A paper, recently published in AMT by Román et al., explains a novel method of deriving the sky radiance field from a CCD
camera which has the capability to give sky conditions with both angular and
time high resolution.
The absolute calibration of this instrument
is based on the comparison against clear sky outputs of a radiative transfer model
(libRadtran), which in turn is compared to measurements taken with a CIMEL sun-photometer
(mean absolute differences between 2% and 15%). The calibration method proposed
in this paper is simpler and cheaper than the methodologies found in literature
which need laboratory calibration. Additionally, the authors analyze the sky radiances
for three particular cases corresponding to cloud-free, overcast and partially
cloudy skies.
A very interesting application of this calibration
method could be the use of radiances for the retrieval of cloud properties at
any angular direction such as, for example, the cloud optical depth which is one
of the most poorly measured climate variables due to the difficulty for its
remotely observing.