Shuki Ronen has shown that a dip spectrum in 2-D
may be characterized by a 1-D Prediction Error Filter (PEF)
after his ``pyramid transform'' where

-space is
transformed to

-space.
The transform to

-space creates empty locations (missing data).
Thus we have the question of unknown PEF along with missing data.
Here we propose to find both simultaneously by iterative
linear least squares.