  Using scanning tunneling spectroscopy at T = 4.2 K, we perform simultaneously
the topographic imaging and the quasiparticle density of states (DOS) mapping
in granular MgB2. We observe a new type of spectrum, showing a pronounced
double gap, with the magnitudes of Delta_S = 3.9 meV and Delta_L = 7.5 meV,
i.e. well below and well above the BCS limit. The largest gap value gives the
ratio 2*Delta_L/k_B T_c = 4.5, which implies strong electron-phonon coupling.
Other superconducting regions are found to have a characteristic BCS-shaped
DOS. However, the variation of the spectral shape and lower gap widths, from
2.0 meV to 6.5 meV, indicate the importance of surface inhomogeneity and
proximity effects in previously published tunneling data. Our finding gives no
evidence for any important gap anisotropy. Instead, it strongly supports the
multiple gap scenario in MgB2 in the clean limit, and the single gap scenario
in the dirty limit.
