NASA's Scientifically Calibrated In-Flight Imagery (SCIFLI) project team at NASA's Langley Research Center in Hampton, Virginia, had their eyes, cameras and telescopes trained on the Falcon with the help of two long-range aircraft provided by NASA and the U.S. Navy.
Nose-mounted gimbaled IR system
A NASA WB-57, a twin jet engine high-altitude research aircraft from Johnson, was equipped with a long-range infrared optical system to capture the images. It is a unique full-motion video camera system that is gimbal-mounted on the nose of the WB-57. It collects full-color high definition and infrared video.
A Navy NP-3D Orion aircraft from the Naval Air Systems Command Weapons Division's Air Test and Evaluation Squadron-30 at Point Mugu, California, was equipped with a long-range infrared optical system and also took thermal images of the launch.
On launch day, the WB-57 and NP-3D Orion reached their observation locations about 50 miles from the projected rocket trajectory. After launch, the rocket emitted enough thermal energy for the plane's infrared cameras to catch a glimpse. Both flight crews then worked to obtain data as the first stage descended at supersonic speeds off the coast of Georgia.
Source: http://www.nasa.gov/press/2014/october/new-commercial-rocket-descent-data-may-help-nasa-with-future-mars-landings/#.VEUZ3h_HmkA