Mean cosine response of twenty-three
SQ series quantum sensors (error bars
represent two standard deviations
above and below mean). Cosine
response measurements were made by
direct side-by-side comparison to the
mean of four reference thermopile
pyranometers, with solar zenith angle-
dependent factors applied to convert
total shortwave radiation to PPFD. Blue
points represent the AM response and
red points represent the PM response.
Directional, or cosine, response is defined as the
measurement error at a specific angle of radiation
incidence. Error for Apogee SQ series quantum
sensors is approximately ± 2 % and ± 5 % at solar
zenith angles of 45° and 75°, respectively.