Comparing the NEATM with a Rotating, Cratered Thermophysical Asteroid Model

A cratered asteroid acts somewhat like a retroflector, sending light and infrared radiation back toward the Sun, while thermal inertia in a rotating asteroid causes the infrared radiation to peak over the ``afternoon'' part. In this paper a rotating, cratered asteroid model is described, and used to generate infrared fluxes which are then interpreted using the Near Earth Asteroid Thermal Model (NEATM). Even though the rotating, cratered model depends on three parameters not available to the NEATM (the dimensionless thermal inertia parameter and pole orientation), the NEATM gives diameter estimates that are accurate to 10 percent RMS for phase angles less than 60 degrees. For larger phase angles, such as back-lit asteroids, the infrared flux depends more strongly on these unknown parameters, so the diameter errors are larger. These results are still true for the non-spherical shapes typical of small Near Earth objects.