Object depth is a simple characteristic that can indicate an object's type. Popular instruments like radar, metal
detectors, and magnetometers are often used to detect the presence of a subsurface object. The next question
is often, "How deep is it?" Determining the answer, however, is not as straight forward as might be expected.
This paper explores the determination of depth using metal detectors. More specifically, it looks at a popular
metal detector (the Geonics EM61) and makes use of its vertically separated coils to generate a depth estimate.
Estimated depths are shown for UXO and small surface clutter from flush buried down to 48". Ultimately
a statistical depth resolution is determined. An alternative approach is then considered that casts the depth
determination problem as one of classification. Only two classes are considered important "deep" and "shallow".
Results are shown that illustrate the utility of the classifier approach. The traditional estimator can provide a
depth estimate of the object, but the classifier approach can distinguish between small shallow, large deep, and
large shallow object classes.