Comparison of scalar and cosine instruments for measuring photosynthetically available radiation in L. Neagh, N. Ireland

Summary

Changes in the quality and quantity of upwelling and downwelling photosynthetically available radiation (PAR) were measured with broad and narrow waveband cosine collectors in Lough Neagh, N. Ireland. The upwelling/downwelling quantum irradiance ratio (R) for PAR is low and varies seasonally (0.018 to 0.059). These values contrast with the higher and more depth variable R values found in deep oligotrophic lakes in the Salzkammergut region of Austria (0.015 to 0.16). Comparisons between cosine and scalar collecting instruments, in a range of depths and weather conditions in L. Neagh, showed that cosine values were between 64 and 80% of scalar values.