Across-track vs along-track scanners — examples?
essential sensors

Two scanning geometries used by multispectral sensors:

  • 🔄 Across-track (whiskbroom)
    • How: discrete detectors + scanning mirror sweeps perpendicular to flight
    • Examples: Landsat MSS, TM, ETM+
    • Drawback: moving mirror = mechanical wear
  • ➡️ Along-track (pushbroom)
    • How: linear array of detectors — no moving parts
    • Examples: SPOT HRV, IRS LISS, IKONOS, QuickBird, Landsat 8/9 OLI
    • Wins on: longer dwell time → better SNR, more reliable
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Whiskbroom WIGGLES a mirror (Landsat 1–7). Pushbroom PUSHES a linear array straight ahead (SPOT, IKONOS, Landsat 8/9 OLI). No wiggle, no breaking part.

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