A n up-to-date hydrome-teorological observationnetwork is expected to

produce real-time measurementdata that is more accurate anddense both geographically and inrelation to time than ever before.It is also expected to include newmeasurement parameters.

The capacity requirementsfor observation networks growwith the number of applications.The significance of traditionalhydrology applications, such asflood forecasting, water level reg-ulation and irrigation control,increase continuously. At thesame time, new fields of applica-tion come into being, particular-ly in relation to water quality,the effects of climate change,and the maintenance of waterand sewage systems. Fortunatelythe simultaneous advancementsin data processing capacity facil-itate the handling of increasingquantities of data as well asquick response times for manyapplications, for example real-time flood forecasts.

Although the rapid develop-ment of remote sensing systems– such as weather radars andsatellite measurement – partlycaters for these requirements, in-situ measurement will continueto form the basis of hydrologicaland meteorological measure-ments in the future. The chal-lenge is to implement increas-ingly dense and geographicallydecentralized observation net-works with reasonable initial in-vestment, maintenance and data

14 167/2005

Samuli RäisänenProduct Development Manager

Heikki TurtiainenSenior ScientistVaisalaHelsinki, Finland

Vaisala Solutions for Telemetry andModern telemetry and measurement system automation help to gather morecomprehensive data on our water systems. The improved performance ofmeasurement equipment, reduced power usage and unit price, together with newwireless communications systems, enable dense observation networks. The real-time utilization of data is possible thanks to the Internet. The biggest challengesfacing the observation networks are maintenance and sensor calibration.

processing costs. The solutionlies in measurement automationand telemetry.

Measurement automationMeasurement automation is aby-product of technological ad-vancement. The main drivingforce is cost minimization, ashuman observation becomes in-creasingly costly with dense net-works and shorter sampling in-tervals. The evolution of elec-tronics, telecommunicationsand sensor technology enablehuman observers to be replacedby automated telemetric equip-ment in almost all hydrometeo-rological applications.

When observation stationsare located in remote and deso-late regions, automation is facedwith power supply and equip-ment maintenance challenges.

With the development of elec-tronics, the power consumptionof measurement equipment hasgone down. This has enabled theuse of reasonably priced solarcell & battery combinations as apower source.

The maintenance costs ofobservation stations havebeen considerably reduced bytelecommunications networks inremote maintenance, configura-tion, diagnostics and softwareupdates. The person responsiblefor the maintenance of the ob-servation network is now able torun all these operations from hisor her PC, without having toleave the office. However, thesensors continue to require regu-lar on-the-spot calibration andmaintenance. Maintenance costswill present the biggest challengefor the expansion and thicken-ing of observation networks in

the near future. Equipmentmanufacturers will thereforecontinue to address the chal-lenge of developing sensors thatrequire less and less mainte-nance.

Telemetry – remote access to mea-surement dataThe complete automation of ob-servation networks also requiresthe automatic transfer of mea-surement data to the user. Thereare a number of methods forthis, either via radio waves, te-lephony or information net-works. In a typical hydrometeo-rological application, data istransferred at regular intervals,the quantity of data is reason-ably small, and mostly, to ensurereliability, more than one datatransfer method is supported.

The most reliable way to

transfer measurement data con-tinues to be either the traditionalmodem via fixed telephone lineor, increasingly, information net-works – typically implementedwith local area network (LAN)architecture. One benefit of thelatter is the easy connectivity ofthe observation station to the In-ternet or the organization's In-tranet. If the measurement in-strument or observation stationis equipped with a serial inter-face port (RS232/485), the Eth-ernet connection can be imple-mented easily with a so-calleddevice server, or COM server.

SMS messaging is the bestmethod when it is necessary toget the data direct to the user,typically to a mobile device. It ismost advantageous in conjunc-tion with applications sendingalarm signals. SMS messaging al-so enables inquiries for measure-ment data to be sent as the needoccurs: e.g. for road weatheralong a route.

When measurement data isbeing collected at regular inter-vals or when there is a lot of it, itis more economical to use aGSM or GPRS modem. A GSMdata call is charged as a normalcall – according to the connec-tion time – whereas a GPRS con-nection is open all the time andcharges are based on the amountof data transferred. In hydrome-teorological applications, theamount of data is typicallysmall, which makes the use ofGPRS modems economical.

When it comes to reliability,the wireless network is reason-ably stable. However, servicebreaks due to overloading arepossible, so it should not be usedas the only data transfer methodfor telemetry that requires ex-treme reliability or speed.

A radiomodem using VHFor UHF frequencies is a tradi-tional data transfer method

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Automation in Environmental Monitoring

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Vaisala MetMan™ Network Software forhydrometeorological data includes all the requiredsoftware and databases (MS Access or Oracle) forthe maintenance of observation networks andstation configuration.

which is still in use, particularlywhere no reliable mobile net-work is available. Typically ra-diomodems are used as nodalpoints between the measurementinstrument and the closest fixedtelephone or GSM network. Theadvantage of radiotelemetry isthat, after the equipment invest-ment, it is nearly free for the user.

The use of radiomodem, likeany other radio transmitter, nor-mally requires a license from theauthorities. However, low powertransmitters operating on so-called license free frequenciesare exempt from the license pro-cedures. These radiomodemsreach at best a few kilometers’operating range.

Communications satellitesenable wireless data transfer from

almost anywhere on Earth, in-cluding the seas. Satellite systemsare divided into LEO (Low EarthOrbit), which consist of satellitescirculating a low orbit and GEO(Geostationary Earth Orbit),which orbit the Earth on the so-called geostationary path at theequator - looking stationary whenobserved from the Earth. LEOsystems offering a global commer-cial service include ORBCOMM,consisting of 30 satellites. Anotheris Iridium. A corresponding globalGEO system is Inmarsat. Hydro-logical and meteorological mea-surements in the U.S. are mostlyenabled by data transfer providedby the geostationary GOESweather satellite, as its use is free tomany public organizations.

The selection of a suitable

telemetry method is influencedby the geographic location of theobservation station, transmissiondistance, amount of data trans-ferred and sample intervals, reli-ability and response time re-quirements, and by the transmis-sion methods available at the lo-cation. Since there is no one-size-fits-all solution, it is possible touse several alternative telemetricmethods at modern hydromete-orological stations.

A significant part of the ope-rations of observation networksis data quality control, the man-ner of expressing and controllingdata as well as network mainte-nance, configuration and up-dates. These require network anddata management software, suchas the Vaisala MetMan™ Net-work Software.

Future outlookThe unit prices of intelligentwireless measurement equip-ment will continue to drop whiletheir performance grows andpower consumption decreases. Alow unit price enables redundantmeasurement. Thanks to lowpower consumption, the equip-ment will run on the same bat-tery or (in the future) fuel cell forseveral years. Together, these de-velopments enable the lengthen-ing of service intervals and thusthe considerable reduction ofmaintenance cost per station.

Wireless data transmissionenabled by cellular networks iscurrently in a strong develop-ment phase. As the traditionalmobile market becomes saturat-ed, telecommunications busi-nesses seek new markets withinso-called machine-to-machine orM2M communications. The de-velopment of M2M technolo-gies simplifies data transmissionsolutions and reduces costs bothfor equipment and data transfer– though only in geographic are-as with wireless infrastructure.

Due to the trends men-tioned, increasingly dense andcomprehensive observation net-works will become technicallyand economically feasible in

densely populated areas. Howev-er, sparsely populated areas likeSiberia or African rainforests willcontinue to depend on satelliteconnections and thus limiteddata transfer capacity.

The advancement of tech-nology in both telecommunica-tions (more bandwidth) and pro-cessing power (more intelligentsensors) seems to offer two alter-native ways forward for observa-tion stations. The first is a moreconventional solution: data col-lection is performed by a centralunit, which processes and com-presses the measurement databefore passing it on. This solu-tion remains the most suitablefor those locations where datatransfer is costly or data transfercapacity is limited. In locationswhere the capacity of communi-cations networks is good, anoth-er option is more probable: themeasurement and processing ofdata will be distributed to intelli-gent sensors. The sensors will bedirectly connected to a telemet-ric unit, rendering a separatecentral unit unnecessary.

Connecting observation net-works to the Internet is a cleartrend. The observed data will beavailable wherever and to all rele-vant people in nearly real-time.Communications networks alsoenable the combining of datafrom different sources. The reli-ability and coverage of environ-mental measurement data will sig-nificantly improve when integrat-ed observation systems are intro-duced. They will simultaneouslybenefit from all in-situ, radar andsatellite measurement data. ●

16 167/2005

Summary

A dvanced telemetry en-ables the development

of comprehensive real-timeobservation networks. In thefuture, our water systems willbe observed with integratedsystems that benefit from theInternet. ●

The VaisalaHydroMet™AutomaticWeather StationMAWS301 is especiallybuilt for locations thatare not served bycommercial power orcommunicationsnetworks. It provides acontinuous stream ofhigh-quality data over agreat range ofmeteorological andhydrological parameters,such as wind velocityand direction, airpressure, temperature,relative humidity andprecipitation.