Question

Which one of the following options influences the pixel size of an image obtained from a whiskbroom optical remote sensing sensor?

• A. Sampling interval of the sensor (\(\Delta T\))
• B. Ground Projected Instantaneous Field of View (GIFOV)
• C. Ground Projected Field of View (GFOV)
• D. Both \(\Delta T\) and GIFOV

Hint:

Separate the optical footprint of a single detector (GIFOV) from how often that signal is digitized (the sampling interval); pixel size in the digital image tracks the latter.

Answer 1

The Correct Option is A

Step 1: Recall how a whiskbroom scanner builds an image.
A whiskbroom (across-track) scanner uses a single detector (or a small set of detectors) whose field of view is swept across the swath by a rotating or oscillating mirror, while the platform moves forward to build up successive scan lines. The detector's optics continuously receive radiance from the ground, and this continuous analog signal is digitized at regular time intervals to produce discrete picture elements.
Step 2: Distinguish the GIFOV from the pixel size.
The Ground-projected Instantaneous Field of View (GIFOV) is the ground footprint that the detector sees at any single instant; it depends on the detector's angular Instantaneous Field of View (IFOV) and the sensor altitude, and it fixes the spatial resolving power (the smallest ground feature the optics can distinguish, i.e. it governs blur). It does not by itself fix the number of digital samples recorded.
Step 3: Identify what actually sets the pixel size.
As the mirror scans and the analog detector output is sampled at a fixed sampling interval \(\Delta T\), each sample becomes one pixel. The ground distance covered between two consecutive samples, i.e. the ground sampling distance or pixel size, is therefore \(\Delta T \times (\text{angular scan rate}) \times (\text{altitude})\), a quantity controlled purely by the electronic sampling rate \(\Delta T\), independent of the optical footprint size (GIFOV).
Step 4: Note that GIFOV and pixel size can differ.
Many whiskbroom systems deliberately sample faster than one GIFOV-width per sample (oversampling) to reduce aliasing, so the pixel spacing can be smaller than the GIFOV footprint; conversely, undersampling can make pixels wider than the footprint. This shows pixel size and GIFOV are independently controllable, so GIFOV alone (option B) cannot be the answer, and both together (option D) is also incorrect since GIFOV does not directly set the sample spacing.
Step 5: Rule out GFOV.
The Ground Field of View (GFOV) describes the total ground swath imaged in one scan line (the full angular sweep projected on the ground), not the spacing of individual pixels within that swath, so option (C) is irrelevant to pixel size.
Step 6: Conclude.
The quantity that directly controls the ground sampling distance, i.e. the pixel size, of a whiskbroom sensor is its electronic sampling interval \(\Delta T\).
\[ \boxed{\text{Pixel size is set by the sampling interval } \Delta T} \]