Since the radar/target distance is provided by GPS with a good accuracy, geometrical parameters of targets, including their depths, are not of an interest here. The main goal of the publication [24] was to calculate ratios R of dielectric constants
R = ε r (target) ε r (bckgr) ,(1)
where ε r (target) is the dielectric constant of the background medium. If ε r (bckgr) is known, then (1) enables one to calculate ε r (target). If a target is located above the ground, then ε r (bckgr) = ε r (air) = 1. Unfortunately, dielectric constants were not measured during the **data** collection process. Therefore, the authors of [24] had no choice but to rely on tables of dielectric constants [32, 33] when evaluating the accuracy of results. In our mathematical  
R = max [0,1] R(x) if R(x) ≥ 1, ∀x ∈ (0, 1), min [0,1] R(x) if R(x) < 1, ∀x ∈ (0, 1).(2)
Hence, in (1) we actually have R := R, and by (2) ε r (target) = Rε r (bckgr).