Is Cloud-Free SST Real Data or Interpolated?

Both, depending on the pixel. Where a satellite actually measured the surface, a composite carries that real reading. Where cloud blocked every sensor at once, the composite fills the gap with a modeled estimate built from nearby and recent real measurements, and the honest answer is that most fishing apps don't tell you which pixel is which.

What “analysis” means in GHRSST's own terms

Chlorofishy's SST composite is GHRSST's MUR Level 4 product. GHRSST's own product definitions classify Level 4 explicitly as an analysis: a gap-free, spatially complete field produced by combining and modeling data from multiple sources, distinct from Level 2 and Level 3 products, which carry only pixels a sensor directly measured. That's not a euphemism for “made up”: the modeling is constrained by real, recent measurements from nearby in space and time, but it is a different kind of number than a raw pass pixel.

Why this distinction matters for finding fish

A modeled estimate smooths toward its neighbors. If a real, sharp temperature break exists under a cloud bank, a composite can blur it or miss it entirely: the analysis has no way to know the break is there if every sensor that could have seen it was blocked. A raw pass never has this problem, because it never invents a reading: it just has a hole instead. That's the core tradeoff: composite coverage vs. pass precision.

How Chlorofishy labels the difference

Every layer on the map states which product type you're looking at and never presents a composite as raw pass data, one of Chlorofishy's non-negotiable data-integrity rules. Where a composite genuinely has no coverage at all (not modeled, not measured), it's labeled “No data (gap),” distinct from a pass's “No usable data.” See how cloud-free SST charts work for the blending mechanism itself, and why there are holes for how the two no-data labels work on the map.

Compare a pass against the composite yourself on the SST map, or see pricing for access to raw passes in your region. Back to Learn.