Activity Cluster C: UV Radiation
Activity C1: Explore use of small, inexpensive diode array spectrometers
There are now several small, relatively inexpensive spectrometers on the market that use diode array or CCD detectors, permitting instantaneous measurement of a large spectral range. At present these instruments cannot provide the same performance in the UVB region as the scanning spectroradiometers, but with technical and data processing improvements they are becoming increasingly viable as UV monitoring instruments. In principle they allow full spectral data to be gathered at similar capital cost to current broadband radiometers.
- preparation of a document with recommendation on instrument specifications, instrument characterization and calibration
- workshop to explore current state of the art in CCD spectrometer technology and application to UV measurements
Activity C2: Improve access to UV instrument calibration centres
GAW Regional UV calibration centres exist in NOAA, Boulder, Colorado, USA and in
PMOD/WRC, Davos, Switzerland. There is no world calibration centre for UV measurements. The lack of facilities, and cost of using those available, is detrimental to data quality and the stability of long-term monitoring.
- identify potential regional calibration centres in under-represented areas
- intercomparisons between existing and new calibration centres
- identify potential world calibration centre (could be an existing regional centre)
Activity C3: Further develop and validate satellite UV algorithms
Different satellites / satellite products require more extensive validation for a wider range of sites and climatic conditions.
- extend satellite validations to more sites with extensive UV records
- improve the treatment of aerosols in satellite retrieval algorithms
- improve the treatment of clouds in satellite retrievals, especially for the short-term data products such as daily doses where actuals can be very different to statistics and climatology
- improve the treatment of snow cover
Status: Open. On-going projects at FMI: EUMETSAT Satellite Application Facility on Ozone and Atmospheric Chemistry Monitoring (O3M SAF), OMI UVB processing and delivery.
Activity C4: Improve the knowledge base of the UV effects in relation to UV monitoring
Currently there is widespread use of the CIE erythema weighting function to represent biological effects. However, there are severe differences between published spectra for erythema. Even if the weighting function is appropriate, there are many other UV effects on humans (e.g. skin cancer, eye diseases, immune suppression...) and on plants (reduced growth, DNA damages...) that need to be considered as well. Often the threshold values for these other effects are not known. The present knowledge is assessed every four years by the UNEP effects assessment panel.
- organize a joint conference for information exchange between the UV monitoring and the UV effects community
- identify action spectra to be reported in addition to CIE erythema
Activity C5: Extend the knowledge of UV for other receiving geometries
UV irradiance on a horizontal surface is a widely accepted geometry for studying the UV impact (e.g. for UV index). However, it is not the only relevant geometry to be considered. Depending on the application actinic flux, spectral radiance, or irradiance on tilted surfaces may be the more appropriate measure. In addition, polarization effects may be important in some applications.
- assessment of the natural variability of UV radiance under various meteorological conditions
Activity C6: Improve the understanding of the factors affecting UV
The impact of total ozone on UV irradiance has been studied quite extensively in the past. While there has been progress in recent years, the influence of other factors determining UV irradiance such as clouds, aerosols and albedo, are less well understood. The importance of such studies is highlighted by the fact that these other factors will probably be affected by climate change. These changes may have a higher impact on UV than changes in ozone. The analysis might include statistical investigations on future UV irradiance changes, with time and location dependency.
- new process studies on the impact of clouds, aerosols and albedo
- analysis of existing data series to study the UV variability due to changes in clouds, aerosols and albedo