radiosounding system allows to measure the profile of some meteorological quantities (temperature, humidity, pressure) from the ground up to a certain altitude. Such systems are continuously used by meteorological services in order to perform periodical measurements during the day, at 

pre-determined times. The evolution of instrumentation technology leads to a fast obsolescence of equipment

through time, so that, inevitably, new instrumentation replaces the old one. The new VAISALA Radiosound RS92 has been recently introduced to substitute previous model RS90. The RS90 is currently used by many national and international institutes, including the Italian Air Force Meteorological Service (Servizio Meteorologico dell’Aeronautica Militare). In order to assess the way in which the substitution of RS90s with the new RS92s would affect measures performed by the altitude observation network with regard also to the historical series, several comparative measurements have been conducted by the “Reparto Sperimentazioni di Meteorologia Aeronautica” at Vigna di Valle (Rome). During this testing series,

Company VAISALA has given a remarkable level of cooperation by a continuous presence of technicians. The entire test has been performed according to WMO (World Meteorological Organization) protocols

Casu, G.

Foti, F.

Malaspina, F.

Vuerich, E.

English

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2005-10016-6IL NUOVO CIMENTO Vol. 27 C, N. 5 Settembre-Ottobre 2004Radiosounding: Possible change in aerological data due toinstrument changeF. Malaspina(∗), F. Foti, E. Vuerich and G. CasuAeronautica Militare, Reparto Sperimentazioni di Meteorologia AeronauticaVia braccianese Km18, 00062 Bracciano (Rome), Italy(ricevuto il 20 Gennaio 2005)Summary. — A radiosounding system allows to measure the profile of some me-teorological quantities (temperature, humidity, pressure) from the ground up to acertain altitude. Such systems are continuously used by meteorological services inorder to perform periodical measurements during the day, at pre-determined times.The evolution of instrumentation technology leads to a fast obsolescence of equip-ment through time, so that, inevitably, new instrumentation replaces the old one.The new VAISALA Radiosound RS92 has been recently introduced to substituteprevious model RS90. The RS90 is currently used by many national and inter-national institutes, including the Italian Air Force Meteorological Service (ServizioMeteorologico dell’Aeronautica Militare). In order to assess the way in which thesubstitution of RS90s with the new RS92s would affect measures performed by thealtitude observation network with regard also to the historical series, several com-parative measurements have been conducted by the “Reparto Sperimentazioni diMeteorologia Aeronautica” at Vigna di Valle (Rome). During this testing series,Company VAISALA has given a remarkable level of cooperation by a continuouspresence of technicians. The entire test has been performed according to WMO(World Meteorological Organization) protocols.PACS 93.85.+q – Instrumentation and techniques for geophysical research.PACS 92.60.Ry – Climatology.PACS 92.70.Cp – Atmosphere.1. – IntroductionRadiosondes have for several dacades been the primary means of obtaining atmo-spheric vertical profile data from the surface to the lower stratosphere. They are rou-tinely used as input to the operational meteorological analyses that are used in numericalweather prediction and meteorological diagnostics. The network of stations RBSNs (Re-gional Basic Synoptic Networks stations), which provide the service for the meteorological(∗) E-mail: f.malaspina@katamail.comc© Societa` Italiana di Fisica 503504 F. MALASPINA, F. FOTI, E. VUERICH and G. CASUFig. 1. – Availability of temp reports from RBSNs during the monitoring period October 1st to15th, 2002 (the percentage of received reports is based on Part A of message Temp for 0000 and12 UTC) [2].Fig. 2. – Map of temp reports from GUAN. Availability of temp reports from GUAN is contin-uously monitored by ECMWF http://www.ecmwf.int.RADIOSOUNDING: POSSIBLE CHANGE IN AEROLOGICAL DATA ETC. 505Fig. 3. – Map of only Air Force Italian radiosounding stations.model initialization, is described in fig. 1. Such a system is used for real-time local atmo-spheric monitoring, performed by tracing thermodynamic diagrams, too. The instrumentpackages carried aloft by ballons are generally equipped with temperature, humidity andpressure sensors, whose measurements are radio-trasmitted to a ground receiving station.Wind data are also obtained by tracking the position of the instruments during ascent.An excellent overview of radiosonde instruments, including discussion of measurementerror characteristics, is provided by the World Meteorological Organization [1].Radiosonde observations have recently been used to assess trends of atmosphericconditions above surface, even though they were not designed for this purpose. Thestatistical analysis of long historical radiosounding series can be applied to the investiga-tion of climatological changes through time (see fig. 2). To recognize the limits of suchstatistical analyses it is necessary to know, along with the numerical values stored in thedatabases, the features of the measurement instruments by which the data acquisitionhas been performed.A sub-set of the network is used with the additional purpose of analyzing the changein temperature on a global level, by studying the historical temperature-profile series, sothat the analysis is not limited to the mere data coming from surface stations.As far as Italy is concerned, the Servizio Meteorologico dell’Aeronautica Militareoperates a network of 6 stations from which 4 launches are performed, once every 6hours. Among these stations, one is also included in the GUAN network (GCOS Upper-Air Network, GCOS is Global Climate Observing System) and, furthermore, the Vigna diValle station (which does not belong to the group) can be added in case of experimentalor operational needs (see fig. 3).506 F. MALASPINA, F. FOTI, E. VUERICH and G. CASUFig. 4. – Aerial picture of ReSMA. The Experimental Site includes six equipped areas underboth automatic and manual control everyday.2. – Purpose and site of testingThere have been many and widespread changes of radiosonde sensor durino the historyof the global radiosonde network. The instrumentation used by the Servizio Meteoro-logico in performing radiosounding has been produced by VAISALA. This company hasrecently ceased the production of radiosound RS90 (present on market since 1997), withthe new RS92. The difference between the two types is mostly related to the transmissionsystem, which was analog on the RS90 and is now digital on the RS92. Even thoughthe sensors stay the same on both models, there are some changes in the calibration-at-launch system and in the humidity measurement system. With regard to the latter, thereare now two separate sensors; in order to prevent freezing during ascent, in this phasethe sensors are used alternatively: one performs measures, while the other is heated todefrost. Instrument details and specifications are presented in [3].In order to assess differences in temperature, humidity and pressure measures whichresult from the described modifications, testing has been conducted with the sole pur-pose of comparing the two devices and provide the prospective user with a reference fortrend analysis. The goal was to determine whether systemic errors could be found inthe modified system; therefore, no attention was given to the correspondence betweenmeasures performed by each sound and the real data.The performed test was an evaluation of the measure reproducibility according to theISO and WMO standards.The location for the test was the “Reparto Sperimentazioni di Meteorologia Aero-nautica”, Servizio Meteorologico dell’Aeronautica Militare, a historical site for Italianmeteorology, inaugurated in 1907 (see fig. 4).3. – Materials and methodsIn agreement with VAISALA and in accord to the WMO intercalibration instruc-tions [4], two receivers have been provided at the site. The receivers had similar features.An experimental protocol was developed, discussed and agreed upon. The complianceof testing operations with such protocol was ensured by the continuous presence of bothItalian Air Force and VAISALA technicians.The launches were scheduled as shown in table I.Testing was not conducted by grouping several launches per day, as it would beRADIOSOUNDING: POSSIBLE CHANGE IN AEROLOGICAL DATA ETC. 507Table I.Launch time 13.00 (Local time) 18.00 (local time)Friday 7th RS92-SGP and RS90-AG-CEMon 10th RS92-SGP and RS90-AG-CETue 11th RS92-SGP and RS90-AG-CEWed 12th RS92-SGP and RS90-AG-CEFri 14th RS92-SGP and RS90-AG-CEMon 17th RS92-SGP and RS90-AG-CEWed 19th RS92-SGP and RS90-AG-CE RS92-SGP and RS90-AG-CEThu 20th RS92-SGP and RS90-AG-CEdesirable from an economic point of view; rather, several days were chosen so that alllaunches could be made at corresponding times. This allowed to compare the soundsperformance in different weather but under similar solar radiation conditions.Each launch was done with both sounds suspended under the same balloon, at a fixeddistance between one another (see fig. 5). Data were sampled once every 2 seconds as innormal operation.Significant figures used in describing results as well as in error calculation are consis-tent with measure precision not according to resolution, which is display-device depen-dent, but according to sensor errors [1]; some specifications related to temperature aregiven in table II.A similar management was done for the other quantity.Fig. 5. – Scheme of the experimental facility.508 F. MALASPINA, F. FOTI, E. VUERICH and G. CASUTable II. – Meteorological sensors.Temperature Vaisala F-THERMOCAPcapacitive wireMeasurement range +60 ◦C to −90 ◦CResponse time (63.2%, 6 m/s flow)1000 hPa < 0.4 s100 hPa < 1 s10 hPa < 2.5 sResolution 0.1 ◦CAccuracyTotal uncertainty in sounding (*) 0.5 ◦CRepeatability in calibration (**) 0.15 ◦CReproducibility in sounding (***)1080–100 hPa 0.2 ◦C100–20 hPa 0.3 ◦C20–3 hPa 0.5 ◦C(∗) 2-sigma (k = 2) confidence level (95.5%). Cumulative uncertainty including:– Repeatability.– Long-term stability.– Effects due to measuring conditions.– Dynamic effect (such as response time).– Effects due to measurement electronics.(∗∗) Standard deviation of differences between two successive repeated calibrations, k = 2 confidencelevel.(∗∗∗) Standard deviation of differences, in twin sounding.4. – Results and discussionData was analyzed using the new RSK32 software which is the official WMO com-parison software. During the analysis, according to what was done in similar WMOactivities, data has been broken down by 1000 m layers and each layer has been analyzedas a group of independent measures, under the hypothesis that within each one of themvariations of sensor performance were negligible.Performance variations become sensible, and no longer negligible, when comparingdifferent layers. The new transmission system gives a remarkable improvement in thequantity of sampled and received data. Average received information levels from thesondes are shown in table III.Both the radiosondes started to measure from a specific demarcation value of pressureand the timing error resulted to be negligible. Data quantity when both measures arepresent, see fig. 6, and comparable indicate a more-than-sufficient amount of cases.Table III. – PTU data availability.Pressure Temperature HumidityRS92-SGP 98.6% 97.5% 99.3%RS90-AG-CE 86.7% 92% 92.6%RADIOSOUNDING: POSSIBLE CHANGE IN AEROLOGICAL DATA ETC. 509Fig. 6. – Data availability by “layer”, pressure and temperature’s line are overlap.Fig. 7. – Humidity, average direct differences calculated with RS92-SGP as a reference. Also“standard deviation” line is presented.510 F. MALASPINA, F. FOTI, E. VUERICH and G. CASUTable IV. – PTU average direct differences calculated with RS92-SGP as reference and standarddeviation.Height Diff. Temp. St.m Temp. Diff. Hum. St.d. Hum. Diff.Press. St.d. Press.(m) (◦C) (◦C) (%) (%) (hPa) (hPa)500 −0.4 0.4 −1 2 −0.2 0.71500 −0.4 0.4 −1 3 −0.1 0.82500 −0.3 0.4 0 4 0.0 0.73500 −0.3 0.4 0 3 0.0 0.74500 −0.3 0.3 0 2 0.0 0.65500 −0.1 0.4 0 3 0.0 0.56500 −0.2 0.3 −2 5 0.0 0.57500 −0.2 0.3 −1 4 0.0 0.58500 −0.2 0.2 −1 3 0.1 0.59500 −0.2 0.2 0 4 0.1 0.410500 −0.2 0.2 0 3 0.0 0.411500 −0.2 0.2 0 3 0.0 0.312500 −0.2 0.2 0 4 0.0 0.213500 −0.2 0.2 2 2 0.0 0.214500 −0.2 0.2 2 1 0.0 0.215500 −0.2 0.2 2 2 0.0 0.216500 −0.3 0.4 2 1 0.0 0.217500 −0.3 0.3 2 1 0.0 0.218500 −0.2 0.4 2 1 0.0 0.219500 −0.3 0.3 2 1 0.0 0.120500 −0.3 0.4 2 1 0.0 0.221500 −0.2 0.4 1 1 0.0 0.222500 −0.2 0.3 1 1 0.0 0.123500 −0.1 0.4 1 1 0.0 0.224500 −0.3 0.6 1 1 0.0 0.225500 −0.2 0.4 1 1 0.0 0.226500 −0.1 0.4 1 1 0.0 0.227500 −0.1 0.5 2 1 0.0 0.228500 0.0 0.4 2 1 −0.1 0.229500 0.0 0.4 1 1 −0.1 0.230500 −0.3 0.4 1 3 −0.1 0.231500 −0.1 0.7 1 3 −0.1 0.232500 0.0 0.5 1 2 −0.1 0.233500 −0.2 0.6 0 3 −0.1 0.2average −0.2 0.4 1 2 0.0 0.3Averageuntil 10500 −0.3 0.3 0 3 0.0 0.6In each layer, any value given by the difference of the measurements by the two devicesis a result of an experiment, i.e. a random variable. The sampling space is continuous,the number of tests is high; we make the reasonable hypothesis that the random errordepends on many independent factors, all of them having the same order and each oneof them producing a very small error, of any sign. Then only under these conditions,according to the central limit theorem, the error distribution function is coincident withGauss’ [5].RADIOSOUNDING: POSSIBLE CHANGE IN AEROLOGICAL DATA ETC. 511Fig. 8. – Pressure, average direct differences calculated with RS92-SGP as a reference. Also“standard deviation” line is presented.We expect a Gaussian distribution of the average of PTU (Pressure, Temperature andhUmidity) variable differences; particularly, we expect a Gaussian distribution aroundzero and random errors. Indeed, such a situation would ensure the continuity of thehistorical series.The provided data are presented in figs. 7, 8, 9 and table IV by showing the averagedifference and the standard deviation. It should be remembered that up to 10 km we arestill in the troposphere, i.e. the region which is involved in meteorological phenomena.By analyzing temperature, it can be noted that, in addition to the random error,there is a not-null difference. In all layers there is a systemic error which causes theRS92 to indicate higher temperature values than the RS90.The difference average as calculated in different layers results to be between 0.0 ◦Cand 0.4 ◦C, showing higher values in the troposphere. The sigma assessment, i.e. theassessment of temperature measurement “reproducibility” varies between 0.2 ◦C and0.7 ◦C.The described systemic error is not detected in humidity and temperature measures.The reported data have been analyzed and discussed with VAISALA which, in itsreport about the testing, stated that the detected systemic error in temperature measure“is a well-known phenomenon in RS90 (Luers article) and corrected in RS92”. Accordingto such a statement, it would result that RS92 provides an improved measurement. Sinceno certified baroclimatic chamber was available, this circumstance could not be verified.512 F. MALASPINA, F. FOTI, E. VUERICH and G. CASUFig. 9. – Temperature, average direct differences calculated with RS92-SGP as a reference. Also“standard deviation” line is presented.5. – Conclusions and remarksThe described test has demonstrated the excellent performance of instruments andconfirmed the improvements of the new radiosonde.The impact of the future instrumentation change from RS90 to RS92, considering themeasurement accuracy required by current working standards will be negligible wheneveratmospheric sounding is used for local monitoring or for model initial analysis. In theclimatological field, however, since the statistical analysis is performed taking into ac-count tenth or even hundreth Celsius degrees precisions (for example Hurrel et al. foundthat global trends for 1979-1998 were (0.04 ± 0.07) ◦C/decade for radiosondes [7]), con-sequences could be relevant should the presented results be confirmed and not properlytaken into account during the analysis. In fact, as the new equipment will replace the oldone, a gradual and progressive atmospheric heating indication will result from records.For climatological studies which are supposed to properly take into account, beyondmathematics, physics as well, it is necessary to store not only meteorological data, butalso meta-data about the detection systems features. Such features, along with properoperation of measurement equipment, should be under control of specific “quality man-agement systems”.∗ ∗ ∗We acknowledge the cooperation in welcoming and supporting our experimentationshown by “Ufficio Generale per la Meteorologia”, company VAISALA and EUROELET-TRONICA Icas. The radiosonde comparison software was originally written by MrSergei.RADIOSOUNDING: POSSIBLE CHANGE IN AEROLOGICAL DATA ETC. 513REFERENCES[1] World Meteorological Organization – Guide n.8 to Meteorological Instrument and Methodsof observation, 1996.[2] World Meteorological Organization – 40 Years of World Weather Watch 1963-2003,www.wmo.int.[3] http://www.vaisala.com.[4] World Meteorological Organization, Executive Summary of the WMO. Intercomparison ofGPS Radiosondes, Alcantara, Brazil 20 May-10 June 2001.[5] Ro B.P., Probability and Statistics in Experimental Physics (Springer Verlag) 1992.[6] Executive summary of RS92-SGP and RS90-AG-CE comparative Experiment – Italy 2003– Report Vaisala 11-02.2004.[7] National Research Council, Reconciling observations of global temperature change (2000).

Radiosounding: Possible change in aerological data due to

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Radiosounding: Possible change in aerological data due to instrument change

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