OK let's talk. Why would anyone need to hide on the "under side" of earth? It is far too easy already for those in power to hide in the most remote places on known territory, places that are completely inaccessible to the normal population.
The only thing I can think of would be to hide weapons testing or even a separate population, but still all of that can be done in the Arctic or in underground chambers.
"Satellites" can detect almost anything on the planet, but we have no way of launching them under the planet and still maintaining control or contact. The underside can work in complete secrecy, so it makes complete sense for an advanced society to build and develop a true invasion force. Similar to the Nazi base depicted being on the dark side of the moon in the movie Iron Sky.
Are you not interested in what goes on on the dark side of the earth?