  We report 491 new near-infrared spectroscopic measurements of 420 near-Earth
objects (NEOs) collected on the NASA InfraRed Telescope Facility (IRTF) as part
of the MIT-Hawaii NEO Spectroscopic Survey (MITHNEOS). These measurements were
combined with previously published data (Binzel et al. 2019) and bias-corrected
to derive the intrinsic compositional distribution of the overall NEO
population, as well as of subpopulations coming from various escape routes
(ERs) in the asteroid belt and beyond. The resulting distributions reflect well
the overall compositional gradient of the asteroid belt, with decreasing
fractions of silicate-rich (S- and Q-type) bodies and increasing fractions of
carbonaceous (B-, C-, D- and P-type) bodies as a function of increasing ER
distance from the Sun. The close compositional match between NEOs and their
predicted source populations validates dynamical models used to identify ERs
and argues against any strong composition change with size in the asteroid belt
between ~5 km down to ~100 m. A notable exception comes from the over-abundance
of D-type NEOs from the 5:2J and, to a lesser extend, the 3:1J and nu6 ERs,
hinting at the presence of a large population of small D-type asteroids in the
main belt. Alternatively, this excess may indicate preferential spectral
evolution from D-type surfaces to C- and P-types as a consequence of space
weathering, or to the fact that D-type objects fragment more often than other
spectral types in the NEO space. No further evidence for the existence of
collisional families in the main belt, below the detection limit of current
main-belt surveys, was found in this work.
