Question 1

A false-color infrared (CIR) composite typically displays which band in the red channel, causing healthy vegetation to appear bright red?

Accepted Answer

The near-infrared band. In a standard color-infrared composite, the NIR band is mapped to red, the red band to green, and the green band to blue. Because vegetation reflects strongly in NIR, it appears bright red, which makes CIR imagery useful for vegetation analysis.

Question 2

An analyst wants to map surface temperature differences between urban and rural areas. Which spectral region is most appropriate?

Accepted Answer

Thermal infrared. Thermal infrared sensors measure emitted heat (radiant temperature) from surfaces, making them appropriate for mapping land surface temperature and urban heat island effects. Near-infrared and SWIR primarily measure reflected, not emitted, energy.

Question 3

An organization needs sub-meter detail for property-boundary mapping but also wants daily revisit for monitoring. A single sensor rarely provides both at once primarily because of:

Accepted Answer

The inherent tradeoff among the resolutions; very high spatial resolution usually comes with a narrow swath and longer revisit time. There is a fundamental tradeoff among the four resolutions. Very high spatial resolution typically means a narrow imaging swath and a longer time to revisit a given site (lower temporal resolution), while broad-swath sensors with frequent revisit tend to have coarser spatial resolution. Constellations of satellites are one way to mitigate this.

Question 4

An 8-bit image has most of its pixel values clustered between 40 and 120, appearing dull and low-contrast. Applying a linear contrast stretch will:

Accepted Answer

Reassign the input range (40-120) to span the full display range (0-255), increasing visual contrast. A linear contrast stretch maps the actual input brightness range to the full available display range (0-255 for 8-bit), spreading the values out so that subtle differences become visible. It improves visual interpretation but does not change the underlying information content the way correction steps do.

Question 5

A bi-temporal change-detection study compares two images of the same area. Before differencing the images, which preprocessing step is MOST critical to avoid spurious change?

Accepted Answer

Precise co-registration (geometric alignment) and radiometric/atmospheric normalization between the two dates. Reliable change detection requires that pixels in both images represent the same ground location (accurate co-registration) and that brightness values are comparable (radiometric/atmospheric normalization). Misregistration or uncorrected atmospheric/illumination differences create false change that is unrelated to actual surface change.

Data Acquisitions: GISP practice questions

A false-color infrared (CIR) composite typically displays which band in the red channel, causing healthy vegetation to appear bright red?

An analyst wants to map surface temperature differences between urban and rural areas. Which spectral region is most appropriate?

An organization needs sub-meter detail for property-boundary mapping but also wants daily revisit for monitoring. A single sensor rarely provides both at once primarily because of:

An 8-bit image has most of its pixel values clustered between 40 and 120, appearing dull and low-contrast. Applying a linear contrast stretch will:

A bi-temporal change-detection study compares two images of the same area. Before differencing the images, which preprocessing step is MOST critical to avoid spurious change?

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