Directional Signatures – Variations of reflectivity/emissivity The changes in reflectivity or emissivity with time are termed as what kind of variation?

Introduction / Context:
Remote sensing signals depend on wavelength (spectrum), location (space), viewing/illumination geometry (angle), and time. Properly naming each variation helps interpret multitemporal imagery for change detection and monitoring.

Given Data / Assumptions:

• Quantity of interest: reflectivity/emissivity of a target.
• Axis of change under consideration: time.

Concept / Approach:
Terminology: spectral = across wavelengths; spatial = across locations; temporal = across time; angular/bidirectional = across viewing/illumination angles (BRDF/BTDF). Time-based changes, such as seasonal vegetation dynamics or diurnal thermal cycles, are therefore “temporal variation”.

Step-by-Step Solution:
Identify the dimension of change: time.Map to term: temporal variation.Exclude spectral, spatial, and angular categories.

Verification / Alternative check:
Time-series analyses (e.g., NDVI curves, nighttime land surface temperature cycles) are canonical examples of temporal variation in remote sensing signals.

Why Other Options Are Wrong:

• Spectral: wavelength dependence, not time.
• Spatial: geographic dependence.
• Angular: geometry-dependent BRDF effects.
• None: incorrect because a standard term exists.

Common Pitfalls:
Confusing temporal trends with spectral signatures or BRDF, leading to misinterpretation of multitemporal datasets.

Final Answer:
Temporal variation