Traceability of solar UV measurements using the Qasume reference spectroradiometer.

One major objective of the European Joint Research Project "Traceability for surface spectral solar ultraviolet (UV) radiation" was to reduce the uncertainty of spectral UV measurements. The measurement instrument used for this work was the portable UV European reference spectroradiometer Qasume. The calibration uncertainty of this instrument was decreased and validated by a comparison of direct calibrations against a primary standard for spectral irradiance, a high temperature blackbody radiator, and against a reference detector using a spectrally tunable laser as a monochromatic source.

Stray light correction of array spectroradiometers for solar UV measurements.

An approach is presented to characterize and correct stray light in spectra measured with array spectroradiometers and caused by out-of-spectral range radiation. A prerequisite for out-of-range stray light correction is knowledge of the spectral irradiance not measured by the instrument itself. A way of solving this problem for solar UV measurements is shown.

Atmospheric CO enrichment of alpine treeline conifers.

•   Experimental CO enrichment of mature Larix decidua and Pinus uncinata trees and their understory vegetation was used to test the carbon limitation hypothesis of treeline formation at the alpine treeline in Switzerland. •   Forty plots (each 1.1 m ) were established; half of them were exposed to elevated (566 ppm) atmospheric CO using a free air CO enrichment (FACE) system releasing pure CO , and the other half were treated as controls at current ambient [CO ].