  The degree to which the properties of protostars are affected by environment
remains an open question. To investigate this, we look at the Orion A and B
molecular clouds, home to most of the protostars within 500 pc. At ~400 pc,
Orion is close enough to distinguish individual protostars across a range of
environments in terms of both the stellar and gas projected densities. As part
of the Herschel Orion Protostar Survey (HOPS), we used the Photodetector Array
Camera and Spectrometer (PACS) to map 108 partially overlapping square fields
with edge lengths of 5 arcmin or 8 arcmin and measure the 70 micron and 160
micron flux densities of 338 protostars within them. In this paper we examine
how these flux densities and their ratio depend on evolutionary state and
environment within the Orion complex. We show that Class 0 protostars occupy a
region of the 70 micron flux density versus 160 micron to 70 micron flux
density ratio diagram that is distinct from their more evolved counterparts. We
then present evidence that the Integral-Shaped Filament (ISF) and Orion B
contain protostars with more massive envelopes than those in the more sparsely
populated LDN 1641 region. This can be interpreted as evidence for increasing
star formation rates in the ISF and Orion B or as a tendency for more massive
envelopes to be inherited from denser birth environments. We also provide
technical details about the map-making and photometric procedures used in the
HOPS program.
