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PubMed2002

Fundamental radar properties: hidden variables in space-time.

A derivation of the properties of pulsed radiative imaging systems is presented with examples drawn from conventional, synthetic aperture, and interferometric radar. A geometric construction of the space and time components of a radar observation yields a simple underlying structural equivalence among many of the properties of radar, including resolution, range ambiguity, azimuth aliasing, signal strength, speckle, layover, Doppler shifts, obliquity and slant range resolution, finite antenna size, atmospheric delays, and beam- and pulse-limited configurations. The same simple structure is shown to account for many interferometric properties of radar: height resolution, image decorrelation, surface velocity detection, and surface deformation measurement. What emerges is a simple, unified description of the complex phenomena of radar observations. The formulation comes from fundamental physical concepts in relativistic field theory, of which the essential elements are presented. In the terminology of physics, radar properties are projections of hidden variables--curved worldlines from a broken symmetry in Minkowski space-time--onto a time-serial receiver.

Journal Article↗
PubMed2005

All-cause mortality among Belgian military radar operators: a 40-year controlled longitudinal study.

BACKGROUND: It has been suggested that exposure to radiofrequency/microwaves radiations could be associated with greater health hazards and higher mortality. METHODS: The all-cause mortality of 27,671 Belgian militaries who served from 1963 until 1994 in battalions equipped with radars for anti-aircraft defence was studied over the period 1968-2003. End of the seventies, technical modifications brought to the shielding of the micro-wave generators resulted in a reduction in irradiations. A control group was formed by 16,128 militaries who served during the same period in the same military area but who were never exposed to radars. Administrative procedures for identifying militaries and their vital status were equivalent in the radar and the control groups. RESULTS: The age-standardized mortality ratio (SMR) in the radar battalions was 1.05 (95% CI: 0.95-1.16) in professional militaries, and 0.80 (95% CI: 0.75-0.85) in conscripts. In professional militaries no difference in mortality was found according to duration (less than, or five years or more) or to period of service (before 1978 or after 1977). CONCLUSIONS: During a 40-year period of observation, we found no increase in all-cause mortality in Belgian militaries who were in close contact with radar equipments of anti-aircraft defence battalions.

Adolescent↗
PubMed2000

The use of vertical-looking radar to continuously monitor the insect fauna flying at altitude over southern England.

The continuous automatic monitoring of the aerial density, biomass and relative diversity of high-flying insect faunas has been made practicable by a new, vertical-looking radar. This inexpensive radar system, with its novel signal analysis capability, represents a major advance over earlier vertical-beam radars because it provides estimates of the body mass of individual overflying insects, as well as measurements of their direction and speed of movement. This paper summarizes data collected over a three-month period by the new radar in the height range from 150 m to c.1 km, over agricultural land in Worcestershire, England. The day-to-day variation in the numbers of insects and their altitudinal and diurnal patterns of flight activity are presented. Examples are also given of distributions of mass, displacement speed and direction, and orientation direction. The potential of the new radar for various research and operational monitoring tasks is briefly discussed.

Altitude↗
PubMed2004

Detection of tree roots and determination of root diameters by ground penetrating radar under optimal conditions.

A tree's root system accounts for between 10 and 65% of its total biomass, yet our understanding of the factors that cause this proportion to vary is limited because of the difficulty encountered when studying tree root systems. There is a need to develop new sampling and measuring techniques for tree root systems. Ground penetrating radar (GPR) offers the potential for direct nondestructive measurements of tree root biomass and root distributions to be made. We tested the ability of GPR, with 500 MHz, 800 MHz and 1 GHz antennas, to detect tree roots and determine root size by burying roots in a 32 m3 pit containing damp sand. Within this test bed, tree roots were buried in two configurations: (1) roots of various diameters (1-10 cm) were buried at a single depth (50 cm); and (2) roots of similar diameter (about 5 cm) were buried at various depths (15-155 cm). Radar antennas were drawn along transects perpendicular to the buried roots. Radar profile normalization, filtration and migration were undertaken based on standard algorithms. All antennas produced characteristic reflection hyperbolas on the radar profiles allowing visual identification of most root locations. The 800 MHz antenna resulted in the clearest radar profiles. An unsupervised, maximum-convexity migration algorithm was used to focus information contained in the hyperbolas back to a point. This resulted in a significant gain in clarity with roots appearing as discrete shapes, thereby reducing confusion due to overlapping of hyperbolas when many roots are detected. More importantly, parameters extracted from the resultant waveform through the center of a root correlated well with root diameter for the 500 MHz antenna, but not for the other two antennas. A multiple regression model based on the extracted parameters was calibrated on half of the data (R2 = 0.89) and produced good predictions when tested on the remaining data. Root diameters were predicted with a root mean squared error of 0.6 cm, allowing detection and quantification of roots as small as 1 cm in diameter. An advantage of this processing technique is that it produces results independently of signal strength. These waveform parameters represent a major advance in the processing of GPR profiles for estimating root diameters. We conclude that enhanced data analysis routines combined with improvements in GPR hardware design could make GPR a valuable tool for studying tree root systems.

Biomass↗
PubMed2002

Developments in radar and remote-sensing methods for measuring and forecasting rainfall.

Over the last 25 years or so, weather-radar networks have become an integral part of operational meteorological observing systems. While measurements of rainfall made using radar systems have been used qualitatively by weather forecasters, and by some operational hydrologists, acceptance has been limited as a consequence of uncertainties in the quality of the data. Nevertheless, new algorithms for improving the accuracy of radar measurements of rainfall have been developed, including the potential to calibrate radars using the measurements of attenuation on microwave telecommunications links. Likewise, ways of assimilating these data into both meteorological and hydrological models are being developed. In this paper we review the current accuracy of radar estimates of rainfall, pointing out those approaches to the improvement of accuracy which are likely to be most successful operationally. Comment is made on the usefulness of satellite data for estimating rainfall in a flood-forecasting context. Finally, problems in coping with the error characteristics of all these data using both simple schemes and more complex four-dimensional variational analysis are being addressed, and are discussed briefly in this paper.

Algorithms↗
PubMedDate not supplied

Radar determination of the spatial structure of hydraulic conductivity.

Spatial variability of hydraulic conductivity exerts a predominant control on the flow of fluid through porous media. Heterogeneities influence advective pathways, hydrodynamic dispersion, and density-dependent dispersion; they are, therefore, a key concern for studies of ground water resource development, contaminant transport, and reservoir engineering. Ground-penetrating radar contributes to the remote, geophysical characterization of the macroscale variability of natural porous media. On a controlled excavation of a glacial-fluvial sand and gravel deposit in the Fanshawe Delta area (Ontario, Canada), the hydraulic conductivity field of a 45 x 3 m vertical exposure was characterized using constant-head permeameter measurements performed on undisturbed horizontal sediment cores. Ground-penetrating radar data were collected along the excavation face in the form of both reflection and common midpoint surveys. Comparison of geostatistical analyses of the permeameter measurements and the radar data suggests thatthe horizontal correlation structure of radar stack velocity can be used to directly infer the horizontal correlation structure of hydraulic conductivity. The averaging nature of the common midpoint survey is manifest in the vertical correlation structure of stack velocity, making it less useful. Radar reflection data do not exhibit a spatial structure similar to that of hydraulic conductivity possibly because reflections are a result of material property contrasts rather than the material properties themselves.

Data Collection↗
PubMed1995

Signatures of deterministic chaos in radar sea clutter and ocean surface winds.

Several time series of wind components and X-band Doppler radar signals, gathered concurrently over a approximately 0.01 km(2) area of the ocean surface, were examined for evidence of a low-dimensional dynamical attractor with the Grassburger-Procaccia algorithm. Only the vertically polarized radar reflectivity and the horizontal surface wind speed time series suggested the presence of such an attractor. The correlation dimension for these two observables appeared to be nearly the same. This suggested a working hypothesis that the dynamical behavior of both the vertically polarized radar reflectivity and the horizontal surface winds are controlled by a single low-dimensional dynamical system. The hypothesis was further examined by predicting winds from radar reflectivity, using a neural network deterministic model, and comparing the prediction performance with that of the SEASAT statistical algorithm for retrieving surface winds from radar backscatter. It was found that the deterministic model did, in fact, achieve a higher prediction correlation coefficient for a limited time period. (c) 1995 American Institute of Physics.

Journal Article↗
PubMed1996

New technology in wound ballistics: the Doppler radar.

The feasibility of using Doppler radar to obtain more accurate measurements of velocity and yaw angle of bullets was investigated. Anesthetized pigs were shot at a range of 9-10 meters, and velocity measurements were obtained using Doppler radar and photocells. The data from the two types of equipment was compared. Excellent correspondence was found between the measurements of entry velocities of low, medium, and high velocity bullets, i.e., an average deviation of less than 1% (range 0-2%). Measurements of exit velocities of low and medium velocity bullets corresponded just as well, but measurements of exit velocities of high velocity bullets was complicated in both methods by signal cluttering caused by fragments of tissue released from the exit wound and by the deflection of the bullet. A Doppler radar was used to follow the movements of the bullet, to determine the velocity, and, if possible, to determine when the bullet stabilizes and the exact yaw angles continuously. We were able to design a system in which even small caliber bullets could be followed for 15-20 meters. It was possible to detect yaw even with these small calibers, and the radar was not disturbed by additional equipment. Using Doppler radar to measure velocity offers important benefits--simple set up, minimal risk of damage to equipment by stray bullets, and very good accuracy. The results of measuring yaw angles of bullets are promising, as far as determining the point of stability is concerned, but further work is necessary to be able to measure the angle of yaw exactly.

Animals↗
PubMed2004

Use of equivalent spheres to model the relation between radar reflectivity and optical extinction of ice cloud particles.

The effect of ice crystal size and shape on the relation between radar reflectivity and optical extinction is examined. Discrete-dipole approximation calculations of 95-GHz radar reflectivity and ray-tracing calculations are applied to ice crystals of various habits and sizes. Ray tracing was used primarily to calculate optical extinction and to provide approximate information on the lidar backscatter cross section. The results of the combined calculations are compared with Mie calculations applied to collections of different types of equivalent spheres. Various equivalent sphere formulations are considered, including equivalent radar-lidar spheres; equivalent maximum dimension spheres; equivalent area spheres, and equivalent volume and equivalent effective radius spheres. Marked differences are found with respect to the accuracy of different formulations, and certain types of equivalent spheres can be used for useful prediction of both the radar reflectivity at 95 GHz and the optical extinction (but not lidar backscatter cross section) over a wide range of particle sizes. The implications of these results on combined lidar-radar ice cloud remote sensing are discussed.

Journal Article↗
PubMed2005

Aircraft-protection radar for use with atmospheric lidars.

A modified X-band radar system designed to detect aircraft during atmospheric lidar operations is described and characterized. The capability of the radar to identify aircraft approaching from a variety of directions was tested, and first detections were found to occur between the -10 and -3 dB perimeters of the gain horn's antenna pattern. A model based on the radar equation projects the performance of the radar for different sizes of aircraft and at different altitude levels. Risk analysis indicates that the probability of accidently illuminating an aircraft with the laser beam during joint lidar-radar operations is low.

Journal Article↗
PubMed2006

Target-adaptive polarimetric synthetic aperture radar target discrimination using maximum average correlation height filters.

We report the development of a technique for adaptive selection of polarization ellipse tilt and ellipticity angles such that the target separation from clutter is maximized. From the radar scattering matrix [S] and its complex components, in phase and quadrature phase, the elements of the Mueller matrix are obtained. Then, by means of polarization synthesis, the radar cross section of the radar scatters are obtained at different transmitting and receiving polarization states. By designing a maximum average correlation height filter, we derive a target versus clutter distance measure as a function of four transmit and receive polarization state angles. The results of applying this method on real synthetic aperture radar imagery indicate a set of four transmit and receive angles that lead to maximum target versus clutter discrimination. These optimum angles are different for different targets. Hence, by adaptive control of the state of polarization of polarimetric radar, one can noticeably improve the discrimination of targets from clutter.

Journal Article↗
PubMed1994

Doppler radar velocity measurements for wound ballistics experiments.

Bullet velocity is a basic parameter in wound ballistics studies. It is usually measured electronically by means of a variety of solid or photoelectric barriers connected to equipment measuring the time elapsing between impulses, enabling the velocity to be calculated. With the advent of Doppler radar velocity measurement of large calibre artillery shells, the use of this equipment for wound ballistics experiments was investigated. Anaesthetized pigs were shot at a range of 9-10 metres and the velocities measured by Doppler radar and photocells were compared. A very good correspondence between the measured entry and exit velocities in low and medium velocity bullets was found, i.e. an average deviation of less than 1% (range 0-2%) between the two types of equipment. In high velocity bullets measurement of entry velocities was just as good, but in both methods measurement of the exit velocity was complicated by the cluttering of signals by fragments of tissue released from the exit wound and the deflection of the bullet, Doppler radar offers important benefits - simple set up, minimal risk of damage of equipment by stray bullets and very good accuracy - and may replace photocells and similar equipment in studies involving low and medium velocity bullets. Measurement of the exit velocity of high velocity bullets is unsatisfactory in both methods, and it is necessary to improve the Doppler radar method in order to measure that as well.

Acceleration↗
PubMed2001

Application of radar to detect pedestrian workers near mining equipment.

Between 1990 and 1996, 133 accidents occurred and 23 mine workers were killed when haulage trucks used in surface mines collided with another smaller vehicle, a mine structure, or a pedestrian worker. These accidents were caused by a lack of visibility from the cab of the truck. Similar accidents are common with other types of equipment, such as front-end loaders and shovels. There are several methods for improving the operator's awareness of objects or people around the equipment including improved mirror designs, video cameras, and sensor technologies. Researchers at the National Institute for Occupational Safety and Health (NIOSH) are evaluating collision warning systems that are based on radar technology. These systems are mounted on the mining equipment to monitor one or more of the blind areas. An alarm is provided to the operator if an object or person enters the radar's detection area. Tests consisted of mounting the systems on a 50-ton-capacity truck typically used in quarries and a 240-ton-capacity truck used at a surface mine. This article summarizes the test procedure and results of evaluations of several off-the-shelf and prototype radar systems. False alarm rates and reliable detection zones for pedestrians were recorded for various mounting configurations on the rear of the trucks. Mounting radar systems on large equipment presents several challenges; however, the technology does show promise for this application.

Accidents, Occupational↗
PubMed2005

Safety and economic impacts of photo radar program.

OBJECTIVE: Unsafe speed is one of the major traffic safety challenges facing motorized nations. In 2003, unsafe speed contributed to 31 percent of all fatal collisions, causing a loss of 13,380 lives in the United States alone. The economic impact of speeding is tremendous. According to NHTSA, the cost of unsafe speed related collisions to the American society exceeds 40 billion US dollars per year. In response, automated photo radar speed enforcement programs have been implemented in many countries. This study assesses the economic impacts of a large-scale photo radar program in British Columbia. The knowledge generated from this study could inform policy makers and project managers in making informed decisions with regard to this highly effective and efficient, yet very controversial program. METHODS: This study establishes speed and safety effects of photo radar programs by summarizing two physical impact investigations in British Columbia. It then conducts a cost-benefit analysis to assess the program's economic impacts. The cost-benefit analysis takes into account both societal and funding agency's perspectives. It includes a comprehensive account of major impacts. It uses willingness to pay principle to value human lives saved and injuries avoided. It incorporates an extended sensitivity analysis to quantify the robustness of base case conclusions. RESULTS: The study reveals an annual net benefit of approximately 114 million in year 2001 Canadian dollars to British Columbians. The study also finds a net annual saving of over 38 million Canadian dollars for the Insurance Corporation of British Columbia (ICBC) that funded the program. These results are robust under almost all alternative scenarios tested. The only circumstance under which the net benefit of the program turns negative is when the real safety effects were one standard deviation below the estimated values, which is possible but highly unlikely. CONCLUSION: Automated photo radar traffic safety enforcement can be an effective and efficient means to manage traffic speed, reduce collisions and injuries, and combat the huge resulting economic burden to society. The cost-effectiveness of the program takes on special meaning and urgency when considering the present and future government funding constraints. The application of the program, however, should be planned and implemented with caution. Every effort should be made to focus on and to promote the program on safety improvement grounds. The program can be easily terminated because of political considerations, if the public perceives it as a cash cow to enhance government revenue.

Accidents, Traffic↗
PubMed1983

Monitoring variations of biological impedances using microwave Doppler radar.

A microwave Doppler radar for continuously monitoring time-varying biological impedances is described. The radar compares the phase of the signal scattered from a region of biological tissue with that of the transmitted signal. The phase changes of the scattered signal are an indication of the net impedance changes within the test region due to various physiological processes, for example, the displacements of blood vessels during the cardiac cycle. A Doppler radar, equipped with a matched antenna, was tested with a simulation model and its detection characteristic was found to be a sinusoidal function of the antenna-object spacing. Tests with healthy human subjects were also performed at 3 GHz and 10.5 GHz. It was found that the 3 GHz Doppler radar has significantly greater penetration in tissues but is less sensitive to changes of the biological impedance than the 10.5 GHz system.

Doppler Effect↗
PubMed2000

Interferometric radar measurements of water level changes on the Amazon flood plain

Measurements of water levels in the main channels of rivers, upland tributaries and floodplain lakes are necessary for understanding flooding hazards, methane production, sediment transport and nutrient exchange. But most remote river basins have only a few gauging stations and these tend to be restricted to large river channels. Although radar remote sensing techniques using interferometric phase measurements have the potential to greatly improve spatial sampling, the phase is temporally incoherent over open water and has therefore not been used to determine water levels. Here we use interferometric synthetic aperture radar (SAR) data, acquired over the central Amazon by the Space Shuttle imaging radar mission, to measure subtle water level changes in an area of flooded vegetation on the Amazon flood plain. The technique makes use of the fact that flooded forests and floodplain lakes with emergent shrubs permit radar double-bounce returns from water and vegetation surfaces, thus allowing coherence to be maintained. Our interferometric phase observations show decreases in water levels of 7-11 cm per day for tributaries and lakes within approximately 20 km of a main channel and 2-5 cm per day at distances of approximately 80 km. Proximal floodplain observations are in close agreement with main-channel gauge records, indicating a rapid response of the flood plain to decreases in river stage. With additional data from future satellite missions, the technique described here should provide direct observations important for understanding flood dynamics and hydrologic exchange between rivers and flood plains.

Journal Article↗
PubMed2005

The Mid-Canada Radar Line and First Nations' people of the James Bay region, Canada: an evaluation using log-linear contingency modelling to analyze organochlorine frequency data.

Abandoned radar line stations in the North American arctic and sub-arctic regions are point sources of contamination, especially for PCBs. Few data exist with respect to human body burden of organochlorines (OCs) in residents of communities located in close proximity to these radar line sites. We compared plasma OC concentration (unadjusted for total lipids) frequency distribution data using log-linear contingency modelling for Fort Albany First Nation, the site of an abandoned Mid-Canada Radar Line station, and two comparison populations (the neighbouring community of Kashechewan First Nation without such a radar installation, and Hamilton, a city in southern Ontario, Canada). This type of analysis is important as it allows for an initial investigation of contaminant data without imputing any values. The two-state log-linear model (employing both non-detectable and detectable concentration frequencies and applicable to PCB congeners 28 and 105 and cis-nonachlor) and the four-state log-linear model (using quartile concentration frequencies for Aroclor 1260, PCB congeners [99,118,138,153,156,170,180,183,187], beta-HCH, p,p'-DDT +p,p'-DDE, HCB, mirex, oxychlordane, and trans-nonachlor) revealed that the effects of subject gender were inconsequential. Significant differences (p < 0.05) between the groups examined were attributable to the effect of location on the frequency of detection of OCs or on their differential distribution among the concentration quartiles. In general, people from Hamilton had higher frequencies of non-detections and of concentrations in the first quartile (p < 0.05) for most OCs compared to people from Fort Albany and Kashechewan (who consume a traditional diet of wild meats that does not include marine mammals). An unexpected finding was that, for Kashechewan males, the frequency of many OCs was significantly higher (p < 0.05) in the 4th concentration quartile than that predicted by the four-state log-linear model, but significantly lower than expected in the 1st quartile for beta-HCH. The levels of PCBs found for women in Fort Albany and Kashechewan were greater than those reported for Dene (First Nation people) and Métis (mixed heritage) of the western Northwest Territories (NWT) who did not consume marine mammals, and for Inuit living in the central NWT (occasional consumers of marine mammals). Moreover, the levels of total p,p'-DDT were greater for Fort Albany and Kashechewan women compared to these same aboriginal groups.

Animals↗
PubMed2003

Maternal induction of ventral fate by zebrafish radar.

In vertebrate embryos, maternal determinants are thought to preestablish the dorsoventral axis by locally activating zygotic ventral- and dorsal-specifying genes, e.g., genes encoding bone morphogenetic proteins (BMPs) and BMP inhibitors, respectively. Whereas the canonical Wntbeta-catenin pathway fulfills this role dorsally, the existence of a reciprocal maternal ventralizing signal remains hypothetical. Maternal noncanonical WntCa(2+) signaling may promote ventral fates by suppressing Wntbeta-catenin dorsalizing signals; however, whether any maternal determinant is directly required for the activation of zygotic ventral-specifying genes is unknown. Here, we show that such a function is achieved, in part, in the zebrafish embryo by the maternally encoded transforming growth factor beta (TGF-beta) signaling molecule, Radar. Loss-of-function experiments, together with epistasis analyses, identify maternal Radar as an upstream activator of bmps expression. Maternal induction of bmps by Radar is essential for zebrafish development as its removal results in larval-lethal dorsalized phenotypes. Double-morphant analyses further suggest that Radar functions through the TGF-beta receptor Alk8 to initiate the expression of bmp genes. Our results support the existence of a previously uncharacterized maternal ventralizing pathway. They might further indicate that maternal TGF-betaRdr and WntCa(2+) pathways complementarily specify ventral cell fates, with the former triggering bmps expression and the latter indirectly repressing genes encoding BMP antagonists.

Animals↗