Statistics and Physical Oceanography (1993) / Chapter Skim
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4: Feature Identification
4: Feature Identification
Pages 27-32
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From page 27... ...
found that subjective identification of the north wall was more accurate than that enabled by any "conventional algorithm," such as the location of the maximum SST gradient, and found that the root-mean-square difference between the AVHRR-derived location and a traditional definition based on in situ temperature measurements was less than 15 km. Ring motion is generally determined by the ring displacement over periods of tens of days, but there may be substantial changes in ring structure and motion over these time periods.
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From page 28... ...
Mariano's method requires a pattern recognition algorithm to first delineate the contours in each type of data, before the optimal estimate of the final contour location can be made. All of these statistical characterizations using images have in common the problem of detecting features in the presence of extensive cloud contamination or instrument noise; subjective methods have probably been most successful because the human eye can compensate for slight changes in the values of the field and locate a feature by its shape.
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From page 29... ...
ESTIMATION OF HORIZONTAL VELOCITIES FROM IMAGE SEQUENCES Another oceanographic problem that might benefit from the application of advanced statistical methods is the estimation of horizontal ocean velocities using pairs of satellite images. One method of estimating these velocities is to track identifiable features in a tracer field, usually the sea surface temperature (SST; Emery et al., 1986)
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From page 30... ...
As in the MCC method, there is an optimal temporal lag ~ between images for the inversion: approximately 12 hours, compared to values of 4 to 6 hours preferred for the MCC method. Velocity fields that include the along-isoline velocity component can be obtained by adding constraints on the velocity solution, notably the minimization of horizontal divergence, with a weighting factor a relative to the heat equation (4.~)
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From page 31... ...
The horizontal velocity problem has been examined by many scientists and engineers. Other methods include the use of a single image in conjunction with the thermal wind equation, which relates horizontal SST gradients to vertical velocity shear (Kouzai and Tsuchiya, 1990)
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From page 32... ...
The emphasis is on inference of the dynamics of the field from the feature evolution and statistics; and 4. Estimation of oceanic velocity using a time series of tracer fields, where the relationship between the velocity field and the tracer is not unique and the velocity field is subject to some dynamical constraints.
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