EMRP ENV03
“Traceability for surface spectral solar
ultraviolet radiation”
Julian Gröbner
Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center,
Davos Switzerland
The European Metrology Research Programme (EMRP) is jointly funded by the EMRP
participating countries within EURAMET and the European Union.
Project Overview
Duration:
Total Budget:
August 2011 to July 2014
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/
Motivation
10
Challenges
500
Large natural variability
Dynamic range >105
Radiation levels µW m-2nm-1
Wavelength uncertainty <0.02% (0.05 nm)
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
Primary Irradiance
Standard
Transfer Standard
Reference
Spectroradiometer
End-User Devices
Calibrated UV Network
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
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)
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
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
EMRP ENV03: Traceability chain for spectral irradiance
Cryogenic radiometer
Detector
cw-Laser Sources
Source
Si-trap detector + aperture
Spectrally tuneable source
Filter Radiometer
(Aim of the project)
Blackbody + aperture
Tunable Lasers
Spectroradiometer
Spectral irradiance
standard
Stability controlled by
relative measurements
using portable Sources
QASUME
Validated
in this
Project
QASUME
(QASUME was calibrated
directly against the
blackbody in 2004)
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, 134—139, 2005.
Portable sources using UV-LEDs
Design goal: aging rate of 0.05 %h-1
1,00
2,0410-2
:E
:I
:U
0,96
210-4
0,94
2,0310-2
2,0210-2
h-1
2,0110-2
2,0010-2
0
20
40
60
80
100
Burning time / h
120
7,0
6,8
6,6
U/V
0,98
7,2
I/A
Normalized signal
2,0510-2
Compact LDLS source as transfer standard
Spectral Irradiance output :
•
comparable to 1000 W FEL Lamp
•
Nearly Constant output over UV range
Preliminary results
Source stability < 0.2%
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)
WP 2: Array Spectroradiometers …
4 Development of two wavelength scale characterisation devices (METAS)
• For scanning and array spectroradiometers
0.32
• U = 0.01 nm, wavelength 280 nm - 400 nm.
•2. Polarisation gradient filter (VSL)
Mica based Fabry Perrot
0.3
Normalized amplitude
• 1. Fabry-Perot etalon (METAS)
0.28
0.26
0.24
0.22
0.2
0.18
270
290
310
330
350
Wavelength, nm
370
390
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)
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).
Stray light correction procedure for array spectroradiometer
YIB  A1 Ymeas  C Ymeas
In-range straylight matrix
from Zong et al, 2006
Slit Functions obtained from tunable
laser setup (PLACOS-PTB)
Calculated Straylight
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
In&Out-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
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 sensitivity range of the silicon
CCD detector (390-1100 nm).
UG11X
Uncorrected
In-range stray light
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
Solid State Detector Systems (SSDS)
Reset
CINT
i L - iD
iL
Hold
-
Rsh
Si photodiode S1227 33 BQ
Noise Equivalent Power measured
with V/I gain of 1011 (0.1 s)
iD
+
Switched Integrator
Vout
Vout t   
t INT
I IN
CINT
Calculated SSDS noise performances
for QASUME typical UV solar spectral
measurement
1 % at 298 nm
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
Task 4.2 New Diffuser design
1) Design software
2) Validation through prototype
measurements
3) Realisation and commercialisation
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
Knowledge Dissemination
• UVNET Mailing list at http://metrology.tkk.fi/uvnet/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/