  In this work we study the spectral properties (3600 - 6800 A) of the nuclear
region of early-type galaxies at low (|b|<25, intermediate (including
surroundings of the Magellanic Clouds) and high (South Polar Cap) Galactic
latitudes. We determine the E(B-V) reddening values of the galaxies by matching
their continuum distribution with respect to those of reddening-free spectral
galaxy templates with similar stellar populations. We also compare the
spectroscopic reddening value of each galaxy with that derived from 100 micron
dust emission (E(B-V)_{FIR}) in its line of sight, and we find that there is
agreement up to E(B-V)=0.25. Beyond this limit E(B-V)_{FIR} values are higher.
Taking into account the data up to E(B-V) \approx 0.7, we derive a calibration
factor of 0.016 between the spectroscopic E(B-V) values and Schlegel et al.'s
(1998) opacities. By combining this result with an A_K extinction map built
within ten degrees of the Galactic centre using Bulge giants as probes (Dutra
et al. 2003), we extended the calibration of dust emission reddening maps to
low Galactic latitudes down to |b|=4 and E(B-V)= 1.6 (A_V \approx 5). According
to this new calibration, a multiplicative factor of approximately 0.75 must be
applied to the COBE/IRAS dust emission reddening maps.
