As radio frequency increases, how does the absorption (attenuation) of a ground wave by the Earth’s surface typically change?

Introduction / Context:
Ground-wave propagation dominates at low and medium frequencies. Understanding frequency-dependent ground losses helps in selecting operating bands and predicting coverage for AM broadcast and LF/MF communication systems.

Given Data / Assumptions:

• Ground wave hugs the Earth's surface and interacts with lossy ground.
• Soil has finite conductivity and permittivity, causing frequency-dependent attenuation.

Concept / Approach:

As frequency rises, the ground's effective loss tangent and surface impedance lead to greater attenuation of waves traveling along the surface. Hence, ground-wave range shortens with higher frequency, motivating MF/LF for long-range ground-wave services.

Step-by-Step Solution:

Verification / Alternative check:

Coverage charts for AM broadcast show reduced ground-wave range at higher MF compared to lower MF/LF bands for comparable power and soil conditions.

Why Other Options Are Wrong:

• Decreases/Remains same: contradict empirical data and surface-wave theory.
• Independence above a threshold is not accurate for real soil parameters.

Common Pitfalls:

Confusing sky-wave behavior (ionospheric) with ground-wave; assuming free-space loss applies unchanged to surface waves.

Final Answer:

Increases with increasing frequency