segmentation of tree crowns

which edge detection technique(gradient magnitude) gives better performance for tree crown delineation using marker controlled watershed segmentation algorithm.

i have used sobel,LOG edge detection but it doesnt give accurate results.so plzz help me with appropriate code.i hav tried matlab demo marker controlled watershed segmentation algorithm.the image i have taken is http://www.google.co.in/imgres?imgurl=http://www.fhcpresb.org/wp-content/uploads/2009/03/googleearth.jpg&imgrefurl=http://www.fhcpresb.org/about-us/facilities/&h=377&w=498&sz=79&tbnid=m10reizB0LJNVM:&tbnh=91&tbnw=120&zoom=1&usg=__6iwgHhb5TlUhes7YOhlnsCtsMKM=&docid=QsKeYdRctty_IM&hl=en&sa=X&ei=hu8MUNKZOsrirAfZv-jNCA&ved=0CEoQ9QEwBQ&dur=319

[Walter Roberson]

I would have thought that determining how to best do this task is an important part of your research, not something you should be asking other people to answer for you.

Note: your question as phrased is not a MATLAB question.