Match scale and time to coastal change

The 2023 design baseline gives the visible/near-infrared camera 200-metre regional and 800-metre global sampling at nadir. It separately describes 400-metre regional sampling for the near-/shortwave-infrared camera. These are dated requirements for different channels and scenarios, not evidence that every future product will contain equally detailed information.

An ideal 800-metre square covers sixteen 200-metre squares: four along each side. That area ratio explains why a narrow coastal feature may be diluted in a coarser cell. It does not prove a sixteen-fold increase in measurement accuracy, and resizing the coarse image does not recover the lost independent observations. Product uncertainty depends on more than cell size.

Consider a fictional 800-metre cell crossed from edge to edge by a 200-metre-wide plume. In a simple aligned model, one quarter of the cell is plume and three quarters is surrounding water. If a chosen signal is eight units inside and two outside, an area-weighted average is 0.25 × 8 + 0.75 × 2 = 3.5 units. The coarse value is neither of the two pure signals.

This linear mixing example is a teaching approximation, not a chlorophyll retrieval or a claim that every optical effect mixes linearly. The actual coast may include land adjacency, suspended sediment and changing water depth. Before comparing a narrow estuary with open ocean, check whether the spatial scale and algorithm suit both environments. A fine-looking screen display cannot resolve that question.

A narrow plume can be diluted in a coarse cell

The mission overview describes a two-day revisit target. For an optical ocean study, an opportunity does not guarantee a clear, valid observation. In an original sequence, day 0 is usable, day 2 is cloudy and day 4 is usable. The observed comparison spans four days; the missing middle scene is not a zero chlorophyll measurement and should not be plotted as one.

A multi-day composite can increase valid coverage while combining observations made at different times. Record the contributing dates, quality screening and number of accepted samples. If a plume moves rapidly, a composite can blend stages of that motion. Choose a product whose time window answers the question rather than assuming that a more complete-looking map is a single simultaneous view.