SAR processing algorithms are available in open world academic literature (papers and books). Though I don’t know the specifics of the system in the article to

SAR processing algorithms are available in open world academic literature (papers and books). Though I don’t know the specifics of the system in the article to know whether that specific algorithm is subject to any sort of export restrictions. Most implementations I’ve come across are variations of the standard textbook approaches, with modifications made for computational efficiency or a little company-specific secret sauce (think proprietary techniques) thrown in. If you’re looking for some search terms, you might try: “polar format”, “range migration”, or “tomographic backprojection”. The first two are Fourier-transform based approaches that are relatively computationally efficient. The last, in its textbook form is O(n^3) — less efficient.