R. Boers et al., CORRECTION OF AIRCRAFT PYRANOMETER MEASUREMENTS FOR DIFFUSE RADIANCE AND ALIGNMENT ERRORS, J GEO RES-A, 103(D13), 1998, pp. 16753-16758
A method is outlined whereby the orientation of upward pointing pyrano
meters on an aircraft is fully characterized. The incoming solar flux
is corrected by means of a method that incorporates the fact that the
flux is composed of partly diffuse and partly direct radiation. After
the angle correction is found, a practical method is outlined to find
the pyranometer normal with respect to the aircraft normal. It uses th
e heading of the aircraft and the position of the sun to adjust the py
ranometer to the aircraft horizontal level. While the method is genera
l enough to be used for any aircraft, it is applied here specifically
for the National Center for Atmospheric Research C-130 aircraft in the
configuration flown during the First Aerosol Characterization Experim
ent (ACE 1). It was found that when the difference between the sun azi
muth angle and the aircraft heading is near either 0 degrees or 180 de
grees, special care has to be taken in interpreting the incoming flux,
as it is enhanced by a few percent due to reflections off elements of
the aircraft frame.