How to differentiate a surface plot?

I have a matrix of (Z) data, the data is height data (Z), each line of data is a scan (Y) and each line has 300 points(X). I am able to create a surface plot and pull out the stats i need except the slope information. I would like to know the rate of change in slope over the surface to be able to understand the severity.

How can i do this with this type of data?

[jonas]

Have a read here

https://se.mathworks.com/help/matlab/ref/gradient.html