Satellite remote sensing allows rapid and synoptic assessment of the South Florida marine
environment
Chuanmin Hu, University of South Florida
Compared with other means to collect oceanographic data, remote sensing from operational
satellite instruments such as AVHRR (Advanced Very High Resolution Radiometer), SeaWiFS
(Sea-viewing Wide Field-of-view Sensor), and MODIS (Moderate Resolution Imaging
Spectroradiomter) provides rapid, frequent (daily), and synoptic measurements of the surface
ocean properties in near real-time (within one or two hours of the satellite overpass). These
properties include Sea Surface Temperature (SST) and ocean color (precisely, reflected solar
light in many wavelengths between 400 and 900 nanometers) as well as other properties,
including water clarity and turbidity, algae abundance (through chlorophyll-a concentration), and
other suspended and dissolved materials. Although in some areas these remote measurements
may not be as accurate as the direct shipboard measurements, because of the wide coverage and
near real-time data availability, they provide critical and timely information to study water
quality events, monitor pollutions, help guide ship surveys, reveal connectivity between different
ecosystems, as well as to assess the long-term coastal environmental changes to help
management. Indeed, satellite remote sensing is an indispensable component in any ocean
observing systems (OOS) around the world. A few examples are shown here to illustrate how
satellite remote sensing can be used to study and monitor the South Florida coastal ecosystems.
10/19/2003
MODIS/Aqua
1/30/2002
MODIS/Terra
Fig. 1. Enhanced Red-Green-Blue MODIS images showing two examples of how different South
Florida ecosystems are connected. The darkish colors resulted from light absorption by high
concentrations of algae and/or dissolved materials in water. The dark plume on 10/19/2003 (left)
is due to significant rainfall that led to higher-than-normal river discharge from the
Caloosahatchee River and Peace River into Charlotte Harbor. The “black water” patch on
1/30/2002 (right) is a result of earlier red tides in the north and runoff from the everglades rivers.
The timely detection of the “black water” event helped coordinate ship surveys, which found
toxic and non-toxic algae in the waters. Following this event, significant benthic decline (dieoffs
of sponges and corals) occurred in the lower Keys.
(a)
Channel 5
(b)
Long Key
Channel
7-mile Bridge
Channel
Florida Shelf water
(c)
(d)
Eddies
Mississippi River water
Mississippi River water
Fig. 2. MODIS images showing how Florida Keys National Marine Sanctuary is affected by various waters. The images are
color coded to show the algae abundance (through chlorophyll-a concentrations in milligrams per cubic meter). For Florida
Bay and other shallow waters the value may be off by a factor of 2, but the emphasis here is on the spatial patterns. (a)
MODIS image on 11/23/2005 showing the Florida Bay water intrusion through the channels to FKNMS; (b) MODIS image
on 2/12/2003 showing waters from the Florida Shelf entering the FKNMS; (c) Mississippi River water in the Florida Strait
on 8/1/2004. Note the 20-km eddies near the FKNMS; (d) Mississippi River water diluted and reached the FKNMS on
8/8/2004. It was estimated that ~23% of the entire Mississippi discharge between July and September 2004 entered the
Florida Straits, equivalent to 4 times of the entire Lake Okeechobee.
Toxic Algae Bloom
(Red Tide)
Fig. 3. Two examples to show how satellite imagery are used to monitor the environmental health
of the SW Florida ecosystems. Left: MODIS image on 11/13/2004 shows a red tide patch. The
property color coded here is the solar-stimulated fluorescence (“glow” of algae under sun light).
Red color shows high concentrations. Right: Sea surface temperature anomaly for September
2005. FKNMS and Florida Bay are 1oC warmer than usual for more than two months. Some
degree of coral bleaching occurred at several reef sites in the Keys.
Further ReadingCharlotte
Harbor
Charlotte
Harbor
Hu, C., K. E. Hackett, M. K. Callahan, S. Andréfouët, J. L. Wheaton, J. W. Porter, F. E. MullerKarger (2003). The 2002 ocean color anomaly in the Florida Bight : a cause of local coral reef
decline? Geophys. Res. Lett. 30(3), 1151, doi:10.1029/2002GL016479.
Hu, C., F. E. Muller-Kager, G. A. Vargo, M. B. Neely, and E. Johns (2004). Linkages between
coastal runoff and the Florida Keys ecosystem: A study of a dark plume event. Geophys. Res.
Lett. 31, L15307, doi:10.1029/2004GL020382.
Hu, C., J. Nelson, E. Johns, Z. Chen, R. Weisberg, and F. E. Muller-Karger (2005). Mississippi
River water in the Florida Straits and in the Gulf Stream off Georgia in summer 2004. Geophys.
Res. Lett., 32, L14606, doi:10.1029/2005GL022942.
Hu, C., F. E. Muller-Karger, C. Taylor, K. L. Carder, C. Kelble, E. Johns, and C. Heil (2005).
Red tide detection and tracing using MODIS fluorescence data: A regional example in SW
Florida coastal waters. Remote Sens. Environ., 97:311-321.
Hu, C., et al. (in press). Building an automated integrated observing system to detect sea surface
temperature anomaly events in the Florida Keys. IEEE Transactions of Geoscience and Remote
Sensing.
Sponaugle, S., T. N. Lee, V. Kourafalou, and D. Pinkard (2005). Florida Current frontal eddies
and the settlement of coral reef fishes. Limnology & Oceanography, 50(4):1033-1048.
Lee, T. N., and N. Smith (2002). Volume transport variability through the Florida Keys tidal
channels. Continental Shelf Research, 22:1361-1377.
http://imars.usf.edu