  We report the comparison between unresolved reflectance spectroscopy of Solar
System small bodies and laboratory measurements on reference surfaces. We
measure the bidirectional reflectance spectroscopy of a powder of howardite and
a sublimation residue composed of a Ceres analogue. The spectra are then
inverted using the Hapke semi-empirical physical model and the MRTLS parametric
model to be able to simulate the reflectance of the surfaces under any
geometrical configuration needed. We note that both models enable an accurate
rendering of the reflectance spectroscopy, but the MRTLS model adds less noise
on the spectra compared to the Hapke model. Using the parameters resulting from
the inversions, we simulate two spherical bodies and the small bodies (1)Ceres
and (4)Vesta whose surfaces are homogeneously covered with the Ceres analogue
and powder of howardite respectively. We simulate various scenarios of
illumination and spectroscopic observations, spot-pointing and fly-bys, of
these small bodies for phases angles between 6{\deg} and 135{\deg}. The
unresolved reflectance spectroscopy of the simulated bodies is retrieved from
the resulting images, and compared to the reflectance spectroscopy of the
reference surface. Our results show that the photometric phase curves of the
simulated bodies are different from the reference surfaces because of the
variations of the local incidence and emergence angles due to the shape and
topography of the surface. We observe the maximum differences at wide phase
angles with the various simulated observations of (4)Vesta due to its high
surface topography. Finally, we highlight the differences in the spectral
parameters derived from the unresolved observations at 30{\deg} with laboratory
measurements acquired under a single geometrical configuration.
