A variety of strategies have been employed to remotely sense changes in the upper atmosphere due to sprites and elves. These include the use of low-light video imagery, cooled CCD cameras, radio receivers from ultra-low to very-high frequencies, photometers, radar systems, spectrographs, and high speed imagers. The primary method used in this work involves an array of high speed photometers designed specifically for the detection of elves, but the photometric measurements are supplemented by ELF/VLF radio recordings and various image-intensified video systems.
The atmospheric propagation of radio and optical signals is discussed below in Sections 3.1 and 3.2. Section 3.3 addresses the theory of photometric measurements made over a wavelength range that is large compared with details in the observed spectrum and with variations in the instrument response. The subsequent sections cover the optical instrumentation used and discuss calibration and determination of pointing direction.