about 0.01 to 0.1 m
-1 in open oceans, and about an order of magnitude greater in coastal
waters (Kirk, 1994). At these levels, the effect of CDOM on chl a estimation should be
greatly reduced.
Figure 22. CDOM absorption values (m
-1 ) at 440 nm versus salinity for stations along the mixing
zone and offshore plume of the St. Marys River on the Georgia/Florida border. Note the nearly
conservative mixing during dilution in 1997, and non-conservative mixing in 1998 and 1999 at
highly reduced flow conditions. Measurements of surface waters were taken each year in early
summer (late June or early July). River flows (m
3 /sec) are for a U.S. Geological Survey gauging
station just above the estuarine mixing zone and the values represent averages of the daily values
for the months of May and June in each year.
8. OACs and Reflectance Spectra Along Longitudinal Transects
Several examples from my research in Southeastern U.S. estuaries and near-shore
waters illustrate the interactions of OACs and the composite impact of longitudinal
gradients on water reflectance (Figures 23, 24). Sapelo Sound, at the north end of
Blackbeard and Sapelo Islands, Georgia, receives only localized drainage. Sapelo
Sound is relatively saline, has low levels of CDOM, and has less physical-chemical
variation than the neighboring estuarine complex to the south, which is impacted by
variability in flows of the Altamaha River. A transect from the Sound to adjacent near
shore waters was made in July, 2000 aboard the R.V. Spartina (University of Georgia
Marine Institute, Sapelo Island, Georgia). Salinity on the transect's six stations,
beginning in mid-Sound, increased from about 30.9 to 35.3 ppt (Figure 23). Both
chlorophyll and seston decreased by an order of magnitude (from 19.4 to 1.2 µg/l and
21.1 to 1.0 mg/l respectively). However, the percent of organic matter in the seston
increased about 3 fold, from 26.7 to 74.2%. Secchi disk transparency increased from 0.78
to 5.30 m, while CDOM ABS 440 values declined about two fold, from 0.43 to 0.20 m
-1
57
Optical Remote Sensing Techniques
-1 in open oceans, and about an order of magnitude greater in coastal
waters (Kirk, 1994). At these levels, the effect of CDOM on chl a estimation should be
greatly reduced.
Figure 22. CDOM absorption values (m
-1 ) at 440 nm versus salinity for stations along the mixing
zone and offshore plume of the St. Marys River on the Georgia/Florida border. Note the nearly
conservative mixing during dilution in 1997, and non-conservative mixing in 1998 and 1999 at
highly reduced flow conditions. Measurements of surface waters were taken each year in early
summer (late June or early July). River flows (m
3 /sec) are for a U.S. Geological Survey gauging
station just above the estuarine mixing zone and the values represent averages of the daily values
for the months of May and June in each year.
8. OACs and Reflectance Spectra Along Longitudinal Transects
Several examples from my research in Southeastern U.S. estuaries and near-shore
waters illustrate the interactions of OACs and the composite impact of longitudinal
gradients on water reflectance (Figures 23, 24). Sapelo Sound, at the north end of
Blackbeard and Sapelo Islands, Georgia, receives only localized drainage. Sapelo
Sound is relatively saline, has low levels of CDOM, and has less physical-chemical
variation than the neighboring estuarine complex to the south, which is impacted by
variability in flows of the Altamaha River. A transect from the Sound to adjacent near
shore waters was made in July, 2000 aboard the R.V. Spartina (University of Georgia
Marine Institute, Sapelo Island, Georgia). Salinity on the transect's six stations,
beginning in mid-Sound, increased from about 30.9 to 35.3 ppt (Figure 23). Both
chlorophyll and seston decreased by an order of magnitude (from 19.4 to 1.2 µg/l and
21.1 to 1.0 mg/l respectively). However, the percent of organic matter in the seston
increased about 3 fold, from 26.7 to 74.2%. Secchi disk transparency increased from 0.78
to 5.30 m, while CDOM ABS 440 values declined about two fold, from 0.43 to 0.20 m
-1
57
Optical Remote Sensing Techniques