Russia has had nearly six months to prepare the ground for Ukraine's anticipated counteroffensive this spring, building an elaborate array of defenses in occupied territory near the front lines.

Breaking through will present a huge challenge for Kyiv's troops, with obstacles extending hundreds of miles across the meandering southern front – where Ukrainian forces are expected to concentrate their attacks in the coming weeks.

Satellite imagery reviewed by CNN and other news organizations shows the extent of Russia's defenses: layers of anti-tank ditches, obstacles, minefields and trenches.

The challenge for Ukrainian troops will be to bypass or overcome such obstacles at speed, creating momentum that causes Russian command and control to melt down.

Months of preparation: Ground defenses began to appear after Russian forces withdrew from part of the Kherson region in November, and they essentially established a new defensive line stretching across largely rural areas of southern Ukraine.

The defenses, including concrete "dragons' teeth" tank obstacles, are only as good as the Russian forces assigned to each sector. On their own, they are a limited impediment.

Moscow has pushed more units into southern Ukraine over recent weeks, but it remains to be seen how many Russian troops – and of what quality – are assigned to each section of such a long front line.

No surprises: Ukrainian officials have acknowledged that unlike last September’s sudden sweep through much of the northeastern Kharkiv region, they may lack the element of surprise in any larger counteroffensive.

Ukraine does have the advantage of choosing where and when to go, and with what concentration of forces. Once the assault begins, other factors could come into play: everything from the weather to Russia’s capacity and desire to counterattack, plus aerial fighting.

Read more and view satellite images of Russia's defenses here.

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