Multilooking

Hi
I have a problem as below:
When I first multi look the interferogram and then subtract dem, my result have a big difference with the result that I first subtract the dem and then multi look the interfeogram. Why?

Thanks

19
Is there any one who could solve my problem?
Regards

You’re taking the average of two different things. It’s going to be different.
Remove the topo phase first and then multilook