Echo Power Research Articles

Superconducting coplanar waveguide resonators for low temperature pulsed electron spin resonance spectroscopy

We discuss the design and implementation of thin film superconducting coplanar waveguide micro-resonators for pulsed electron spin resonance experiments. The performance of the resonators with P doped Si epilayer samples is compared to waveguide resonators under equivalent conditions. The high achievable filling factor even for small sized samples and the relatively high Q-factor result in a sensitivity of 4.5 × 10(8) spins per shot, which is superior to that of conventional waveguide resonators, in particular to spins close to the sample surface. The peak microwave power is on the order of a few milliwatts, which is compatible with measurements at ultra-low temperatures. We also discuss the effect of the nonuniform microwave magnetic field on the Hahn echo power dependence.

A detailed view into the eruption clouds of Santiaguito volcano, Guatemala, using Doppler radar

Using Doppler radar technology we are able to show that eruptions at Santiaguito volcano, Guatemala, are comprised of multiple explosive degassing pulses occurring at a frequency of 0.2 to 0.3 Hz. The Doppler radar system was installed about 2.7 km away from the active dome on the top of Santa Maria volcano. During four days of continuous measurement 157 eruptive events were recorded. The Doppler radar data reveals a vertical uplift of the dome surface of about 50 cm immediately prior to a first degassing pulse. Particle velocities range from 10 to 15 m/s (in the line of sight of the radar). In 80% of the observed eruptions a second degassing pulse emanates from the dome with significantly higher particle velocities (20–25 m/s again line of sight) and increased echo power, which implies an increase in mass flux. We carry out numerical experiments of ballistic particle transport and calculate corresponding synthetic radar signals. These calculations show that the observations are consistent with a pulsed release of material from the dome of Santiaguito volcano.

Radio-echo probing of Black Rapids Glacier, Alaska, USA, during onset of melting and spring speed-up

AbstractRadio-echo soundings were collected on Black Rapids Glacier, Alaska, USA, from mid-May to mid-July 1993 to investigate spring speed-up and summer slowdown including high-speed events associated with three lake drainages. Temporal changes in echo power from all depths were highly correlated, indicating a strong effect from varying amounts of near-surface water. Evaluation of bed reflectivity was corrected for this effect based on the time variation of spatially stable patterns of internal scattering identified using principal component analysis. Hourly time series collected at two fixed locations over the deepest part of two valley cross sections showed no detectable change in bed reflection power (<5%) or phase (<0.05 rad). Reoccupation of fixed locations toward the margins at several-day intervals revealed changes in bed power reflectivity up to 50%, but with no definable relation to lake drainages. Theoretical analyses indicate that changes in reflectivity of <5% from a rock bed constrain basal water thickness changes to centimeter scale or less. Conductive basal till degrades the constraint to decimeter scale or more. Changes in bed reflectivity of 50% indicate probable absence of thick conductive till at such locations, and that the changes were caused by centimeter to decimeter changes in equivalent water thickness.

Ground Reflectivity Data Resolution Enhancement Technology for Geostationary Doppler Weather Radar

Aiming at the low resolution ground reflectivity data of more than 12 km in Geostationary Doppler weather radar, a linear inversion mathematics formula between sub resolution volume echo power and multiple partially correlated radar measurements in horizon is present based on radar meteorology integrated equation, its solution is pursued by means of a super resolution numerical procedure based on the truncated singular value decomposition (TSVD) method using known radar antenna weight function. Numeric simulation uses the airborne precipitation radar reflectivity to simulate the Geostationary Doppler weather radar measurement data and evaluate the resolution enhancement performance. Results show that the reconstructed data of super-resolution from NIS simulation measurement are better than those of reconstructed before and are all close to those of simulated reflectivity data of high resolution of 4 km, more fine weather structure among these reflectivity data could be present after reconstruction.

Study on effect of wind waves on radar echoes in atmosphere duct oversea

The Wen's wave spectrum model is adopted to describe the rough sea surface, and the relation between wind and ocean waves using sea wave spectrum theory is derived. The improved discrete mixed Fourier transform algorithm and the modified rader scattering coefficient model are used to calculate radio propagation loss and radar cross section respectively. On this basis, the influence of wind waves on radar echoes in the environment of atmosphere ducts is analysed by using numerical calculations. The results show that the influences of wind on propagation loss at different heights are different; wich respect to the propagation loss, rader scattering coefficient influenced by waves of factors is large, which results in large change in the radar echo power.

Eddy Diffusivities for Momentum and Heat in the Upper Troposphere and Lower Stratosphere Measured by MU Radar and RASS, and a Comparison of Turbulence Model Predictions

Abstract Recently, middle- and upper-atmosphere Doppler radar (MU radar) has enabled the measurement of middle-atmosphere turbulence from radar backscatter Doppler spectra. In this work, eddy diffusivities for momentum Km in the upper troposphere and lower stratosphere during clear-air conditions were derived from direct measurements of the Reynolds stress and vertical gradient of mean wind velocity measured by MU radar. Eddy diffusivity for heat Kh below 8 km was determined from measurements of temperature fluctuations by the Radio Acoustic Sounding System (RASS) attached to the MU radar. The eddy diffusivity for momentum was on the order of 10 m2 s−1 in the upper troposphere and decreased gradually in the stratosphere by an order of magnitude or more. The eddy diffusivity for heat was almost of the same order of magnitude as Km. Estimates of eddy diffusivity from the radar echo power spectral width give fairly good values compared with the direct measurement of Km. Applicability of three turbulence models—the spectral width method, the k–ɛ model modified for stratified flows, and the algebraic stress model—were also examined, using radar observation values of turbulent kinetic energy k and turbulent energy dissipation rate ɛ together with atmospheric stability observations from rawinsonde data. It is concluded that the algebraic stress model shows the best fit with the direct measurement of Km, even in the free atmosphere above the atmospheric boundary layer once k and ɛ values are obtained from observations or a model.

The Study of Optical Properties of Laser Identification Friend or Foe System

The optical properties is essential to the process of identification in Laser Identification Friend or Foe (Laser-IFF) system. The corner cube reflector (CCR), composed of three mutually orthogonal reflective micromirrors, is extensively used in Laser-IFF system for it can reflect incident light at any angle to its incoming direction. So the micromachined CCR array is set to be the most important component of the responder. And assuming the Laser-IFF system is used in missiles, we present an analysis of the optical properties about the responder sectional area, the signal power of the responder and the echo power from the responder to the inquirer, considering at different effect distances between the inquirer and responder, divergence half-angle, CCR arrays reflectivity and other factors. Further field testing about the system can reference obtained experimental results and conclusions.

Collision-induced photon echo at the transition0↔1in ytterbium vapor: Direct proof of depolarizing collision anisotropy

A collision-induced photon echo arising at the transition $0\ensuremath{\leftrightarrow}1$ of ytterbium in the presence of heavy atomic buffer is investigated. Collision-induced echo signal appears in the case of mutually orthogonal linear polarizations of exciting pulses and it is absent without buffer. Collision-induced echo power grows with buffer pressure up to the maximum value and decays exponentially at further buffer pressure growth. Collision-induced echo power is essentially less than that of the ordinary echo generated by pulses with parallel polarizations in the same mixture, and its polarization is linear with the polarization vector directed along that of the first exciting pulse. All the properties of collision-induced photon echo are explained on the basis of collision relaxation dependence on the direction of active atom velocity.

Polarization in Bistatic Radar Probing of Planetary Surfaces: Application to Mars Express Data

Spacecraft-to-ground bistatic radar provides a straightforward method for surveying planetary surfaces on scales of importance to landers and rovers. Centimeter wavelengths, currently in use for deep-space telecommunications, interact with surface structure of similar to somewhat larger scales. For the quasi-specular component of scattering and for surfaces uniformly illuminated by monochromatic signals from an orbiting or flyby vehicle, the echo Doppler dispersion is proportional to the root mean square (rms) surface slope. When the specular condition occurs within 10°-20° of the Brewster angle, the surface dielectric constant can be derived from relative echo power measured simultaneously in orthogonal polarizations and the Fresnel reflection laws. Cross spectra, computed from outputs of the orthogonally polarized receivers, may be used to calculate a complete description of the polarization properties of the scattered fields. Application to planetary studies requires accurate amplitude and phase calibration of the polarization channels, including correction for any leakage between the two receiving paths, such as from imperfectly isolated antenna feeds. We illustrate these techniques using Mars Express results from “Stealth” (Medusae Fossae), a region on Mars that has not previously been detected by Earth-based radar, and from a long profile including Acidalia Planitia. Single-location Stealth observations support previous conclusions that the surface is rough and porous (dielectric constant ≈ 1.4). But the longest experiment (in which the specular point was followed for an hour) yields relatively high dielectric constants (2.8), suggesting that the model is incomplete. The surface of Acidalia Planitia has low dielectric constants ( ≈2.6) over 60-90 W at 50 N and higher values (≈3.6) as the specular point moves south and crosses the equator.

Based on the Minimum Variance Spectral Estimation of Radar Wind Profile Analysis

In this paper, we apply minimum variance method for removing automatically ground and intermittent clutter (airplane echo) from wind profiler radar data. Using the concept of discrete multi-resolution analysis and non-parametric estimation theory, we develop Doppler echo power spectral, which allow us to identify the coefficients relevant for clutter and to suppress them in order to effectively restrain and remove clutter and increase the wind profile radar detection range and accuracy; must be on the air back to the effective spectrum of the spectral moments estimation. Using MATLAB simulation analysis , compared with the conventional method of analysis to verify the feasibility and effectiveness of the algorithm, also, try the algorithm is applied to the complexity of the weather with a strong interference case of precipitation particles; Data analysis showed that the actual detection, from the library in the lower spectrum moment estimation has been improved significantly.

A Spectral Moment Estimation Method for Wind Profile Radar

Spectrum in the wind profile radar data processing, radar detection of low-level spectral data from the library there are usually clutter, intermittent clutter, clutter and atmospheric echoes magnetic mixed overlap situation. In order to effectively restrain and remove clutter and increase the wind profile radar detection range and accuracy, must be on the air back to the effective spectrum of the spectral moments estimation. Based on the wind profile radar Doppler echo power spectral analysis, maximum likelihood method based on estimated spectral data of radar echo spectrum method using MATLAB simulation analysis , compared with the conventional method of analysis to verify the feasibility and effectiveness of the algorithm, also, try the algorithm is applied to the complexity of the weather with a strong interference case of precipitation particles; Data analysis showed that the actual detection, from the library in the lower spectrum moment estimation has been improved significantly.

Nonspecular meteor trail altitude distributions and durations observed by a 50 MHz high‐power radar

High‐power large‐aperture (HPLA) radars frequently observe nonspecular meteor trail echoes that result from plasma turbulence driven by the intense pressure gradients on the trail edges. This paper analyzes the altitude range, duration, and dependence on head echo strength of nonspecular trails using two large data sets from the 50 MHz HPLA radar at the Jicamarca Radio Observatory. Over 2100 trails were used to build altitude profiles that extend from 86 km to 120 km altitude, with 97% of events occurring between 90 km and 110 km. Longer‐duration trails tend to form at lower altitudes than shorter‐duration echoes. The peak of the altitude distribution of trails lasting at least 5 s can be up to 12 km lower than the peak of the distribution of trails shorter than 5 s. Further, the data show a clear power law relationship for the frequency of both head echo and nonspecular trail power. An improved knowledge of nonspecular trails will allow researchers to better understand meteor trail evolution and their use in monitoring lower thermospheric winds.

The geometry of Strombolian explosions: insights from Doppler radar measurements

SUMMARY Observations of Strombolian volcanic explosions were carried out at Etna's southeast crater on 2001 July 4 using a ground-based pulsed Doppler radar (VOLDORAD). To obtain quantitative constraints on the geometry of the explosions, we modelled synthetic Doppler spectra by combining the outputs of a ballistic model to compute the theoretical velocities of gas and particles, and an electromagnetic scattering model to calculate the synthetic echo power. This allowed us to reproduce the shapes of recorded Doppler spectra for each volcanic explosion. We examined the geometrical distribution of ejected pyroclasts for about 200 explosions and found two main types of explosion, each showing a distinctive spectral signature. The first type, characterized by the triangular shape of their Doppler spectra, represents 34 per cent of the explosions. This spectrum shape is related to a Gaussian distribution of the pyroclast ejection angles, where most of the volcanic material is ejected vertically within a narrow cone, with the particle concentration decreasing radially. The second type represents about 12 per cent of the explosions, and is characterized by a top-hat-shaped spectrum. It is produced by a uniform distribution of pyroclast ejection angles. In this case, the bubbles tend to burst above the crater rim and eject the ballistic clasts hemispherically without preferential orientation. The majority of the Strombolian explosions analysed (54 per cent) are intermediate between these end-member shapes, and show a triangular spectra truncated by a plateau. They result from a uniform distribution of ejection angles around the jet axis. The continuous radar recordings allowed us to carry out a statistical analysis on the geometrical features of the same 200 Strombolian explosions. Thus we find that 40° is a statistically representative aperture of the dispersion cone characterized by uniform ejecta distribution for explosions having a plateau component (i.e. 2/3 of all explosions studied). We also find that 80 per cent of the total particle load remains within this 40° dispersion cone, which in our case is oriented nearly vertically. Such quantification of the geometrical features of Strombolian explosions can provide constraints on shallow conduit processes. For example, the time evolution of the top-hat Doppler spectra during the paroxysm suggests that the magma level varies over a 15 min timescale.

Lower-thermospheric wind fluctuations measured with an FPI during pulsating aurora at Tromsø, Norway

Abstract. Simultaneous observations were conducted with a Fabry-Perot Interferometer (FPI) at a wavelength of 557.7 nm, an all-sky camera at a wavelength of 557.7 nm, and the European Incoherent Scatter (EISCAT) UHF radar during the Dynamics and Energetics of the Lower Thermosphere in Aurora 2 (DELTA-2) campaign in January 2009. This paper concentrated on two events during periods of pulsating aurora. The lower-thermospheric wind velocity measured with the FPI showed obvious fluctuations in both vertical and horizontal components. Of particular interest is that the location of the fluctuations was found in a darker area that appeared within the pulsating aurora. During the same time period, the EISCAT radar observed sporadic enhancements in the F-region backscatter echo power, which suggests the presence of low-energy electron (1 keV or lower) precipitation coinciding with increase in amplitude of the electromagnetic wave (at the order of 10 Hz or higher). While we have not yet identified the dominant mechanism causing the fluctuations in FPI-derived wind velocity during the pulsating aurora, the frictional heating energy dissipated by the electric-field perturbations may be responsible for the increase in ionospheric thermal energy thus modifying the local wind dynamics in the lower thermosphere.

Physical and Physiological Effects on Otoacoustic Emissions in Hypobaric Hypoxia

Tinnitus and dizziness are symptoms of acute mountain sickness. We investigated the mechanism by which high altitude (i.e. hypobaric hypoxia) affects inner ear function by measuring transient evoked otoacoustic emissions (TEOAE) and distortion product otoacoustic emissions (DPOAE) under conditions of normobaric normoxia (1,013 hPa; 760 mm Hg) and hypobaric hypoxia (540 hPa; 405 mm Hg). The possibility that air pressure effects on the eustachian tube impacted our findings was excluded by the use of tympanograms. The nonphysiological effects of hypobaric hypoxia on TEOAE and DPOAE were also assessed using an ear simulator. Under conditions of hypobaric hypoxia, both TEOAE and DPOAE levels were reduced. The amount of reduction that occurred was approximately 4 dB in the total echo power and signal-to-noise ratio of the TEOAE, and in the 2f₁ – f₂ element level of the DPOAE. Stimulus levels that were measured using an ear simulator were also reduced by approximately 4 dB under conditions of hypobaric hypoxia. These results do not indicate that stimulus levels affected TEOAE and DPOAE levels because these levels were actually only slightly affected by changes in the stimulus level. Instead, this reduction was likely due to the nonphysiological hypobaric effects of the sound pressure emitted from the tympanic membrane. We conclude that the impact of hypobaric hypoxia on cochlear function was negligible up to pressures of 540 hPa.

The 3–5 MHz global reflectivity map of Mars by MARSIS/Mars Express: Implications for the current inventory of subsurface H 2O

We extracted the surface echo power from 2 years of MARSIS measurements. The retrieved values are calibrated to compensate for changes in the distance of the spacecraft to the surface and for the attenuation of the signal by the ionosphere. The results are used to build the first global map of surface echo power at 3–5 MHz. The surface echo power variations are primarily caused by kilometer-scale surface roughness. Then, we derive the values of dielectric constant of the shallow subsurface materials by normalizing the surface echo power map using a simulation of MARSIS signal from the MOLA topography. As a result, we obtain a map that characterizes the dielectric properties of the materials down to a few decameters below the surface. Dielectric properties vary with latitude, with high values in mid-latitudes belts (20–40°) and lower values at both equatorial and high latitudes. From the comparison of MARSIS reflectivity map to GRS observations, we conclude that the reflectivity decrease observed poleward of 50–60° corresponds to the onset of water-ice occurrence within the regolith. Assuming homogenous ground composition and texture at the scale of the MARSIS resolution cell, our inferred volume of ground water ice is of 10 6 km 3, equivalent to a polar cap. Low reflectivity areas are also observed in equatorial regions. From radar studies alone, equatorial low dielectric constant values could have different interpretations but the correlation with GRS hydrogen distribution rather points toward a water-related explanation.

Dry–Wet Bedrock Interface Detection by Radio Echo Sounding Measurements

In this paper, a method to distinguish a wet or dry bedrock-ice interface is proposed. It is based on the analysis of radio echo sounding (RES) measurements, a widely employed method for determining bedrock topography in Antarctica. In particular, the RES system has played an important role in subglacial lake exploration and hydrogeological studies at the bedrock-ice interface. Recently, bedrock characterization has been improved through the analysis of the power of radar echoes. Signal power depends on bedrock reflectivity and its specific physical condition. In this paper, a linear model describing the loss term (internal ice absorption) is proposed. This model, together with other known quantities, contributes toward an assessment of power variation of bedrock reflectivity in order to determinate wet and dry bedrock interfaces in the Dome C region in Antarctica.

Simultaneous Observations of Thin Humidity Gradients in the Lower Troposphere with a Raman Lidar and the Very High-Frequency Middle- and Upper-Atmosphere Radar

Abstract Humidity is, among other things, a key parameter in the evolution of atmospheric dynamics and in the formation of clouds and precipitation through latent heat release. The continuous observation of its vertical distribution is thus important in meteorology. In the absence of convection, humidity in the lower troposphere is distributed into nearly horizontally stratified layers. The thin humidity gradients at the edges of these layers are known to be the main cause of very high-frequency (VHF) stratosphere–troposphere (ST) radar backscatter in the lower troposphere. This property has been experimentally demonstrated many times in the literature from comparisons between balloon measurements and low-resolution radar observations. In the present work, original results of comparisons between Raman lidar measurements of water vapor and middle- and upper-atmosphere (MU) radar measurements of echo power using a range-imaging technique are shown at high spatial and temporal resolutions (∼50 m, ∼20 s). Other tremendous advantages of such comparisons are the simultaneity, time continuity, and colocalization of the lidar and radar measurements. The results show that the radar can be used for continuously monitoring the thin positive and negative gradients of humidity when operated in range-imaging mode. With additional information from balloon measurements, it would be possible to retrieve humidity profiles in the lower troposphere at an unprecedented vertical and time resolution.

RESEARCH ON LASER ALTIMETER'S FIELD OF VIEW

Laser altimeter's field of view(FOV) is an important parameter affecting system's performance.The effect of the field of view on the detection performance of system was discussed.Because of the straylight and the sensor's nonuniformity,the FOV changes as the echo's power changes.At the same time the echo's power will be varied with the detecting distance.The testing way of detecting FOV was put forward,and the factual working status was simulated.For system with inner short-range delay protecting circuit,a new method was brought forward.A laser altimeter with the FOV of 1.5mrad was tested.The FOV of the system is 1.46mrad when its detecting distance is 200km and the echo's power is 5×10-8W.

Real-time target recognition system simulation based on laser near-field detection

This paper constructs a simulation system of near-field laser imaging for 3D grid model of target, provides some methods for the key problems, such as the modeling of target and laser transceiver, the calculation of laser echo power, the imaging algorithms and so on. A target image library is established by a new imaging method in any rendezvous conditions. The four real-time recognition algorithms which are efficient and suitable for hardware implementation are presented at the conditions of the image incompleteness, intensive noise and arbitrary attitude of target. The experimental results show that all the four algorithms can independently recognize the target effectively and a better recognition effect is obtained by the integration of four algorithms.