  Type-II superconductors owe their magnetic and transport properties to vortex
pinning, the immobilization of flux quanta through material inhomogeneities or
defects. Characterizing the potential energy landscape for vortices, the
pinning landscape (or short, pinscape), is of great technological importance.
Besides measurement of the critical current density $j_c$ and of creep rates
$S$, the $ac$ magnetic response provides valuable information on the pinscape
which is different from that obtained through $j_c$ or $S$, with the Campbell
penetration depth $\lambda_{\rm \scriptscriptstyle C}$ defining a
characteristic quantity well accessible in an experiment. Here, we derive a
microscopic expression for the Campbell penetration depth $\lambda_{\rm
\scriptscriptstyle C}$ using strong pinning theory. Our results explain the
dependence of $\lambda_{\rm \scriptscriptstyle C}$ on the state preparation of
the vortex system and the appearance of hysteretic response. Analyzing
different pinning models, metallic or insulating inclusions as well as $\delta
T_c$- and $\delta \ell$-pinning, we discuss the behavior of the Campbell length
for different vortex state preparations within the phenomenological $H$-$T$
phase diagram and compare our results with recent experiments.
