Jose G. Colom-Ustariz

Remote Sensing of Weather Hazards Using a Low-Cost and Minimal Infrastructure Off-the-Grid Weather Radar Network

Operational weather radars in the U.S. and other countries in the world are challenged in providing low-altitude observations of rainfall due to the Earths curvature and their deployment in “sparse” networks spaced hundreds of km apart. Given this limitation, work is underway to explore the feasibility of “dense” networks of small X-band radars. One approach developed by a student team from the U.S. Engineering Research Center for Collaborative and Adaptive Sensing of the Atmosphere (CASA) uses low-cost networks of simple, single-polarization radars that are not dependent on existing infrastructure, operating using solar energy and ad-hoc wireless networks, providing gap-filling data with improved temporal and spatial resolution. This “off-the-grid” (OTG) concept is one that might offer a means to monitor rainfall and provide useful data where it is not feasible or cost-effective to deploy more costly and more accurate radars. This paper describes the OTG concept and design, and presents examples of collected data and respective comparisons from this OTG network with measurements from an S-band NEXRAD radar as well as rainfall data from a set of rain gauges located in Puerto Rico. Results show that CASA OTG radars can provide improved spatial and temporal rainfall estimates with consistent or smaller estimated errors when compared to the S-band radar. End user validation was demonstrated in collaboration with the U.S. National Weather Service during system deployment for the XXI Central American and Caribbean Games celebrated at Mayaguez, Puerto Rico during the Summer of 2010.

Development of an Off-The-Grid X-band radar for weather applications

The Student Led Test Bed (STB) is part of the NSF Engineering Research Center CASA and is currently focused in developing low-cost and low infrastructure radar networks to fill lower atmosphere gaps not covered by current technology. The first radar node, which is part of a small region radar network, will significantly improve the time and spatial resolution of the radar data measured for the lower atmosphere. This paper describes the development of an Off-The-Grid (OTG) X-band radar node that requires minimum infrastructure for its deployment and can operate using solar energy and wireless communication links. The OTG radar was developed for meteorological applications modifying a commercially available marine radar. Hardware modifications for meteorological purposes were performed as well as the design and implementation of a photovoltaic system to power the radar using solar energy. The system was moved to the Colorado State University (CSU)-CHILL National Weather Radar facility for a cross-calibration and system evaluation. Satisfactory results were obtained where it was demonstrated that the OTG radar can provide precipitation measurements with improved spatial and temporal resolution, both necessary to have better lower troposphere measurements. This OTG node is the first prototype of a low infrastructure X-band weather radar network to aid forecasts in the western region of Puerto Rico.

Frequency-agile microwave components using ferroelectric materials

The non-linear electric field dependence of ferroelectric thin films can be used to design frequency and phase agile components. Tunable components have traditionally been developed using mechanically tuned resonant structures, ferrite components, or semiconductor-based voltage controlled electronics, but they are limited by their frequency performance, high cost, hgih losses, and integration into larger systems. In contrast, the ferroelectric-based tunable microwave component can easily be integrated into conventional microstrip circuits and attributes such as small size, light weight, and low-loss make these components attractive for broadband and multi-frequency applications. Components that are essential elements in the design of a microwave sensor can be fabricated with ferroelectric materials to achieve tunability over a broad frequency range. It has been reported that with a thin ferroelectric film placed between the top conductor layer and the dielectric material of a microstrip structure, and the proper DC bias scheme, tunable components above the Ku band can be fabricated. Components such as phase shifters, coupled line filters, and Lange couplers have been reported in the literature using this technique. In this wokr, simulated results from a full wave electromagnetic simulator are obtained to show the tunability of a matching netowrk typically used in the design of microwave amplifiers and antennas. In addition, simulated results of a multilayer Lange coupler, and a patch antenna are also presented. The results show that typical microstrip structures can be easily modified to provide frequency agile capabilities.

Microwave research at the University of Puerto Rico at Mayagüez

Microwave research at the UPRM have been focused in weather radar systems, tunable circuits and antennas, antenna characterization and array design, and the analysis of weather radar data. Most recently, the group has been working in the development of a weather radar network for western PR, OTG weather radars, and antennas for Body-Area-Networks. Initial observations from the first radar network node and from the OTG radars show good correlation to NEXRAD measurements. Slot-type antennas have been characterized, resulting in designs with good bandwidth and gain.

Polarization effects on a single polarized off-the-grid X-band radar

The electromagnetic signal propagation with vertical or horizontal polarization from a meteorological radar and the interaction with precipitation particles were studied by [1]. As a result of the studies, the researchers identified how a vertical polarized signal interaction with a precipitation particle differs from that of a horizontal polarized signal. This was also examined by [2]. In their work it was found that the attenuation experienced, horizontal polarization tended to be slightly larger than that undergone by vertical polarization [2], where the main cause of this phenomenon was identified as the raindrops distortion when falling. For heavy rain events, raindrops distortion is more noticeable than in light rain, since the raindrop diameter is extremely small and the shape is spherical, while, for heavy rain the diameter increases and the shape becomes oblate.

Weather radar data visualization using first-order interpolation

In this article we present the visualization of NEXRAD reflectivity data by means of first-order (bilinear) interpolation. We provide the comparison of the raw and interpolated data with the corresponding values obtained from TropiNet radar for weather events occurred in Puerto Rico. The analysis of the relative error of the interpolated data confirms that bilinear interpolation gives better reflectivity estimates than nearest-neighbor interpolation. The efficiency of the bilinear interpolation algorithm makes it suitable for real-time radar data visualization.

Low cost and minimal infrastructure Off-the-Grid XBand radar network development for the west coast of Puerto Rico

The Puerto Rico Test Bed (PRTB) is part of the CASA NSF Engineering Research Center, and is currently focused on developing Off-the-Grid (OTG) X-band low infrastructure and low cost radar networks in the west coast of Puerto Rico. These radars will fill lower atmosphere gaps (< 2 km) not covered by current technology. The radar units operate using solar energy and ad-hoc wireless networks, and provide data with improved temporal and spatial resolution. Currently, there is a concern among National Weather Service forecast meteorologists and emergency managers regarding the need for more accurate radar data from the lower layers of the atmosphere. In this particular region, the earths curvature impedes weather observations due to the long ranges covered by todays current technology. This is the case in the western region of Puerto Rico. The CASA OTG network consists of three radar nodes, whose locations are strategically selected to cover the desired area. These radars were developed from commercially available marine navigation radars. They measure precipitation with the resolution required to meet scientific needs and to also complement measurements taken with the current NWS NEXRAD radar. This low-cost, low-infrastructure X-band weather radar network will aid with forecasts for any region of the world that is in need of observing the lower atmosphere and has limited resources. This paper will provide an overview of system design and development and initial results of the CASA OTG radar network in Puerto Rico.