Processing of ELT Signals for Search and Rescue Satellite Aided Tracking (SARSAT) using the MEM and FFT

Abstract

<p>The proposed methods of search and rescue (SAR) of mobile platforms use low altitude polar orbiting satellites to detect signals emanating from emergency locator transmitter (ELT) systems on board the distress platform. The uplink transmission receives a doppler shift due to the radial velocity of the satellite. Extracting the doppler from the signal is necessary for calculating the position of the ELT system. These ELT units were originally designed for reception by ordinary hand held receivers and detection by the human ear. For this reason the transmitters employ a distinct type of modulation often referred to as a chirp. Detection and estimation of the doppler by signal processing is complicated by this swept modulation. This dissertation compares two methods of spectral estimation, namely, Fourier analysis (in the form of an FFT algorithm) and the maximum entropy method (MEM) for application to ELT signals. The signals to be processed are divided into two categories, single and multiple signals. Multiple signal processing is necessary when two or more ELT systems are transmitting simultaneously and the time separation between transmissions is small enough to cause overlapping of signals in time. Results indicate that the enhanced detection capability by using the MEM offers a significant improvement in processing signals from an ELT.</p>