How can I create a mean surface?

Hi, I have a question and I need and help :D

I loaded an image that describe my problem:

I've got a matrix (100x100) with 3 types of value: 0-1-2 that you can see in blue-light blue and yellow (the white part is NaN). This is the salt intrusion process. To obtaining this matrix I summed two kind of data(values 0-1): the first one, on the right, within the black line, the classical approach of the salt intrusion and the second one, especially on the left and on the cells with value "2" (1 salt intrusion + 1 of this phenomena), about pumping effects.

I would like to create a mean surface only for the value 1. I imagine that at the bottom of the image the black line will be moving to the left. Therefore, I need one matrix that describe the mean surface, so I can count the "cells with the value 1".