May 16, 2013:
Many new sensors have been developed for large UAVs in the last decade, and this has greatly increased the amount of digital data that has to be transmitted back to operators for analysis and action. This quick increase exceeded the amount of satellite bandwidth (how much data could be handled at once) available. Video images and radar data take up a lot of bandwidth, and it soon got to the point where a few UAVs pumping out a lot of data could exhaust the satellite communications capability available or force the user to buy a lot of very expensive commercial bandwidth.
To overcome this problem, new software was developed that screens the video and other sensor (radar, infrared, and so on) data and only transmits what is useful. This is possible because most of the video transmitted is of terrain, with no people, or much of anything moving. It's been discovered that you can place sufficient computer hardware on a UAV, along with the proper software, to check the video as it is coming in and only pass on, via the satellite, images that shows signs of having information the operators are looking for. A video buffer on the UAV keeps some of the "unneeded" video, in case the operators want to double check. Operators also appreciate the fact that they no longer have to spend so much time staring at nothing. This reduces operator fatigue and reduces the number of operators needed. Tests soon revealed that these systems work and greatly reduce the amount of satellite capacity (bandwidth) required to support UAVs. Not all UAVs have this software yet and it will be years before all can be equipped with this solution.
Many UAVs use another solution, which is sending the video directly to the user. This limits how far the UAV can be from the base station but it eliminates the expense and limitations of a satellite link. All this enables more UAVs to be up there at the same time. Sometimes the satellite communications can still be used (reducing the need for a second set of communications gear) by directing it to balloons or aircraft carrying satellite type transponders that relay the data to ground stations, where there are personnel and equipment for analysis.
As a growing number of more powerful sensors are being installed in large (one ton and up) UAVs, the onboard analysis software becomes essential, given the limited amount of satellite bandwidth available and the expense of using what is available (either on military communications satellites or commercial ones).