How can I crop a matrix with ocean boundaries?

This is figure that plot with satellite data using my research.

It is 8640*4320 matrix.

I want to crop the matrix with ocean boundaries, but i don't know how i can do this.

I already cropped matrix like upper image, but it's boundaries are not fittable to my research.

How can i do this like lower image?

I hope I can get answer ASAP.

have a nice day.

[Erin]

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Answer 1

[Image Analyst]

You'll have to do that manually with coordinates known in advance rather than have some algortihm figure it out, because for example where you split the South Atlantic and the Indian Ocean is not unique - there are several other columns that could just as well be the division line.