  The existence of multiple layers in the inner Orion Nebula has been revealed
using data from an Atlas of spectra at 2" and 12 km/s resolution. These data
were sometimes grouped over Samples of 10"x10"to produce high Signal to Noise
spectra and sometimes grouped into sequences of pseudo-slit Spectra of
12.8"--39" width for high spatial resolution studies. Multiple velocity systems
were found: Vmif traces the Main Ionization Front (MIF), Vscat arises from
back-scattering of Vmif emission by particles in the background Photon
Dissociation Region (PDR), Vlow is an ionized layer in front of the MIF and if
it is the source of the stellar absorption lines seen in the Trapezium stars,
it must lie between the foreground Veil and those stars, Vnew may represent
ionized gas evaporating from the Veil away from the observer. There are
features such as the Bright Bar where variations of velocities are due to
changing tilts of the MIF, but velocity changes above about 25"arise from
variations in velocity of the background PDR. In a region 25" ENE of the
Orion-S Cloud one finds dramatic changes in the [OIII]components, including the
signals from the Vlowoiii and Vmifoiii becoming equal, indicating shadowing of
gas from stellar photons of >24.6 eV. This feature is also seen in areas to the
west and south of the Orion-S Cloud.
