Table A1. Cloud cover categories.
Category
Cloud cover, C
Clear
0
Scattered
0.33
Broken
0.67
Overcast
1
Obscured
1
Partially obscured
1
Missing
--
estimates based on the cloud cover reported at the Lebanon Regional Airport, in
West Lebanon, New Hampshire. These two locations are separated by a distance of
about 6 miles. The results of the comparison are shown in Figure A1. In Figure A1
we plot the total daily solar radiation and the accumulated solar radiation. The
accumulated solar radiation is a summation of the daily radiation to date. The ac-
cumulated solar radiation is set to zero on the day the leaves were put on the ice.
The discrepancy between the two sites is generally less 25%. The largest discrep-
ancies occur on thickly overcast days where the estimates overpredict the incom-
ing radiation by a factor of 2 to 5. However, looking at the accumulated solar radia-
tion, we found that on average the errors in the estimate seem to cancel each other
out over the long term. As a result we see that both the measured and estimated
values agree very well.
60
1994
40
Hanover
Test Cell
20
Lebanon
Airport
0
6
Hanover
Test Cell
4
Lebanon
Airport
2
0
1 Mar
6
11
16
21
26
31
Figure A1. Comparison of solar radiation measurements taken at the Hanover
test cell located at CRREL and the estimated solar radiation based on cloud
cover data at Lebanon Regional Airport, Lebanon, New Hampshire.
17
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