Question

Spectral signature of an object in a satellite image does NOT depend on the

• A. season of the year
• B. wavelength of electromagnetic spectrum
• C. swath width of the satellite
• D. reflectance value from the object

Hint:

The spectral signature is primarily influenced by the reflectance of the object at different wavelengths and environmental factors like the season. The satellite’s swath width only determines the area of coverage, not the spectral signature.

Answer 1

The Correct Option is C

In remote sensing, the spectral signature of an object refers to the pattern of reflectance and absorption of electromagnetic radiation as a function of wavelength. This signature is unique to each material, and it helps to identify or classify objects in satellite images.
The spectral signature depends on several factors:
- Season of the year (Option A): The season can significantly affect the spectral signature of an object because the amount of sunlight, atmospheric conditions, and the physical state of the object (e.g., vegetation growing during different seasons) vary throughout the year. For example, vegetation reflects more infrared radiation during growing seasons than in winter. Therefore, the spectral signature can vary with the season.
- Wavelength of electromagnetic spectrum (Option B): The wavelength of the electromagnetic spectrum used in remote sensing also plays a crucial role in determining the spectral signature. Different materials absorb and reflect electromagnetic radiation at different wavelengths. For example, vegetation may have a high reflectance in the near-infrared part of the spectrum, while water may have a low reflectance in the same region.
- Swath width of the satellite (Option C): The swath width refers to the width of the ground area that the satellite’s sensor can cover in a single pass. While the swath width affects the area of observation, it does not directly affect the spectral signature of the object. The spectral signature is more related to the characteristics of the object itself and how it interacts with different wavelengths of light. Therefore, the swath width of the satellite does not influence the spectral signature.
- Reflectance value from the object (Option D): The reflectance value of an object is a direct measure of how much electromagnetic radiation is reflected by the object at various wavelengths. This is the core of the spectral signature, as the reflected radiation is what the satellite sensor detects and records. The spectral signature is highly dependent on this reflectance.
Conclusion:
The correct answer is (C) because the swath width of the satellite only affects the area covered by the satellite’s sensor and does not affect the material’s reflectance or its spectral signature. The spectral signature depends on the object’s properties, the wavelength of the electromagnetic spectrum used, and the season in which the observation occurs.