Raw Satellite Pass vs. Composite SST
A raw pass is exactly what one satellite measured during one overflight: real gaps where cloud blocked the view, usually a few hours old. A composite is a processed daily analysis, blended from multiple sources to fill those gaps, usually a day or more old. They're not two views of the same product; they're different products with different tradeoffs.
What a raw pass is
Every raw pass on Chlorofishy comes from a named instrument on a named satellite (VIIRS aboard Suomi-NPP, NOAA-20, or NOAA-21; MODIS aboard Aqua) and carries its own resolution and capture time. VIIRS SST passes run about 2km native resolution; MODIS SST passes run about 1km. Nothing is filled in: if cloud sat over a stretch of ocean during that specific overflight, that stretch shows up as no data, because the sensor genuinely couldn't see through it. See why your chart is blank for the mechanics of that gap.
What a composite is
Chlorofishy's SST composite is NASA's GHRSST MUR (Multi-scale Ultra-high Resolution) Level 4 analysis: a single blended picture of the entire global ocean, 1km resolution, built once a day from several sensors combined. It publishes on a measured lag of about 34 hours after the observation date. A Level 4 product like MUR is explicitly an analysis, not a direct observation. GHRSST's own product definitions describe it as a gap-free, spatially complete estimate built by combining and modeling multiple data sources, distinct from the swath-level Level 2 and Level 3 products that carry only directly-measured pixels. See how cloud-free SST charts work for the mechanism, and is cloud-free SST real or interpolated for how much of a composite pixel is a real reading versus a modeled estimate.
Side by side
| Raw pass | Composite | |
|---|---|---|
| Coverage | Real gaps where cloud blocked the sensor | Gap-filled, complete |
| Age | Typically a few hours | ~34 hours (SST), ~12–14 hours (chlorophyll) |
| Source | One named sensor, one overflight | Blended from multiple sensors |
| Best for | Freshness and precision: finding a break where it is today | A reliable, complete daily picture for scouting |
Which one to use
Start with the composite to scout a region: it's always there and always complete. Switch to a raw pass when timing or precision matters more than coverage, which is most of the time you're actually trying to find a specific break. See finding temperature breaks for that exact workflow on the map, or open the SST map to see both product types side by side for any region. For what each plan unlocks, see pricing. Back to Learn.