Systematic errors in spaced antenna wind estimators under inhomogeneous flow conditions

Improved techniques for measuring horizontal and vertical wind components and state variables on research aircraft are presented. They include a filtering method for correcting ground speed and position Inertial Navigation System data with Global Positioning System data, use of moist-air thermodynamic properties in the true airspeed calculation, postflight calculation of the aircraft vertical velocity, and calibration of airflow attack and sideslip angles from the two air-data systems on each aircraft—a radome gust probe and a pair of fuselage-mounted Rosemount 858Y probes. Winds from the two air-data systems are compared for the National Oceanic and Atmospheric Administration WP-3D aircraft. As an evaluation of these techniques, data from the two aircraft during side-by-side low-level constant-heading runs are compared for mean and turbulent measurements of wind, ambient temperature, and absolute humidity. Small empirical offsets were determined and applied to the two latter scalars as well as to static and dynamic pressures. Median differences between mean horizontal wind components from nine comparisons were within 0.1 ± 0.4 m s−1. Median differences in latent heat and sensible heat fluxes and momentum flux components were 3.5 ± 15 W m−2, 0 ± 2.5 W m−2, and 0 ± 0.015 Pa, respectively.

Measurements of the horizontal and vertical wind component by a crosswind scintillometer during foehn, the chinooklike downslope windstorm in the Alps, are presented. Because of the sparsity of vertical velocity measurements in the immediate vicinity, the scintillometer calibration is checked mainly with horizontal wind measurements. Then it is assumed that the calibration is the same for both components. The concept was tested during the Mesoscale Alpine Programme field campaign in the autumn of 1999, during which two scintillometers were deployed. Strong, long-lasting, quasi-stationary downward motions on the order of 5 m s^-1 and horizontal wind speeds of over 30 m s^-1 were detected during strong foehn phases within the valley. Aircraft measurements of various transects near the light paths are compared with two crosswind evaluation techniques. One of them, the slope method, tends to overestimate the actual wind speed by about 20%, whereas the peak technique gives values that are about 10% too low for high wind speeds. The peak method also fails to measure meaningful vertical crosswind speeds. The scintillometer data of one particular foehn storm are compared with nearby Doppler lidar data. The agreement of the horizontal measurements is reasonable. Discrepancies are attributed to topographic and dynamic effects that cause significant spatial inhomogeneities in the wind field. The applicability of continuous scintillometer vertical crosswind measurements in mountainous terrain is demonstrated.

The gamma-ray burst location algorithm used to produce the BATSE burst locations in the 3B catalog data is described. The software algorithm and data processing procedures have been improved to minimize the effect of systematic errors on burst locations. Our current estimate of the RMS systematic error for the 3B catalog, based on IPN and COMPTEL located bursts, is approximately 1.6°, as opposed to 4° for the 2B catalog. The improvements in the 3B algorithm remove many of the outliers from the burst location error distribution. The differences between the 2B and 3B location algorithms are discussed to explain changes in burst locations between the two catalogs. Estimates of the systematic errors on burst locations are presented.

This paper constructs estimates of income and consumption inequality for the world (124 countries), using various measures of inequality. It then goes on to examine the possible effects of various sources of error in the estimates, and attempts to set rough limits to the size of such effects. Among the sources of error examined are purchasing power parities used for currency conversion, systematic errors in estimates of per capita incomes, differences in age structure, government tax and expenditure policy, and lifetime income effects. The paper concludes that, although the level of uncertainty in the estimates is too great to permit conclusions about, for instance, trends over time, it is clear that the level of world inequality is extreme, and that it is primarily due to differences in average incomes across countries rather than to intra‐country inequality.

Aiming to solve the track refined correlation problem of the group targets with systematic errors, based on the characteristics of the group tracks, an algorithm of track refined correlation with in group targets based on systematic error compensation is proposed with the error estimation technique and the track correlation technique. In this algorithm, the groups are identified with the tracks of the sensors based on the circulatory threshold model firstly. Secondly, the preparatory correlation groups with the nearest resolving state are searched or established based on group track state identification model. Thirdly, the final systematic errors are estimated with group track systematic error estimation model and error validation model. What is more, the error compensation is completed. Finally, group track refined correlation is done with the traditional track correlation algorithms. The analysis results of the simulation data show that the general performance of this algorithm, which can meet the engineering requirement of the track refined correlation of the group targets with systematic errors very well, is better than that of fuzzy track alignment-correlation algorithm based on target topological information, track alignment-correlation algorithm based on iterative closest track and modified weighted track correlation algorithm.

Software beam synthesis by postset beam steering (PBS) technique is used to derive the horizontal wind velocities from multireceiver phased-array radar data. In order to improve the efficiency of beam synthesis, the Capon beamforming method is used to synthesize time series signals in the desired line-of-sight angle within the radar transmit beam volume (3.6 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> beamwidth). This paper describes beam synthesizing in optimum directions to reduce the error in the measurement of horizontal wind velocities using the PBS technique. For this purpose, beams are synthesized at various tilt angles with multibeam configuration. From the synthesized beam, power spectral distribution is obtained by one of the subspace methods, i.e., eigenvector (EV). The mean Doppler frequency and radial wind velocity at the desired line-of-sight angle are derived by an adaptive-moment estimation method from an EV-produced power spectrum. Using the moments obtained in various radial directions, horizontal wind components are derived by the conventional method for wind profiler radars. Also, an analysis is done for the required number of beams to improve PBS-based wind estimation. The statistical comparisons of performances of various tilt angles and beam configurations are being studied using the data collected from a multireceiver phased-array radar system (middle and upper atmosphere radar, Shigaraki, Japan). The analyzed results show that beam synthesis at the tilt angle from 1.5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> to 2.0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> using a 16-beam configuration minimize the error in horizontal wind estimation by PBS technique.

Precise knowledge of winds and temperatures in the middle atmosphere is critical for the localization and characterization of infrasound sources. We present the concept, design, and measurement capabilities of a compact, mobile Doppler lidar system developed at the Leibniz Institute of Atmospheric Physics (IAP). This system, is designed for Doppler-Mie, -Rayleigh, and -resonance measurements in the middle atmosphere.The daylight-capable instrument features a compact volume of about 1 m&amp;#179; and is engineered for easy deployment as part of an array of lidar units. We highlight recent results, emphasizing collocated, high-resolution measurements of wind and temperature. By employing three to five individual fields of view, the system can measure both horizontal and vertical wind components. Between altitudes of 3 and 25 km, the instrument utilizes the narrowband properties of Mie backscatter, relying solely on aerosol backscatter to achieve precise three-dimensional wind measurements. In this altitude range, a novel method enables the measurement of vertical winds with an accuracy better than 0.5 m/s and a time resolution of just 60 seconds.Above 25 km, winds will be measured using Doppler-Rayleigh and -resonance techniques. Concurrent Rayleigh temperature measurements utilize advanced aerosol correction methods, taking advantage of the instrument's high sensitivity to aerosols.The feasibility of integrating this lidar system into a European lidar array is being investigated within the EULIAA (European Lidar Array for Atmospheric Climate Monitoring) project. The transfer of this technology to industry is currently being developed through the LidarCUBE project.

Mean and Turbulence Statistics in a Wintertime Convectively-mixed Boundary Layer Over Lake Michigan

Two networks of meteorological stations are used to investigate the spatial variability of temperature, wind speed, turbulent kinetic energy, turbulent fluxes and turbulent spectra over horizontal distances of tens to hundreds of metres . The networks are located in regions of moderately complex terrain, with stations located at elevation differences as large as 37 m at Pedras Altas and 10 m at Santa Maria. The spatial temperature variability is largely enhanced on very stable, weak-wind nights. At Pedras Altas, the temperature difference reaches 12 K between stations horizontally separated by less than 500 m. Obstacles also play an important role, as obstructed sites may have temperatures a few K lower than unobstructed sites at the same elevation. The maximum wind speed over the network (Vmax) controls the horizontal variability of mean and turbulent quantities. Despite the terrain and horizontal scale differences, variables such as mean temperature, standard deviations of horizontal and vertical wind components and the turbulent fluxes of sensible heat, latent heat and carbon dioxide share the dependence on Vmax at both sites. The regime transition between the very stable and weakly-stable boundary layers occurs at much lower wind speeds at an obstructed site than at a hilltop.

A two-dimensional, nonhydrostatic, coupled, earth/atrnospheric model has been used to simulate mean and turbulent atmospheric characteristics near lines of extreme surface heating. Prognostic equations are used to solve for the horizontal and vertical wind components, potential temperature,and turbulent kinetic energy (TKE). The model computes nonhydrostatic pressure deviations from a derived atmospheric continuity equation. Hori- zontal pressure gradients generated from surface heating are calculated from thermal wind principles. Model simulations indicate the development of buoyancy-induced horizontal roll vortices near regions with surface temperatures typical of wildland fires. Model results are qualitatively similar to previous wind-tunnel experiments. When surface temperatures are increased, the circulations associated with the roll vortices become more vigorous. The introduction of a weak ambient flow in a direction perpendicular to the line of heating has a major influence on the simulated circulation patterns aid nonhydrostatic pressure deviations near the line of heating. The effect is more pronounced for lower surface temperatures at the heating line. The TKE profiles reveal preferred regions of TKE growth that can be attributed mainly to buoyancy or advection effects.

Systematic errors between VLBI and GPS precipitable water vapor estimations from 5-year co-located measurements

Abstract. Wind lidars are widespread and important tools in atmospheric observations. An intrinsic part of lidar measurement error is due to atmospheric variability in the remote-sensing scan volume. This study describes and quantifies the distribution of measurement error due to turbulence in varying atmospheric stability. While the lidar error model is general, we demonstrate the approach using large ensembles of virtual WindCube V2 lidar performing a profiling Doppler-beam-swinging scan in quasi-stationary large-eddy simulations (LESs) of convective and stable boundary layers. Error trends vary with the stability regime, time averaging of results, and observation height. A systematic analysis of the observation error explains dominant mechanisms and supports the findings of the empirical results. Treating the error under a random variable framework allows for informed predictions about the effect of different configurations or conditions on lidar performance. Convective conditions are most prone to large errors (up to 1.5 m s−1 in 1 Hz wind speed in strong convection), driven by the large vertical velocity variances in convective conditions and the high elevation angle of the scanning beams (62∘). Range-gate weighting induces a negative bias into the horizontal wind speeds near the surface shear layer (−0.2 m s−1 in the stable test case). Errors in the horizontal wind speed and direction computed from the wind components are sensitive to the background wind speed but have negligible dependence on the relative orientation of the instrument. Especially during low winds and in the presence of large errors in the horizontal velocity estimates, the reported wind speed is subject to a systematic positive bias (up to 0.4 m s−1 in 1 Hz measurements in strong convection). Vector time-averaged measurements can improve the behavior of the error distributions (reducing the 10 min wind speed error standard deviation to &lt;0.3 m s−1 and the bias to &lt;0.1 m s−1 in strong convection) with a predictable effectiveness related to the number of decorrelated samples in the time window. Hybrid schemes weighting the 10 min scalar- and vector-averaged lidar measurements are shown to be effective at reducing the wind speed biases compared to cup measurements in most of the simulated conditions, with time averages longer than 10 min recommended for best use in some unstable conditions. The approach in decomposing the error mechanisms with the help of the LES flow field could be extended to more complex measurement scenarios and scans.

The MHD virial theorem may be used to estimate the magnetic energy of active regions on the basis of vector magnetic fields measured at the photosphere or chromosphere. However, the virial estimate depends on the measured vector magnetic field being force-free. Departure from the force-free condition leads to an unknown systematic error in the virial energy estimate and an origin dependence of the result. We present a method for estimating the systematic error by assuming that magnetic forces are confined to a thin layer near the photosphere. If vector magnetic field measurements are available at two levels in the low atmosphere (e.g., the photosphere and the chromosphere), the systematic error may be directly calculated using the observed horizontal and vertical field gradients, resulting in an energy estimate that is independent of the choice of origin. If (as is generally the case) measurements are available at only one level, the systematic error may be approximated using the observed horizontal field gradients together with a simple linear force-free model for the vertical field gradients. The resulting improved virial energy estimate is independent of the choice of origin but depends on the choice of the model for the vertical field gradients, i.e., the value of the linear force-free parameter α. This procedure is demonstrated for five vector magnetograms, including a chromospheric magnetogram.

The development and applications of a new class of water-soluble compounds suitable for molecular tagging diagnostics are described. These molecular complexes are formed by mixing a lumophore, an appropriate alcohol, and cyclodextrin. Using 1-BrNp as the lumophore, cyclohexanol is determined to be the most effective overall among the alcohols for which data are currently available. Information is provided for the design of experiments based on these complexes along with a less complex method for generating the grid patterns typically used for velocimetry. Implementation of a two-detector system is described which, in combination with a spatial correlation technique for determining velocities, relaxes the requirement that the initial tagging pattern be known a priori, eliminates errors in velocity estimates caused by variations in the grid pattern during an experiment, and makes it possible to study flows with non-uniform mixtures. This detection and analysis combination also solves one of the problems associated with using caged fluorescein to study high-speed flows. In addition to the traditional implementation for velocimetry, novel applications for studying the Lagrangian evolution of both reacting and non-reacting interfaces and obtaining combined passive scalar/velocity measurements are demonstrated.

Numerical estimation of physical properties from digital pore microstructures has drawn great attention and is being used for quantifying interrelation between various physical properties. The pore microstructures are commonly obtained by the X-ray microtomographic technique, which can give fairly accurate pore geometry. However, there is minor distortion due to the limited resolution or smoothing. This distortion can cause errors in estimating physical properties by pore-scale simulation techniques. Among the properties, seismic velocity would have relatively large errors since a small amount of change in grain contacts can cause significant over-estimation. In this paper, we analyzed the errors in seismic velocity by resolution and smoothing of pore geometry using three samples: an unconsolidated sand pack and two medium-porosity sandstones with different degrees of consolidation. As the resolution becomes poor, the calculated velocity increases linearly, while smoothing gives nonlinear trends; higher errors in the early stage of smoothing. As we expected, soft rocks have higher sensitivity, since the grain contacts are small and are sensitive to minor distortion. Within similar ranges, the resolution causes larger errors than smoothing. In addition, smoothing does not cause velocity over-estimation once the resolution becomes poor, while the resolution can create considerable errors in velocity even after significant smoothing. We conclude that the resolution should be considered in the first place when obtaining digital pore microstructures to minimize errors in velocity estimation. We can also suggest that a good care should be taken when applying smoothing filters, if a sample is suspected to be poorly-consolidated or to have high porosity.