| Description: | As before, there is good agreement between the two up-looking
PIRs. However, there has been an unusual change in the relationship
between the two instruments. Prior to the RESET visit at the end of
August, the two instruments agreed to within 1 W/m^2 at night and
on sunny days, the unshaded radiometer reported higher values during
the day. The difference between the two instruments exhibited a
cosine-like diurnal curve peaking at about 5 W/m^2 near solar noon.
On 970830, the data logger was reconfigured and since that time,
the behavior has been different. Now, there is a 5-10 W/m^2
difference between the two radiometers with the *shaded* instrument
reading higher than the unshaded during the day. At night, the two
still agree within about 1 W/m^2. There is still a cosine-like
diurnal dependance to the instrument discrepancy during the day - with
the offset, this actually results in closer agreement between the two
radiometers near solar noon than in the morning or afternoon.
Note: the unshaded PIR is incorrectly named "shaded2" during this
time period. This is covered in a separate DQR. |