To define the tolerance limits for the calibration of UV spectroradiometers contributing to a single database, to determine protocols for calibration procedures and instrument characterisation, and to assess methods of maintaining calibration to a communal reference standard during operation of spectroradiometers at isolated sites.
The programme aims to improve methods for the long term maintenance of absolute calibration of UV spectroradiometers. Methodologies, guidelines and the practical means to maintain calibration of UV spectroradiometers to a uniform standard are the expected achievements. The investigation will be based on practical experience with a wide range of instruments and will define realistic levels of compliance with a given standard, and the expected long-term operational stability of this calibration reference and the associated spectroradiometers.
The main focus of the study will therefore be on instrumental characteristics and calibration protocols, which will be examined in laboratory experiments and in a spectroradiometer intercomparison at Ispra, Italy, during summer 1995.
As a contribution to SESAME, a programme of ultraviolet irradiance measurements has been incorporated into the project. The programme will consist of field measurement campaigns at four sites during SESAME Phase III (winter 1994-95). Data from operational UV stations may also be recorded during the SESAME observing periods. The objective is to obtain intensive data on days when correlative ozone column and profile data are available, in order to determine the extent to which observed ultraviolet irradiance agrees with expectations based on radiative transfer calculations. Final choice of stations and timing will be made on the bases of scheduled SESAME operations, taking into account the viewing geometry of Dobson and Brewer column ozone instruments, length of day and range of solar elevation, likely trajectories of planned ozone flights, the horizontal homogeneity of the lower stratosphere, the availability of suitable laboratory facilities for lamp calibrations, and logistic constraints. A Scandinavian Arctic site will be chosen from Andøya, Kiruna and Sodankylä, and a second site will be selected from Lerwich and Aberstwth if appropriate correlative data are likely to be available. Spectroradiometers already deployed at the SESAME sites of Reykjavik and Thessaloniki will also contribute to the campaign. At all observing sites, absolute measurements of the global spectral solar ultraviolet irradiance will be made at intervals of 30 minutes or less, from sunrise to sunset on a daily basis for a period of about 20 days, subject only to the operational requirements of instrument maintenance and laboratory irradiance calibrations.
Funding SchemeCSC - Cost-sharing contracts
3720 BA Bilthoven
CB3 0ET Cambridge
3730 AE De Bilt