Remote Detection of Eutrophic Events: MODIS and SeaWiFS

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Remote Detection of Eutrophic EventsMODIS and
SeaWiFS

• Joshua Moody jmoody18_at_eden.rutgers.edu Graduate
  Program in Ecology Evolution Haskin Shellfish
  Research Laboratory Rutgers, the State
  University of New Jersey 6959 Miller Ave, Port
  Norris NJ 08349
• [phone] x4319

Large Algal Bloom in the Gulf of Mexico 6/2009
http//water-is-life.blogspot.com/2009/06/large-de
ad-zone-predicted-for-gulf-of.html
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What is Eutrophication

• Process whereby water bodies receive excess
  nutrients that stimulate excessive plant growth
  (algae, periphyton attached algae, and nuisance
  plants weeds).
• Nutrients can come from many sources
• Fertilizers
• Nitrogen from the atmosphere
• Erosion of soils containing nutrients
• Sewage treatment plant discharges.
• Why we care Subsequent decomposition of plant
  material reduces dissolved oxygen in the water
• Source USGS, http//toxics.usgs.gov/definitions/e
  utrophication.html

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Extent of Continuous Eutrophic Conditions US
Estuaries

• High expressions of eutrophic conditions (US)
• 44 estuaries
• 40 of the national estuarine surface area
• Moderate expressions of eutrophic conditions (US)
  
• 40 estuaries
• When considered together
• 65 of the nation's estuarine surface area (NOAA
  get full citation from laptop)

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Indicators of Eutrophic Conditions

• Primary
• elevated levels of chlorophyll a
• Secondary
• depleted dissolved oxygen

MODIS Chlorophyll image from Indian Sub-continent
http//visibleearth.nasa.gov/view_rec.php?id64
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Detection of Chlorophyl a

• Visual
• Algal blooms
• Green water
• May be hard to detect visually
• Chemical
• In situ N and P levels
• Remote
• Reflectance 500-600nm and 700nm-3.5um
• Absorption 400-500nm and 600-700nm

The absorption maxima of chlorophyll a are
lambda 430 and lambda 662 nm, that of
chlorophyll b are at 453 and 642
nm. http//www.biologie.uni-hamburg.de/b-online/e2
4/3.htm
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Sensors

• MODIS MODerate-resolution Imaging
  Spectroradiometer
• SeaWiFS Sea-viewing Wide Field-of-view Sensor

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MODIS

• Aboard Terra and Aqua Satellites
• Viewing the entire Earth's surface every 1 to 2
  days
• 36 spectral bands
• Orbit 705 km, 1030 a.m. descending node (Terra)
  or 130 p.m. ascending node (Aqua),
  sun-synchronous, near-polar, circular
• Swath 2330 km (cross track) by 10 km (along
  track at nadir)
• Bands 1 (620nm 670nm), 3 (459nm 479nm) 4
  (545nm 565nm) commonly used
• Bands 8 (405nm-420nm) to 16 (862nm 877nm)
  primary use is for Ocean Color/Phytoplankton/
• Biogeochemistry
• Spatial Resolution 250 m (bands 1-2)500 m
  (bands 3-7)1000 m (bands 8-36)
• http//modis.gsfc.nasa.gov/index.php

http//earthobservatory.nasa.gov/Library/ESE/ese_2
.html
http//www.nasa.gov/centers/goddard/news/topstory/
2003/0122japansnow.html
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MODIS Two-Wavelength Empirical Algorithm

• (De Cauwer et al., 2004)

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Aqua/MODIS - Phytoplankton Bloom in the Black
Sea Bands 1,4,3 June 27, 2006
http//visibleearth.nasa.gov/view_rec.php?id20903
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SeaWiFS

• Aboard GeoEye's OrbView-2 (SeaStar) satellite, an
  industry/government partnership with NASA's Ocean
  Biology Processing Group at Goddard Space Flight
  Center
• Utilizes 8 spectral bands with narrow wavelength
  ranges from 402nm to 885nm
• Orbit 705 km circular sun-synchronous
• Orbital Period 99 minutes
• Swath Between 1,502km 2,800km depending on
  datafile storage (LAC/GAC)
• Spatial Resolution 1.1Km LAC 4.5 Km GAC
• Specifically designed to monitor ocean
  characteristics such as chlorophyll-a
  concentration and water clarity
• Band 1 centered at 412nm specifically to identify
  yellow substances through increased blue
  wavelength adsorption
• Band 3 centered at 490nm to increase sensitivity
  to chlorophyll concentrations
• Band 7 (765nm) and Band 8 (865nm) in NIR are to
  specifically remove atmospheric attenuation-
  aerosols adsorb linearly in NIR
• Able to tilt up to 20 degrees to avoid sunlight
  from the sea surface- important at equatorial
  latitudes where glint from sunlight often
  obscures water color
• http//oceancolor.gsfc.nasa.gov/SeaWiFS/

http//www.orbital.com/SatellitesSpace/ImagingDefe
nse/OV2/index.shtml
http//deepseanews.com/2007/09/
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SeaWiFS Ocean Chlorophyll 4 Maximum Band Ratio
Algorithm
(De Cauwer et al., 2004)
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SEaWiFS natural color and a chlorophyll a map of
the southern Atlantic Ocean of the Brazilian and
Uruguayan coasts 12-06-04
http//www.fas.org/irp/imint/docs/rst/Sect14/Sect1
4_13.html
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How are the Events Detected?

• Bio-optical reflectance and adsorption properties
  of organisms containing chlorophyll are known
• Surface, and just below surface, concentrations
  of chlorophyll a are determined by the radiance
  received by the sensor
• But satellite detection of chlorophyll
  concentrations suffer from uncertainties in the
  atmospheric correction and interference of other
  colored compounds. (Hu, 2005)

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Atmospheric Correction

• Retrieve water-leaving radiance
• Calculate atmospheric effects at 750nm and 865 nm
  (NIR) where water-leaving radiance is minimal.
• Extrapolate to visible wavelengths where
  chlorophyll a absorption is taking place
• Input desired wavebands, extraterrestrial
  irradiance, wind speed, Rayleigh scatter, and
  aerosol/ozone concentration.
• Output is normalized water leaving radiances at
  the 415-681 nm ocean wavebands

http//oceancolor.gsfc.nasa.gov/VALIDATION/atm.htm
l
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Problem Detecting Algal Blooms in Coastal Waters

• Coastal waters can be the hosts of algal blooms-
  including harmful varieties (HABs)
• The color of the ocean, i.e., the spectral
  water-leaving
• radiance, is the combined result of the
  properties of various colored constituents in the
  surface ocean
• Water molecules
• Phytoplankton
• Detritus
• Colored dissolved organic matter
• Suspended sediments
• Bottom reflectance
• These factors become a greater issue in shallow
  water where they can accumulate near the surface.
• (Hu, 2005)

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Problem

• Coastal areas have specific regional bio-optic
  properties
• Algorithms (MODIS, MERIS and SeaWiFS) designed
  for use at a global scale-particularly for open
  ocean waters
• Higher amounts of suspended matter and yellow
  substances can make it impossible to detect the
  contribution of chlorophyll a absorption in the
  blue range

(De Cauwer et al., 2004)
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Remote sensings contribution to evaluating
eutrophication in marine and coastal waters
Evaluation of SeaWIFS data from 1997 to 1999 in
the Skagerrak, Kattegat and North Sea (Sorensen
et al., 2002)

• Chlorophyll-a maps obtained from SeaWiFS
  satellite images overestimate in situ
  observations of chlorophyll-a.
• The use of a rescaling function for
  chlorophyll-a values, defined with in situ data
  taken at the same time as the satellite images,
  has significantly decreased the uncertainties in
  the chlorophyll-a maps, even though some coastal
  areas still highlight chlorophyll-a
  overestimates.

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Red tide
detection and tracing using MODIS fluorescence
data A regionalexample in SW Florida coastal
waters (Hu et al., 2005)

• MODIS sensors are equipped with several bands
  specifically designed to measure the fluorescence
  of phytoplankton
• MODIS Chl a was estimated using a band-ratio
  algorithm (of all bands used to determine Ocean
  color)
• MODIS FLH (Fluorescence Line Height) was
  estimated using a baseline subtraction algorithm
  of Bands 13 (667nm), 14 (678nm) and 15 (748nm) (A
  baseline is first formed between radiances for
  Bands 13 and 15, and then subtracted from Band 14
  radiance to obtain the FLH.
• MODIS FLH data showed the highest correlation
  with near-concurrent in situ chlorophyll-a
  concentration

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MODIS medium resolution bands and Turbidity Index

• Left Column MODIS bands 1, 4, and 3 can clearly
  identify the distribution of the algal bloom
• Right Column turbidity index, a
  semi-quantitative measure of the amount of
  particulate material in the near-surface water.
  Darker areas show higher turbidity
• While turbidity is not specific to algal blooms,
  it can be an estimate of the intensity of the
  bloom

(Kahru et al., 2004)
http//spg.ucsd.edu/Satellite_Projects/Various_HAB
s/Satellite_detection_of_HABs.htm
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The Future

• Higher resolution needed (as always)- for small
  scale blooms
• Greater differentiation between algae and yellow
  particulate material- refined algorithms

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Literature Cited

• http//toxics.usgs.gov/definitions/eutrophication.
  html
• http//modis.gsfc.nasa.gov/index.php
• http//envisat.esa.int/instruments/meris/
• http//oceancolor.gsfc.nasa.gov/VALIDATION/atm.htm
  l
• http//oceancolor.gsfc.nasa.gov/SeaWiFS/
• http//spg.ucsd.edu/Satellite_Projects/Various_HAB
  s/Satellite_detection_of_HABs.htm
• Carder, Kendall L. , F. Robert Chen, Zhongping
  Lee, Steve K. Hawes, and Jennifer P. Cannizzaro .
  2003. MODIS Ocean Science Team Algorithm
  Theoretical Basis Document ATBD 19 Case 2
  Chlorophyll a Version 7. College of Marine
  Science, University of South Florida.
• De Cauwer, Vera, Kevin Ruddick, YoungJe Park,
  Bouchra Nechad and Michael Kyramarios. 2004.
  Optical Remote Sensing in Support of
  Eutrophication Monitoring in the Southern North
  Sea. EARSeL eProceedings 3 208-222.
• Hu, Chuanmin, Frank E. Muller-Karger, Charles
  (Judd) Taylor, Kendall L. Carder, Christopher
  Kelble, Elizabeth Johns and Cynthia A. Heil.
  2005. Red tide detection and tracing using MODIS
  fluorescence data A regional example in
  Southwest Florida coastal waters. Remote Sensing
  of Environment 97 (2005) 311 321.
• Kahru, M., B.G. Mitchell, A. Diaz, M. Miura.
  MODIS Detects a Devastating Algal Bloom in
  Paracas Bay, Peru. EOS, Trans. AGU, Vol. 85, N
  45, p. 465-472, 2004.
• Sørensen, Kai , Gunnar Severinsen, Gunni
  Ærtebjerg, Vittorio Barale, Christian Schiller,
  and Anita Künitzer. 2002. Remote sensings
  contribution to evaluating eutrophication in
  marine and coastal waters Evaluation of SeaWIFS
  data from 1997 to 1999 in the Skagerrak, Kattegat
  and North Sea . European Environment Agency.
  Copenhagen, Denmark.