Wave phase: select the correct statements about how phase is defined, referenced, and commonly expressed for a periodic wave.

Introduction / Context:
Phase describes the relative position within a wave cycle and is fundamental to understanding interference, coherence, and time alignment in remote sensing signals (e.g., SAR interferometry) and signal processing in general.

Given Data / Assumptions:

• A periodic signal and a consistent reference point are assumed.
• Phase can be represented in degrees or radians.
• Zero-crossings are common practical references for phase measurements.

Concept / Approach:
Phase quantifies how far a point is through its cycle relative to a reference, often at a specific time or location. Expressing phase as an angle maps one full cycle to 360° (or 2π radians). Selecting a consistent reference—such as the last negative-to-positive zero-crossing—ensures reproducible comparisons between signals.

Step-by-Step Solution:
Define phase as a fraction of the cycle (0 to 1) or in angular units (0° to 360°).Adopt a reference event: commonly the zero-up crossing in time-series.Note that degrees or radians are both valid; the key is consistency.All listed statements (A–C) are correct; hence choose “All of these.”

Verification / Alternative check:
Signal processing texts define phase in exactly these terms; interferometric SAR uses phase differences modulo 2π.

Why Other Options Are Wrong:

• Insisting on radians only is unnecessary; degrees are equally valid in practice.

Common Pitfalls:
Mixing degree and radian units; failing to document the phase reference point, which can lead to misinterpretation.

Final Answer:
All of these