The largest temporary Russian base near the Ukrainian border is seeing more activity, according to an analysis of the latest satellite imagery.
Pictures reveal further accommodation being constructed, armoured vehicles being moved, and troop tents being occupied.
But what they don't show might be just as important.
Despite reports of tanks and missile launchers being moved across Russia toward Ukraine and Belarus, much of this equipment hasn't been picked up in the latest imagery.
It has prompted analysts to ask if Russia is covertly storing this hardware and to question exactly where it is being moved to.
The base at Yelnya is the largest near the border, 150 miles from Ukraine. A build-up of equipment began at Easter, resulting in dozens of vehicles stationed there by October, as seen here.
By November, tanks, armoured vehicles and missiles had moved to the base, with more troop tents also springing up.
And by late December a blanket of snow covered yet more military hardware.
The latest satellite imagery from 19 January shows a further increase in activity at Yelnya.
A closer look reveals where Russian troops are living at the base and which vehicles are being moved.
This image from 19 January shows almost the entire base, covering nearly a square mile.
Much of the recent changes have occurred in this southern corner of the camp.
32 tents have been constructed here - at least 10 more than were present on 29 December.
This walled compound has also been built in recent weeks. It is thought to be a temporary control centre, with trucks used as offices.
Back over in the northern section, there have been fewer changes. Here 35 tanks are parked and like many of the vehicles at the base, most do not appear to have moved for some time.
Few tire tracks and heavy snow suggest the 564 vehicles and pieces of equipment in this central area also show little sign of activity.
Alternatively, at this nearby site the road is muddied and a number of vehicles have been cleared of snow.
Likewise a further group of vehicles nearby appear to have been active. A military analyst told Sky News it is likely they have been fired up for maintenance purposes.
But if vehicles are moving, where are the soldiers?
Another image taken on 19 January can help reveal the troop activity.
The picture below shows an area a few hundred metres above that shown in the previous image.
In December tents had been erected but few visible paths in the snow suggest little sign of activity.
But this latest image shows the tents in the centre clear of snow - likely due to them being heated - and heavy footfall trampling the surrounding area.
While activity at the camp appears to have changed, an analyst at the defence intelligence company Janes told Sky News they estimate there are still only about one-half to a third of the number of troops needed to fully operate the equipment at the base.
In light of numerous reports of yet more hardware being moved towards the borders of Belarus and Ukraine, the increase in equipment build-up is moderate at Yelnya.
Two more bases however, far closer to the Ukrainian border, have been identified in the latest imagery.
This picture taken of a storage facility in Klimovo eight miles from the Ukrainian border shows armoured personnel carriers, alongside numerous logistics vehicles.
Most of the vehicles in Klimovo are trucks, but the rounded edges of armored vehicles can be seen in one corner of the base.
And the picture below shows another site within 30 miles of both the Ukrainian and Belarusian borders now populated with logistics trucks.
Analysis of open-source satellite data suggests the trucks likely moved in between 19-25 December.
But what is notable is that tanks and artillery are absent in these photos. This is despite the fact that social media videos have shown their presence in the wider area.
Janes, the defence intelligence company, told Sky News: "We monitored lots of armoured vehicles heading towards this area. We haven't seen them in these pictures, but it doesn't mean they are not there. The tanks could be undercover, in warehouses, or in an undiscovered site."
It is thought there could be more small operating bases being populated with equipment.
Yelnya is unusual in having so much stored at one site, but finding these smaller bases in the vast expanse of Russia, according to one analyst, can be "needle in a haystack stuff - you need to be lucky to find it".
Credits
Writing and Reporting: Kieran Devine
Graphics: Pippa Oakley
Digital Production: Kieran Devine and Jack Taylor
Satellite Imagery: Maxar, Planet Labs PBC
The Data and Forensics team is a multi-skilled unit dedicated to providing transparent journalism from Sky News. We gather, analyse and visualise data to tell data-driven stories. We combine traditional reporting skills with advanced analysis of satellite images, social media and other open source information. Through multimedia storytelling we aim to better explain the world while also showing how our journalism is done.
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