Echo Profiles Research Articles

Echocardiographic Profiling Predicts Clinical Outcomes After Mitral Transcatheter Edge-to-Edge Repair.

Prior studies investigating the impact of residual mitral regurgitation (MR), tricuspid regurgitation (TR), and elevated predischarge transmitral mean pressure gradient (TMPG) on outcomes after mitral transcatheter edge-to-edge repair (TEER) have assessed each parameter in isolation. We sought to examine the prognostic value of combining predischarge MR, TR, and TMPG to study long-term outcomes after TEER. We reviewed the records of 291 patients who underwent successful mitral TEER at our institution between March 2014 and June 2022. Using well-established outcomes-related cutoffs for predischarge MR (≥moderate), TR (≥moderate), and TMPG (≥5 mm Hg), 3 echo profiles were developed based on the number of risk factors present (optimal: 0 risk factors, mixed: 1 risk factor, poor: ≥2 risk factors). Discrimination of the profiles for predicting the primary composite end point of all-cause mortality and heart failure hospitalization at 2 years was examined using Cox regression. Overall, mean age was 76.7±10.6 years, 43.3% were women, and 53% had primary MR. Two-year event-free survival was 61%. Predischarge TR≥moderate, MR≥moderate, and TMPG≥5 mm Hg were risk factors associated with the primary end point. Compared with the optimal profile, there was an incremental risk in 2-year event-rate with each worsening profile (optimal as reference; mixed profile: hazard ratio (HR), 2.87 [95% CI, 1.71-5.17], P<0.001; poor profile: HR, 3.76 [95% CI, 1.84-6.53], P<0.001). Echocardiographic profile was statistically associated with the 2-year mortality end point (optimal as reference; mixed profile: HR, 3.55 [95% CI, 1.81-5.96], P<0.001; poor profile: HR, 3.39 [95% CI, 2.56-7.33], P=0.02). The echocardiographic profile integrating predischarge TR, MR, and TMPG presents a novel prognostic stratification tool for patients undergoing mitral TEER.

Key Agreement on IoT Devices With Echo Profiling

Secure Device-to-Device (D2D) communication is important for the Internet-of-Things (IoT) devices. Key agreement between devices is the important first step in building a secure D2D channel. Due to the lack of third-party certification, key agreement for IoT devices has to rely on the untrusted channel between them, which makes the pairing process vulnerable to attacks such as eavesdropping, jamming, and predictable channel attack. We solve this problem with a novel key agreement method named, where two nearby devices can generate a symmetric key independently, leveraging the ambient sound signal that can be locally collected by devices. The intuition of this idea is that the propagation delays of the ambient sounds and the echoes will carry fine-grained information about the spatial context of the receiving device, which can be transformed to a special key for that device. So, nearby devices which have similar spatial context will generate similar echo profiles. We implement a prototype of and evaluate its performance in resisting different attacks. The results tell that, with, the key agreement process is even undetectable by an attacker which is only 50cm away from the pairing devices, and is thus resistant to all attacks mentioned above.

Halide Substitution Effects on Lithium-Ion Diffusion in Protonated Antiperovskites

Solid-state electrolytes (SSEs) for all-solid-state lithium-ion batteries are generating intense interest because these batteries can improve the safety and performance compared with devices fabricated with conventional, flammable liquid electrolytes. In these SSEs, it has been suggested that Li+ ion diffusion in the grain boundaries is hindered and is a critical determinant of the overall ionic conductivity (σ). However, Li+ ion diffusivities in the grain (DG) and the grain boundary (DGB) are difficult to determine experimentally, with few techniques capable of distinguishing the individual contributions. Here, we distinguished the DG and DGB for the protonated lithium antiperovskites (pLiAPs) SSEs: Li2OHCl, Li2OHBr, Li2OHF0.1Cl0.9, Li2OHF0.1Br0.9, and Li2OHCl0.37Br0.63. The measurements were obtained directly from 7Li pulsed-field gradient nuclear magnetic resonance (PFG-NMR) at 353 K. The 7Li PFG-NMR echo profiles were composed of two primary components with additional secondary oscillatory components – the so-called NMR diffraction phenomenon. The length scale separating the two main components corresponds to a diffusion length of ∼1.7 μm, which is thought to be the average grain size (by diameter). The short-range (≤1.7 μm) diffusion component associated with DG (≈10–11 m2/s) varied minimally with halide substitution, while the long-range (≥1.7 μm) component DGB (≈10–12 to 10–15 m2/s) was highly sensitive to the substitution of halides and closely correlated with σ. In addition, from the comparison of the ratio DGB/DG to Dτ (the Li+ ion diffusion coefficient estimated from the rotational correlation time, τc), it was determined that the fractional contribution of DG to σ is negligible; 0.01–0.04 in the pLiAPs studied here. These insights provide a fundamental understanding of the halide substitution effects on Li+ ion grain vs grain boundary diffusion and suggest that careful engineering of the grain boundaries at the microscopic level is necessary to achieve high-performance pLiAP SSEs.

EarIO

This paper presents EarIO, an AI-powered acoustic sensing technology that allows an earable (e.g., earphone) to continuously track facial expressions using two pairs of microphone and speaker (one on each side), which are widely available in commodity earphones. It emits acoustic signals from a speaker on an earable towards the face. Depending on facial expressions, the muscles, tissues, and skin around the ear would deform differently, resulting in unique echo profiles in the reflected signals captured by an on-device microphone. These received acoustic signals are processed and learned by a customized deep learning pipeline to continuously infer the full facial expressions represented by 52 parameters captured using a TruthDepth camera. Compared to similar technologies, it has significantly lower power consumption, as it can sample at 86 Hz with a power signature of 154 mW. A user study with 16 participants under three different scenarios, showed that EarIO can reliably estimate the detailed facial movements when the participants were sitting, walking or after remounting the device. Based on the encouraging results, we further discuss the potential opportunities and challenges on applying EarIO on future ear-mounted wearables.

Trends in the development of systems for monitoring the state of water bodies and the development of a Geo-information system Dniester on the basis of an industrial ІоТ

The work shows that inadequate and untimely hydrological forecasting of the level of flood development leads to significant annual economic damage and loss of life. The latter requires constant control and monitoring of the state of water bodies, which is possible with modern automated control and monitoring systems. The analysis showed that the information and measurement systems (AIMS) for flood control, which are operated in Ukraine, their quantity, cost and technical characteristics do not provide the information necessary for predicting the development of floods.&#x0D; Analysis of trends in the development of systems for automated control and monitoring of the state of water bodies showed that modern foreign systems that are at the stage of development or testing are based on the use of microcontrollers, "smart" converters of physical quantities, modern communication systems and Internet of Things technology, as well as the use of smartphones with a Raspberry Pi camera for determining the water level in rivers.&#x0D; The development with the use of the industrial Internet of Things of the basic version of the geoinformation system for control and monitoring of the state of water bodies GIS-Dniester is given. The structure, components and functions of GIS-Dniester are considered. The tasks of organizing hardware and software for parameterizing and diagnosing "smart" converters, establishing a communication environment for industrial communication, developing algorithms for collecting, processing and transmitting data, studying the characteristics of measuring signals are being solved. The results of the study of the echo profiles of the XPS10 ultrasonic level sensor with “smart” -converters Multiranger 100, as well as the procedure for working with the GIS-Dniester are presented. The use of the developed GIS-Dniester has shown its effectiveness and reliability in operation.

Exploring phenotypes in hypertrophic cardiomyopathy with machine learning data integration. A multicentric, multimodality pilot study

Abstract Background Interpreting patient phenotypes is a challenge when screening for hypertrophic cardiomyopathy (HCM). Machine learning (ML) can potentially help with advanced data integration - combining information contained in whole-cardiac cycle echo deformation and velocity profiles with standard clinical variables. The aim is to apply an ML approach to integrate whole cardiac cycle echo data with clinical variables to explore HCM phenotypes. Methods The cohort consisted of 138 participants from two centres: HCM patients (n=91) and relatives (n=47). Echocardiography was performed, whereas magnetic resonance and genetic testing in 48% and 82%, respectively. Whole cardiac cycle echo data (mitral and aortic velocity profiles, and six regional left ventricular (LV) deformation curves) were combined with clinical variables (age, sex, heart rate, e' medial and e' lateral) and used as the ML input. An unsupervised ML algorithm created a representative space where participants were positioned based on integrated data, blinded to disease status. Clustering was used to determine phenogroups and estimate the average characteristics. Data on family history (FHx), genotype, arrhythmias or syncope, implantable cardioverter-defibrillators (ICD), and late gadolinium enhancement (LGE) were used to interpret the phenogroups. As the LA diameter was not available in the dataset, the HCM risk for sudden cardiac death (SCD) was not calculated, however, the Table shows relevant variables to infer clinical risk. Results Clustering divided the participants into 6 phenogroups (P1–6) (Figure). Average echo profiles are shown in the Figure, while the clinical data in the Table. P1/2 was defined by symptomatic patients with a high prevalence of positive genotypes, a positive FHx of SCD, and a burden of comorbidities. Echo findings showed pronounced structural/functional remodeling, and P1 was associated with severe septal hypertrophy and outflow tract obstruction. The high prevalence of ICD devices defined P1/2 as high risk groups. In comparison, patients in P3/4 were younger, with milder LV hypertrophy, but still considerable functional impairment. P3 had a higher burden of FHX and a higher prevalence of pathogenic mutations, whereas P4 a higher incidence of hypertension, high heart rate, mitral inflow fusion and findings of LGE. Finally, P5/6 consisted of younger individuals, predominantly HCM relatives, with a mild phenotype and, thus, low inferred risk. As expected, the majority of patients with the genetic variants of undetermined significance were located in P5. Conclusion ML can help derive clinically interpretable phenotypes in HCM based on the automated integration of whole cardiac cycle deformation and velocity data with conventional clinical parameters. The derived phenogroups correspond with established risk profiles in HCM. An expanded dataset is needed to enable further exploration of the phenotype-genotype relations and to define prognostic value. Funding Acknowledgement Type of funding sources: Public grant(s) – EU funding. Main funding source(s): This work was supported by the Horizon 2020 European Commission Project H2020-MSCA-ITN

Triple-frequency meteor radar full wave scattering

Context. Radar scattering from meteor trails depends on several poorly constrained quantities, such as electron line density, q, initial trail radius, r0, and ambipolar diffusion coefficient, D. Aims. The goal is to apply a numerical model of full wave backscatter to triple frequency echo measurements to validate theory and constrain estimates of electron radial distribution, initial trail radius, and the ambipolar diffusion coefficient. Methods. A selection of 50 transversely polarized and 50 parallel polarized echoes with complete trajectory information were identified from simultaneous tri-frequency echoes recorded by the Canadian Meteor Orbit Radar. The amplitude-time profile of each echo was fit to our model using three different choices for the radial electron distribution assuming a Gaussian, parabolic-exponential, and 1-by-r2 electron line density model. The observations were manually fit by varying, q, r0, and D per model until all three synthetic echo-amplitude profiles at each frequency matched observation. Results. The Gaussian radial electron distribution was the most successful at fitting echo power profiles, followed by the 1∕r2. We were unable to fit any echoes using a profile where electron density varied from the trail axis as an exponential-parabolic distribution. While fewer than 5% of all examined echoes had self-consistent fits, the estimates of r0 and D as a function of height obtained were broadly similar to earlier studies, though with considerable scatter. Most meteor echoes are found to not be described well by the idealized full wave scattering model.

Seeking Echoes of Circumstellar Disks in Kepler Light Curves

Abstract Light echoes of flares on active stars offer the opportunity for direct detection of circumstellar dust. We revisit the problem of identifying faint echoes in postflare light curves, focusing on debris disks from ongoing planet formation. Starting with simulations, we develop an algorithm for estimating the radial extent and total mass from disk echo profiles. We apply this algorithm to light curves from over 2100 stars observed by NASA’s Kepler mission, selected for multiple short-lived flares in either the long-cadence or short-cadence data sets. While flux uncertainties in light curves from individual stars preclude useful mass limits on circumstellar disks, catalog-averaged light curves yield constraints on disk mass that are comparable to estimates from known debris disks. The average mass in micron- to millimeter-sized dust around the Kepler stars cannot exceed 10% of an Earth mass in exo-Kuiper belts or 10% of a lunar mass in the terrestrial zone. We group stars according to IR excess, based on WISE W1–W3 color, as an indicator for the presence of circumstellar dust. The mass limits are greater for stars with strong IR excess, a hint that echoes are lurking not far beneath the noise in postflare light curves. With increased sensitivity, echo detection will let time-domain astronomy complement spectroscopic and direct-imaging studies in mapping how, when, and where planets form.

The effect of surfactants on the initiation and development of air–water slug flow in hilly terrain pipeline

In hilly terrain pipelines, gas–liquid slug flow usually forms in the low-lying elbow and develops in the inclined ascending pipe at a low superficial liquid velocity and influences the effective and safe natural gas transportation. The surfactant additive has a significant effect on this flow and promotes the liquid drainage in hilly terrain pipelines. To further understand the interaction mechanism between surfactants and gas–liquid flow, an experimental investigation of the initiation and development of slug flow with and without surfactants was performed. The acrylic test tubes consisted of an inclined descending pipe, a horizontal pipe and an inclined ascending pipe with a 50 mm ID and inclination angles of ±10°. The 100 parts per million (ppm) of sodium dodecyl sulfate (SDS) and 100 ppm of sodium dodecyl benzoyl sulfate (SDBS) were respectively used as surfactant additives in this work. The flow behavior of slug initiation and development was observed by a visual system and measured using multiple 2 MHz ultrasonic transducers in the elbow and inclined pipeline. The flow morphology of slug flow changed significantly with the foam formation in the air–surfactant solutions flow. The slug frequency, the liquid film and velocity variation and the velocity characteristics of slug flow were obtained and analyzed based on the measured echo and velocity profiles. The addition of surfactants weakened the strong gas–liquid interaction at the front of liquid slug and increased the velocity of backflow in the liquid film. The experiment results make the effect of surfactants on the gas–liquid interface and velocity characteristics of slug flow in hilly terrain pipelines more clear.

Applying ADCPs for Long‐Term Monitoring of SSC in Rivers

AbstractThe flow rate and the suspended sediment concentration (SSC) of two different rivers draining into the Adriatic Sea basin, the Secchia in Italy and the Devoll in Albania, were analyzed by processing the data collected in a 245‐day period at monitoring stations equipped with side‐looking acoustic Doppler current profilers (H‐ADCPs). SSC was determined as a by‐product of the echo profiles along the horizontal aligned acoustic beams emitted by H‐ADCPs. For the first time, the effect of organic matter other than a change of inorganic particles size distribution was evaluated as a possible reason for backscatter and attenuation variations during hydrological events. This reduced average deviations between acoustically inferred and sampled concentrations from 1 order of magnitude to 20% of actual values. The improvement required the measuring of attenuation to backscatter ratio (ABR) in addition to sound attenuation. The validation interval covered 3 orders of magnitude from to g L . In this paper the potential of the ABR method using H‐ADCP to continuously monitor suspended sediment fluxes is tested in two different rivers, enabling single peak flood analysis and reliable assessment of sediment budget across a river cross section. The advantages and disadvantages of this method are presented and discussed.

Classification and Diurnal Variations of Precipitation Echoes Observed by a C-band Vertically-Pointing Radar in Central Tibetan Plateau during TIPEX-III 2014-IOP

This study investigates classification and diurnal variations of the precipitation echoes over the central Tibetan Plateau based on the observations collected from a C-band vertically-pointing frequency-modulated continuous-wave (C-FMCW) radar during the Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX-III) 2014-Intensive Observation Period (2014-IOP). The results show that 51.32% of the vertical profiles have valid echoes with reflectivity > –10 dBZ, and 35.06% of the valid echo profiles produce precipitation at the ground (precipitation profiles); stratiform precipitation with an evident bright-band signature, weak convective precipitation, and strong convective precipitation account for 52.03%, 42.98%, and 4.99% of the precipitation profiles, respectively. About 59.84% of the precipitation occurs in the afternoon to midnight, while 40.16% of the precipitation with weaker intensity is observed in the nocturnal hours and in the morning. Diurnal variation of occurrence frequency of precipitation shows a major peak during 2100–2200 LST (local solar time) with 59.02% being the stratiform precipitation; the secondary peak appears during 1300–1400 LST with 59.71% being the weak convective precipitation; the strong convective precipitation occurs mostly (81.83%) in the afternoon and evening with two peaks over 1200–1300 and 1700–1800 LST, respectively. Starting from approximately 1100 LST, precipitation echoes develop with enhanced vertical air motion, elevated echo top, and increasing radar reflectivity. Intense upward air motion occurs most frequently in 1700–1800 LST with a secondary peak in 1100–1400 LST, while the tops of precipitation echoes and intense upward air motion reach their highest levels during 1600–1800 LST. The atmospheric conditions in the early morning are disadvantageous for convective initiation and development. Around noon, the convective available potential energy (CAPE) increases markedly, convective inhibition (CIN) is generally small, and a super-dry-adiabatic layer is present near the surface (0–400 m). In the early evening, some larger values of CAPE, level of neutral buoyancy, and total precipitable water are present, suggesting more favorable thermodynamic and water vapor conditions.

Combining echo and hydrodynamic measurements for estimating non uniform sand transport under waves and currents

We present recently obtained measurements in the Atlantic coast of Uruguay, with a 1 MHz ADCP (Sentinel V20, Teledyne RDI, USA). The ADCP was deployed at 16 m depth for 4 months using a light weight structure deployed from a small boat. During the deployment, 3.6 m significant high, 12 s peak period waves, and 0.8 m/s currents were recorded. The vertical distribution of suspended sediment in this environment is controlled by the turbulence level induced by both currents and waves. Assuming a representative sediment size and adapting the Rouse-Vanoni profile showed to give results that did not agree with the concentration profiles inverted from the recorded echo profiles. Therefore, a method that combined variations of the sediment size distribution with the turbulence level was developed showing very good agreement with the information from the echo profile. In the developed method, the turbulent sediment diffusivity was computed from the mean current and wave measurements. However, this showed limitations for conditions with strong waves and weak currents. As an alternative, direct measurements of the turbulent fluctuations from the instantaneous beam velocity recordings were used to compute the turbulent diffusivity. In addition, different turbulent diffusivity distributions for combined current-wave conditions were evaluated.

A SEmi-Adiabatic matched-phase spin echo (SEAMS) PINS pulse-pair for B1 -insensitive simultaneous multislice imaging.

Simultaneous multislice (SMS) imaging is a powerful technique that can reduce image acquisition time for anatomical, functional, and diffusion weighted magnetic resonance imaging. At higher magnetic fields, such as 7 Tesla, increased radiofrequency (RF) field inhomogeneity, power deposition, and changes in relaxation parameters make SMS spin echo imaging challenging. We designed an adiabatic 180° Power Independent of Number of Slices (PINS) pulse and a matched-phase 90° PINS pulse to generate a SEmi-Adiabatic Matched-phase Spin echo (SEAMS) PINS sequence to address these issues. We used the adiabatic Shinnar Le-Roux (SLR) algorithm to generate a 180° pulse. The SLR polynomials for the 180° pulse were then used to create a matched-phase 90° pulse. The pulses were sub-sampled to produce a SEAMS PINS pulse-pair and the performance of this pulse-pair was validated in phantoms and in vivo. Simulations as well as phantom and in vivo results, demonstrate multislice capability and improved B1 -insensitivity of the SEAMS PINS pulse-pair when operating at RF amplitudes of up to 40% above adiabatic threshold. The SEAMS PINS approach presented here achieves multislice spin echo profiles with improved B1 -insensitivity when compared with a conventional spin echo.

WE-G-17A-02: MRI-Based Lung Tumor Tracking with Navigator Echo Pulses

Purpose: To evaluate the feasibility of directly tracking the displacement of lung tumors in MRI using navigator echo pulses, and to compare the navigator-derived tumor positions with manually-identified tumor positions. Methods: Twelve patients with lung tumors underwent free-breathing sagittal MR scans under an IRB-approved protocol for 8–12 min. We used a multi-slice 2D TruFISP pulse sequence on a 1.5T Siemens Avanto scanner. Scan parameters were as follows: TE=1.29ms, TR=2.57ms, flip angle=60°, pixel matrix=176×256, resolution=1.95mm × 1.95 mm × (9–16) mm, acquisition time=2.5s. One-dimensional profiles of the images in the SI and AP directions that passed through the center of the tumor were selected for analysis as simulated navigator echo profiles. The tumor position was identified through edge detection and tracked throughout the temporally varying images in each direction. The navigator-tracked direct tumor positions were compared with tumor centroid positions manually identified by an expert physician on the full images (200 acquisitions per scan). The correlation coefficient and pixel distance between the two tumor positions were calculated. In addition, respiratory surrogate navigator positions of the diaphragm and chest wall were also evaluated for correlation with the manually-identified tumor positions. Results: Direct tracking of the lung tumor position with navigator echoes was more highly correlated to the manual tumor positions than surrogate tracking in 72% of cases with significant correlations (p<0.005). Only four patients exhibited strong linear correlations (R2>0.6). The average distance between the navigator tumor positions and the manually-identified tumor positions was 0.99±0.74 pixels (1.93±1.44 mm). Conclusions: Lung tumor displacement can be tracked using navigator echoes to within 2 mm (1 pixel) of manually identified tumor positions. This work was supported in part by Grant No. CA124766 from the NIH/NCI, and Varian Medical Systems (Palo Alto, CA).

Analysis of Convergence Boundaries Observed during IHOP_2002

Abstract An analysis of six convergence boundaries observed during the International H2O Project (IHOP_2002) is presented. The detailed kinematic and thermodynamic structure of these boundaries was examined using data collected by an airborne Doppler radar and a series of dropsondes released by a jet flying at ∼500 mb. The former and latter platforms were able to resolve the meso-γ- and meso-β-scale circulations, respectively. Convection initiated on three of the days while no storms developed in the regions targeted by the mobile platforms on the other days (referred to as null cases). The airborne radar resolved the finescale structure of four drylines, a cold front, and an outflow boundary on the six days. Horizontal profiles through radar-detected thin lines revealed “bell-shaped distributions” and there appeared to be a seasonal dependence of the peak values of radar reflectivity. The echo profiles through the fine line in May were, in general, greater than those plotted for the June cases. There was no apparent relationship between the intensity of the low-level updraft and convection initiation. The strongest updraft resolved in the dual-Doppler wind synthesis was associated with a null case. There was also no relationship between the strength of the moisture discontinuity across the boundaries and convection initiation. The three days during which the storms developed were all associated with two convergence boundaries that were adjacent to each other. The two boundaries collided on one of the days; however, the boundaries on the other two days were approximately parallel and remained separated by a distance of 5–15 km. The total derivative of the horizontal vorticity rotating along an axis parallel to the boundary was calculated using dropsonde data. The horizontal gradient of buoyancy was the largest contributor to the change in vorticity and revealed maximum and minimum values that would support the generation of counterrotating circulations, thus promoting vertically rising air parcels. These updrafts would be more conducive to convection initiation. The null cases were characterized by a low-level vorticity generation of only one sign. This pattern would support tilted updrafts. The results presented in this study suggest that it is not necessary for two boundaries to collide in order for thunderstorms to develop. Solenoidally generated horizontal circulations can produce conditions favorable for convection initiation even if the boundaries remain separate.

Observed Self-Similarity of Precipitation Regimes over the Tropical Oceans

Abstract A K-means clustering algorithm was used to classify Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) scenes within 1° square patches over the tropical (15°S–15°N) oceans. Three cluster centroids or “regimes” that minimize the Euclidean distance metric in a five-dimensional space of standardized variables were sought [convective surface rainfall rate; ratio of convective rain to total rain; and fractions of convective echo profiles with tops in three fixed height ranges (&amp;lt;5, 5–9, and &amp;gt;9 km)]. Independent cluster computations in adjacent ocean basins return very similar clusters in terms of PR echo-top distributions, rainfall, and diabatic heating profiles. The clusters consist of shallow convection (SHAL cluster), with a unimodal distribution of PR echo tops and composite diabatic heating rates of ∼2 K day−1 below 3 km; midlevel convection (MID-LEV cluster), with a bimodal distribution of PR echo tops and ∼5 K day−1 heating up to about 7 km; and deeper convection (DEEP cluster), with a multimodal distribution of PR echo tops and &amp;gt;20 K day−1 heating from 5 to 10 km. Each contributes roughly 20%–40% in terms of total tropical rainfall, but with MID-LEV clusters especially enhanced in the Indian and Atlantic sectors, SHAL relatively enhanced in the central and east Pacific, and DEEP most prominent in the western Pacific. While the clusters themselves are quite similar in rainfall and heating, specific cloud types defined according to the PR echo top and surface rainfall rate are less similar and exhibit systematic differences from one cluster to another, implying that the degree to which precipitation structures are similar decreases when one considers individual precipitating clouds as repeating tropical structures instead of larger-scale cluster ensembles themselves.

Underwater Scan Matching using a Mechanical Scanned Imaging Sonar

Underwater environments are extremely challenging to perform localization. Autonomous Underwater Vehicles (AUV) are usually endowed with acoustic devices such as a Mechanically Scanned Imaging Sonar (MSIS). This sensor scans the environment by emitting ultrasonic pulses and it provides echo intensity profiles of the scanned area. Our goal is to provide self-localization capabilities to an AUV endowed with a MSIS. To this end, this paper proposes a scan matching strategy to estimate the robot motion. This strategy extracts range information from the sensor data, deals with the large scan times and performs a probabilistic data association. The proposal is tested with real data obtained during a trip in a marina environment, and the results show the benefits of our proposal by comparing it to other well known approaches.

Analysis and interpretation of Cassini Titan radar altimeter echoes

The Cassini spacecraft has acquired 25 radar altimeter elevation profiles along Titan's surface as of April 2008, and we have analyzed 18 of these for which there are currently reconstructed ephemeris data. Altimeter measurements were collected at spatial footprint sizes from 6–60 km along ground tracks of length 400–3600 km. The elevation profiles yield topographic information at this resolution with a statistical height accuracy of 35–50 m and kilometer-scale errors several times greater. The data exhibit significant variations in terrain, from flat regions with little topographic expression to very rugged Titanscapes. The bandwidth of the transmitted waveform admits vertical resolution of the terrain height to 35 m at each observed location on the surface. Variations in antenna pointing and changes in surface statistics cause the range-compressed radar echoes to exhibit strong systematic and time-variable biases of hundreds of meters in delay. It is necessary to correct the received echoes for these changes, and we have derived correction algorithms such that the derived echo profiles are accurate at the 100 m level for off-nadir pointing errors of 0.3° and 0.6°, for leading edge and echo centroid estimators, respectively. The leading edge of the echo yields the elevation of the highest points on the surface, which we take to be the peaks of any terrain variation. The mean value of the echo delay is more representative of the mean elevation, so that the difference of these values gives an estimate of any local mountain heights. Finding locations where these values diverge indicates higher-relief terrain. Elevation features are readily seen in the height profiles. Several of the passes show mountains of several hundred m altitude, spread over 10's or even 100's of km in spatial extent, so that slopes are very small. Large expanses of sub-100 m topography are commonplace on Titan, so it is rather smooth in many locations. Other areas exhibit more relief, although the overall observed variation in surface height on any pass is less than about 1 km. Some elevation features correspond to observed changes in brightness in Cassini infrared images, but many do not. Correspondence between the imaging SAR ground tracks and the altimeter paths is limited, so that identifying elevation changes with higher resolution SAR features is premature at present.

Estimation of Humidity Profiles by Combining Co-Located VHF and UHF Wind-Profiling Radar Observation

The turbulence echo intensity observed by a wind-profiling radar is closely related to the vertical gradient of refractive index squared (M 2 ), which largely depends on the vertical humidity gradient in a moist atmosphere. We have developed a radar remote-sensing technique for determining humidity profiles by using the turbulence echo characteristics. The sign of M is determined so that the precipitable water vapor determined by the radar agrees with that derived from the GPS measurements. In this study we have combined the results collected with two co-located radars; the MU (Middle and Upper atmosphere) and Lower Troposphere Radar (LTR) operating at 46.5 MHz and 1.3 GHz frequencies, respectively, and humidity profiles determined at 0.3-7.5 km. The echo power profiles (signal-to-noise ratio, SNR) with the two radars are connected smoothly in a height range between 1.5 and 1.95 km, by considering reduction of the receiver sensitivity for the MU radar due to leakage of the transmission signal. The retrieved humidity profiles show detailed time-height variations, which agree well with the simultaneous Raman lidar and radiosonde measurements.

Characterizing large river history with shallow geophysics: Middle Yukon River, Yukon Territory and Alaska

Changes in longitudinal valley-fill thickness can provide inferences about fluvial behaviour over millennia. Increased thickness of channel deposits may reveal climate-induced accelerated sediment supply, basin subsidence, tectonic displacements, or rising downstream base level. Decreases in thickness, expressed as terraces, may suggest active uplift, decreased sediment flux, or falling base level within a reach. To date, methods to characterize valley fills have depended largely on borehole data. However, recent developments in shallow geophysics make such investigations possible and provide a practical methodology to investigate alluvial rivers. We carried out a longitudinal geophysical survey, coupled with floodplain chronologies to characterize a 1000 km reach of the middle Yukon River between western Yukon Territory and central Alaska. Ground penetrating radar (GPR) and electrical resistivity ground imaging (ERGI) profiles along the middle Yukon River between central Yukon and Alaska, coupled with channel-bottom echo profiles, demonstrates that there is little variation in thickness of gravel fill and depth of active scour holes. GPR surveys near the White River, the largest sediment source in the upper Yukon, show no significant longitudinal variation in gravel thickness (8–16 m) up to near Circle, Alaska (530 km of wandering channels). Geophysical profiles across the Yukon Flats sedimentary basin (430 km of braided and wandering channels) show an increase in gravel thickness (25–30 m), but this is consistent with compaction of underlying lacustrine sediment and maximum depths of contemporary scour holes. From the western margin of the Yukon Flats to the Dalton Highway bridge (30 km, confined valley with no floodplain or braid bars), borehole data at the bridge indicates 6–10 m of gravel on bedrock beneath 3–6 m of water. Floodplain stratigraphy indicates there is little evidence of fluvial aggradation of the middle Yukon during the Holocene. Radiocarbon ages from the gravel–overbank silt contact near present river level demonstrate a general vertical stability of the river with a period of rapid eolian accumulation during the late Pleistocene and early Holocene. The consistency of gravel-fill and scour hole depth, and lack of Holocene terraces along the 1000 km reach of the Yukon, indicate that the river has been in a state of mass-balance equilibrium of sediment transport (input=output) over the Holocene. Despite massive sediment influxes from the glacial-fed White River and crossing major faults, variation in valley-fill depth is not significant. And further, the Yukon Flats reach shows no evidence of bed aggradation during the Pleistocene and has probably existed in equilibrium since the late Pliocene.