= Solution
Near the \b[north magnetic pole], take the inducing <magnetic field> and induced <magnetic moment> as vertically downward. Directly above the car, its anomalous field reinforces the main field: a positive central <total-field magnetic anomaly> results. Along a horizontal traverse, the vertical-dipole approximation gives a symmetric central high flanked by weaker negative side lobes:
$$
\Delta T(x)\propto\frac{2h^2-x^2}{(x^2+h^2)^{5/2}},
$$
where $h$ is the depth from the sensor to the effective dipole centre. The anomaly width scales with $h$; no absolute amplitude can be calculated without the car's <magnetic moment>.
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