GIS - Geographic Information System Remote Sensing and Imagery Questions and Answers — Questions and Answers
Question 1: An agricultural analyst needs to monitor the health of crops throughout a growing season to detect stress and optimize irrigation. This requires frequent observation of the same area to track changes in vegetation vigor. Which type of remote sensing resolution is most critical for this application?
- Spectral Resolution
- Temporal Resolution (Correct answer)
- Radiometric Resolution
- Spatial Resolution
Correct answer: Temporal Resolution
Temporal resolution refers to the revisit frequency of a satellite or sensor over a specific location. For monitoring dynamic phenomena like crop growth, high temporal resolution (i.e., frequent revisits) is essential to capture changes as they happen. [2, 7]
Question 2: An analyst is performing a land cover classification. They have extensive ground-truth data and need to create a map with specific, predefined classes such as 'Urban', 'Coniferous Forest', and 'Agriculture'. Which image classification method is most appropriate for this task?
- Unsupervised Classification
- Object-Based Classification
- Supervised Classification (Correct answer)
- Principal Component Analysis
Correct answer: Supervised Classification
Supervised classification requires the analyst to provide the algorithm with 'training sites'—representative samples of known land cover types. The algorithm then uses the spectral signatures from these sites to classify the rest of the image into the predefined classes. [3, 8, 11]
Question 3: The Normalized Difference Vegetation Index (NDVI) is a widely used indicator of live green vegetation. Its calculation relies on the unique reflectance properties of plants in which two portions of the electromagnetic spectrum?
- Blue and Green
- Green and Red
- Red and Near-Infrared (NIR) (Correct answer)
- Near-Infrared (NIR) and Short-Wave Infrared (SWIR)
Correct answer: Red and Near-Infrared (NIR)
NDVI is calculated using the formula (NIR - Red) / (NIR + Red). It leverages the fact that healthy vegetation strongly absorbs red light for photosynthesis and strongly reflects near-infrared light due to its cellular structure. [4, 9, 13]
Question 4: A remote sensing satellite with high radiometric resolution is particularly valuable for which of the following tasks?
- Distinguishing between very small, adjacent objects on the ground.
- Identifying a wide range of different mineral types based on their unique reflectance.
- Detecting subtle variations in water turbidity or soil moisture. (Correct answer)
- Monitoring rapid changes in land cover, such as the daily melting of snow.
Correct answer: Detecting subtle variations in water turbidity or soil moisture.
Radiometric resolution refers to the sensor's ability to discriminate very slight differences in energy, which translates to the number of brightness values it can record (e.g., 8-bit vs. 12-bit). [19, 29, 30] High radiometric resolution is crucial for applications that require detecting subtle changes in surface properties, such as water quality or soil moisture content.
Question 5: A GIS analyst has a high-resolution (1-meter) panchromatic image and a lower-resolution (4-meter) multispectral image of the same area, acquired at the same time. To create a single, high-resolution color image that combines the spatial detail of the first image with the spectral information of the second, which image processing technique should be used?
- Orthorectification
- Supervised Classification
- Pan-sharpening (Correct answer)
- Georeferencing
Correct answer: Pan-sharpening
Pan-sharpening is an image fusion technique that uses a higher-resolution panchromatic (grayscale) image to increase the spatial resolution of a lower-resolution multispectral (color) dataset. The result is a single image with the best characteristics of both inputs: high spatial detail and multiple spectral bands. [1, 6, 18]
Question 6: Which of the following describes the spectral resolution of a satellite sensor?
- The size of the smallest object on the ground that can be distinguished in an image.
- The frequency with which the sensor can acquire an image of the same location.
- The number and width of the specific wavelength bands the sensor can capture. (Correct answer)
- The sensitivity of the sensor to differences in signal intensity or brightness.
Correct answer: The number and width of the specific wavelength bands the sensor can capture.
Spectral resolution defines the ability of a sensor to distinguish between different wavelengths of the electromagnetic spectrum. A sensor with high spectral resolution can capture data in many, narrow bands, which is useful for identifying specific materials based on their unique spectral signatures. [21, 23]
GIS - Geographic Information System Remote Sensing and Imagery Questions and Answers
An agricultural analyst needs to monitor the health of crops throughout a growing season to detect stress and optimize irrigation.
This requires frequent observation of the same area to track changes in vegetation vigor.
Which type of remote sensing resolution is most critical for this application?