How Often Do SST Satellites Actually Pass Overhead?

A single polar-orbiting satellite crosses any given patch of ocean roughly twice a day. Chlorofishy ingests four such satellites (three VIIRS, one MODIS) plus two Sentinel-3 satellites for chlorophyll composites, so the real revisit rate you experience is considerably faster than any one satellite's own schedule.

Why polar orbiters see everywhere, but not often

VIIRS and MODIS both fly on polar, sun-synchronous orbits: the satellite crosses from pole to pole while the Earth rotates underneath it, so each orbit images a different north-south strip. NOAA's own JPSS program describes its satellites circling pole to pole 14 times a day, which adds up to full global coverage roughly twice daily per satellite. That's the tradeoff against a geostationary weather satellite, which stares at the same hemisphere continuously but can't resolve ocean detail the way a low-orbiting sensor can.

More satellites, more chances per day

Twice a day from one satellite isn't the whole story, because Chlorofishy doesn't rely on one. VIIRS flies aboard three separate satellites (Suomi-NPP, NOAA-20, and NOAA-21), each on its own orbital track, so a given region can see a VIIRS overflight several times a day rather than twice. Add MODIS aboard Aqua, and the realistic number of chances for a clear pass over any one region in a 24-hour window is well above what a single-satellite schedule would suggest. See do all fishing apps use the same satellite data for why the number of satellites an app actually ingests matters as much as which sensor it uses.

The chlorophyll composite's source: Sentinel-3, in tandem

The two Sentinel-3 satellites (3A and 3B) fly the same orbit 180° out of phase specifically to shorten revisit time. ESA's own Sentinel-3 OLCI documentation states the two-satellite configuration achieves global coverage in under two days at the equator, versus roughly four days for a single Sentinel-3 satellite alone, the whole reason ESA operates them as a pair.

Per-pass cadence

Chlorofishy's own backup routing measures new granules arriving from VIIRS at roughly every 101 minutes and from AMSR2 at roughly every 99 minutes during active coverage windows, a practical, per-route cadence figure distinct from (and faster than) any single satellite's full-orbit revisit time, since it reflects how often a usable new pass actually shows up in the pipeline.

For per-product resolution alongside this cadence, see native resolution, explained. Step through today's actual passes on the SST map. Back to Learn.