Depending on the present atmospheric conditions a considerable part of the direct solar radiation can be scattered into the circumsolar region closely surrounding the solar disk. This forward scattered radiation, the circumsolar radiation, is widely detected by pyrheliometers, while concentrating solar collectors can only use a concentrator specific fraction of it. This lower response to circumsolar radiation can lead to systematic overestimations of the collector performance. We use a Sun and Aureole Measurement system (SAM) combined with AERONET sun photometer measurements to determine the circumsolar radiation, and compare the results to a newly developed 2-channel pyrheliometer instrument BPI-CSR460.