What is largely responsible for radar signal attenuation in the W-band?

In the context of radar signal attenuation, particularly within the W-band (which operates at frequencies between 75 GHz and 110 GHz), the primary factor is the absorption caused by oxygen molecules in the atmosphere. At these frequencies, oxygen molecules have specific absorption lines that lead to significant attenuation of radar signals. This is because W-band radar operates very close to the resonance frequencies of oxygen, making it particularly susceptible to scattering and absorption.

While water vapor and rainfall can also cause attenuation, their effects are generally more pronounced at lower frequencies compared to the specific behaviors observed at W-band frequencies. Dust particles may scatter radar waves but do not contribute significantly to the absorption component that markedly impacts signal strength in the W-band compared to the absorption due to oxygen.

Thus, the dominance of oxygen in causing signal attenuation at W-band frequencies is well-established in radar meteorology, highlighting why this is the correct answer.