EMRP ENV03

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EMRP ENV03 Traceability for surface spectral
solar ultraviolet radiationJulian
GröbnerPhysikalisch-Meteorologisches
Observatorium Davos, World Radiation Center,
Davos SwitzerlandThe European Metrology
Research Programme (EMRP) is jointly funded by
the EMRP participating countries within EURAMET
and the European Union.
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Project Overview

• 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

http//projects.pmodwrc.ch/env03/
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Motivation
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• Challenges
• Large natural variability
• Dynamic range gt105
• Radiation levels µW m-2nm-1
• Wavelength uncertainty lt0.02 (0.05 nm)

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Project Objectives

• Enhance the reliability of spectral solar UV
  radiation measured at the Earth surface
• Improved SI 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

Calibrated UV Network
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Project Structure
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
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Project Outputs

• 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)

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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

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WP 1 Spectral Irradiance Traceability (PTB)

• 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 the primary standard 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

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EMRP ENV03 Traceability chain for spectral
irradiance
Cryogenic radiometer
Detector
cw-Laser Sources
Source
Si-trap detector aperture
Spectrally tuneable source
Filter Radiometer
Blackbody aperture
Spectroradiometer
(QASUME was calibrated directly against the
blackbody in 2004)
Spectral irradiance standard
QASUME
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Validation of the QASUME irradiance reference in
2004
blackbody BB3200pg at PTB
Measurement of BB3200pg at PTB on 15 June 2004
Expanded uncertainty of PTB transfer
standards 3 New expanded uncertainty of the
QASUME irradiance reference (based on these
blackbody measurements) 2
Gröbner J., and P. Sperfeld, Direct traceability
of the portable QASUME irradiance scale to the
primary irradiance standard of the PTB,
Metrologia, 42, 134139, 2005.
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Portable sources using UV-LEDs
Design goal aging rate of 0.05 h-1
2?10-4 h-1
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Compact LDLS source as transfer standard

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

Preliminary results
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WP 2 Array Spectroradiometer characterisation
(METAS)

• 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)

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WP 2 Array Spectroradiometers

• 4 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)
• 5 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)

Mica based Fabry Perrot
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Effect of stray light on solar irradiance
measurements
Array Spectroradiometer with nominal wavelength
range 280-440 nm.
In-range Straylight
array spectroradiometer
Double monochromator
Out-range Straylight
Detector arrays are made from silicon (spectral
sensitivity up to 1100 nm) and are therefore
sensitive to radiation which is not meant to fall
on the detector (out-range straylight).
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Stray light correction procedure for array
spectroradiometer
In-range straylight matrix
Calculated Straylight
from Zong et al, 2006
Slit Functions obtained from tunable laser setup
(PLACOS-PTB)
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Example for in- and out-range Straylight

• This Array Spectroradiometer
• Nominal Sensitivity 280 440 nm
• Out-range Radiation from 440 nm to 1100
  (Silicon) nm

Raw Measurement
Out-range Corrected
InOut-range Corrected
Double MC
Ratio to Double Monochromator
NOTE Out-range Stray-Light Correction requires
knowledge of the spectral radiation distribution
which is not measured by the instrument itself!!
Correction works, but is very complex
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Modified array Spectroradiometer to suppress
out-range radiation
We placed a DUG11X solarblind filter in the beam
path to suppress out-range radiation in the
sensi-tivity range of the silicon CCD detector
(390-1100 nm).
UG11X
Uncorrected In-range stray light
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WP 3 Improvement of Reference Spectroradiometers
(CMI)

• 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
• 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

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Solid State Detector Systems (SSDS)
Switched Integrator

• Si photodiode S1227 33 BQ

Calculated SSDS noise performances for QASUME
typical UV solar spectral measurement
Noise Equivalent Power measured with V/I gain of
1011 (0.1 s)
1 at 298 nm
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WP 4 New Technologies (Aalto)

• 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

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Task 4.2 New Diffuser design

1. Design software
2. Validation through prototype measurements
3. Realisation and commercialisation

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WP 4 New Technologies

• 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

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Knowledge Dissemination

• UVNET Mailing list at http//metrology.tkk.fi/uvne
  t/source/lists.html
• Workshops
• International Radiation Symposium, Berlin, August
  2012
• UVNet Workshop ENV03 session, Davos, 27-28
  August 2013
• Spectral solar UV Intercomparison at Davos
  Final ENV03 Workshop, 2 Weeks in June/July 2014
• Presentations, Guidelines, Publications can be
  found at the project web-site

http//projects.pmodwrc.ch/env03/
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Feasibility study of a Fourier transform
spectrometerfor solar UV irradiance measurements

• Key features
• Spectrum measured within lt30 sec
• high wavelength accuracy
• High spectral Resolution

Spectrum of a Xe lamp with interference filter
IF 406 nm
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Solid State Detector Systems (SSDS)
Switched Integrator

• Si photodiode S1227 33 BQ

Calculated SSDS noise performances for QASUME
typical UV solar spectral measurement
Noise Equivalent Power measured with V/I gain of
1011 (0.1 s)
1 at 298 nm
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Spectral stray light characterization of array
spectroradiometers using tuneable lasers

• PLACOS setup at PTB (Pulsed Laser for Advanced
  Characterisation of Spectroradiometers)

• pulsed operation (20 Hz, 5 ns)
• easy to handle
• automatic change of wavelength

OPO, optical parametric oscillator SHG, second
harmonic generator

• S. Nevas, M. Lindemann, A. Sperling, A. Teuber,
  R. Maass, Colorimetry of LEDs with Array
  Spectroradiometers, MAPAN - Journal of Metrology
  Society of India 24, 153-162 (2009)
• S. Nevas, G. Wübbeler, A. Sperling, C. Elster,
  A. Teuber, Simultaneous correction of bandpass
  and stray-light effects in array
  spectroradiometer data, Metrologia 49, S43-S47
  (2012)

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Spectral stray light characterization of array
spectroradiometers using tuneable lasers
Characterization and correction of UV array
spectroradiometers for in-range and out-of-range
stray light effects