Choose between detail and coverage

ASAL describes AlSat-1’s multispectral ground sampling as 32 metres, with green, red and near-infrared bands. Near-infrared is outside ordinary human vision; displaying it in a visible colour can make vegetation patterns easier to inspect. The displayed colour is a representation of selected measurements, not necessarily how the ground looked to a person.

Ground sampling distance describes the spacing of samples projected onto the ground. In a simplified square-grid model, a 32-metre sample covers 32 times 32, or 1,024 square metres. That does not guarantee that every object of that size is separately recognizable. Blur, contrast, mixed land cover, atmosphere and viewing geometry affect interpretation. A narrow road can influence a pixel without yielding a reliable road-width measurement.

For ALSAT-1B, the technical descriptions specify 24-metre multispectral and 12-metre panchromatic imaging. A panchromatic channel measures light over a broader wavelength range rather than providing the same set of separate colour measurements. In a square-grid teaching model, one 24-metre cell covers the area of four 12-metre cells: 576 divided by 144 equals four.

ASAL also describes an enhanced 12-metre multispectral product made by combining information from the panchromatic and multispectral observations. This process, often called pan-sharpening, can help show spatial structure with colour. It does not mean each original multispectral band independently measured every 12-metre cell. When comparing products, ask what was acquired and what was inferred or transformed during processing.

One large cell, four smaller cells

Swath is the width of the strip observed across the ground. The original Alsat-1 design emphasized a broad swath, while SSTL describes a 140-kilometre swath for ALSAT-1B. A finer sampling number alone does not say how much territory fits in one image, how often the satellite can see a target or whether clouds obscure it. Choose a mode for the actual task.

For a fictional 280-kilometre-wide rectangle, two perfectly aligned 140-kilometre strips span the width if there are no gaps or overlap. A real acquisition plan may need more because of overlap, edge geometry, terrain, clouds and scheduling. This is a minimum geometric illustration, not a promise to map a region in two passes. Coverage, useful detail and delivery time must be considered together.