Question

For a push-broom (along-track) sensor the following are known:
Field of view (FoV) = 2 degrees
Instantaneous FoV = 1 milli-radian
Time to scan one full scanline = $2 \times 10^{-2}$ s
Height above ground = 100 km
The dwell time for a single pixel of this sensor is ............................. s. (Rounded off to 2 decimal places)

Hint:

Push-broom: pixel dwell time $=$ line (frame) time.
Whisk-broom: pixel dwell time $=$ (scanline time) / (number of instantaneous pixels across-track).

Answer 1

For a push-broom sensor, an entire cross-track line is imaged simultaneously by an array of detectors. Hence a ground pixel remains within the detector’s view for the duration of one line acquisition (frame time). Therefore, the pixel dwell time equals the scanline time: \[ t_{\text{dwell}} = t_{\text{scanline}} = 2\times 10^{-2}\;\text{s} = 0.02\;\text{s}. \] (The given FoV and IFOV are useful to find the number of detectors: $N \approx \frac{2^\circ}{1\,\text{mrad}} \approx \frac{0.0349}{0.001}\approx 35$, but they do not reduce dwell time for push-broom; they would for a whisk-broom scanner, where $t_{\text{dwell}}=t_{\text{scanline}}/N$.)