Plan observation opportunities

Canada launched the RADARSAT Constellation Mission, or RCM, on June 12, 2019. Its three radar satellites extend a national observation program that began with RADARSAT-1. The archive records RCM 1, RCM 2 and RCM 3 identify separate spacecraft sharing a mission; the existing RADARSAT family course supplies the wider history. RCM became operational in late 2019, after deployment and commissioning.

The satellites operate roughly 600 kilometres above Earth in a common orbital plane. With an orbital period near 96 minutes and three evenly spaced spacecraft, the interval along that orbit is about 96 ÷ 3 = 32 minutes. That spacing creates additional viewing opportunities. It does not mean the same place on the rotating Earth is photographed every 32 minutes.

The launch photograph shows the Falcon 9 first stage returning with its landing legs extended. Recovering the booster was a different operation from deploying and checking the satellites. A successful landing photograph cannot demonstrate that the radar instruments are calibrated or their data are reaching users.

CSA describes daily access to much of Earth and frequent opportunities over Canada’s north. Access means the spacecraft and sensor can potentially view a location. Acquisition means an instrument actually records it. Usability adds the appropriate mode, quality and timing for the question being asked. Those are three separate conditions.

Imagine a flood analyst requests a new image of a river valley. A suitable pass must intersect the area, the radar must be scheduled in an appropriate mode, and the system must have enough available power, recording capacity and downlink opportunity. Other requests compete for the same resources. A map of potential coverage does not promise that every requested image already exists.

In an original scheduling exercise, assume a satellite has a 15-minute imaging allocation for one orbit. Three requests need 6, 5 and 7 minutes. Their total is 18 minutes, so they cannot all fit unchanged. A planner might shorten a request with the user’s agreement, choose a different pass or prioritize an urgent need. These values illustrate allocation; they are not a reconstruction of an RCM operations schedule.

From access to an observation

A relook can observe a place from a different viewing geometry. An exact orbital repeat returns to a repeating ground-track geometry. RCM’s constellation supplies a four-day exact repeat, whereas a single member has a twelve-day cycle. Those numbers describe the orbital design, not a guarantee that every matching pair was collected.

For a changing coastline, a different-angle image tomorrow may answer an urgent extent question. For a careful interferometric comparison, matching geometry and compatible radar settings become much more important. The best observation schedule depends on the measurement, not only on which date comes first.

Keep the actual acquisition time beside the result. A frequently revisiting constellation can still supply an old image if a request was missed, a suitable product failed quality checks or the archive selection used the wrong date.