Mõõtemääramatuse hindamine Eesti massi riigietaloni laboratooriumis

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Riigi mõõteinfrastruktuuri tase ja sujuv toimimine on riigi konkurentsivõime, teaduslik-tehnoloogilise suutlikkuse ja elukeskkonna turvalisuse väga oluline element. Alates 2001.a on Eestis Metroloogia keskasutuses Metrosert sisse seatud massi, pikkuse, temperatuuri ja elektriliste suuruste riigietalonid rahvusvahelisel sekundaartasemel. Reeglina kehastab mõõteetalon riigi tipptaset vastavas teaduslik-tehnilises valdkonnas, kuid selle võimalusi saab täielikult ära kasutada vaid siis, kui on kindlustatud etaloni ja nende abil osutatud mõõtetenuste mõõtemääramatuse usaldusväärne hindamine ja rahvusvaheline ekvivalentsus. Etalonide tase ja rahvusvaheline ekvivalentsus ilmneb rahvusvahelise koostöös, eelkõige hea kooskõla kaudu võrdlusmõõtmistel, kusjuures võtmeks tulemuste kooskõla hindamisel on mõõtemäätamatus. Eesti massi riigietaloni laboratoorium realiseerib ja esitab massiskaala piirkonnas 1 mg kuni 50 kg, on võimeline kalibreerima rahvusvahelise klassifikatsiooni järgi kõige täpsemate OIML E1 klassi vihtide massi ja leppelist massi. Võimalik on määrata vihtide magnetiliste omaduste vastavust täpsusklassi nõuetele ja piirkonnas 1 g kuni 2 kg kalibreerida vihtide tihedust. Laboratooriumi käsutuses on kolm automaatset massikomparaatorit, rohkem kui sada vihti ja mitmeid abimõõtevahendeid. Laboratoorium asub konditsioneeritud filtreeritud õhuga mõõteruumis, milles kontrollitakse õhu temperatuuri ja suhtelist niiskust. Mõõtmised põhinevad neljale kogu mõõtepiirkonna ulatuses hoolikalt kontrollitud mõõtemudelile. Mõõtemääramatuse hindamist hõlbustab kõigile olulistele mõõtevahenditele viieteist aasta jooksul kogunenud ulatuslik kalibreerimisajalugu. Lisaks on läbi viidud mitu spetsiaalset uurimust, mis lubavad hinnata mõõtemääramatust paremini kui rutiintöös saadavad üsna napid andmed. Mõõtemääramatuse hindamise aluseks massi riigietaloni laboratooriumis on rahvusvaheline juhend GUM. Üldiselt vastavad selle alusel saadud määramatuse hinnangud enamiku rakenduste nõuetele, kuid praktikas esineb olukordi, mille korral GUM ei anna optimaalset lahendust. Üheks keerulisemaks küsimuseks on mõõteseeria keskmise alusel määratud mõõtetulemuse määramatuse hindamine, kui seeria tulemused omavahel korreleeruvad. Teiseks mitte vähem keeruliseks probleemiks komparaatori tulemuste hindamisel on süstemaatiliste efektide kindlakstegemine ja elimineerimine või siis vähemalt nende panuse arvessevõtmine mõõtemääramatuses. Mõlemad probleemid võivad tähelepanuta jätmisel viia mõõtemääramatuse ekslikule hindamisele. Antud uurimistöös väljatöötatud meetodid võimaldavad mõlemat ohtu vähendada ja neid saab rakendada ka teistes mõõtevaldkondades. Massi riigietaloni laboratooriumi mõõtetulemuste ja määramatuse hinnangute usaldusväärsust kinnitab hea kooskõla, mida on näidatud arvukatel rahvusvahelistel võrdlustel.A high-level well-working national measurement infrastructure is essential for competitiveness of country, for the advancement of science and technology, and for quality of life. Since 2001 in Estonia at the Central Office of Metrology, Metrosert, the national standards for mass, length, temperature and electric quantities are established at the internationally secondary level. National measurement standard usually represents the top level competence of the country in respective scientific-technical field. However, in order to use its capabilities effectively confidence in the measurement uncertainty and international equivalence of offered services is needed. Technical level and international equivalence of the standard are validated by international experts on the basis of inter-comparisons and peer evaluations, whereby measurement uncertainty is a key element for meaningful determination of the degree of equivalence between the standards and measurement results. Estonian standard laboratory for mass (NSLM) is realizing and representing the mass scale from l mg to 50 kg, being able to calibrate the mass and conventional mass value of the weights with the highest OIML E1 accuracy class. NSLM can test the conformity of magnetic properties of the weights to the requirements of the respective accuracy class. NSLM can calibrate the density of the weights in the range from 1 g to 2 kg. Mass laboratory is equipped with three automatic mass comparators, with more than 100 weights, and with many auxiliary instruments; laboratory is accommodated in air-conditioned measurement rooms with temperature and humidity control, and with filtered air. At the NSLM preferably four measurement models are used; these models are carefully validated for the whole relevant measurement range. For evaluation of the uncertainty in measurement for major part of instruments extensive calibration histories are available. Additionally, some special studies are conducted, in order to get better data base for uncertainty estimation as provided by routine measurements. Uncertainty of the weights representing the mass scale at the NSLM is estimated following the GUM standard procedures. In general, uncertainty evaluated according to GUM performs satisfactorily for majority of applications. Nevertheless, there are some situations in practice allowing improvement if sufficient measurement information is available. Not easy to handle is the effect of nonzero serial correlation. Another similarly complicated problem is revealing possible systematic effects in comparator readings in order to eliminate them or at least to take them into account in measurement result and uncertainty estimate. If not treated the uncertainty may be substantially underestimated. Methods proposed in this study will at least partly solve both problems and reduce risk of underestimation, and they are applicable in many other measurement fields. The agreement between the inter-comparison results presented by the NSLM and comparison reference values demonstrated to date shows that measurement methods, calibration procedures and respective uncertainty estimates developed and tested at the NSLM can reliably be applied in practice

A Review of Protocols for Fiducial Reference Measurements of Water-Leaving Radiance for Validation of Satellite Remote-Sensing Data over Water

This paper reviews the state of the art of protocols for measurement of water-leaving radiance in the context of fiducial reference measurements (FRM) of water reflectance for satellite validation. Measurement of water reflectance requires the measurement of water-leaving radiance and downwelling irradiance just above water. For the former there are four generic families of method, based on: (1) underwater radiometry at fixed depths; or (2) underwater radiometry with vertical profiling; or (3) above-water radiometry with skyglint correction; or (4) on-water radiometry with skylight blocked. Each method is described generically in the FRM context with reference to the measurement equation, documented implementations and the intra-method diversity of deployment platform and practice. Ideal measurement conditions are stated, practical recommendations are provided on best practice and guidelines for estimating the measurement uncertainty are provided for each protocol-related component of the measurement uncertainty budget. The state of the art for measurement of water-leaving radiance is summarized, future perspectives are outlined, and the question of which method is best adapted to various circumstances (water type, wavelength) is discussed. This review is based on practice and papers of the aquatic optics community for the validation of water reflectance estimated from satellite data but can be relevant also for other applications such as the development or validation of algorithms for remote-sensing estimation of water constituents including chlorophyll a concentration, inherent optical properties and related products

A review of protocols for fiducial reference measurements of water-leaving radiance for validation of satellite remote-sensing data over water

© 2019 by the authors. This paper reviews the state of the art of protocols for measurement of water-leaving radiance in the context of fiducial reference measurements (FRM) of water reflectance for satellite validation. Measurement of water reflectance requires the measurement of water-leaving radiance and downwelling irradiance just above water. For the former there are four generic families of method, based on: (1) underwater radiometry at fixed depths; or (2) underwater radiometry with vertical profiling; or (3) above-water radiometry with skyglint correction; or (4) on-water radiometry with skylight blocked. Each method is described generically in the FRM context with reference to the measurement equation, documented implementations and the intra-method diversity of deployment platform and practice. Ideal measurement conditions are stated, practical recommendations are provided on best practice and guidelines for estimating the measurement uncertainty are provided for each protocol-related component of the measurement uncertainty budget. The state of the art for measurement of water-leaving radiance is summarized, future perspectives are outlined, and the question of which method is best adapted to various circumstances (water type, wavelength) is discussed. This review is based on practice and papers of the aquatic optics community for the validation of water reflectance estimated from satellite data but can be relevant also for other applications such as the development or validation of algorithms for remote-sensing estimation of water constituents including chlorophyll a concentration, inherent optical properties and related products

A review of protocols for Fiducial Reference Measurements of downwelling irradiance for the validation of satellite remote sensing data over water

This paper reviews the state of the art of protocols for the measurement of downwelling irradiance in the context of Fiducial Reference Measurements (FRM) of water reflectance for satellite validation. The measurement of water reflectance requires the measurement of water-leaving radiance and downwelling irradiance just above water. For the latter, there are four generic families of method, using: (1) an above-water upward-pointing irradiance sensor; (2) an above-water downward-pointing radiance sensor and a reflective plaque; (3) a Sun-pointing radiance sensor (sunphotometer); or (4) an underwater upward-pointing irradiance sensor deployed at different depths. Each method-except for the fourth, which is considered obsolete for the measurement of above-water downwelling irradiance-is described generically in the FRM context with reference to the measurement equation, documented implementations, and the intra-method diversity of deployment platform and practice. Ideal measurement conditions are stated, practical recommendations are provided on best practice, and guidelines for estimating the measurement uncertainty are provided for each protocol-related component of the measurement uncertainty budget. The state of the art for the measurement of downwelling irradiance is summarized, future perspectives are outlined, and key debates such as the use of reflectance plaques with calibrated or uncalibrated radiometers are presented. This review is based on the practice and studies of the aquatic optics community and the validation of water reflectance, but is also relevant to land radiation monitoring and the validation of satellite-derived land surface reflectance