OCEANOGRAPHIC FEATURE DETECTION AND LOCATION FROM HIGH-RESOLUTION SATELLITE IMAGES Ramprasad Balasubramanian, Ayan Chaudhuri, Sourish Ray(Computer and Information Science), Avijit Gangopadhyay(Physics and SMAST)

1
OCEANOGRAPHIC FEATURE DETECTION AND LOCATION
FROM HIGH-RESOLUTION SATELLITE IMAGES
Ramprasad Balasubramanian, Ayan Chaudhuri,
Sourish Ray(Computer and Information Science),
Avijit Gangopadhyay(Physics and SMAST)
Chlorophyll_a (March 17, 2002)
Structure of the Eddy
Schema
Abstract

• The Structuring element was tested onto the
  entire March 18, 2002 chlorophyll image to see
  its effectiveness. The testing was done using the
  following methodology
• The structuring element was traversed over the
  entire image.
• For each set of 5x5 pixels on the image,
  corresponding pixels
• were subtracted from the element.
• These differences were then squared and added
  the analogy
• being if the point is an eddy center, then the
  sum of squares of
• the differences between the image and the
  element would
• equate to zero.
•  

NASA satellites, Terra (EOS AM) and Aqua (EOS PM)
view the entire Earth's surface every 1 to 2
days, acquiring data in 36 spectral bands.
Moderate Resolution Imaging Spectroradiometer
(MODIS), the key instrument aboard these
satellites plays a vital role in collecting
observations that will help in predicting global
changes accurately and concisely. Our research
focuses on analysis and processing of
high-resolution (250 meters/pixel) MODIS Ocean
color (Chlorophyll) and Sea surface temperature
(SST) data. Our objective is to detect and locate
oceanographic features, utilizing their dominant
patterns and variability. Our approach is to
identify, spatially segment and temporally track
these features. One such feature an Eddy, in
the Gulf of Mexico is studied here. An automatic
eddy identification procedure is presented. The
eddy structuring element construction method is
presented. This approach is demonstrated on a
level-2 MODIS ocean color image of Chlorophyll_a.


columns
rim
core
filament
Chlorophyll_a ( March 18, 2002)
Introduction
Eddy Pattern Equation
(5x5)Structuring element
rows
T(r) Tc - Tc - Tk 1-exp(-r/R) r is the
radial distance from the center of the eddy. Tk
is the background temperature . Tc is the core
temperature. R 5R0, where R0 is the Rossby
radius.
The MODIS Ocean Level 2 files represent 5 minutes
of spacecraft viewing at 1 km spatial resolution.
There are 144 files per day of the ocean color
products (daytime only) and 288 files per day of
the sea surface temperature products (day time
and night time).
---The MODIS files are grouped together into
several HDF ( Hierarchical Data Format)
files. ---The following HDF files have been used
for our research MODOCL2B ?Ocean Color
Group 2 Products. MODO28L2 ?Sea-surface
temperature and related products. MODO3
?Corresponding geolocation file. ---The
Chlorophyll_a product (MOD21, parameter 27) is
based on a semi- analytic algorithm,
involving the inversion of a spectral
reflectance model to solve for chlorophyll in
the presence of other substances that affect the
waters optical properties. ---SST(Sea
Surface Temperature) is derived from the MODIS IR
channels using two channels in either the
thermal IR (11-12 um)or channels in the mid-IR
region (3.8-4.1 um).
The GOMex Eddy Detection
The figure alongside shows the plots of the four
minimum values obtained from applying the
structuring element on the March 18, 2002
chlorophyll image. The error percentage was about
2.5. From observation we could see that the
structuring element was quite successful in
determining the location of the eddy, although it
was not very accurate and also detected a few
false negatives.
Image Analysis Technique
Analysis began with the extraction of the visible
eddy from the March 18 chlorophyll image.This
was done by specifying the latitude(19.6 to 21.2
degrees) and longitude(-94.8 to -93.2 degrees)
range for the eddy feature. Thereafter, the above
equation which is an eddy tracer was used on this
sub-image to derive the range of T(r) temperature
values. In the equation the value of R, Tc and
Tk were empirically taken to be 75 km, 0.6520
(maximum value) and 0.3700 respectively. The
radius (r) was calculated by finding the root of
the squares of the longitudinal and latitudinal
differences of each point with respect to the
core (Tc).The range of T(r) values obtained were
high around the core, however diminishing while
approaching the outer boundary. This conformed to
the characteristics of an eddy that has a strong
intensity in the center and decays out towards
the edges. Subsequently a generic pattern was to
be created to encapsulate our analysis. The
entire range of T(r) values was divided into a
5x5 grid by taking their average to populate each
element of the grid. This 5x5 grid became our
structuring element or generic template for eddy
detection.
Sea Surface Temperature
Data Acquisition and Processing
MODIS Level2 Ocean Color Derived Products were
ordered from the Goddard Earth Sciences
Distributed Active Archive Center ( GEC DAAC), by
accessing the following website
http//daac.gsfc.nasa.gov/data/dataset/ ---
Focus was on data granules for March 2002. ---
Spatial Coordinates were supplied to the
system. --- A list of granules were returned via
the Web Interface. --- The granules most suited
for our research were ordered for and
acquired for each day using FTP Pull. --- The
data was processed using the ModisGui and
relevant MATLAB Functions. --- SST and
Chlorophyll_a plots were extracted from the data.
--- The images were cropped to our analysis
region. --- The best images were selected and
converted into MPEG files for tracking the
flow of eddies.
March 18, 2002
March 17, 2002
Can the eddy be resolved using SST?
Future Objectives
The Structuring Element

• One of our primary concerns will be to make the
  structuring element larger so
• that it would detect eddy features more
  accurately.
• We will proceed to test the structural element
  out on other chlorophyll
• images,thus training our algorithm even
  further in eliminating false negatives.
• Another concern will be to investigate eddy
  detection hgiven sea surface
• temperature information,correlating the effects
  of sea surface temperature on
• chlorophyll and vice versa.

0.4652 0.4813 0.4852 0.4728
0.4510 0.4999 0.5397 0.5592
0.5268 0.4824 0.5068 0.5602
0.6036 0.5544 0.4966 0.4771
0.5056 0.5224 0.5090 0.4774
0.4420 0.4552 0.4624 0.4589
0.4457
AcknowledgementsUMD Foundation Grant

Jasmine Nahorniak, Oregon State University