fft2 of interferometric image - how to interpret the result in term of dominant frequency

I have an interferometric image which shows fringes at a certain frequency, basically a dominantly periodic signal overlaying the information that I want to extract. See image :

 The size of the image is 1024x4067 pixels. So using matlab I performed fft2(im,n) with n = size of image, giving me this fft-image

with maximum values given at (9,24) and it's symetric (1017,4045). I am totally confused now as of how to interprete this result. Does that mean I have a frequency of 9 in y and 24 in x direction making it some sort of Acos(2pi/9y+2pi/24x)+Bisin(2pi/9y+2pi/24x) wave!? I'm guessing this it totally wrong and stupid, but I'm really confused.. :-/ thanks for your help!