EMRP ENV03 “Traceability for surface spectral

solar ultraviolet radiation”

The European Metrology Research Programme (EMRP) is jointly

funded by the EMRP participating countries within EURAMET and

the European Union.

Project Objectives • Enhance the reliability of spectral solar UV radiation measured at the Earth

surface

• Improved traceability, improved methodologies, improved devices

• Uncertainties better than 2% in the wavelength region 300 nm – 400 nm (current state of the art is 5%)

• Develop techniques and devices for using cost-effective array-spectroradiometers for solar UV measurements

Primary Irradiance Standard

Transfer Standard Reference Spectroradiometer

End-User Devices Calibrated UV Network

• Duration: August 2011 to July 2014

• Total Budget: 3.9 M€

• Project coordinator : Julian Gröbner Davos, Switzerland

• 8 Partners from European Metrology Institutes and 2 from Industry

• 4 Researcher Excellence Grants (REG) from Universities & Health Institute

• 5 Collaborators, open-call

Project Overview

http://projects.pmodwrc.ch/env03/

WP WP Name WP Leader Active JRP Partners

WP1 Spectral Irradiance Traceability

Saulius Nevas PTB, METAS, SFI Davos, VSL, Kipp

WP2 Array Spectroradiometer Characterisation

Peter Blattner METAS, Aalto, LNE, PTB, PMOD/WRC, VSL, REG(IMU)

WP3 Improvement of Reference Spectroradiometers

Marek Šmíd CMI, INRIM, PTB, PMOD/WRC

WP4 New Technologies Petri Kärhä Aalto, CMI, METAS, INRIM, LNE, PTB, PMOD/WRC, CMS, Kipp, REG(IMU)

WP5 Impact Julian Gröbner PMOD/WRC, All

WP6 Management Julian Gröbner PMOD/WRC, All

Project Structure

Devices: • UV LED-based transfer standards (WP 1)

• Transfer standard based on Laser Driven Light Source LDLS (WP 1)

•Wavelength scale characterisation devices (WP2)

•Solid state detectors to replace PMTs (WP 3)

• Modified Fourier-Transform Spectrometer (WP 3)

• UV hyperspectral imaging camera (sky radiance) (WP 4)

• Global input optics (improved diffuser design) (WP 4)

• Two array spectroradiometers optimized for UV (WP 4)

Project Outputs

Software: • Tool to determine the uncertainty budget for array spectroradiometers (WP 2) • Tool for bandwidth and wavelength homogenisation and stray light correction (WP 2)

Knowledge Transfer: • Guidelines (WP 2) • Conference Presentations (WP 5) • Technical Workshops (WP 5) • Refereed publications (WP 5) • Intercomparison campaign at Davos

Project Outputs

Goal: Shorten the traceability chain of solar UV measurements to SI units and reduce transfer uncertainties (U = 1 - 2%)

1 Detector-based traceability chain using an absolute radiometer and tunable UV laser facility (PTB)

•Tuneable laser source 280 – 400 nm

• Traceability to cryogenic radiometer via a trap detector

2 Development of stable, portable and robust reference sources based on UV-LEDs (PTB)

• For monitoring purposes, near-field conditions

• Replacement of halogen lamps susceptible to transportation and aging

3 Compact laser-induced UV source as transfer standard (VSL)

• Laser Driven Light Source (LDLS™) from Energetic

WP 1: Spectral Irradiance Traceability (PTB)

Cryogenic radiometer

(Aim of the project)

Spectral irradiance standard

cw-Laser Sources

Si-trap detector + aperture

Filter Radiometer

Blackbody + aperture

Tunable Lasers

Detector

Source

Spectroradiometer

Spectrally tunable source

QASUME QASUME

Stability controlled by relative measurements using UV-LED Sources

Traceability chain for the QASUME Spectroradiometer

(QASUME was calibrated directly against the blackbody in 2004)

Talk by P. Sperfeld 9:45

0 20 40 60 80 100 120Burning time / h

0,94

0,96

0,98

1,00

Norm

alize

d sig

nal

2,00⋅10-2

2,01⋅10-2

2,02⋅10-2

2,03⋅10-2

2,04⋅10-2

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I / A

6,6

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7,2U

/ V

: E: I: U

250 300 350 400 450Wavelength / nm

0,0

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Spec

tral

Irra

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ce /

a.u.

Stability investigation of UV-LEDs

2⋅10-4 h-1

AlGaN

Design goal: ageing rate of 0.05 %h-1

Irradiance using 4 LEDs

Talk by S. Nowy 12:30

Compact LDLS source as transfer standard

Source stability < 0.2%

Spectral Irradiance output : • comparable to 1000 W FEL Lamp • Nearly Constant output over UV range

Preliminary results

Poster by O El.Gawhary P105

Talk by M. Blumthaler 10:00

Goal: New characterisation techniques for the most relevant uncertainty components – stray light, bandwidth, linearity, wavelength

1 “A guide to measuring solar UV spectra using array spectroradiometers” (IMU)

• Specification of array spectrometers to meet the requirements for solar UV measurements

• Recommended measurement sequences for typical measurement setup

• A standardized protocol for saving measurement data, and ancillary information

2 “Uncertainty estimation in array spectroradiometer measurements of Solar UV spectra” (LNE)

• Guideline, software and methodology

3 Stray light characterisation and correction methods (PTB)

WP 2: Array Spectroradiometer characterisation (METAS)

Percentage of stray light in array spectroradiometer signal when measuring quartz-halogen lamp (calculated using the determined correction matrix)

Effect of stray light on irradiance measurements

200 400 600 800Wavelength / nm

1

510

50100

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tion

of st

ray

light

/ %

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Spec

tral

irra

dian

ce /

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.: Stray light: E200 300 400 500 600 700 800

Wavelength / nm10-710-610-510-410-30.010.1

1

LSF

/ a.u

.

Slit Functions obtained from tunable laser setup (PLACOS)

1

Determination of Stray-Light contribution from Slit function measurements 2

Talk by F. Shindo 10:15

Talk by S. Nevas 11:30

Talk by A. Kreuter 11:45

4 Bandwidth and wavelength correction methodologies applied to solar spectra (PMOD/WRC)

• Algorithm, which converts measured solar spectra onto a uniformly spaced wavelength grid with a nominal spectral resolution.

5 Development of two wavelength scale characterisation devices (METAS)

• For scanning and array spectroradiometers

• U = 0.01 nm, wavelength 280 nm - 400 nm.

• 1. Fabry-Perot etalon (METAS)

•2. Polarisation gradient filter (VSL)

6 Linearity of array spectroradiometers (PTB)

• Three different procedures and measurement setups for linearity characterisation of array spectroradiometers (broad-band source, monochromator-based and tunable laser source)

WP 2: Array Spectroradiometers …

Mica based Fabry Perrot

Goal: New detection systems and entrance optics for scanning spectroradiometers to achieve field measurement uncertainties of 2% for solar UV measurements

1 New detection system for reference scanning spectroradiometers (CMI)

• Solid state detectors (Si, SiC, ZnO) and switched integrator amplifier

• High sensitivity, high dynamic range, low noise

• Substitute to PMT at longer wavelengths

2 Validation of optimised transportable QASUME reference spectroradiometer (PMOD/WRC)

• New Detector-System

• New Entrance Optic with improved Cosine response

• Improved traceability to SI and stability check using UV LEDs

3 Adaptation of a Fourier-transform spectroradiometer as reference instrument for solar UV irradiance measurements (PTB)

• Evaluate suitability of Fourier -transform spectroradiometer as a reference instrument for solar UV irradiance measurements

WP 3: Improvement of Reference Spectroradiometers (CMI)

Talk by M. Smid 12:45

Talk by P. Meindl 12:15

1 Realisation of a UV hyperspectral camera (INRIM)

• Imaging device for spectral UV sky radiance measurements

• Fish-eye UV collection optics

• Scanning Fabry-Perot device

• Improve cosine correction methods

2 Improved entrance optics for global solar UV spectroradiometers (Aalto)

• Cosine error less than ±1 % downto 80°

• Material studies and design software

• Study new fused silica-based diffuser materials

• Two designs for Brewer and fiber coupled optics

WP 4: New Technologies (Aalto)

Talk by P. Kärhä 10:30

3 Array spectroradiometer with improved stray light rejection using adaptive optics (CMI)

• Studies and comparison of methods

• MEMS tuneable grating technology

• Digitally modulated micro mirror devices (DMD).

• Prototype of improved spectrograph

4 Array spectroradiometer with improved stray light rejection using band pass filters (LNE)

• Jobin-Yvon spectroradiometer optimized for solar UV measurements

• Target value for stray light rejection using a tailored band pass filter 106

WP 4: New Technologies …

Talk by L. Egli 12:00

Knowledge Transfer • National and international conferences (IRS 2012, DACA13, NEWRAD12)

• Publications in peer-reviewed publications

• UV-Net mailing list and "UVNews" newsletters http://metrology.tkk.fi/uvnet/ • Guideline Documents

Training • Workshops (UV-NET 2013 , Davos 2014) • Stray light and linearity characterisation of array spectroradiometers using tunable laser

systems at PTB (open to collaborators)

• Spectral solar UV Intercomparison at Davos, June/July 2014 • Instrumental characterisations during the intercomparison

Exploitation

• Exploit the knowledge and Intellectual Property developed during the project

WP 5: Creating Impact (PMOD/WRC)