Lessons for radar: Waveform diversity in echolocating mammals

Copyright © 2008 IEEEEcholocating mammals such as bats, whales and dolphins have been using waveform diversity for over 50 million years. Synthetic systems such as sonar and radar have existed for fewer than 100 years. Given the extraordinary capability of echolocating mammals it seems self-evident that designers of radar (and sonar) systems may be able to learn lessons that may potentially revolutionize current radar-based capability leading to truly autonomous navigation, collision avoidance, and automatic target classification. Echolocating mammals have been little studied in relation to the operation of radar and sonar systems. In this article, we introduce a range of strategies employed by bats and consider how these might be exploitable in the radar systems of tomorrow. Specifically, we concentrate on the functions necessary for autonomous navigation. Echolocating mammals are known to vary their waveforms via modification to the pulse-repetition frequency (PRF), also known to biologists as pulse-repetition rate (PRR), power, and frequency content of their transmitted waveforms. This has enabled them to evolve highly sophisticated orientation techniques and the ability to successfully forage for food. Moreover, recent developments in technology mean that it is now possible to replicate these parametric variations in synthetic sensing systems such as radar and sonar.Michele Vespe, Gareth Jones and Chris J. Bake

Bioinspired low-frequency material characterisation

New-coded signals, transmitted by high-sensitivity broadband transducers in the 40–200 kHz range, allow subwavelength material discrimination and thickness determination of polypropylene, polyvinylchloride, and brass samples. Frequency domain spectra enable simultaneous measurement of material properties including longitudinal sound velocity and the attenuation constant as well as thickness measurements. Laboratory test measurements agree well with model results, with sound velocity prediction errors of less than 1%, and thickness discrimination of at least wavelength/15. The resolution of these measurements has only been matched in the past through methods that utilise higher frequencies. The ability to obtain the same resolution using low frequencies has many advantages, particularly when dealing with highly attenuating materials. This approach differs significantly from past biomimetic approaches where actual or simulated animal signals have been used and consequently has the potential for application in a range of fields where both improved penetration and high resolution are required, such as nondestructive testing and evaluation, geophysics, and medical physics

MIMO Radar Ambiguity Properties and Optimization Using Frequency-Hopping Waveforms

The concept of multiple-input multiple-output (MIMO) radars has drawn considerable attention recently. Unlike the traditional single-input multiple-output (SIMO) radar which emits coherent waveforms to form a focused beam, the MIMO radar can transmit orthogonal (or incoherent) waveforms. These waveforms can be used to increase the system spatial resolution. The waveforms also affect the range and Doppler resolution. In traditional (SIMO) radars, the ambiguity function of the transmitted pulse characterizes the compromise between range and Doppler resolutions. It is a major tool for studying and analyzing radar signals. Recently, the idea of ambiguity function has been extended to the case of MIMO radar. In this paper, some mathematical properties of the MIMO radar ambiguity function are first derived. These properties provide some insights into the MIMO radar waveform design. Then a new algorithm for designing the orthogonal frequency-hopping waveforms is proposed. This algorithm reduces the sidelobes in the corresponding MIMO radar ambiguity function and makes the energy of the ambiguity function spread evenly in the range and angular dimensions

Sonar signal design and evaluation with emphasis on diver detection

Sonar-based underwater surveillance, including the problem of diver detection, is a challenging task. In harbors and coastal areas the environment is often reverberation dominated, due to the numerous backscattering objects and boundaries like ship wrecks, harbor walls, seabed, or the water surface. Reflections from the target and the background are often very similar, except for the fact that the target is typically moving and the background is not. The object movement causes a Doppler e_ect that can be used to improve the separation of moving objects from the quasi-stationary background. Therefore, the ideal active sonar transmit signal would simultaneously provide very good range and Doppler resolution. In this work, existing sonar signal designs are thoroughly analyzed and special emphasis is set to understand the sources of their advantages and disadvantages. Among all the investigated waveforms, frequency modulation (FM) signals have the best properties, but they lack Doppler selectivity that is required to detect small moving targets in reverberation limited environments. This motivates the development of a new design - called cutFM signal. The goal is to create a Doppler selective waveform based on a linear frequency modulated signal. The basic concept is to cut out frequency components from the base signal, in order to obtain a comb like spectrum. The effect of cutting is analyzed in detail and it is shown that the cutting period has to be carefully selected in order to achieve the desired result - a Doppler selective signal. The cutFM signal is compared theoretically and via simulations with corresponding known alternatives. It is characterized by a very good Doppler processing gain and excellent performance in reverberation limited channels. In addition, compared to the known continuous wave (CW) based signals that have equivalent Doppler processing gains, the cutFM signal provides improved range resolution