User Manual

Cosine 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.
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.