Simulation of Airborne Radiometric Detection of Wake Vortices

This paper describes an analysis of the potential of using an airborne Fourier transform spectrometer (FTS) or radiometer to detect wake vortices. The goal was to determine the requirements for an infrared (IR) FTS to effectively detect wake vortices. Initially, a theoretical analysis of wake vortex detection by thermal radiation was realized in a series of simulations. The first stage used the Terminal Area Simulation System (TASS) dynamic model to simulate wake vortex temperature, moisture, and velocity fields. The second stage used these fields as input to the line-by-line radiative transfer model (LBLRTM) to simulate responses from both an imaging IR hyperspectral FTS and an IR imaging radiometer. These numerical simulations generated FTS and radiometer imagery that was compared with the original temperature data. This research supported an effort, using ground-based imaging FTS instruments, to make measurements of wake vortices of various landing aircraft. Results from two different field campaigns have been previously reported. Instrument specifications for wake vortex thermal detection are recommended for an imaging radiometer sensitive within the following two narrow spectral bands: 670–750 cm⁻¹ and 2200–2350 cm⁻¹ . The instrument must have at the very minimum a noise equivalent differential temperature < 2 mK and a spectral resolution of at least 32 cm⁻¹.