A LHCP Printed Cross Dipole Antenna for Glacial Environmental Sensor Networks

A left hand circularly polarized antenna called SPD-PCD (Symmetric phase difference - printed cross dipole) has been designed, developed, and experimentally validated for use with glacier telemetry surface receivers. The antenna is portable and easy to fabricate. It provides a gain of 5.9 dBic at 433 MHz, a 57 % -10 dB fractional bandwidth, and a -3 dB angular width of 60° in the vertical planes. The antenna offers good circular polarization with the axial ratio remaining below 1.1 dB between 330-580 MHz. The co-polarization is at least 10 dB stronger than cross-polarization within a beam width of 80° in both the vertical planes. This work also validates the 433 MHz band is suitable to achieve communication ranges of up to 2300 m through ice

A New Multistatic FMCW Radar Architecture by Over-the-Air Deramping

© 2015 IEEE. Frequency modulated continuous wave (FMCW) radar is widely adopted solution for low-cost, short to medium range sensing applications. However, a multistatic FMCW architecture suitable for meeting the low-cost requirement has yet to be developed. This paper introduces a new FMCW radar architecture that implements a novel technique of synchronizing nodes in a multistatic system, known as over-the-air deramping (OTAD). The architecture uses a dual-frequency design to simultaneously broadcast an FMCW waveform on a lower frequency channel directly to a receiver as a reference synchronization signal, and a higher frequency channel to illuminate the measurement scene. The target echo is deramped in hardware with the synchronization signal. OTAD allows for low-cost multistatic systems with fine range-resolution, and low peak power and sampling rate requirements. Furthermore, the approach avoids problems with direct signal interference. OTAD is shown to be a compelling solution for low-cost multistatic radar systems through the experimental measurements using a newly developed OTAD radar system

Over-The-Air Deramping For Multistatic Perimeter Surveillance

This paper explores the use of an over-the-air deramping (OTAD) system as a solution for perimeter surveillance. Over-the-air deramping is a technique for wirelessly synchronising distributed passive FMCW radar nodes to a dual-frequency master FMCW transmitter node. Such a system allows simultaneous monostatic and multistatic measurements for improved clutter resilience, and multiple looks at a target for reduced susceptibility to signal fading due to target scintillation. To prove the latter, a simultaneous monostatic and OTAD bistatic node were set up with a 5 m baseline and a walking person was measured. The results show that signal fading occurs in both the monostatic and the bistatic node, but rarely at the same time. Hence, combining the measurements from the two nodes gives a consistent response from the target. This demonstrates OTAD as a compelling system for a robust perimeter surveillance system

Transmitter noise considerations in super-Nyquist FMCW radar design

A design consideration for super-Nyquist frequency modulated continuous-wave (FMCW) radar systems relating to transmitter to receiver noise leakage is introduced. Phase noise curves comparing the fundamental direct digital synthesisers frequency and its second super-Nyquist image show a significant increase in relative noise level at all offsets from the carrier. This results in a reduced transmitter signal-to-noise ratio. It is shown with a simple example that this can lead to a significant degradation in receiver sensitivity if not managed properly. A design rule-of-thumb that can be used by radar designers to avoid or mitigate this problem is provided

OFDM based WiFi Passive Sensing: a reference-free non-coherent approach

WiFi based passive sensing is attracting considerable interest in the scientific community for both research and commercial purposes. In this work, we aim at taking a step forward in an endeavor to achieve good sensing capabilities employing compact, low-cost, and stand-alone WiFi sensors. To this end, we resort to a reference-free non-coherent signal processing scheme, where the presence of a moving target echo is sought by detecting the amplitude modulation that it produces on the direct signal transmitted from the WiFi access point. We first validate the proposed strategy against simulated data, identifying advantages and limitations. Then, we apply the conceived solution on experimental data collected in a small outdoor area with the purpose of detecting a small cooperative drone

High-resolution radar measurements of snow avalanches

Two snow avalanches that occurred in the winter 2010-2011 at Vallée de la Sionne, Switzerland, are studied using a new phased array FMCW radar system with unprecedented spatial resolution. The 5.3 GHz radar penetrates through the powder cloud and reflects off the underlying denser core. Data are recorded at 50 Hz and have a range resolution better than 1 m over the entire avalanche track. We are able to demonstrate good agreement between the radar results and existing measurement systems that record at particular points on the avalanche track. The radar data reveal a wealth of structure in the avalanche and allow the tracking of individual fronts and surges down the slope for the first time. Key Points Validation between our radar results and existing point measurement systems High-resolution radar allows tracking of fronts and surges from start to finish Velocity linked with topography may be used to measure rheology of snow ©2013. American Geophysical Union. All Rights Reserved

Looking inside an avalanche using a novel radar system

Snow avalanches are a significant natural hazard in alpine regions and their flow dynamics have similarities to pyroclastic flows and other geological mass movements. However, the potential for artificial release and the temporary nature of their deposits makes them somewhat easier to study. This article explains recent developments in radar technology for imaging these flows. These new data mean that, for the first time, we are seeing the whole flow averaged over spatial scales that are dynamically relevant. This provides an opportunity to properly test existing models for the dynamics used in risk applications and to gain knowledge of the flow physics, which will guide the next generation of model formulations

Variability in Basal Melting Beneath Pine Island Ice Shelf on Weekly to Monthly Timescales

Ocean-driven basal melting of Amundsen Sea ice shelves has triggered acceleration, thinning, and grounding line retreat on many West Antarctic outlet glaciers. Here we present the first year-long (2014) record of basal melt rate at sub-weekly resolution from a location on the outer Pine Island Ice Shelf. Adjustment of the upper thermocline to local wind forced variability in the vertical Ekman velocity is the dominant control on basal melting at weekly to monthly timescales. Atmosphere-ice-ocean surface heat fluxes or changes in advection of modified Circumpolar Deep Water play no discernible role at these timescales. We propose that during other years, a deepening of the thermocline in Pine Island Bay driven by longer timescale processes may have suppressed the impact of local wind forcing on high-frequency upper thermocline height variability and basal melting. This highlights the complex interplay between the different processes and their timescales that set the basal melt rate beneath Pine Island Ice Shelf