Particle-associated backscatter in chesapeake bay: hurricane isabel, before and after

Abstract

Hurricane Isabel made landfall near Drum Inlet, North Carolina, on September 18, 2003, then proceeded on a north-northwesterly [westerly or easterly?] track up the mid-Atlantic seaboard. Among the storm’s major impacts was a great deal of sediment mobilization in the estuarine, barrier island, shoreface and shelf environments of North Carolina and the Delmarva region. This effect can be clearly seen in satellite imagery of the area in the wake of Isabel.

Preliminary estimates of particle-associated backscatter, b_bp, in the Chesapeake Bay region before and after Isabel’s passage have been derived from radiance values obtained by the SeaWiFS ocean-color satellite. Preceding Isabel (Sept. 16), apparent b_bp values are generally lowest [value range?] near the western shore of the bay, increasing eastward to maximum values near the Pocomoke. In the first post-storm image (Sept. 19), b_bp values have markedly increased bay-wide [value range?], indicating that bay waters are particle-laden. Over the subsequent week (by Sept. 24), as suspended solids sink out of the water column, b_bp conditions return approximately to their pre-storm state. These results are consistent with field observations of a temporary, subtstantial decrease in water clarity associated with storm surge and wave effects. A persistent low-b_bp feature near the mouth of the Potomac River is also evident in the derived maps. Yet the ecological impact of the episodic events, such as Hurricane Isabel, remains to be studied.

Hurricane Isabel
On September 18, 2003, 13:00 EDT, Hurricane Isabel made landfall near Drum Inlet, NC (Fig. 1), as a category 2 storm with sustained winds of approximately 85 knots (National Climatic Data Center, 2003). The effects of the hurricane were felt along much of the eastern seaboard, from eastern North Carolina to western Pennsylvania. For Chesapeake Bay residents, the most visible immediate effects included significant flooding (Fig. 2) associated with a record-high storm surge (Fig. 3).
[Insert Figure 1 ~ here] http://rapidfire.sci.gsfc.nasa.gov/gallery/?2003261-0918/Isabel.A2003261.1555.2km.jpg
[Insert Figure 2 ~ here]

[http://mddnr.chesapeakebay.net/eyesonthebay/isabel_impacts.html , Fig. 2]

[Insert Figure 3 ~ here] http://www.usna.edu/PAO/isabel/images/HillBridgeWestEnd.jpg

Multi-platform Estuarine Monitoring

An optimal approach to estuarine characterization and monitoring combines automated, real-time in situ sensing with spatial wide-field-of-view/synoptic sensing. Information about Chesapeake Bay water quality and Isabel storm effects is available from a variety of sources, including:

• 
  Long-term monitoring stations along the mainstem of the bay and in many tributaries (Fig. 4); sampling frequency ~ once per month + special-event cruises
  
• 
  Continous monitoring stations in selected bay tributaries (e.g., Fig. 2); sampling frequency ~ once every 15 mins.
  
• 
  Ocean-color satellites (e.g., SeaWiFS, MODIS); sampling frequency ~ once per day if cloud-free
  
• 
  Spatially intensive sampling in selected bay tributaries
  
• 
  Occasional field reports from selected site visits (e.g., SAV study sites)
  

[Insert Figure 4 ~ here]

[This figure can be deleted if necessary due to space constraints.]

The View from SeaWiFS

In ocean-color satellite (SeaWiFS) imagery of the Cheapeake Bay region, one of the most noticablenoticeable Isabel impacts was the suspension of marine sediments in the coastal estuaries and on the adjacent shelf (Fig. 5).

[Insert Figure 5 ~ here]

http://daac.gsfc.nasa.gov/www/gallery/isabel/seawifs/

turbidity.jpg

[This figure should be large.]
The source of the shelf sediments is believed to be local (as opposed to terrestrial, as was observed in the wake of Hurricane Floyd, 1999). Within Chesapeake Bay, some sediment arrived via rivers, where turbidity spikes were observed in association with the storm’s passage (e.g., Fig. 6). Some of the sediment is due to resuspension from the bottom, while most of the sediment delivery to the bay seems to have come from shoreline erosion (Fig. 7) due to the combined effects of wave action and storm surge.
[Insert Figure 6 ~ here]

[http://mddnr.chesapeakebay.net/eyesonthebay/isabel_impacts.html, Figure 4]

[Insert Figure 7 ~ here]

http://www.nps.gov/hurricane/photos/gewa1.jpg

Water-quality Measurements from Space? A Preliminary View

Based on radiative transfer modeling and fieldwork in Tampa Bay, Florida, Lee et al. (1999) developed an algorithm to derive a number of water-quality parameters from satellite-derived measurements of water-leaving radiance (Figs. 8 and 9).

[Insert Figure 8 ~ here]

fig2reflectance_rev.tif

[Insert Figure 9 ~ here]

modelfFlowChart_SeaWiFS.ppt

Hu et al. (20021) adapted this algorithm for application to coastal satellite imagery, and their method was applied to SeaWiFS data available for the Chesapeake Bay region immediately preceding and in the wake of Hurricane Isabel. Estimates of particle-associated backscatter at 400 nm, b_bp, are shown in Fig. 10. These data should be considered preliminary, offering a qualitative first look at general patterns.
Preceding Isabel (Sept. 16), apparent b_bp values are generally lowest near the western shore (e.g., near the mouth of the Potomac River), increasing eastward to maximum values near the Pocomoke (Fig. 10A).
In the first post-storm image sufficiently free of cloud cover (Sept. 19), SeaWiFS-derived b_bp values have markedly increased bay-wide, indicating that bay waters are particle-laden (Fig. 10B). Lowest values are again observed near the mouth of the Potomac. Elevated b_bp values are also observed on the shelf and within the “jet” seen in the true-color image (Fig. 5).
Over the subsequent week (by Sept. 24), as suspended solids sink out of the water column, b_bp conditions return approximately to their pre-storm state. As before, lowest b_bp values are observed near the Potomac River, and highest values are observed near the Pocomoke. Relative to pre-storm conditions, backscattering remains slightly elevated in the mainstem area off Mobjack Bay.
Over the subsequent days (Sept. 26 and Sept. 27), changs are small relative to those observed immediately post-storm (Figs. 10D and 10E). Although an increase in particle backscatter is observed near the mouth of the Potomac, the general pattern is one of continued general clearing.
[Insert Figure 10 ~ here]

http://imars.marine.usf.edu/~hu/river/cbay/imgs/Isabel

(A) S200325917_map_cbay_opt_bbp400.png

(B) S200326217_map_cbay_opt_bbp400.png

(C) S200326717_map_cbay_opt_bbp400.png

(D) S200326917_map_cbay_opt_bbp400.png

(E)S200327018_map_cbay_opt_bbp400.png
color bar: http://imars.marine.usf.edu/~hu/river/cbay/imgs/month/colorbars/bbp_colorbar.png]
[These figures are the point of the poster – should be large.]

[Figs. 10D and 10E can be eliminated if need be.]

These results are consistent with field observations of a temporary, substantial decrease in water clarity in tidal portions of the estuary during and immediately after the storm. These effects are attributed to sediment resuspension and shoreline erosion associated with storm surge and wave effects (Maryland Department of Natural Resources, 2003).

Acknowledgements
This work was funded primarily by the U.S. Geological Survey (USGS) Coastal and Marine Geology Program’s portion of the Atlantic Estuaries Project, in association with the USGS Chesapeake Bay Science Program. Additional support was provided by the USGS Mendenhall Postdoctoral Fellowship Program and the National Aeronautics and Space Administration (NASA grant # NAG5-10738). SeaWiFS data acquisition and processing were made possible by the SeaWiFS Project at NASA Goddard Space Flight Center and ORBIMAGE. Laurinda Frye (USGS) was our valued partner in poster production.
References
Hu, C., Z.P. Lee, F. E. Muller-Karger, and K. L. Carder (2002). Application of an optimization algorithm to satellite ocean color imagery: A case study in Southwest Florida coastal waters. SPIE proceedings 4892 (Ocean Remote Sensing and Applications, edited by R. J. Frouin, Y. Yuan, and H. Kawamura), pp 70-79. (http://imars.marine.usf.edu/~hu/papers/SPIE/)Hu, C. et al. (2001) Application of an optimization algorithm to satellite ocean color imagery: a case study of southwest Florida waters. SPIE.
Lee, Z., K. Carder, C. Mobley, R. Steward, and J. Patch (1999) Hyperspectral remote sensing for shallow water: 2. Deriving bottom depths and water properties by optimization. Applied Optics 38(18): 3831-3843.
Maryland Department of Natural Resources (2003) Hurricane Impacts on the Chesapeake Bay. http://www.dnr..state.md.us/bay
National Climatic Data Center (2003) Climate of 2003: Atlantic Hurricane Season. http://www.ncdc.noaa.gov/oa/climate/research/2003/hurricanes03.html

Figure 1. Hurricane Isabel landfall, September 18, 2003. This image is from the Moderate Resolution Imaging Spectrometer (MODIS) sensor ~700 km above the Earth’s surface. Image courtesy of NASA MODIS Program.
Figure 2. Preliminary water level data, Annapolis, MD, 15 - 22 September 2003. Data courtesy of NOAA National Ocean Service CO-OP.
Figure 3. Chesapeake Bay flooding, courtesy of Hurricane Isabel’s record-high storm surge. U.S. Naval Academy, Annapolis , MD. Photo courtesy of U.S. Naval Academy, Public Affairs Office.
Figure 4. Chesapeake Bay Program water quality monitoring stations. Map courtesy of the Chesapeake Bay Program.
Figure 5. The left image, acquired by SeaWiFS on September 2, 2003, shows the relatively clear waters characteristic of normal (calm) conditions. The right image, acquired on September 19, one day after Isabel landfall, indicates a large area of suspended marine sediments. Some of these sediments have been captured and transported northeastward by the Gulf Stream, a strong ocean current. Images provided courtesy of the NASA SeaWiFS Project and ORBIMAGE.
Figure 6. In the few places where continuous monitoring stations are established, spikes in turbidity were typically observed in association with Hurricane Isabel’s passage. These data are from Stonington on the Magothy River. Typical “background” levels for this station during the year 2003 are ~ 10 NTU. Data courtesy of the Maryland Department of Natural Resources.
Figure 7. At the George Washington Birthplace National Monument, the shoreline receded approximately 50 feet overnight (the equivalent of 15-20 years of erosion in preceding years). Image courtesy of the National Park Service.

Figure 8. Total radiance measured at the satellite sensor, L_T, includes not only contributions from the water column and the benthos – targets of primary interest in Chesapeake Bay – but also from the atmosphere. An area of active research is the development to algorithms to remove this atmospheric “contamination.”

Figure 9. Schematic representation of the multiparameter optimization scheme of Lee et al. (1999) and Hu et al. (2001). Inputs to the model include satellite-derived estimates of water-leaving radiance plus a number of model assumptions. Output parameters include total absorption at 440 nm, a(440); particle-associated backscatter, a_p(440); gelbstoff-associated absorption, a_g(440); and particle backscatter, b_bp(400).

Figure 10. Particle-associated backscatter (b_bp) as preliminarily derived from data collected by the Sea-viewing Wide Field-of-View (SeaWiFS) sensor orbiting ~700 km above the Earth’s surface: (A) two days before Hurricane Isabel landfall, (B) one day after landfall, and (C) six days after landfall

Logos:
USGS

University of South Florida

Directory: ~hu -> scratch
~hu -> Rendering aesthetic impressions of text in color space
~hu -> English: The Lightest Weight Programming Language of them all
~hu -> Its sources remain unclear because it has insufficient
~hu -> Biographical Sketch Clenora Hudson-Weems
~hu -> Clenora Hudson-Weems
scratch -> Global Particulate Organic Carbon Flux to the Ocean Floor: The Importance Of Continental Margins
~hu -> Ph. D. General Examinations General Area Exam (Prof. Pattie Maes, Examiner) Xinyu Hugo Liu

Download 22.42 Kb.

Share with your friends: