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Record 11 of 349
Time scales of pattern evolution from cross-spectrum analysis of advanced very high resolution radiometer and coastal zone color scanner imagery
External Online Source: doi:10.1029/93JC02149
Author and Affiliation:
Denman, Kenneth L.(Inst. of Ocean Sciences, Sidney, British Columbia, Canada)
Abbott, Mark R.(Oregon State Univ., Corvallis, OR, United States)
Abstract: We have selected square subareas (110 km on a side) from coastal zone color scanner (CZCS) and advanced very high resolution radiometer (AVHRR) images for 1981 in the California Current region off northern California for which we could identify sequences of cloud-free data over periods of days to weeks. We applied a two-dimensional fast Fourier transformation to images after median filtering, (x, y) plane removal, and cosine tapering. We formed autospectra and coherence spectra as functions of a scalar wavenumber. Coherence estimates between pairs of images were plotted against time separation between images for several wide wavenumber bands to provide a temporal lagged coherence function. The temporal rate of loss of correlation (decorrelation time scale) in surface patterns provides a measure of the rate of pattern change or evolution as a function of spatial dimension. We found that patterns evolved (or lost correlation) approximately twice as rapidly in upwelling jets as in the 'quieter' regions between jets. The rapid evolution of pigment patterns (lifetime of about 1 week or less for scales of 50-100 km) ought to hinder biomass transfer to zooplankton predators compared with phytoplankton patches that persist for longer times. We found no significant differences between the statistics of CZCS and AVHRR images (spectral shape or rate of decorrelation). In addition, in two of the three areas studied, the peak correlation between AVHRR and CZCS images from the same area occurred at zero lag, indicating that the patterns evolved simutaneously. In the third area, maximum coherence between thermal and pigment patterns occurred when pigment images lagged thermal images by 1-2 days, mirroring the expected lag of high pigment behind low temperatures (and high nutrients) in recently upwelled water. We conclude that in dynamic areas such as coastal upwelling systems, the phytoplankton cells (identified by pigment color patterns) behave largely as passive scalars at the mesoscale and that growth, death, and sinking of phytoplankton collectively play at most a mariginal role in determining the spectral statistics of the pigment patterns.
Publication Date: Apr 15, 1994
Document ID:
19950029617
(Acquired Dec 28, 1995)
Accession Number: 95A61216
Subject Category: OCEANOGRAPHY
Document Type: Journal Article
Publication Information: Journal of Geophysical Research (ISSN 0148-0227); 99; C4; p. 7433-7442
Publisher Information: United States
Financial Sponsor: NASA; Canada
Organization Source: NASA; Washington, DC, United States
Description: 10p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright
NASA Terms: ADVANCED VERY HIGH RESOLUTION RADIOMETER; CHLOROPHYLLS; COASTAL ZONE COLOR SCANNER; OCEANOGRAPHY; PACIFIC OCEAN; PHYTOPLANKTON; SATELLITE IMAGERY; SEA WATER; SPECTRUM ANALYSIS; UPWELLING WATER; FAST FOURIER TRANSFORMATIONS; NIMBUS 7 SATELLITE; SPATIAL DISTRIBUTION; STATISTICAL CORRELATION
Imprint And Other Notes: Journal of Geophysical Research vol. 99, no. C4 p. 7433-7442 April 15, 1994
Miscellaneous Notes: Research sponsored by NASA, ONR, and Canadian Dept. of Fisheries and Oceans
Availability Source: Other Sources
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