This paper presents the issues in snow water equivalent (SWE) determination using acoustic reflectometry. To determine SWE, the density and the depth of each layer of snow in a snow pack need to be estimated. A noninvasive acoustic reflectometry technique to estimate the SWE is proposed in the mentioned paper, in which it is shown that SWE of the snowpacks with approximately 100 cm depth can be determined using a maximum length sequence (MLS) of length 7 as a probe signal. We performed similar experiments as reported in the mentioned paper to determine SWE using acoustic reflectometry but failed to replicate the given method. The signal processing-related issues such as design of probe signal, direct pickup problem, and so on of the mentioned paper are investigated and presented in this communication. We show that it is not possible to extract the reflection response by using the MLS of length 7 as a probe signal. The amount of sound attenuation and absorption in the snow medium is very high, of the order of 1 dB/cm and greater depending on the frequency, as reported in the literature and measured by us. Hence, the depth of snowpack investigated in the mentioned paper is practically difficult to achieve using conventional loudspeaker and microphone. Also, it has been explained how the cross-correlation peak width and, hence, the layer resolution achieved by the authors of the mentioned paper is not practically feasible by their reported method. We have also demonstrated that Wiener spiking deconvolution-based technique is not able to obtain the sharp peaks as shown in the mentioned paper.

In this correspondence, in an extension of Piret's bound for codes over phase-shift keying (PSK) signal sets, we investigate the application of the Gilbert-Varshamov (GV) bound to a variety of distance-uniform (DU) signal sets in Euclidean space. It is shown that four-dimensional signal sets matched to binary tetrahedral, binary octahedral, and binary icosahedral groups lead to better bounds compared to the bounds for signal sets matched to dicyclic groups with the same number of signal points and comparable symmetric PSK signal sets.

A novel technique for implementing the CZT-beamformer for high-resolution sector scanning sonar which results in a very compact hardware is presented. A Delta-modulator is used to encode the spatially sampled sensor signals from a linear array in single-bit format, thus allowing the use of shift registers in place of analog bbd's. Another novel feature is the combination of bandpass sampling and spatial multiplexing into a single operation. The paper discusses this implementation of the CZT-beamformer, and provides simulation results and comparison with the conventional CZT-beamformer. These results demonstrate the potential of the novel technique for compact systems. A complete beamformer hardware has also been developed for a specific application.

The complexity of implementing a multi-channel real-time FFT processor is examined with emphasis on memory specifications and processor performance, Design alternatives are considered and finally the design of an optimal processor is presented. The designed system is microprogrammed and optimised for pipeline processing. A reduction of a factor of four in the mass storage speed has been achieved at the expense of a small size high-speed memory.

A new Beamformer (BF) technique using Linear Deltamodulation (DM) on the spatially sampled circular array sensor signals is presented. In this method, the FIR-type of beam-former implementation for circular arrays results in an extremely simplified hardware which does away with multipliers and retains basically adders. Thus, the immediate problem of large word-size is considerably resolved. The DM-type of BF by virtue of the implementation, provides an additional advantage of beam-space interpolation. Various aspects of array gain, sidelobes and noise performance are dealt with the help of simulation studies. Hardware structures both for fixed and programmable beamformer coefficients are also proposed which bring out the potential of this technique for compact sonar systems.