Remote Sensing Signatures – Which statements are correct? Consider the nature of spectral and polarimetric signatures used for Earth observation. Identify the correct statements about how signatures are represented, how polarization behaves, and how reliably signatures identify targets.

Difficulty: Easy

A graph of spectral reflectance versus crop growth stage depicts a phenologic pattern.
A change in the polarization state of reflected/emitted radiation is termed polarization variation.
The degree of polarization is a target-dependent characteristic that aids identification.
Signatures reflect statistical behaviour and are not perfectly deterministic in the field.
All of these.

Correct Answer: All of these.

Explanation:

Introduction / Context:
Remote sensing analysts use “signatures” to distinguish land covers and materials. Signatures can be spectral (variation of reflectance/emittance with wavelength), temporal/phenologic (how those responses change with growth stage or season), angular (BRDF behaviour), and polarimetric (state and degree of polarization). Understanding what a signature encodes and its limitations is essential for reliable classification and change detection.

Given Data / Assumptions:

Passive optical and active microwave observations are considered.
Field and image signatures are affected by illumination, atmosphere, geometry, and sensor noise.
Targets are natural/agricultural surfaces that vary through time.

Concept / Approach:

A spectral reflectance curve of a crop, traced over successive dates, exhibits a phenologic pattern related to chlorophyll, water content, and structure. Polarization variation denotes how the polarization state (for example, degree and angle) of reflected or emitted radiation changes due to surface roughness, moisture, and geometry. Because the observed scene is influenced by many factors, signatures are best treated as statistical rather than fixed constants; hence libraries store ranges and variances, not single lines only.

Step-by-Step Solution:

Evaluate Option A: Time-series spectral curves across growth stages indeed form crop phenologic signatures.Evaluate Option B: Changes in polarization state of radiation from a target are referred to as polarization variation and are a central concept in polarimetry.Evaluate Option C: Degree of polarization depends on the target and illumination-view geometry, assisting target discrimination.Evaluate Option D: Field signatures vary; noise and environmental factors make them statistical rather than strictly deterministic.Therefore, all statements are correct.

Verification / Alternative check:

Standard texts on spectral libraries and SAR/optical polarimetry emphasize temporal profiles for crops and the diagnostic value of polarization while cautioning users about variability and the need for probabilistic classifiers.

Why Other Options Are Wrong:

No single statement is wrong; choosing any one would discard other equally valid properties, so the combined option is appropriate.

Common Pitfalls:

Expecting a unique “fingerprint” under all conditions; ignoring viewing geometry, soil background, and atmosphere; overlooking that signature statistics shift with phenology and moisture.

Final Answer:

All of these.

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Remote Sensing Signatures – Which statements are correct? Consider the nature of spectral and polarimetric signatures used for Earth observation. Identify the correct statements about how signatures are represented, how polarization behaves, and how reliably signatures identify targets.

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