The disclosure is directed to monitoring changes in fly height for a plurality of read heads. Readback signals based upon a first periodic data sequence and a second periodic data sequence are detected using at least a first read head and a second read head at a first point in time corresponding to a first fly height of each read head and at a second point in time corresponding to a second fly height each read head. The difference between the first fly height and the second fly height of the first read head and the difference between the first fly height and the second fly height of the second read head are determined by comparing the respectively detected readback signals. A summation of the difference values, each having been multiplied by a fusion coefficient, is then used to estimate a global change in fly height.