Measurement traceability and data quality are essential requirements by the WMO for monitoring atmospheric optical properties by International radiometer networks. A program of traceability, intercomparison and calibration of master instruments is therefore necessary to make products homogeneous and suitable for climate and satellite mission validation studies. Additionally the development of new on site calibration procedures is an up to date branch of research aimed to reduce the number of instrument expeditions for calibrations toward official calibration centers and therefore the data gaps incurred by the periodical shipments. This proposal aims on organizing joint activities between La Sapienza, ISAC-CNR, and PMOD/WRC (the official center designated by WMO as the World Optical depth Research and Calibration Center for instruments measuring solar radiation), on traceability of aerosol optical depth, water vapour and radiance estimations and measurements. Improvement of the measurement quality, intercomparison studies in different atmospheric conditions and validation and interpretation of the results, will be performed during devoted campaigns at the BAQUININ super site located at the Physics Department of University of Rome La Sapienza. The results obtained from this project will be shown to the scientific community through a publication on international journals and presentation at international conference.
Intercomparison studies among instruments of different type, retrieving atmospheric optical properties, are already regularly performed by PMOD/WRC about every 4 years. However they were only devoted to compare aerosol optical depth, retrieved by different equipment and methodologies. In this project the validation and testing of new ¿on site¿ calibration procedures will add an important improvement to the research, being this aspect particularly requested by the scientists working in this field of research. Infact "on site" calibrations allow the operators to track and evaluate the calibration status on a continuous basis, keeping the revision of the instrument mostly for maintenance reasons and offering the advantage of reducing the number of instrument expeditions. In this way, the data gaps incurred by the periodical shipments are considerably reduced, and the likelihood of instrumental damages attributable to transport also decreases.
The traceability program will be also devoted to water vapour estimation obtained by passive instruments based solar radiation techniques, thanks to the regular comparison against the product provided by the GNSS/GPS.
Finally, for the first time, the aerosol propertied retrieved by the Pandora spectrometer will be included in the intercomparison study and the testing of "on site" calibration procedure.