Satellite Observation and Model Simulation of Water Turbidity in the Chesapeake Bay

1
Satellite Observation and Model Simulation of
Water Turbidity in the Chesapeake Bay
Xiaoming Liu1, Menghua Wang 2 (PRINCIPAL
GOVERNMENT INVESTIGATOR), and Wei Shi3 1SPS,
2NOAA/NESDIS/STAR, 3Colorado State University/CIRA
The 2002-2008 multi-year averaged Kd(490)
data for January, April, July and October derived
from MODIS-Aqua show a detail spatial
distribution pattern of the turbidity in the
Chesapeake Bay. Generally, the region in the
upper Chesapeake Bay is the most turbid with
Kd(490) 2-3 m-1, and the water gradually becomes
less turbid down to the middle and lower Bay
regions. This spatial distribution patter is
found in all the four seasons. The data also show
a clear seasonal variability of the turbidity in
the Chesapeake Bay the water is the most turbid
in January, the turbidity gradually decreases in
April, and reaches its minimum in July, and then
gradually increases in October.
Requirement Use MODIS-Aqua ocean color products
to study the variations of sediment
concentrations in the Chesapeake Bay (CB), which
supports NOAAs 5-year Research Plans ECOSYSTEMS
MISSION GOAL PROTECT, RESTORE, AND MANAGE USE OF
COASTAL AND OCEAN RESOURCES THROUGH ECOSYSTEM
APPROACHES TO MANAGEMENT. Science How the
sediment concentrations vary seasonally and
spatially in the CB, and what are mechanisms for
these variations? Benefit Excess sediment is one
of the most important contributors to degraded
water quality and has adverse effects on critical
habitats and living resources in CB. A better
understanding of the variations of the sediment
concentrations and their mechanisms helps to
predict and improve the water quality in the
Chesapeake Bay.
Normalized Water-Leaving Reflectance Spectra
Chesapeake Bay Kd(490)
January
April
July
October
The upper Chesapeake Bay region is also featured
with enhanced water-leaving reflectance in the
green and red bands between 555 and 645 nm.
Reflecting the seasonal Kd(490) variation,
highest reflectance at 645 nm occurs in the
winter with value over 6 and the lowest during
the summer with value less than 3.
a)
b)
c)
d)
January
Satellite Observations The Shortwave
Infrared (SWIR)-based atmospheric correction
algorithm (Wang and Shi, 2005, 2007 Wang, 2007)
has been developed for deriving MODIS-Aqua ocean
color products, and it has been demonstrated that
the SWIR-based data processing produces better
quality ocean color products over the turbid
coastal waters such as CB (Wang et al. 2009).
April
October
July
0
3.0 m-1
1.5
2002-2008 Multi-Year Average
Location of (39.29N, 76.32W)
Model Simulations Regional Ocean Modeling
Systems (ROMS) implementation in the CB region by
the ChesROMS community is used in this study, and
the built-in sediment model (Waner et al. 2008)
is used to simulate sediment processes which
represents separate cohesive and non-cohesive
categories. Sensitivities of the sediment
concentrations to the tidal and wind forcing,
sediment settling speed, wind induced waves, are
tested to investigate the mechanisms of the
seasonal and spatial variations of sediment
concentrations in the Chesapeake Bay.
Comparisons of MODIS Ocean Color Products from
NIR, SWIR, and NIR-SWIR Combined Methods
Chlorophyll-a0.01-10 (mg/m3)(Log scale)
Standard Data Processing
July, 2005
Wang, M. and W. Shi (2007), The NIR-SWIR
combined atmospheric correction approach for
MODIS ocean color data processing, Optics
Express, 15, 15722-15733.
Wang, M., S. Son, and W. Shi (2009), Evaluation
of MODIS SWIR and NIR-SWIR atmospheric correction
algorithms using SeaBASS data, Remote Sens.
Environ., 113, 635-644.
Tidal Current vs. Wind
Seasonal Forcing vs. Sediment Settling Speed
Wind and Tide
Tide
Wind
Winter, 0.01 mm/s
Summer, 0.01 mm/s
Summer, 0.1 mm/s
NIR-SWIR Data Processing
July, 2005
Satellite derived diffuse attenuation
coefficient at the wavelength 490 nm (Kd(490))
can be used to relate water turbidity. Wang et
al. (2009) developed a new algorithm for the
Kd(490) derived from MODIS-Aqua for turbid water,
and it has been applied and evaluated for the
Chesapeake Bay.
Kd(PAR) Matchup Comparisons for the Chesapeake Bay
New Kd(490) for U.S. East Coastal Region
NASA Standard Data Processing
Science Challenges The satellite measurement of
Kd(490) from MODIS-Aqua shows a significant
seasonal turbidity variation in the Chesapeake
Bay. Kd(490) has its maximum in winter, and
gradually decreases from spring to summer. Wind
speed and direction, vertical mixing, wave, river
runoff and sediment particle size are all
possible factors that make the sediment
concentrations vary seasonally. Next Step The
high-frequency (3-hourly) wind forcing with the
wind-wave enabled is being further investigated
for the effect on the seasonal sediment
concentration variations.
New Algorithm
New Algorithm
Wang, M., S. Son, and L. W. Harding Jr.,
Retrieval of diffuse attenuation coefficient in
the Chesapeake Bay and turbid ocean regions for
satellite ocean color applications, J. Geophys.
Res. (2009).