The calculations for radar reflectivity and other variables are based on five main assumptions about the radar beam, the targets, and the atmosphere:

1. The beam travels at the original inclination angle.
2. The targets absorb very little of the radar's electromagnetic energy.
3. Target particles are small, homogeneous precipitation spheres with diameters much smaller than the radar's wavelength.
4. All targets are either liquid or frozen, but not a mixture.
5. Targets are uniformly distributed throughout the sample volume.