Removal of aircraft altitude variation from laser profiles of the arctic ice pack

Standard high-pass-filtering procedures are not in general adequate for removal of aircraft altitude variation from laser profiles of the arctic pack ice because of the spectral overlap between the surface roughness spectrum and the aircraft height variation spectrum. Owing to this overlap, a high-pass filter tends to depress high ridges and thus makes the resulting profile unsuitable for ridge height analysis. To bypass this difficulty, a straight-forward three-step process is presented. The technique is first to carry out a conventional high-pass-filtering operation and then to estimate minimum points, which can then be used to estimate an ice roughness base line. The estimated ice roughness base line is then low-pass-filtered. This process can be used routinely for processing various profiles, since the filter cutoffs are not critical. The filtering operations are performed by small-error low-pass filters with guaranteed maximum errors of <0.9% outside the transition band.