Thinking about the main question here, not the example question (I've just migrated it to Astronomy since it went into public beta maybe an hour ago), this question of remote sensing is gonna be really tricky to define in advance, in my opinion. We do have a few guidelines though, I'll describe them later.
I would say that any technological or scientific aspects of payloads that have space application should be on topic, but we have already established before that Earth observations aren't on topic, even though they would easily fall in the first category I described. To make it somewhat easier on me, I'll just quote that accepted and much upvoted answer by @DeerHunter for sake of convenience also here, and we'll try to build from there:
questions about lithosphere, atmosphere, hydro/cryosphere, ionosphere of Solar System bodies, if these questions can be
answered with current or near future technology (regardless of where
the scientific equipment is - down here on the Earth, in LEO, in orbit
around the body, or on the ground).
questions and answers that describe engineering considerations of concrete technologies used to solve planetary science puzzles
planetary geography questions
paleogeology questions for Solar System bodies that have been answered or can be practically answered in the near future
- speculative questions about exo-solar planets (until we have the technical means to narrow down the list of competing hypotheses)
- questions about Terran geology/atmosphere/hydrosphere insofar they don't relate to exploration of other Solar System bodies
- questions that require in-depth discussion of physics involved without touching upon practical engineering issues (migratable to
- questions about relativistic phenomena unless relevant for spaceflight
So Earth science is not on topic. There is an Area 51 proposal for Geoscience that I guess most such questions would be better cattered at, once the site is launched.
So taking all this into account, as far as payloads go:
Questions about technological or scientific aspects of payloads that have space application and are not asking about Earth science are on topic.
And inverse for off-topic. Well, my take at least, tho I might have forgotten to include/exclude something...