The Advanced Very High Resolution Radiometer (AVHRR) on NOAA
meteorological satellites has been used in this study. Currently, over
600 usable scenes are available from some 1500 covering a period from
December 1989 to the present. AVHRR has a pixel size of about 1.1 km.
The data sets are processed for water reflectance, which is related to
water turbidity variables such as attenuation, Secchi depths, total
particulate matter, and nephelometric turbidity. Tentative
relationships with these variables have been made. (Sea surface
temperature is also determined.) High reflectance corresponds to high
attenuation or particulate loads or shallow Secchi depth. The
individual scenes are also processed to obtain monthly and seasonal
means, with winter corresponding to the period of December to March
and summer to June through September. Initial analyses include the
points corresponding to fixed stations occupied at a monthly interval
by FIU or FDEP.
In examining the average reflectance of the entire Bay, the satellite
imagery does not show a trend between December 1989 and September
1996. The seasonal pattern of high turbidity in winter and low in
summer is evident. Trends over the time period appear in subsections
of the Bay. A substantial increase in water reflectance is evident in
the north-central Bay (which has been documented in field studies),
this region includes Rankin Lake and Johnson Key. However these appear
to have different phasing, with Johnson Key showing an increase in
turbidity about two years earlier than Rankin Lake. Both sites show
the decline in both winter and summer. Twin Key, which has the
clearest water in the Bay, has shown a slight increase. The
southwest portion of the Bay, west of Sprigger Bank, has shown a
decrease in reflectance, indicating clearer water.