Simultaneous measurements of upwelling and downwelling ultraviolet (UV) spectral irradiance were used to deduce the wavelength dependence and the solar zenith angle dependence of the albedo of the ground surface (long grass) at Lauder, New Zealand (45.05°S, 169.68°E). In the UVB region the deduced albedos are approximately 1%. At longer wavelengths the albedo increases to approximately 2% at 400 nm, and 4.5% at 450 nm. These albedos are significantly smaller than those generally quoted for the visible region. The deduced albedos tend to increase at larger solar zenith angles, demonstrating that the surface is not strictly Lambertian.

The amount of solar radiation intercepted by an object depends on the orientation of the object with respect to the sun and the angular distribution of the diffuse component of solar radiation, which is commonly considered to be approximately isotropic. The angular distribution of the diffuse UV, visible and near-infrared insolation was measured at several solar zenith angles between 32" and 68" under cloudless skies at Lauder, New Zealand (45S), and shown to be anisotropic. The diffuse solar UV radiation increases markedly with solar elevation and is a large proportion of the total UV irradiance. The diffuse visible light and infrared radiation are small components of the total irradiance and almost independent of solar elevation. The angular distribution of erythemal UV radiation was tabulated and is available on request.

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An outdoor, solar illuminated growth chamber with modulated UV-B enhancement, is described and its performance characterized. The chamber was clad with Teflon film that transmitted both UV-A and UV-B with little absorption and whose transmission did not change significantly over 1 yr. An array of UV-B emitting fluorescent tubes with cellulose diacetate filters provided additional UV-B radiation inside the chamber with little additional UV-A, while a similar chamber with unenergized tubes provided an ambient control. Ambient and enhanced UV-B levels were measured using a pair of integrating broad band radiometers, and it was found that frequency modulation allowed control of lamp intensity over a range in excess of 100:1. Within the UV-B chamber, enhanced levels of integrated UV-B could be maintained at a constant ratio over ambient throughout the day. However, it was not sufficient simply to maintain a constant ratio of radiometer output voltages: the angular responses of the two radiometers had to be well matched. The shape of the UV-B portion of the enhanced spectrum closely followed that expected under ozone depleted skies, while the enhancement of UV-A was insignificant. The spectral profile obtained in the UV-B depended on the thickness of the cellulose diacetate filters used to block short wavelength UV radiation emitted by the fluorescent tubes. The number (thickness) of cellulose diacetate filters required to achieve this match varied with season. Although the filters did degrade with exposure to UV-B it was not necessary to replace them for several months. This was due to: (i) low rate of filter degradation because the lamps were rarely required to be run at full brilliance except at midsummer midday; and (ii) increased tube intensity compensated for reduced filter transmission.

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