LEGEND 
© MONTHLY MEAN VALUE 
VIS(BILiTY (M} 
Figure 32. Daily surface water visibility 
for 1982 
above. Between April and August the visibility occasionally was greater than 
5 m, but it was generally less than 4 m. During October to December, the 
visibility was less than 2 m 90 percent of the time. The annual mean 
visibility was 2.4 m with a 1.0-m standard deviation (Table 15). Figure 33 
presents the cumulative distribution of visibility measurements for the year 
and indicates a median visibility of only 1.5 m. 
110. 1982 versus previous years. The variability of the 1982 daily sea 
water visibility measurements was similar to that in previous years. With the 
exception of July and August, monthly mean visibility values were also similar 
(Figure 34). The 1982 annual mean was higher than the 1980 and 1981 combined 
value, primarily due to the exceptionally high visibility during July and 
August. Figure 33 shows the distribution of daily measurements was higher in 
1982 in comparison to previous years. 
111. All years combined. At the FRF, over 50 percent of the time the 
visibility at the surface can be expected to be less than 2m. Annual and 
seasonal visibility variations have been consistent from year to year. The 
addition of a third year of data did not change the annual distribution 
significantly. 
69 
