal static discharge and noise. The SC12 Enterprises Ltd, 45 Agion Saranta Str., Moschato, Athens), cable connects the datalogger to the 9-pin port of the SC32A. which has all the PC200W’s capabilities, but also supports Connection to the serial port of a PC is made with an direct or remote communications between the datalogger RS232 cable such as the Campbell Scientific SC25AT. and the PC, as well as data display in a website, statisti- Figure 1 shows a photograph of the datalogger, SC32A cal analysis and graphics presentation. interface, battery and barometric pressure sensor into the The overall scheme of the communication setup dia- enclosure and the relevant connections. gram with the weather station data flux is displayed in the diagram appearing in Figure 2.

System’s requirements; installation and maintenance There are basic requirements that are essential for proper sitting, operation and validation of the weather station. These requirements are depicted clearly in the Guide to Meteoro- logical Instruments and Methods of Observation [32], and can be presented comprehensively at the following catego- ries: Observation requirements: WMO recommendations de- fine the standards that basic meteorological instruments have to satisfy. These standards are pictured in Table 2. By the description and general characteristics of the instruments, given in Table 1, it is clear that these instruments are appropriate for use in our AWS.

FIGURE 1 - A photograph of the datalogger, SC32A interface, Sitting criteria for sensors: The AWS in Agrinio can battery and barometric pressure sensor into the enclosure and monitor the following meteorological parameters continu- the relevant connections for direct communication. ously and on regularly selected time steps: 1) air temperature (oC) 2) relative humidity (%) 3) wind Power supply: Power supply is also an essential fact at speed (m/s) 4) wind direction (o - deg clockwise from N) the whole installation. Most stations mainly operate at 120 5) rainfall (mm) 6) barometric pressure (mbar) 7) solar radia- or 240 V AC supply. In our station, as any 9-16 Vdc source tion (W/m2) 8) soil temperature (oC) 9) soil moisture (%) can power the CR10X; we use a 12V9Ah battery connected 10) IR (earth) radiation (W/m2) 11) sunshine duration (min). in parallel to the datalogger and the 240 V AC network only supports and recharges battery with 13.5 Vdc, through 2 www.campbellsci.com/documents/lit/b_pc200w.pdf

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Digital inputs ARG100 Raingauge

SC32ACommunication Interface CR10X Data Logger CSD1 Sunshine duration meter Personal Com

CS616 Reflectometer 25 to 9 pin CS12 cable RS232 cable (15 m max)

PT100/3 (1/3 DIN PRT Probe) p

uter Analog inputs

CG3 pyrgeometer

Barometric pressure (Druck PRT410F)

CM3 pyranometer

Windsonic 2D Gill Anemometer

MP101A-T7-WAW

FIGURE 2 - The communication setup diagram for direct communication with the overall scheme of the weather station data flux.

TABLE 2 - Instruments and their specifications.

WMO recomendations Variable Unit Range Accuracy requirements Reported resolution Averaging time Air temperature °C -60 to +60°C ± 0.1°C 0.1°C 1 minute Relative humidity % 0 to 100 % ± 5 % 1 % ± 0.5m/s for ≤ 5m/s Wind speed m/s 0 to 75 m/s 0.5 2 minutes ± 10% for > 5m/s Wind direction ° 0 to 360° ± 5% 10o 2 minutes Rainfall mm - 3 % 0.1 mm 100 hPa Atmospheric pressure hPa (within the range from ± 0.1hPa 0.1hPa 1 minute 920 to 1080 hPa)

According to WMO recommendations [32,33] some ground of open terrain. Open terrain is defined as an area sensors don’t demand special requirements for their sit- where the distance between anemometer and any obstruc- ting and can be mounted on the mast, while others, due to tion is at least 10 times the height of the obstruction. Us- the special criteria for the selection of their location, they ing this rule, we should place the station 100 m away from have specific sitting “treatment”. The sensors that belong the 10 m high building of the University to ensure proper to the first category are the wind sensor, the barometric wind flow at the site. This was the main difficulty we had pressure sensor, the pyranometer and the sunshine dura- to face in our AWS in Agrinio, due to the limited open area tion meter. The second category of sensors includes the of the University campus. temperature and humidity sensor, the precipitation gauge, Many urban weather stations have been placed over the soil thermometers and hygrometers and the pyrgeome- short grass in open locations (parks, playing fields), with ter. standards similar to the stations in open rural areas. This The “classic” sitting criteria of WMO [32] suggest that results in the fact that urban stations are actually monitor- the wind sensor should be mounted at 10 m height above ing modified rural-type conditions, not representative urban

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ones and show no urban effect on temperature [33,34]. So, the portable anemometer equivalents (differences are less the WMO standards have to be modified for urban sites than 1.5 % for every direction). Consequently, the 5 m height and urban stations must be centred in sites representative is a satisfying choice for the wind sensor height. There- of the location [33]. For our urban AWS, the better choice fore, as the building is 10 m height, the wind sensor is is the roof of the 10 m height building of the Department placed at 15 m height above the ground level and trans- of Environmental and Natural Resources Management formations to the standard 10 m height [32] should be done (University of Ioannina). Rooftop weather stations have with the use of the power law equation [35]. been installed almost everywhere3,4,5,6,7, allowing constant monitoring and archiving of local weather conditions. The For the pressure sensor (which is also mounted on the usual practice for such weather stations is that most sen- mast) the difference between sensor elevation and field sors are mounted on the mast. However, it is better for many elevation should be less than 30 m [32]. In our AWS this sensors to be placed separately, on such a position that satis- condition is valid, as the roof of the building is about 10 m. fies the more the WMO recommendations [33]. Besides, there is no vicinity of buildings where pressure ‘pumping’ due to gusts is probable, and also interior-exte- The wind sensor must be placed on a mast, high enough rior pressure differences do not exist as the sensor is not above the roof structure, in order to avoid potentially turbu- located into a room. The barometric pressure sensor is kept lent air below. In order to find the best position for the mast in a weatherproof enclosure which is mounted on the mast. and the height of the wind sensor, many tests had to be done on comparing the wind sensor’s values with these As the observed temperature and humidity should be from a certified portable anemometer such as Kestrel 1000 representative of the free air conditions surrounding the Pocket Wind Meter (certified by the USA’s National Insti- station, at a height between 1.25 m and 2.00 m above the tute of Standards and Testing - NIST), placed on a park ground level, this sensor is placed on an iron rod extension near the University building, according to the WMO rec- placed at a corner of the building, at 2.00 m height and is ommendations. The wind characteristics in the park have connected to the datalogger with a wire. WMO recommen- not been influenced from the “rural” standards of that area dations [32,33] emphasize mainly the height of the sensor (as it could happen in temperature or humidity and such (1.25-2.00 m) and also the fact that the sensor must be reasons led us to the selection of the roof, as mentioned housed in a ventilated radiation shield to protect the sensor before). The values from this portable anemometer were from thermal radiation. Several tests had been made involv- transformed to the wind sensor’s height equivalents by the ing the comparison between the measurements taken by the use of the power law equation [35]: temperature sensor placed on an iron rod at the four corners of the building at the height of 2 m and the temperature 1/ 7 v  z  measurements of a simple mercury thermometer placed at sens =  sens  v  z  the same height into a radiation shield, at an open area near- port  port  by. The diversions of the measurements at the four corners

where vsens and vport are the wind speeds at heights and those of the mercury thermometer were less than 1%. zsens and zport of the wind sensor on the mast and the port- Yet, the orientation of the area where the sensor is placed able anemometer, respectively. Wind speed and direction may also be relevant because the systematic sun-shade measurements taken from the wind sensor at several loca- patterns could influence the measurements. As continuous tions and heights on the roof, were compared with the port- monitoring is planned, a south oriented area is favoured able anemometer’s measurements transformed to the wind because there is less phase distortion [33]. sensor’s height equivalents each time. At low heights on For the precipitation gauge, the roof area beside the the roof (2, 3, 4 m), the wind sensor presented significantly mast is suitable, as objects should not be closer to the gauge lower wind speed measurements (more than 10%) from the than a distance twice their height and sites on a slope should portable anemometer’s transformed ones. Moreover, when be avoided [32]. the mast with the wind sensor was placed on the edge of the roof, there was a great divergence in sensitivity, hav- According to WMO recommendations for urban me- ing the biggest problem, especially, when wind flows from teorological stations [33], the main difficulty in measuring the opposite side of the roof. After a long time with sev- outgoing radiation terms accurately is the exposure of the eral tests, it was found that if the wind sensor is mounted down-facing pyrgeometer to view a representative area of on a mast at 5 m or higher and the mast is placed at the the underlying urban surface. CG3 pyrgeometer, although centre of the roof area, there is a significant similarity with the window is flat, has a 150 degrees field of view, which practically means that the instrument “sees” a circular radia- 3 University of Otago (New Zeeland) tive source area of diameter more than seven times the sen- (http://www.physics.otago.ac.nz/eman/weather_station/index.html) o 4 College of Engineering University of Iowa sor height (tan75 = 3.732). For “classic” weather stations, (http://www.iihr.uiowa.edu/facilities/weather/index.html) a sensor height of 2 m is appropriate over a short grass sur- 5 Case Western Reserve University (Cleveland Ohio) (http://studentaffairs.case.edu/living/resources/weather/) face (circular radiative source area of diameter more than 6 Weather Center of Central Connecticut State University 12 m). For urban sites, the radiative source area should (http://www.ccsu.edu/weather/) ideally be a representative sample of the main surfaces con- 7 Cambridge University Computer Laboratory (http://www.cl.cam.ac.uk/research/dtg/attarchive/weather/) tributing to the flux. Clearly a much greater height is nec-

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essary over an urban area in order to sample an area that The selected sitting is an ideal choice, because it of- contains a sufficient population of surface facets to be rep- fers the following advantages: resentative. Considering the case of a radiometer at 10 m 1) There are no obstacles nearby and no shade. (mounted on the rod extension at the most “representative” corner of the roof, beyond the roof’s edge, “looking” 2) Testing of the station and maintenance (examination and towards the ground), the 90% source area has a diameter cleaning of the sensors etc.) can be done easily, since of 60 m at ground level. This might seem sufficient to “see” there is direct access to the station. several buildings and roads. 3) There is direct access to AC power supply, which is The soil thermometers are placed into the soil at the more trust-worthy than independent supplies (solar pan- grass surrounding place next to the building, connected to els etc.), so peripherals consuming a significant amount the datalogger. of power may be supplied in a continuous manner.

The roof of the building is also an appropriate site for The station is secured to interventions from irrelevant radiation sensors, due to shade avoidance. persons or animals, due to building security. The disadvan- The exact position of all sensors is illustrated in the tage of the concrete roof existence and the reflection of schematic sketches of Figure 3. solar radiation, which could influence the temperature and

FIGURE 3 - Schematic sketches of the building with the exact position of all sensors: a) over view; b) side view.

954 © by PSP Volume 16 – No 8. 2007 Fresenius Environmental Bulletin

humidity sensor primarily, have been restricted as this sen- Maintenance: The station has been made up by systems sor is placed on an iron rod extension at a corner of the that are simple to program and easy to operate, by per- building. The influence of the “harsh” thermal properties sonnel at no special experience. The station should have of the concrete roof to the other sensors is negligible, as the ability to be networked, if required. the only instrument that could be affected, the pyrgeome- A weather station, like any other piece of equipment, ter, is “hanging” beyond the roof’s edge, not facing any of requires regular maintenance in order to achieve a good and the roof area. validated performance. Some of the more important routine The wind sensor, the pyranometer and the sunshine maintenance chores can and should be performed by local duration meter are mounted on a mast at the height of 5 m, maintenance personnel since they can access the station supported on wire ropes and no instrumentation towers or on a regular basis, while special work should be performed portable tripods are required. The mast is less weighty, by a trained technician8. cheaper and easier to install. It is not concreted on the roof, but it is fixed with guy ropes, so it can be easily moved Validation of data from site to site even by one person and can be set up on Accuracy checks, calibration and problems’ confront- uneven ground. Moreover, the mast is of stainless-steel, ing: All instruments have been calibrated prior to installa- galvanized, with anti-lightning protection. tion by the manufacturers and could be installed without Since the mounted instruments are exposed to hazards, any additional calibration. However, further calibration [36] we keep some instruments that do not demand directly open was performed and checks were made according to the re- air for their operation, as the datalogger, the interface, the quirements of the sitting location. battery and the barometric pressure sensor, in a weatherproof enclosure which must be mounted on the mast and Regular field checks and calibrations of the used in- is big enough to encapsulate them. The used enclosure has a struments are essential for guaranteeing the high quality and UV-stabilized rectangular protection box, and is made of homogeneity of the observations. These actions and their white, fibreglass-reinforced polyester. Sun protection is results, as information about instrument validation, inspec- achieved with a stainless-steel sunbonnet. There are also gas tion and repair information, instrument inventory and sta- tubes for rugged electrostatic discharge protection. More- tion comparison experiments compose the station’s meta- over, it is ventilated through a small tube that leads air to data and are archived along with the data [37]. the barometric sensor All instruments of our AWS are equipped with calibra- In Figure 4 a photograph of the system with all in- tion certification, but factory calibration should be performed struments mounted can be seen. at least every two years in a calibration laboratory. Till then, it is really essential to check the accuracy of our AWS As mentioned before, the station has being set-up in by field checks with suitable travelling reference instru- Agrinio, Greece, at a longitude: E021o24'56.7", a latitude ments regularly. As professional reference instruments of of: N38o36'45.8" and an altitude of 82 m from the sea sur- known high accuracy are too expensive, this check could face. Operation of this station and systematic observations be done by comparing the station’s data with that from other began on 26 November 2004. The collected meterological reference station in the locality, if the two stations have data cover both research and educational needs. The station similar microclimates. The reference station is a manned is connected to the internet both for educational purposes professional station settled by the Greek Meteorological as well as to establish a direct real time connection. Agency (EMY) in Agrinio airport (IATA code: AGQ, ICAO code: LGAG), equipped with thermometer, barometer, hygrometer and raigauge, three kilometers away from the University, at a similar distance from the lake as our AWS and at rather similar terrain. As the reference station has been settled in an airport, it is characterized by accurate measurements; especially in barometric pressure. Ana- lytically: Field checks for the temperature sensor have been done by comparing our values with these from a simple mercury thermometer with the bulb at exactly the same point in space as the AWS probe. For wind speed and direction measurements, checks have also been done easily by comparing the AWS’s values with the readings from the Kestrel portable anemometer, placed near the wind sensor for a short period.

FIGURE 4 8 The University of Arizona: Sitting and Maintenance of Weather Stations A photograph of the station with all instruments mounted. http://ag.arizona.edu/pubs/water/az1260.pdf

955 © by PSP Volume 16 – No 8. 2007 Fresenius Environmental Bulletin

During the period of the station’s operation, our AWS tion, as there is an airport, have been regularly checked from was characterized by remarkable reliability and endurance the authority for their accuracy and sensitivity, at frequent to external difficult situations (power supply failure, harsh intervals. weather conditions, long period without data gathering etc.). The aim of these comparisons is mainly to check if Only once the PC200W software seemed to be “blocked” the AWS’s data follow the same temporal fluctuations in and real-time monitoring was impossible. This problem was their values as the EMY’s data, in order to strengthen the a superficial instant failure of data presentation, as after re- validation of our station. The similarity in data of both sta- loading the starting program to the datalogger, it performed tions could not achieve a hundred percent, as differences in well, without any loss of the previous data. This problem characteristics of the stations could cause slight differentia- showed that even after possible errors and failures when tions in measurements. data display procedure has been stopped, there is the ability of data recovery. On a monthly basis, Figures 5, 6, 7, 8 and 9 show the temporal variations of the monthly mean measured values Comparison: Since there are too many errors (random, of air temperature, air relative humidity, monthly rainfall systematic, large, micrometeorological) we ought to verify values, rainy days per month and monthly mean baromet- the validity and the quality of the station’s data. The primary ric pressure respectively, for a 19-months period, from the st th purpose of quality control is missing data detection and 1 of December 2004 to the 31 of August 2006 for AWS error detection in order to ensure the highest possible stan- (UNIV) and the Greek Meteorological Agency’s station dard of accuracy and the optimum use of these data. Prior to (EMY) in Agrinio. their use in computation of the parameter values, two types As shown, there is a good agreement between the val- of control were made [3,38]: ues from the two stations for air temperature (correlation Quality control of raw data, drawn from the data ar- coefficient λ=0.998886) as both stations present the same chives, comprised of a) a plausible value check, where we verified that the values are within the acceptable range Air temperature limits and b) a time consistency check on a plausible rate of change, where we verified that there are no unrealistic 30

leaps in values. C) 25 o 20 Quality control of processed data, drawn from the UNIV 15 monitoring of instantaneous ones, consisted of a) a plausi- EMY ble value check and b) a time consistency check on a plau- 10 sible rate of change. 5 Air temperature ( 0 In both types, missing and erroneous values are distin- 0 5 10 15 20 25 guished by appropriate algorithmic routines running in a Month PC. Installation and set-up followed the standard sugges- tions, presented in the instrument and micrologger manu- FIGURE 5 - Temporal variations of the monthly mean measured als. Suggested daily, weekly, and longer term checks, main- values of air temperature for a 19-months period, from the 1st of tenance and set instrument replacements were scheduled December 2004 to the 31th of August 2006 for AWS (UNIV) and the while maintenance logs for each station were kept. Greek Meteorological Agency’s station (EMY) in Agrinio (AWS in direct communication). All instruments have been calibrated prior to installation by the manufacturers and could be installed without any additional calibration. However, further calibration [36] Relative humidity was performed and checks were made according to the 90 requirements of the sitting location. 80 70 The safest way to assess the quality of data from our 60 AWS is to compare them with that from the established 50 EMY 40 UNIV RH (%)RH station of EMY at Agrinio airport. More attention has to 30 be paid to the exposure of the reference station’s sensors 20 and to the accuracy and validation of that station. 10 0 In the EMY’s station, the thermometer is protected by 0 5 10 15 20 25 a natural aspiration radiation shield, (as in the Univer- Month sity’s AWS), the barometer and hygrometer are placed into a wooden shield and the raigauge is exposed directly to FIGURE 6 - Temporal variations of the monthly mean measured values of relative humidity for a 19-months period, from the 1st of the open air, according to WMO recommendations. Con- December 2004 to the 31th of August 2006 for AWS (UNIV) and the sequently, the meteorological instruments in both stations Greek Meteorological Agency’s station (EMY) in Agrinio (AWS in have similar exposure. The instruments in the EMY’s sta- direct communication).

956 © by PSP Volume 16 – No 8. 2007 Fresenius Environmental Bulletin

tions (λ=0.974325), monthly rainfall totals (λ=0.984431) Rainfall values and rainy days per month (λ=0.982505). For monthly mean 350 barometric pressure (λ=0.994632), the values from AWS 300 are systematically lower than those from the EMY’s station 250 by a stable quantity each month, as AWS is settled in upper 200 EMY altitude. 150 UNIV 100

Rainfall (mm) Rainfall On a daily basis, Figures 10 and 11 present the fluc- 50 tuations of air temperature and barometric pressure meas- 0 urements for our AWS (UNIV) and the EMY’s station in 0 5 10 15 20 25 the Agrinio airport during 72 hours (from 00.00 at the 1st Month of December 2004 to 24.00 at the 3rd of December 2004). There is also a strong agreement between these values (co- FIGURE 7 - Temporal variations of the measured values of monthly efficient correlations are: λ=0.996242 for air temperature st rainfall totals for a 19-months period, from the 1 of December 2004 measurements and λ=0.997138 for barometric pressure to the 31th of August 2006 for AWS (UNIV) and the Greek Meteoro- logical Agency’s station (EMY) in Agrinio (AWS in direct communi- measurements respectively). AWS’s air temperature meas- cation). urements also present slightly higher values than those from the EMY’s station, due to the heat island effect. Moreover, EMY’s station barometric pressure measurements have Rainy days systematically higher values than those from AWS, due to the different altitude. By that time, intradiurnal differences 18 16 are been checked out regularly. 14 12 10 EMY 8 UNIV Air temperature 6 Rainy days 4 20 2 0 18 0 5 10 15 20 25

C) 16

Month o UNIV (

air 14 EMY T

FIGURE 8 - Temporal variations of the number of rainy days per 12 month for a 19-months period, from the 1st of December 2004 to the 31th of August 2006 for AWS (UNIV) and the Greek Meteorological 10 Agency’s station (EMY) in Agrinio (AWS in direct communication). 0 20406080 Hour

Barometric pressure FIGURE 10 - Temporal variations of the measured values of air temperature for a 72-hours period, from the 1st of December 2004 to rd 1025 the 3 of December 2004 for our AWS (UNIV) in direct communication and the Greek Meteorological Agency’s station (EMY) in Agrinio. 1020 1015 EMY 1010 (mbar) UNIV Barometric pressure

atm 1005 P 1024 1000 1022 995 0 5 10 15 20 25 1020 UNIV Month 1018 (mbar) EMY

atm 1016 P FIGURE 9 - Temporal variations of monthly mean values of meas- 1014 ured barometric pressure for a 19-months period, from the 1st of December 2004 to the 31th of August 2006 for AWS (UNIV) and the 1012 Greek Meteorological Agency’s station (EMY) in Agrinio (AWS in 0 20406080 direct communication). Hour fluctuations month by month, but the values from our AWS FIGURE 11 - Temporal variations of the measured values of barometric pressure for a 72-hours period, from the 1st of December 2004 are slightly greater than these from EMY’s station, due to to the 3rd of December 2004 for our AWS (UNIV) in direct commu- the heat island effect. There is also a good agreement be- nication and the Greek Meteorological Agency’s station (EMY) in tween the values of air relative humidity from both sta- Agrinio.

957 © by PSP Volume 16 – No 8. 2007 Fresenius Environmental Bulletin

Of course, weather conditions can change over rela- dataloggers and a PC. This 32-bit software supports all tively short distances, but as the region between the two contemporary dataloggers (including the CR1000), all data- stations is relatively flat, the weather conditions are simi- logger operating systems (e.g., mixed-array, table data, lar. Small systematic differentiations between two stations’ PAKBUS), and many retired dataloggers (e.g., CR500, measurements, mainly concern the air temperature meas- CR10, 21X). urements (due to the heat island effect) and measurements of barometric pressure (due to the different altitude) and in no occasion measurements of solar radiation, sunshine duration or even relative humidity, the differentiations of which are by chance and negligible. For wind measurements, the use of the portable anemometer can justify the accuracy and validity of the measurements at the AWS.

REMOTE AWS

Our AWS could also be installed in remote areas. In that occasion, three basic modifications should be performed: change in communications link, in power supply and in software.

Description of the equipment, communications link and power supply The equipment (sensors, battery, mast, guy ropes, enclosure) remains unaltered. Instead of a SC32A opto-isolated interface, a SC932A is used to interface a CSI datalogger to any modem that is configured with an RS-232 DCE (Data Communications Equipment) serial port. The used modem is a M2M Wavecom, with an advanced open software platform: Open AT, with a fixed dialing number, SIM Toolkit Class 2, SIM, locked network and service provider, FIGURE 12 - A photograph of the datalogger, SC932A interface, real time clock, alarm management and software upgrade M2M Wavecom’s modem and dual band antenna into the enclosure and the relevant connections for remote communication. through Xmodem protocol. This modem, which carries a dual band antenna, can also support remote station control LoggerNet is a company’s basic software that supports and other wireless services: GSM/GPRS data, SMS and mainly communication and data collection and less data voice via a simple serial connection. displaying or analysis. For better data presentation through Figure 12 shows the datalogger, the interface, the mo- the internet network and extra advantages and capabilities, dem and the antenna for remote communications, while in the Analyzer ver4.5, that has been also used for direct com- Figure 13 the overall scheme of the communication setup munication, is a more powerful software. diagram with the weather station data flux can be seen. System’s requirements; installation and maintenance When there is no city power supply, the same remote System’s requirements and installation: As in direct com- AWS could be used, without any modification, except of munication, system’s requirements for remote communi- the addition of renewable energy sources, such as a photo- cation are in accordance to WMO recommendations [32]. voltaic solar panel [39], a wind-powered generator or a hy- Installation was performed on a remote site of the roof area, brid of solar panel and wind-powered generator, charging where the distance from the PC is about 150 meters, so a the 12V9Ah rechargeable battery. direct communication could not be established (as the dis-

Software tance is greater than 15 meters). The conditions of this AWS are similar to any other remote site having city power sup- PC200W Campbell’s software supports only direct com- ply. munications. For telemetry and scheduled data collection the company provides LoggerNet support software9, which lets Maintenance: The required maintenance chores are ge- us manage an existing LoggerNet datalogger network from nerally more “painful” than these for the short distance a remote location. This software is based on the client/ ser- AWS, for the instruments’ check requires now longer re- ver network architecture, facilitates programming, commu- moval. A camera connected to a network could possibly nications, and data retrieval between Campbell Scientific help in monitoring the instruments’ good state and operation and in the safety and protection of the instruments at 9 http://www.campbellsci.com/loggernet3x the same time.

958 © by PSP Volume 16 – No 8. 2007 Fresenius Environmental Bulletin

Digital inputs ARG100 Raingauge

SC932A Communication Interface CSD1 Sunshine duration meter modem Wavecom M2M Dual band antenna CR10X Data Logger

CS616 Reflectometer CS12 I/O 9-pin 25 to 9 pin cable RS232 cable

PT100/3 (1/3 DIN PRT Probe)

Analog inputs CG3 pyrgeometer

Barometric pressure (Druck PRT410F)

CM3 pyranometer

Windsonic 2D Gill Anemometer

MP101A-T7-WAW

FIGURE 13 - The communication setup diagram for remote communication with the overall scheme of the weather station data flux.

Validation of data – comparison test and results As in case of the AWS with direct communication, Comparison of Tair validation of data could be done by comparing the station’s 40 data with that from the reference station in the airport. 35 Figure 14 presents the fluctuations of air temperature

C) 30

o EMY

measurements for our remote AWS (UNIV) and the (

air 25 UNIV EMY’s station in Agrinio airport during 72 hours (from T th th 00.00 at the 6 of September 2006 to 24.00 at the 8 of 20

September 2006). There is also a strong agreement between 15 these values (coefficient correlation λ=0.999013). A slight 020406080 differentiation (higher values of UNIV’ station) is due to Hour the heat island effect. As mentioned in the case of the AWS with direct com- FIGURE 14 - Temporal variations of the measured values of air temperature for a 72-hours period, from the 6th of September 2006 to munication, the accuracy and validity of the measurements th at the remote AWS could have been done additionally by the 8 of September 2006 for our AWS (UNIV) in remote communication and the Greek Meteorological Agency’s station (EMY) in Agrinio. field checks (with a simple mercury thermometer for the temperature sensor checking and with the Kestrel portable anemometer for wind speed and direction sensor). For ba- AWS remote capabilities and enhancement rometric pressure sensor and sunshine duration meter, the As a modern and up-to date version of the station, its comparison with the airport’s measurements gives a strong operation can be monitored via a webpage which may dis- validation to the measurements of the AWS and field checks play the status of the AWS network in real-time using suit- are unnecessary. able software. This reduces manual labour and at the same

time enhances data quality. A filter can be installed as a Further work involves the improvement of the station’s quality assurance, cutting erroneous data and alerting main- capabilities, the addition of extra instruments such as a net tenance staff to action via automatic email. The advantage radiation detector and more soil thermometers. While the of this automatic alerting feature is that it enables early de- station is currently connected to the Internet, an extensive tection and fault diagnosis, enhancing data availability [38]. network performance is a further requirement, including services of voice/data information through communication This AWS can be enhanced with network cameras, visi- lines. This procedure is currently on, including a local wire- ble and infrared in order to provide real-time weather pho- less net with cameras and relevant internet facilities. tographs to the University website via broadband network or GPRS [38,40]. They could assist forecasters in monitoring more closely changes in weather conditions as well as the development of strong convective weather [38]. More- ACKNOWLEDGEMENTS over, this could assist in solving problems on disagreements between human and automated observations i.e. when there Mr. Bagiorgas gratefully acknowledges the Greek State is a big difficulty in determine the rainfall. The desired Scholarships Foundation for the attainment of educational –1 0.05 mm h sensitivity, chosen on a recent recommenda- leave and financial support, grant number: 1534/2004. tion for detection of precipitation, was almost impossible to determine from any rain gauge data [24,25]. So, network cameras, turned at the sky, could help, for instance, in slight drizzle, which could never be detected. REFERENCES

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[15] Miyazaki, S., Yasumari, T. and Adyasuren, T. (1999) Abrupt [29] Bagiorgas, H.S., Assimakopoulos, M.N., Theoharopoulos, D., seasonal changes of surface climate observed in Northern Matthopoulos, D. and Mihalakakou, G.K. (2007) Electricity Mongolia by an automatic weather station. J Meteorol Soc generation using wind energy conversion systems in the area of JPN 77(2), 583-593. Western Greece. Energ Convers Manage 48, 1640-1655.

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Received: October 11, 2006 Revised: December 27, 2006; February 07, 2007 Accepted: April 10, 2007

CORRESPONDING AUTHOR

Haralambos S. Bagiorgas University of Ioannina Department of Environmental and Natural Resources Management 2 G. Sepheri Str. 30100 Agrinio GREECE

Phone: +302641074111 Fax: +302641074102 E-mail: [email protected]

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