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Author:Alanen, Juuso
Title:Spektrisen irradianssin mittausten virhelähteitä
Error sources in spectral irradiance measurements
Publication type:Master's thesis
Publication year:2010
Pages:33      Language:   fin
Department/School:Elektroniikan, tietoliikenteen ja automaation tiedekunta
Main subject:Mittaustekniikka   (S-108)
Supervisor:Kärhä, Petri
Instructor:Ojanen, Maija
Electronic version URL: http://urn.fi/URN:NBN:fi:aalto-201203131462
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  664   | Archive
Keywords:spectral irradiance
filter radiometer
trap detector
error source
interference filter
spektrinen irradianssi
suodatinradiometri
loukkuilmaisin
virhelähde
interferenssisuodatin
Abstract (eng): Spectral irradiance is a radiometric quantity that describes the amount of radiant flux coming on a certain area at a certain wavelength.
Metrology Research Institute of Aalto University carries out calibration measurements for spectral irradiance.
The measurements are carried out with a filter radiometer that consists of a trap detector, precision aperture, 14 interference filters and a V(lambda)-filter.
The filter radiometer converts the detected radiation into electrical current.
The spectral irradiance of the source is determined with the help of the currents measured with the filter radiometer.

It has been noted that there is a systematic anomaly in the values measured with certain filters.
It has also been noted in intercomparisons with other National Metrology Institutes, that the irradiance scale of Metrology Research institute of Aalto University is raised compared to the others in the UV-range.
Therefore there has been a need to find out the reason for such anomalies.

In this thesis three different error sources that could cause the perceived anomalies were studied.
The studied sources were the change of the distance between the trap detector and the interference filter, and the angular and spatial responses of the interference filters.

The effect caused by the distance change was studied by measuring the output current of the trap detector while varying the distance between the trap detector and the interference filter.
Angular response was studied by measuring the transmittance of the filter at different incident angles.
Spatial response was studied by shifting the filter sideways and measuring its transmittance.

The effects caused by the distance change and the angular response were observed to be remarkable especially in the UV-range.
Typical values were from 2 % to 5 % The effect of spatial response was mainly minimal, but was most notable in the visual- and NIR-ranges, with typical values from 1 % to 2 %.
Abstract (fin): Spektrinen irradianssi on radiometrinen suure, joka kuvaa kuinka paljon säteilytehoa tulee tietylle pinta-alalle tietyllä aallonpituudella.
MIKES-Aalto Mittaustekniikka suorittaa spektrisen irradianssin kalibrointimittauksia.
Mittaukset tehdään suodatinradiometrillä, joka koostuu loukkuilmaisimesta, tarkkuusapertuurista, 14 interferenssisuodattimesta ja V(lambda)-suodattimesta.
Suodatinradiometri muuntaa havaitsemansa säteilyn virraksi.
Lähteen spektrinen irradianssi määritetään suodatinradiometrillä mitattujen virtojen avulla.

Mittauksissa on havaittu, että tietyillä suodattimilla mitatuissa pisteissä on systemaattimen poikkeama.
Lisäksi vertailututkimuksissa muiden kansallisten mittanormaalilaboratorioiden kanssa on havaittu, että MIKES-Aalto Mittaustekniikan irradianssiskaala on koholla muihin verrattuna UV-alueella.
Näin ollen on ollut tarve selvittää, mistä kyseiset poikkeamat johtuvat.

Tässä työssä tutkittiin kolmea mahdollista virhelähdettä, joista havaitut poikkeamat voisivat johtua.
Tutkitut lähteet olivat suodatinradiometrin loukkuilmaisimen ja suodattimen välisen etäisyyden muutos, suodattimen kulmavaste ja suodattimen spatiaalivaste.

Etäisyyden muutoksen vaikutusta tutkittiin mittaamalla loukkuilmaisimen antamaa virtaa, kun suodattimen ja loukkuilmaisimen välistä etäisyyttä muutettiin.
Kulmavastetta tutkittiin mittaamalla interferenssisuodattimien transmittanssi erilaisilla tulokulmilla.
Spatiaalivastetta tutkittiin liikuttamalla suodatinta sivusuunnassa ja mittaamalla transmittanssi.

Etäisyyden muutoksen ja kulmavasteen vaikutuksen havaittiin olevan merkittävä etenkin UV-alueen suodattimille.
Tyypilliset arvot olivat väliltä 2-5 %.
Spatiaalivasteen vaikutus jäi pääosin vähäiseksi, mutta oli merkittävin näkyvän valon- ja lähi-infrapuna-alueen suodattimille.
Tyypilliset arvot olivat 1-2 %.
ED:2010-08-16
INSSI record number: 40104
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