An Improved RHCP Archimedean Spiral Antenna for Glacial Environmental Sensor Networks

An improved version of a printed RHCP Archimedean spiral antenna for glacial environmental sensor networks is presented. Two changes have been made to the previous design. Firstly, the microstrip connections between the balun and the antenna arms have been tapered. Secondly, the antenna arms have been rounded at the edges towards the antenna boundary. These measures have improved the antenna performance in the following ways. Firstly, the signal quality has been improved by minimizing reflections and signal distortion. Secondly, the microstrip tapering between the balun and the antenna arms has increased the radiating surface area in the region. Resultantly, significant improvements in the antenna’s reflection coefficient, gain, total efficiency, and axial ratio have been observed

Evaluating Effect of Block Size in Compressed Sensing for Grayscale Images

Compressed sensing is an evolving methodology that enables sampling at sub-Nyquist rates and still provides decent signal reconstruction. During the last decade, the reported works have suggested to improve time efficiency by adopting Block based Compressed Sensing (BCS) and reconstruction performance improvement through new algorithms. A trade-off is required between the time efficiency and reconstruction quality. In this paper we have evaluated the significance of block size in BCS to improve reconstruction performance for grayscale images. A parameter variant of BCS [15] based sampling followed by reconstruction through Smoothed Projected Landweber (SPL) technique [16] involving use of Weiner smoothing filter and iterative hard thresholding is applied in this paper. The BCS variant is used to evaluate the effect of block size on image reconstruction quality by carrying out extensive testing on 9200 images acquired from online resources provided by Caltech101 [6], University of Granada [7] and Florida State University [8]. The experimentation showed some consistent results which can improve reconstruction performance in all BCS frameworks including BCS-SPL [17] and its variants [19], [27]. Firstly, the effect of varying block size (4x4, 8x8, 16x16, 32x32 and 64x64) results in changing the Peak Signal to Noise Ratio (PSNR) of reconstructed images from at least 1 dB to a maximum of 16 dB. This challenges the common notion that bigger block sizes always result in better reconstruction performance. Secondly, the variation in reconstruction quality with changing block size is mostly dependent on the image visual contents. Thirdly, images having similar visual contents, irrespective of the size, e.g., those from the same category of Caltech101 [6] gave majority vote for the same Optimum Block Size (OBS). These focused notes may help improve BCS based image capturing at many of the existing applications. For example, experimental results suggest using block size of 8x8 or 16x16 to capture facial identity using BCS. Fourthly, the average processing time taken for BCS and reconstruction through SPL with Lapped transform of Discrete Cosine Transform as the sparifying basis remained 300 milli-seconds for block size of 4x4 to 5 seconds for block size of 64x64. Since the processing time variation remains less than 5 seconds, selecting the OBS may not affect the time constraint in many applications. Analysis reveals that no particular block size is able to provide optimum reconstruction for all images with varying nature of visual contents. Therefore, the selection of block size should be made specific to the particular type of application images depending upon their visual contents

A Low Profile Wideband RHCP Printed Archimedean Spiral Antenna for Glacial Telemetry Applications

Suitability of a RHCP printed Archimedean spiral antenna for glacier telemetry applications in the 433 MHz band has been assessed for the first time. The developed antenna provides a gain of 7.4 dBic at 433 MHz and a -10 dB fractional bandwidth of 47% in snow. The antenna beamwidths in the vertical planes cater for misalignments between the transmitter and receiver antennas due to basal sliding. The measured axial ratio remained below 1.4 dB between 330–580 MHz. Lastly, evidence has been provided towards suitability of the 433 MHz band for achieving communication ranges up to 2300 metres in ice

Landmark Based Audio Fingerprinting for Naval Vessels

This paper presents a novel landmark based audio fingerprinting algorithm for matching naval vessels' acoustic signatures. The algorithm incorporates joint time - frequency based approach with parameters optimized for application to acoustic signatures of naval vessels. The technique exploits the relative time difference between neighboring frequency onsets, which is found to remain consistent in different samples originating over time from the same vessel. The algorithm has been implemented in MATLAB and trialed with real acoustic signatures of submarines. The training and test samples of submarines have been acquired from resources provided by San Francisco National Park Association [14]. Storage requirements to populate the database with 500 tracks allowing a maximum of 0.5 Million feature hashes per track remained below 1GB. On an average PC, the database hash table can be populated with feature hashes of database tracks @ 1250 hashes/second achieving conversion of 120 seconds of audio data into hashes in less than a second. Under varying attributes such as time skew, noise and sample length, the results prove algorithm robustness in identifying a correct match. Experimental results show classification rate of 94% using proposed approach which is a considerable improvement as compared to 88% achieved by [17] employing existing state of the art techniques such as Detection Envelope Modulation On Noise (DEMON) [15] and Low Frequency Analysis and Recording (LOFAR) [16]

An Antenna Solution for Glacial Environmental Sensor Networks

Antennas used in glacial environmental sensor networks and reported in the last two decades have been reviewed. A link budget framework for designing such antenna systems is presented and used to design an antenna system for deployment at the Thwaites glacier, Antarctica. Design details of two left hand circularly polarized cross dipole antennas, one for englacial sensor probes and the other for supraglacial surface receivers are presented. The probe antenna is a 3D bent cross dipole that fits within a borehole of 8 cm diameter while providing a 1 dBic gain at 433 MHz in ice. The surface receiver antenna is a planar printed antenna providing a gain of 6.1 dBic with a quarter wave reflector. Both antennas provide 3 dB beamwidths of at least 50° in the xz and yz vertical planes catering for transmitter-receiver antenna misalignments caused by extended deployments. The antennas displayed good circular polarization and polarization purity traits. The 3 dB axial ratio bandwidths of both the antennas remained 54.9 %. The total efficiencies of the bent cross dipole and the surface receiver antennas were noted as 69.7 % and 86.9 % respectively. Lastly, the 433 MHz band has been validated for achieving englacial communication ranges of up to 2300 metres

Novel DEMON Spectra Analysis Techniques and Empirical Knowledge Based Reference Criterion for Acoustic Signal Classification

This paper presents some novel methods to estimate a vessel’s number of shafts, course, speed and classify it using the underwater acoustic noise it generates. A classification framework as well as a set of reference parameters for comparison are put forth. Identifying marine traffic in surroundings is an important task for vessels in an open sea. Vessels in vicinity can be identified using their signatures. One of the typical signatures emitted by a vessel is its acoustic measurements. The raw sonar data consisting of the acoustic signatures is generally observed manually by sonar operators for suggesting class of query vessel. The valuable information that can be extracted from the recorded acoustic signature includes shaft revolutions per minute (SRPM), number of blades (NOB), number of shafts, course and speed etc. Expert sonar operators use their empirical knowledge to estimate a vessel’s SRPM and NOB. Based on this information vessel classification is performed. Empirical knowledge comes with experience, and the manual process is prone to human error. To make the process systematic, calculation of the parameters of the received acoustic samples can be visually analyzed using Detection of Envelope Modulation on Noise (DEMON) spectra. Reported research mostly focuses on SRPM and NOB. Parameters such as number of shafts and vessel course and speed can effectively aid the vessel classification process. This paper makes three novel contributions in this area. Firstly, some novel DEMON spectra analysis techniques are proposed to estimate a water vessel’s number of shafts, speed, and relative course. Secondly, this paper presents a classification framework that uses the features extracted from DEMON spectra and compares them with a reference set. Thirdly, a novel set of reference parameters are provided that aid classification into categories of large merchant ship type 1, large merchant ship type 2, large merchant ship type 3, medium merchant ship, oiler, car carrier, cruise ship, fishing boat and fishing trawler. The proposed analysis and classification techniques were assessed through trials with 877 real acoustic signatures recorded under varying conditions of ship’s speed and sea state. The classification trials revealed a high accuracy of 94.7%

A Comprehensive Review of Vehicle Detection Techniques Under Varying Moving Cast Shadow Conditions Using Computer Vision and Deep Learning

Design of a vision-based traffic analytic system for urban traffic video scenes has a great potential in context of Intelligent Transportation System (ITS). It offers useful traffic-related insights at much lower costs compared to their conventional sensor based counterparts. However, it remains a challenging problem till today due to the complexity factors such as camera hardware constraints, camera movement, object occlusion, object speed, object resolution, traffic flow density, and lighting conditions etc. ITS has many applications including and not just limited to queue estimation, speed detection and different anomalies detection etc. All of these applications are primarily dependent on sensing vehicle presence to form some basis for analysis. Moving cast shadows of vehicles is one of the major problems that affects the vehicle detection as it can cause detection and tracking inaccuracies. Therefore, it is exceedingly important to distinguish dynamic objects from their moving cast shadows for accurate vehicle detection and recognition. This paper provides an in-depth comparative analysis of different traffic paradigm-focused conventional and state-of-the-art shadow detection and removal algorithms. Till date, there has been only one survey which highlights the shadow removal methodologies particularly for traffic paradigm. In this paper, a total of 70 research papers containing results of urban traffic scenes have been shortlisted from the last three decades to give a comprehensive overview of the work done in this area. The study reveals that the preferable way to make a comparative evaluation is to use the existing Highway I, II, and III datasets which are frequently used for qualitative or quantitative analysis of shadow detection or removal algorithms. Furthermore, the paper not only provides cues to solve moving cast shadow problems, but also suggests that even after the advent of Convolutional Neural Networks (CNN)-based vehicle detection methods, the problems caused by moving cast shadows persists. Therefore, this paper proposes a hybrid approach which uses a combination of conventional and state-of-the-art techniques as a pre-processing step for shadow detection and removal before using CNN for vehicles detection. The results indicate a significant improvement in vehicle detection accuracies after using the proposed approach

Antenna design and optimisation for UHF glacial environmental sensor networks

Our planet’s ice masses play an important role in regulating numerous natural phenomena vital to keep our planet habitable by humans as well as other living species. Since few decades, global climate changes are probably responsible for an increased melt rate of the ice masses causing catastrophes. It is therefore desirable to monitor our planet’s ice masses for predicting catastrophes and timely initiating disaster management measures. This monitoring can also provide scientific evidence for supporting anti-climate change efforts. This research contributes to a joint UCL (University College London) – BAS (British Antarctic Survey) project that aims to develop and deploy an Environmental Sensor Network (ESN) at the Thwaites glacier, Antarctica. Glacial ESNs reported in the last two decades are reviewed, focusing on the antenna types used. A link budget framework for designing such antenna systems is presented. As an example, the framework has been used to design an antenna system for deployment at the Thwaites glacier, Antarctica. Design details of six circularly polarized (CP) antennas, one for the englacial sensor probes and five for supraglacial surface receivers are presented. The probe antenna is a 3D bent cross dipole that fits within a borehole of 8 cm diameter while providing a 1 dBic gain at 433 MHz in ice. The other five antennas are printed ones made for use with glacier surface receivers to receive information transmitted by the englacial sensor probes. Out of five, three are cross dipole antennas, while the remaining two are of Archimedean spiral type. All these six antennas provide 3 dB beamwidths of at least 50º in the xz and yz vertical planes catering for transmitter-receiver antenna misalignments caused by extended deployments. The printed cross dipole versions 1 and 2, and the half ring shaped cross dipole antennas for surface receivers provide realized gains of 6.1 dBic, 5.9 dBic, and 5.9 dBic respectively with a quarter wave reflector. The version 2 antenna provides size reduction at the cost of minor gain loss compared to the version 1 antenna. The half ring cross dipole antenna provides improvements in terms of a lower profile, wider 3 dB beamwidth, smaller axial ratio, and purer polarization over all the other antennas developed for use with surface receivers. The axial ratios of all four cross dipole antennas remained below 1.1 dB within the 330-580 MHz band while the co-polarizations remained adequately stronger than the cross polarizations within a 40º beamwidth in both the vertical planes. The spiral antenna version 1 provides a gain of 7.4 dBic at 433 MHz and a -10 dB fractional bandwidth of 47% in snow. Through some design modifications, the version 2 spiral antenna provides significant improvements in the antenna’s reflection coefficient, gain, total efficiency, and axial ratio over the version 1 spiral antenna. None of the previous works used these antenna types for the said applications. The previous works used helical, coil ferrite, and Dielectric Resonator antennas for the sensor probe. Types of antennas previously used with surface receivers included Yagi, helical, non-printed cross dipole, and log periodic dipole array. Lastly, the feasibility of 433 MHz band has been investigated for communication ranges up to 2300 metres through ice. Previous works used lower frequencies like 30 MHz, and 151 MHz to achieve such ranges

An Antenna Solution for Glacial Environmental Sensor Networks

Antennas used in glacial environmental sensor networks and reported in the last two decades have been reviewed. A link budget framework for designing such antenna systems is presented and used to design an antenna system for deployment at the Thwaites glacier, Antarctica. Design details of two left hand circularly polarized cross dipole antennas, one for englacial sensor probes and the other for supraglacial surface receivers are presented. The probe antenna is a 3D bent cross dipole that fits within a borehole of 8 cm diameter while providing a 1 dBic gain at 433 MHz in ice. The surface receiver antenna is a planar printed antenna providing a gain of 6.1 dBic with a quarter wave reflector. Both antennas provide 3 dB beamwidths of at least 50° in the xz and yz vertical planes catering for transmitter-receiver antenna misalignments caused by extended deployments. The antennas displayed good circular polarization and polarization purity traits. The 3 dB axial ratio bandwidths of both the antennas remained 54.9 %. The total efficiencies of the bent cross dipole and the surface receiver antennas were noted as 69.7 % and 86.9 % respectively. Lastly, the 433 MHz band has been validated for achieving englacial communication ranges of up to 2300 metres