Image Processing Algorithms for Identifying the Gulf Oil Spill Mingrui Zhang, Ph.D. Computer Science Department Winona State University

Oil Spill A marine oil spill is an occurrence where oil is released into the ocean or coastal waters by natural seeps or by human activity. Oil spills may be due to releases of crude oil from tankers, offshore platforms, drilling rigs and wells. Oil also enters the marine environment through natural oil seeps ( 2

Gulf Oil Spill (Apr – Sept 2010) The Gulf of Mexico oil spill in 2010 was the largest offshore spill in U.S. history. 3 Deepwater Horizon oil spill captured by NASA's Terra Satellites on May 24, 2010.

Oil Spills Assessment Tools Computer application, such as Geographic Information System (GIS) tool, has been designed to assist both emergency responders and environmental resource managers who deal with incidents that may adversely impact the environment. Also see "Emergency Response: Responding to Oil Spills". National Oceanic and Atmospheric Administration ( 4

Specific Problem To provide starting points of oil spill for ocean circulation models To map oil contaminated area on the latest satellite images with least human intervention 5

Algorithm Development for Problem Solving Our problem solving strategy cycles through 5 phases –Phase 1 – understand the problem –Phase 2 – study the images with a software tool –Phase 3 – propose a solution –Phase 4 – code program –Phase 5 – apply to images Repeat 5 phases to improve algorithm. 6

Software Functions We have developed a Java application with graphical user interface. –It reads in a satellite image and displays. –It allows user to collect sample pixels on image. –It provides menu items for different oil spill recognition algorithms. –It displays a processed image side by side the original image. Software features are added as needed in solving the problem. 7

Algorithm Development Using the software tool, we repeated the algorithm development cycle in developing oil recognition algorithms. We have explored –The use of scatter plots –Different threshold values/functions –Band rationing technique In redesigning the algorithm, we seek to reduce number of mislabeled oil pixels. 8

Scatter Plot Scatter plots are used in discovering threshold values or functions for oil spills –Its axes are values of color components of sample pixels –When collecting sample pixels, We may use multiple images We collect on the center and edge of oil spills Thresholds could be formulated as constants, a linear or non-linear functions 9

Solution 1 – Threshold Value or Function Scatter plots are used in discovering threshold values or functions –IF red color > 40 THEN pixel is oil –IF green < 3*(red – 20) THEN pixel is oil 10

Tradeoffs in Threshold Functions Simple linear threshold functions + They are easy for interpretation + They take less time to compute – Need multiple functions to define a cluster of sample pixels on a scatter plot Non-linear functions + Handle complex boundaries of cluster of sample pixels – They are slow to compute 11

Images After Processing 12

Solution 2 – Rationing Technique We have explored band rationing technique. –Band rationing is to divide the pixels in one spectral band by the corresponding pixels in a second band. –The differences between the spectral reflectance curves of surface types can be brought out. An example ratio –Oil spill index = (red-blue) / (red + blue) 13

Tradeoffs in Rationing Technique + In theory, it precisely depicts the spectral curves of different remotely sensed objects – Noises are enhanced in processed images It did not work out in this case. 14

Mislabeling of Oil Spill 15 In real-world application, algorithm can never be perfect. We still have mislabeled pixels  Labeled island (keys) as oil spills  Missed oil spill pixels

Additional Software Functions 16 Processing a satellite image needs large memory space, often beyond the size of memory a personal compute has. For example,  The size of an image is big  Image has multiple spectral bands Some useful functions to add to your software tool:  Reducing image size for display  Allowing user to choose a color to display

Benefits to Society Your application can assist in response planning and is accessible to both the command post and to assets in the field during an actual response incident. –It provides integrated and timely information to improve decision-making. –It provides fast visualization of current information. –Also see “The effects of oil spills on wildlife”, NOAA, ( 17

Other Project Considerations The software tool we developed and the problem solving strategy we used for oil recognition can be adapted for solving other real-world problems: –Harmful algal blooms occur around the world — from Florida to Maine, Norway to Africa. It can create health problems for both animals and humans. ( –Any brain tumor is inherently serious and life-threatening to human. MRI images are often used in diagnosis of brain tumor. ( 18

Oil Spill is Still a Threat Oil spill causes many environmental hazards to marine life, such as sea grass, fish or birds. It can be very difficult to control and to predict. Videos –"Hindsight and Foresight, 20 Years After the Exxon Valdez Spill". NOAA ( –“Gulf Oil Plumes Still a Threat?”, National Geographic, ( ment-news/nsf-oil-plumes-joye-vin.html). ment-news/nsf-oil-plumes-joye-vin.html 19