Two scanning geometries used by multispectral sensors, 0.3–14.0 µm:

• Across-track (“whiskbroom”) — a single detector + rotating/oscillating mirror sweeps perpendicular to the flight path. Examples: Landsat MSS, TM, ETM+.

• Along-track (“pushbroom”) — a linear array of detectors (one per pixel in the swath) builds the image as the platform moves forward. Examples: SPOT HRV/HRVIR, IRS LISS, IKONOS, QuickBird.

• Why pushbroom is better: longer dwell time per pixel → higher SNR and finer resolution; no moving mirror.