Optical excitation spectra of the ${\mathrm{Eu}}^{3+}{:\mathrm{Y}\mathrm{A}\mathrm{l}\mathrm{O}}_{3}$ ${}^{7}{\stackrel{\ensuremath{\rightarrow}}{{F}_{0}}}^{5}{D}_{0}$ transition were obtained for ${\mathrm{Eu}}^{3+}$ (0.1, 0.01, 0.001 mol %) at about 2 K. Optical excitation spectra showed more than 60 weak satellite lines spreading over some 400 GHz regardless of the ${\mathrm{Eu}}^{3+}$ concentration. From the dependence of the normalized area on concentration of ${\mathrm{Eu}}^{3+},$ these satellite lines are ascribed to the sites differently perturbed by defects or the other ${\mathrm{Eu}}^{3+}$ ions. For the main and some satellite lines of 0.1 mol % ${\mathrm{Eu}}^{3+},$ optical-rf (radio frequency) double-resonance spectra of the ${}^{7}{F}_{0}$ ground state have been measured. We measured hyperfine splitting frequencies ${\ensuremath{\delta}}_{\mathrm{RF}}$ for given optical frequencies ${E}_{\mathrm{op}},$ and could map site distribution on rf-optical frequency axes. In the inhomogeneous broadening for both the main and satellite lines, we found that the plot of ${\ensuremath{\delta}}_{\mathrm{rf}}$ vs ${E}_{\mathrm{op}}$ had a gradient of +10 kHz/GHz. This finding can be explained by the J-mixing effect. We also obtained several rf resonance frequencies for an optical frequency at many satellites and even at valleys. From these results we can identify the sites which cannot be distinguished by a simple optical measurement.