Stormwater plume detection by MODIS imagery in the southern California coastal ocean

Nikolay P. Nezlin*, Paul M. DiGiacomo, Dario W. Diehl, Burton H. Jones, Scott C. Johnson, Michael J. Mengel, Kristen M. Reifel, Jonathan A. Warrick, Menghua Wang

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

67 Scopus citations


Stormwater plumes in the southern California coastal ocean were detected by MODIS-Aqua satellite imagery and compared to ship-based data on surface salinity and fecal indicator bacterial (FIB) counts collected during the Bight'03 Regional Water Quality Program surveys in February-March of 2004 and 2005. MODIS imagery was processed using a combined near-infrared/shortwave-infrared (NIR-SWIR) atmospheric correction method, which substantially improved normalized water-leaving radiation (nLw) optical spectra in coastal waters with high turbidity. Plumes were detected using a minimum-distance supervised classification method based on nLw spectra averaged within the training areas, defined as circular zones of 1.5-5.0-km radii around field stations with a surface salinity of S < 32.0 ("plume") and S > 33.0 ("ocean"). The plume optical signatures (i.e., the nLw differences between "plume" and "ocean") were most evident during the first 2 days after the rainstorms. To assess the accuracy of plume detection, stations were classified into "plume" and "ocean" using two criteria: (1) "plume" included the stations with salinity below a certain threshold estimated from the maximum accuracy of plume detection; and (2) FIB counts in "plume" exceeded the California State Water Board standards. The salinity threshold between "plume" and "ocean" was estimated as 32.2. The total accuracy of plume detection in terms of surface salinity was not high (68% on average), seemingly because of imperfect correlation between plume salinity and ocean color. The accuracy of plume detection in terms of FIB exceedances was even lower (64% on average), resulting from low correlation between ocean color and bacterial contamination. Nevertheless, satellite imagery was shown to be a useful tool for the estimation of the extent of potentially polluted plumes, which was hardly achievable by direct sampling methods (in particular, because the grids of ship-based stations covered only small parts of the plumes detected via synoptic MODIS imagery). In most southern California coastal areas, the zones of bacterial contamination were much smaller than the areas of turbid plumes; an exception was the plume of the Tijuana River, where the zone of bacterial contamination was comparable with the zone of plume detected by ocean color.

Original languageEnglish (US)
Pages (from-to)141-152
Number of pages12
JournalEstuarine, Coastal and Shelf Science
Issue number1
StatePublished - Oct 20 2008
Externally publishedYes

Bibliographical note

Funding Information:
The authors would like to thank Wei Shi for help in processing MODIS data, and the NASA GSFC for the production and distribution of the MODIS data and images. MODIS data were acquired as part of the NASA's Earth Science Enterprise and were processed by the MODIS Adaptive Processing System (MODAPS), archived and distributed by the Goddard DAAC. The authors thank all participants of the Bight'03 Regional Water Quality Program. Critical comments of Alex Steele, Ivan Valiela and two anonymous reviewers helped to improve the paper significantly. We also thank Karlene Miller for editing the manuscript to make the writing style more accessible. This work was partly supported by a NASA Oceans & Ice Research Award (NRA-04-OES-02) from the NASA Ocean Biology and Biogeochemistry Program (Dr. Paula Bontempi, Program Scientist). The contents of this article are solely the opinions of the authors and do not constitute a statement of policy, decision, or position on behalf of the United States Geological Survey (USGS), the National Oceanic and Atmospheric Administration (NOAA) or the U.S. Government.


  • 32°00'-34°30'N, 120°00'-117°00'W
  • ocean color
  • plumes
  • sea-spectral reflectance
  • southern California Bight

ASJC Scopus subject areas

  • Oceanography
  • Aquatic Science


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