Starting on 05/08/2010 values of short_direct_normal from the NIP instrument were reading
low (up to 50W/m2). This was most apparent during sunny/partly sunny periods. The
values spontaneously returned to normal on 5/14 with no Ops intervention. Data system checks
after that date revealed no apparent problems with instruments or datalogger. The problem
has not recurred.
Only the short_direct_normal values during this time period are suspect. If direct normal
values are needed they can be re-constructed using the following relationship for each
minute of data:
down_short_hemisp = short_direct_normal * cos(zenith angle) + down_short_diffuse_hemisp |