What effect do higher zenith angles have on the attenuation of a radar beam by gas?

Higher zenith angles do, in fact, reduce the attenuation of a radar beam by gas. This is primarily due to the geometry of the radar beam's interaction with the atmosphere. As the zenith angle increases, the radar beam travels a longer path through the atmosphere, effectively passing through a greater volume of air. However, the density of the atmosphere's constituents, including gases, decreases with height above ground level, which leads to lower overall attenuation.

At higher zenith angles, the radar beam also becomes less sensitive to the smaller-scale variations in gas concentrations that are more prevalent at lower angles. Essentially, the radar beam is less impacted by the gases it encounters along its longer path because these gases become less dense in the upper atmosphere compared to closer to the surface. Therefore, the relationship between higher zenith angles and reduced attenuation signifies that the effectiveness of radar in detecting and measuring atmospheric conditions is better preserved even when the beam passes through various gases in the atmosphere.