1. A man-portable locator system for locating hidden objects each characterized by an electromagnetic (EM) field emission, the system comprising: a first EM sensor assembly for detecting three orthogonal EM field emission components and producing a set of three time-varying sensor signals {S x (t), S y (t), S z (t)}, including three substantially-identical EM field sensors each having a radial centroid defining a sensing axis, and a structure for supporting the three substantially-identical EM field sensors such that the corresponding sensing axes are disposed in substantial mutual orthogonality; a second EM sensor assembly, coupled to and spaced apart from the first EM sensor assembly, for detecting the three orthogonal EM field emission components and producing a second set of three time-varying sensor signals {S′ x (t), S′ y (t), S′ z (t)}; an analog-to-digital converter (ADC) coupled to the EM sensor assemblies for producing a sequence of digital samples {D(t)} corresponding to time-varying sensor signals; a processor coupled to the sequence of digital samples {D(t)} for producing a spectrum signal {P(f)} representing the sensor signal energy within each of a first plurality B of predetermined frequency intervals responsive to the sequence of digital samples {D(t)}; at least one adaptive filter coupled to the processor for producing a filter output signal F(t) representing the sensor signal energy within each of a second plurality N<B of predetermined frequency intervals selected responsive to the spectrum signal {P(f)}; a proximity detector coupled to the processor for producing a proximity signal d(f) for each of a third plurality B′≦B of predetermined frequency intervals representing the hidden object proximity to one of the EM sensor assemblies; and a user interface (UI) coupled to the processor for indicating the presence of one or more hidden objects responsive to the filter output signal F(t).