Recovering data and voice recorders following at-sea crashes

The international aviation safety community has concluded that existing methods of blackbox localization and recovery are not effective in deep ocean situations, and occasionally not effective even in relatively shallow water when the acoustic pinger is buried or covered in debris. The majority of these pingers are provided by two companies, Teledyne Benthos and Dukane, according to pre-determined form and function, and these devices are essentially "built to spec." The purpose of this paper is to identify the shortcomings in the existing, decades-old functionality and to recommend the introduction of acoustic modem technology to provide orders of magnitude improvement in blackbox localization and data recovery. Fundamental ocean physics clearly indicates that the following conceptual changes should be considered: 1. The current pinger technology operates at nearly 40 kHz frequency. Simply reducing the frequency to perhaps 12 kHz will substantially increase range in seawater and even improve performance when the device is covered in sand or debris. 2. The devices use very short sinusoidal tones (usually called tonals) as their signals. Ocean propagation often is highly selective in frequency due to the constructive and destructive alignment of propagation paths some frequencies are supported, others are canceled. Furthermore, it is difficult to transmit sufficient energy into the water with these signals. Tonals are very poor candidates for robust, reliable ocean signaling. In addition to fundamental issues, the current system operates by a water-activated commencement of repetitive transmissions (pings) of these short tonals the moment the device enters the water even though no listening devices are present. This is a waste of energy. In this paper, we provide a brief overview of acoustic propagation from the perspective of its differences with more commonly understood radio frequency (RF) propagation. We follow that with our suggestions for substantial changes in operational concept, specifically arguing for wider bandwidth waveforms with more sophisticated receiver processing. However, given the effort to utilize more complex systems, we recommend they be further adapted to support underwater acoustic communications (acomms). This will provide blackbox and crash recovery far more effectively than is now possible, and can support data recovery when the devices themselves cannot be recovered. In particular, acomms modems can be used in support of long-range, accurate position estimation by either manned or unmanned platforms. Our proposed system will be somewhat larger than the present system, but it will significantly enhance the ability to find a submerged black box.