Declared vs. undeclared sites: what satellite imagery can confirm
The distinction matters before you even open the imagery. A declared site is one the state has listed under its safeguards agreement, the facility type, location, and material inventory on file, subject to the access and reporting that declaration carries with it. An undeclared site is everything else a state might be using for related purposes but hasn't put on that list.
It might be flagged by a procurement pattern, a defector account, an intercept, or just a shape in open-source imagery that doesn't match any known civilian use. No inspector has standing access to it. No material balance exists for it. That gap is exactly why imagery ends up doing so much of the early work.
What the imagery layer confirms
A VHR pass over a site answers questions about the ground, not about the program behind it. It can confirm that a foundation has been poured where there was bare earth six weeks ago. The volume of material removed from an excavation is measurable too, which matters when the shape and depth of a cut are consistent with a tunnel portal rather than a drainage project. Hardening shows up the same way: berms going up, a security perimeter extended, overburden added over a structure that wasn't there in the prior pass. A new building's footprint and roofline are confirmable as well, along with whether that footprint has grown or been reconfigured since the last look.
For a declared facility, this is a cross-check against the declaration on file. A cooling tower appears, a new wing goes up, and you compare that physical change against what the state has told the IAEA or the relevant treaty body it's doing there. For a suspected undeclared site, imagery is often the only cross-check available at all. There's no declaration to check it against, so the construction record is the record.
Where the inference stops
None of that tells you what's inside the building once the roof goes on. A footprint consistent with an enrichment hall is also consistent with a dozen other industrial uses, and optical imagery at 0.5 m doesn't resolve centrifuge cascades through a roof. It doesn't give you isotopic composition, material flows, or throughput. It doesn't tell you intent, whether the hardening around a structure reflects a weapons program or a conventional munitions depot getting a facelift. And it has no view of history before your archive starts. A site excavated five years before the first available pass is a blank page, construction-wise, no matter how good the sensor is now.
This is the part worth saying plainly because it gets glossed over in pitches for this kind of tool: imagery narrows where attention and other verification methods should go. It doesn't substitute for environmental sampling, declaration review, or the access an inspector actually gets once a site is on the list. A confirmed excavation is grounds to push harder on declaration review, sampling, and the access channels that can answer what the excavation means.
Declared and undeclared sites need the same discipline
Practically, the workflow looks the same whether the site in question is declared or suspected. Someone has to pull this week's pass, line it up against last week's, and look for what changed. Doing that by hand across an archive, corner by corner, is where fatigue causes flagged activity to get missed, even in imagery that shows the change clearly.
Facility Expansion is built around that one task: a single named site, watched weekly, with new construction, excavation, and hardening flagged as they show up, plus a volumetric read on what's been dug and a footprint read on what's been built. It tells you that the structure is there, how much ground moved, and when it changed, which is the part you need before anything else on your list gets actioned. What's inside the new structure, and why the state built it, stays outside that scope.
If a specific site is on your watch list and the weekly comparison is eating time you'd rather spend on analysis, see how a weekly site watch handles the construction side of that.