Project Objectives

The Joint Research Project "Traceability for surface spectral solar ultraviolet radiation" is a collaboration between National Metrology Institutes, partners from Industry and the research Community in Europe.

This project will significantly enhance the reliability of spectral solar UV radiation measured at the Earth surface by developing new methods of observation (techniques and instruments) to provide traceable solar UV irradiance measurements with an uncertainty of less than 2%.

The activity is essential to unambiguously quantify decadal changes in solar UV radiation due to the expected changes in the global climate system. The project will address these objectives by shortening the traceability chain of the solar UV measurements to the SI unit and to reduce the associated transfer uncertainties. The goal is to approach uncertainties in the field comparable to those currently achieved only for primary spectral irradiance scale realisations at NMI level, i.e., at the level of 1%.

Planned work

To achieve the objective of providing traceable solar UV irradiance measurements with an uncertainty of less than 2%, the European reference spectroradiometer QASUME will be fitted with an improved global entrance optic and newly developed solid state detectors. New portable transfer standards will be developed to transfer the irradiance scale from the primary standard of spectral irradiance held at NMI facilities to spectral solar irradiance measurements.

In view of using cost-effective array spectroradiometers as replacements for current UV filter Radiometers in UV monitoring networks, significant progress needs to be achieved in the characterisation of these devices. New characterisation techniques and post-correction methods will be developed to determine and correct the stray light, linearity, and wavelength scale of array spectroradiometers. These activities will be supported by designing and constructing novel array spectroradiometers with improved stray light characteristics based on band pass filters and micro-electro-mechanical systems (e.g. MEMS and DLP).

The dissemination of the improved irradiance traceability and the demonstration of the tools and methods developed in this project will occur by a large field intercomparison of spectroradiometers at the World Radiation Center, Davos, Switzerland. Participants from the end-user community involved in solar UV measurements will be invited to this field intercomparison. Participating spectroradiometers from the end-users will be characterised and calibrated by the facilities developed in this JRP to provide traceability of spectral solar UV irradiance at this new level of uncertainty to the wider European UV monitoring community. The prototype devices developed in the JRP will be commercialised and the methodologies freely disseminated to create a sustainable basis for improved solar UV measurements in regional and national UV monitoring networks.

Impact

Users from the solar UV community will be involved in the project through the following activities:

• An intercomparison of spectroradiometers(array and scanning) measuring global solar UV irradiance will be organised during about 10 days in May/June 2014 at the World Radiation Center, Davos Switzerland. This intercomparison will be open to the UV community and provide access to the tools and techniques developed during the project in order to significantly decrease current uncertainties in measuring spectral solar UV radiation. The activities during the intercomparison will include:

  1. Intercomparison of global solar irradiance measurements with the QASUME reference spectroradiometer,

  2. On-site absolute spectral irradiance calibrations using traceable transfer standards,

  3. Linearity and wavelength characterisations of array and scanning spectroradiometers,

  4. Workshop for describing the newly developed tools and methods within the project such as new diffusers, UV LED based transfer standards, optimised UV array spectroradiometers, hyperspectral UV imager, stray light and software tools (bandwidth correction algorithm and uncertainty estimation tool).

• Technical workshops will provide a forum for end-users to interact with the Project Consortium. The workshops will give an overview of the project objectives, present current project activities and discuss preliminary results. Presentations will be given by project members and by participants from the user community. Preliminary dates are:

  1. One day during the week of 6-10 August 2012 in conjunction with the UV Session at the International Radiation Symposium, Berlin, Germany.

  2. 13 July 2013 at Davos, Switzerland, in conjunction with the IAMAS-IACS Davos Atmosphere and Cryosphere Assembly.

  3.  Day workshop in May/June 2014 during the UV intercomparison at PMOD/WRC, Davos, Switzerland.

• The bandwidth, spectral stray-light and linearity characteristics of a limited number of stakeholder array-spectroradiometers will be characterised by tuneable-laser facilities operated at NMI labs (PTB and METAS). Due to the significant efforts involved, certain restrictions will apply. Inquiries should be directed to the coordinator of the project (This email address is being protected from spambots. You need JavaScript enabled to view it.).

• The UV Thematic network will be re-activated to serve as communication platform between the project consortium and the UV community. A mailing list will be used to disseminate project news and future project-related events through “UVnews” newsletters.

The research leading to these results has received funding from the European Union
on the basis of Decision No 912/2009/EC.