  We study ensembles of fermionic cold-atom quantum wires with tunable
transverse mode population and single wire resolution. From in situ density
profiles, we determine the temperature of the atomic wires in the
weakly-interacting limit and reconstruct the underlying potential landscape. By
varying atom number and temperature, we control the occupation of the
transverse modes and study the 1D-3D crossover. In the 1D-limit, we observe an
increase of the reduced temperature $T/T_{F}$ at nearly constant entropy per
particle $S/N k_{B}$. The ability to probe individual atomic wires in situ
paves the way to quantitatively study equilibrium and transport properties of
strongly-interacting 1D Fermi gases.
