Move the view and share the weather

A geostationary satellite remains approximately over a particular equatorial longitude. Moving to another longitude changes which region it can observe well. Meteosat 3 supported Atlantic coverage when the American weather-satellite system had a gap. ESA’s 1993 Earthview composite combines Meteosat-3 and Meteosat-4 observations from viewpoints at 50° west and 0°.

The composite makes a broad region easy to see, but it must remain labeled as a combination of two spacecraft views. It is not evidence that one satellite at one location photographed both viewpoints at once. The date belongs to the observations used to construct the composite, while its later publication date is a separate record.

First-generation spacecraft also supplied Indian Ocean coverage from 1998 to 2017. Moving a spacecraft changes the useful viewing region, but it does not turn an old instrument into a new-generation sensor. A shared service can use existing hardware differently to address a geographic gap.

Try an original planning case: two agencies have useful views of neighboring regions, but each has a weak view near its own horizon. Combining their observations can improve the regional picture if times, geometry and processing are understood. That cooperation is a service arrangement, not evidence that the spacecraft have become physically identical.

EUMETSAT operated a first-generation rapid-scanning service over the Alpine region at five-minute intervals from September 2001 to January 2007. Limiting the scanned area allowed faster repeats than the normal full-disc cycle. A five-minute regional product should not be described as five-minute full-Earth coverage.

In an original comparison, a 30-minute schedule has two intervals per hour, while a five-minute schedule has twelve. That is six times as many intervals for the selected region under the simplified schedule. The gain in repeat frequency does not automatically mean six times the spatial detail or six times the geographic coverage.