UV plays a key roll in several biological functions. As consequence of the ozone depletion investigations to study the effects of UV radiation on human health and terrestrial and aquatic ecosystems have been carried out in laboratories and in the field. Experiments performed in laboratories, irradiating samples with lamps often present the inconvenience that light sources do not reproduce properly the solar spectrum. Field experiments are usually carried out comparing samples exposed to ambient irradiance (normal or increased) against 100% UV-B screened samples. This scenario also differs from the real situation of normal irradiance against UV-B increased irradiance. Some authors have solved this problem performing studies under ambient conditions, simulating the ozone depletion by supplementation of the UV-B radiation with lamps. As part of the IAI CNR-26, "Enhanced Ultraviolet-B Radiation in Natural Ecosystems as an added Perturbation due to Ozone Depletion," mesocosms experiments were performed at Rimouski (Canada), Ubatuba (Brasil) and Ushuaia (Argentina) using the supplementing methodology. In this paper we introduce the design of the measurements and lamps setting and the methodology used to calculate the attenuation constant and the irradiance at the water column at the mesocosms during the experiment, emphasizing on the Ubatuba campaign.
The IAI Network for the measurement of ultraviolet radiation in Chile, Argentina and Puerto Rico is composed of ten multi-channel radiometers (GUV 511, Bisopherical Instruments Inc.), which are periodically sun calibrated with a traveling reference GUV (RGUV). The RGUV is calibrated under solar light against a SUV100 spectroradiometer. This calibration is then transferred to each instrument in the network through the RGUV. A previous multi-regression model proved to be suitable to derive narrowband irradiance from broadband irradiance, ozone column and solar zenith angles (SZA). A recent modification of the existing multi-regression model improved the multi-channel instrument sun calibration against spectroradiometers. In this approach, the narrowband irradiance is the SUV spectral irradiance and the broadband is the multi-channel GUV irradiance. We included the azimuth angle as a parameter into the multi-regression equation and we applied a non-linear function, instead of a single coefficient, to correct for SZA. In this paper, the new multi-regression approach is applied to both steps of a GUV calibration: SUV - RGUV and RGUV - GUV and the results are compared with traditional calibration methods. Important improvements are observed in the calibration, in particular for SZA larger than 50°.
When a multi-channel radiometer is calibrated using the sun as calibration source, the error in the calculated calibration constants may be large when solar zenith angles increase. A multi-regression model has proved to be suitable to derive narrowband irradiance from broadband irradiance, ozone column and solar zenith angles (SZA). In this paper, a modification of this model is being proposed to improved the multi-channel instrument sun calibration against spectroradiometers, considering a channel of a multi-channel radiometers as a broadband instrument. The errors in the GUV irradiance, compared to the spectroradiometer irradiance, diminished considerably at all channels for SZA larger than 50<SUP>a</SUP>, then, this technique could be particularly beneficial to calibrate radiometers installed at high latitudes, where SZA during winter, even at noon, are larger than 50<SUP>a</SUP>.
The presence of clouds is responsible for an important variation in the UV and visible radiation at the Earth's surface. Although for practical purposes cloud transmittance is often considered plane in the UV and visible, a wavelength dependence is observed. In this paper we performed a statistical study of cloud transmittance at Ushuaia for wavelengths between 295 and 600 nm, following different procedures. A decrease of the transmittance for increasing wavelengths in the UVA and the visible was observed (0 to 50% decrease at 600 nm regarding to 340 nm) in good agreement with the observations made by other authors. Nevertheless, for wavelengths below 320 nm our results show discrepancy with other papers. Since Ushuaia is a small town n a fairly unpolluted area, a possible reason for this differences is that, as a consequence of low ozone amounts in the troposphere, Rayleigh scatter is more important than ozone absorption, even in this part of the spectrum.
After the discovery of the ozone hole the use of spectral and multiband instruments in UV radiation measurements became more common, but time series for these instruments are still relatively short to determine trends. Nevertheless, systematic measurements of ozone column have been performed since late fifties at several stations and with worldwide coverage since late seventies, and long time series of broadband instruments (Pyranometers, UV and erythemally weighted) are also available at stations all over the world. In this paper we introduce a multi- regressive model that allows inference of spectral or narrowband irradiances from ozone total column and broadband irradiances, in places where a relatively short time series of spectral irradiances is available. To test the model, measurements under all weather, solar zenith angle and ground conditions performed at three of the stations of the NSAF UV Radiation Monitoring Network were used. The model generated very good results over a wide variety of situations. Broadband pyranometer data from the NOAA/CMDL surface radiation budget database for the South Pole Station were used in the model to estimate the daily-integrated narrowband irradiances. A time series of monthly means for the narrowband 303.030-307.692 nm were then computed, dating back to 1978.