Digital Image Processing

- Option (A) is correct because external geometric errors (such as errors due to the satellite's position or orientation) can indeed be corrected using Ground Control Points (GCPs) and a mathematical model that relates the image coordinates to real-world coordinates.
- Option (B) is correct because, during the process of image rectification, transformation coefficients are applied to correct the image’s spatial alignment with a known standard datum and map projection.
- Option (C) is incorrect because spatial interpolation models typically handle missing data or resampling and are not specifically used to correct distortions in remote sensing images.
- Option (D) is incorrect because image registration is usually done between a satellite image and another reference image, not just field data. Step 1: Conclusion
The correct statements are (A) and (B).

- Option (A) is incorrect because higher frequencies in the Fourier Spectrum of an image typically appear at the outer edges, not the center. The center represents low frequencies.
- Option (B) is correct because higher frequencies are located at the outer edges of the Fourier Spectrum, while lower frequencies are at the center.
- Option (C) is correct because in the Fourier Transform of an image, horizontal features correspond to vertical components in the Fourier Spectrum (and vice versa for vertical features).
- Option (D) is incorrect because vertical features in the image are represented as horizontal components in the Fourier Spectrum, not vertical ones. Step 1: Conclusion
The correct answers are (B) and (C).

In visual image interpretation, various elements help analysts understand and classify features. The primary elements include Tone/Color, Texture, Size, Shape, Pattern, and Association.
- Tone/Color is considered the primary element because it provides the most straightforward visual information, representing the intensity of light (shades of gray in black-and-white or actual color in a color image).
- Size, Shape, and Texture are secondary elements because they provide additional details or characteristics of the feature but do not give the immediate information that tone/color does.
Step 1: Analyzing the options. - Option (A) is correct because Tone/Color is a primary element, while Size, Shape, and Texture are secondary elements in visual image interpretation.
- Option (B) is incorrect because Tone/Color is not a secondary element but a primary element.
- Option (C) is incorrect because Texture is more than just the frequency of tonal changes; it includes the spatial arrangement and pattern of tones.
- Option (D) is incorrect because Pattern and Association are secondary elements, not primary, in visual interpretation.
Thus, the correct answer is (A).

Hyperspectral images capture data in many narrow and contiguous spectral bands. These narrow bands allow for detailed analysis of various materials based on their spectral properties.
Step 1: Bandwidth of Hyperspectral Images
- Option (B) is correct because hyperspectral images have narrow bandwidths, meaning each band captures a small range of wavelengths.
- Option (C) is correct because hyperspectral images typically have a large number of bands, which is what distinguishes them from multispectral images.
- Option (D) is correct because the bands in hyperspectral images are contiguous, meaning they follow each other without gaps. Step 2: Conclusion
Therefore, the correct answers are (B), (C), and (D).

In remote sensing, True Color Composite is created by combining the bands that correspond to the colors we perceive visually: the Red, Green, and Blue bands. These bands are superimposed in the same order: - Red band in Red
- Green band in Green
- Blue band in Blue.
Step 1: Analyzing the options. - Option (A) is correct because it correctly describes how True Color Composite is formed: Red in Red, Green in Green, and Blue in Blue.
- Option (B) is incorrect because the Blue band should be mapped to Blue, not to Red.
- Option (C) is incorrect because this describes a False Color Composite where Near Infrared (NIR) is typically shown in red, not a true color composition.
- Option (D) is incorrect because it partially describes the False Color Composite, but it is missing the Green band in Green, which is essential for the true representation.
Thus, the correct answer is (A).

- Option (A): A spheroid is a mathematical model of the Earth. It is a shape that is slightly flattened at the poles and is used as a reference for geographic coordinates. This statement is correct.
- Option (B): The geoid is an equipotential surface of the Earth's gravity field, representing the shape that the Earth's oceans would take under the influence of gravity and rotation, ignoring other influences like winds and tides. This statement is correct.
- Option (C): The true shape of the Earth is not a perfect spheroid but an oblate spheroid, which means it is slightly flattened at the poles and bulging at the equator. Thus, this statement is incorrect.
- Option (D): The WGS-84 (World Geodetic System 1984) datum is a standard reference system used globally and does not vary from country to country. Therefore, this statement is incorrect.
Thus, the correct answers are (A) and (B).