What would be the equation of the following surface?

I have the raw data of X, Y, Z, where X and Y are inputs and Z is the output. Plotting the surface gives the following surface (screenshot shown from different angles for clarity):

Any ideas what could be the rough equation of this surface? I don't know any function which has 2 "humps". The 2D equation need not be exact. I can find the coefficients of the equation using least squares curve fitting.

Answer 1

[Image Analyst]

One assumption might be that it's the sum of two Gaussians, like

z = a1 * exp(-( (x-xctr1).^2 + (y-yctr1).^2) / sigma1) +  a2 * exp(-( (x-xctr2).^2 + (y-yctr2).^2) / sigma2) 

or something like that.

[Aravind Varma Dantuluri]

Thanks