Horizontal Wind Estimates Research Articles

Measuring Wind Speed Using the Internal Stabilization System of a Quadrotor Drone

This article proposes a method of measuring wind speed using the data logged by the autopilot of a quadrotor drone. Theoretical equations from works on quadrotor control are utilized and supplemented to form the theoretical framework. Static thrust tests provide the necessary parameters for calculating wind estimates. Flight tests were conducted at a test site with laminar wind conditions with the quadrotor hovering next to a static 2D ultrasonic anemometer with wind speeds between 0–5 m/s. Horizontal wind estimates achieve exceptionally good results with root mean square error (RMSE) values between 0.26–0.29 m/s for wind speed, as well as between 4.1–4.9 for wind direction. The flexibility of this new method simplifies the process, decreases the cost, and adds new application areas for wind measurements.

Evaluation of EAR Spaced Antenna Performance Using Multiple Receiving Antennas Orientations

AbstractEquatorial Atmosphere Radar (EAR) is a very high frequency (VHF) Doppler radar with an active phased array antenna system operating at 47 MHz. It had originally been equipped with a single receiving channel system since its establishment in 2001 at the equator in Kototabang, West Sumatra, Indonesia (0.20°S, 100.32°E). Recent progress has enabled the implementation of a spaced antenna (SA) method on the EAR through the development of a multichannel receiver using Universal Software Radio Peripheral (USRP) and GNU Radio. However, this approach exhibits limited height observation and horizontal wind estimation accuracy. Here, we present comparison and analysis of EAR SA performance with five different orientations, taking into consideration the size of the receiving antennas and their separation distance. Experiments with the chosen configurations were carried out between April and September 2019, and the horizontal wind profiles were estimated using full correlation analysis (FCA) and compared with the EAR standard data. In addition, FCA with the least squares method is carried out for all configurations with the aim of improving the estimation accuracy. Based on the results, the configuration with the largest aperture shows a clear advantage over the other four configurations but with limited improvement in terms of maximum observable height.

Improved Performance in Horizontal Wind Estimation Using a Spaced Antenna Drift Technique and Signal Processing Approaches

The middle and upper atmospheric (MU) radar at Shigaraki, Japan, is an excellent system to carry out observation using a spaced antenna (SA) technique. Over several years, numerous scientific studies were reported using SAs. In most of the studies, a SA is used to derive wind information, and the array is divided in to three segments and is grouped with three or six channels to obtain the baselines in the form of an equilateral triangle. In previous work, the wind had been estimated by the SA up to a maximum height of 10-14 km. In general, a SA-based wind estimation could not give good height coverage due to a smaller aperture being used for received signals. In this paper, the observation has been conducted for full-array transmission and reception of signal with 25 receiver channels of the profiler. The receiver channels are divided into three equal segments to form the baselines suitable for deriving horizontal wind vector components using full correlation analysis (FCA). FCA is considered as a conventional SA technique. The identification of receive channels for grouping and its phase centers was critical to obtain the good correlation value and to determine the velocity. The grouping is repeated with four different orientations of the array group. In each case, the wind velocity is estimated. The horizontal wind vector components obtained from all orientations are averaged to obtain mean horizontal wind vector components. The results are compared with the wind velocity estimated using a Doppler beam swinging (DBS) technique and that observed by the GPS sonde. It is observed that the new approach adopted using spatially distributed array grouping has yielded higher height coverage up to 20 km and in good agreement with the results obtained using DBS and GPS-sonde observations with a temporal resolution of 1.3 min in clear air condition.

Performance Analysis of Optimum Tilt Angle and Beam Configuration to Derive Horizontal Wind Velocities by Postset Beam Steering Technique

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.

Neutral thermospheric dynamics observed with two scanning Doppler imagers: 1. Monostatic and bistatic winds

Doppler‐shift measurements of the thermospheric 630.0 nm emission recorded by two spatially separated imaging Fabry‐Perot spectrometers in Alaska have been combined to infer F region horizontal wind vectors at approximately 75 locations across their overlapping fields‐of‐view. These “bistatic” horizontal wind estimates rely only on an assumption regarding the local vertical wind (and assume a common observing volume), and thus represent a more direct measurement of the wind than do the monostatic (single‐station) vector wind fields routinely inferred by these instruments. Here we present comparisons between both the independently derived monostatic wind fields from each instrument and the bistatic wind estimates inferred in their common observing volumes. Data are presented from observations on three nights during 2010. Two principal findings have emerged from this study. First, the monostatic technique was found to be capable of estimating the actual large‐scale wind field reliably under a large range of geophysical conditions, and is well suited to applications requiring only a large‐scale, ‘big picture’ approximation of the wind flow. Secondly, the bistatic (or tristatic) technique is essential for applications requiring detailed knowledge of the small‐scale behavior of the wind, as for example is required when searching for gravity waves.

Evaluation of DBS Wind Measurement Technique in Different Beam Configurations for a VHF Wind Profiler

Abstract Atmospheric winds in the troposphere have been observed routinely for many years with wind profiling (VHF and UHF) radars using the Doppler beam swinging (DBS) technique. Accuracy of wind estimates using wind profiling radars with different beam configurations has its limitations due to both the system of observation and atmospheric conditions. This paper presents a quantitative analysis and evaluation of horizontal wind estimation in different beam configurations up to an altitude of 18 km using the mesosphere–stratosphere–troposphere (MST) radar located in Gadanki, India. Horizontal wind velocities are derived in three different ways using two-, three-, and four-beam configurations. To know the performance of each configuration, radar-derived winds have been compared with the winds obtained by simultaneous GPS sonde balloon measurements, which are considered to be a standard reference by default. Results show that horizontal winds measured using three different beam configurations are comparable in general but discrepancy varies from one beam configuration to the other. It is observed that horizontal winds measured using four-beam configuration (east, west, north, and south) have better estimates than the other two-beam configurations. The standard deviation was found to be varying from 1.4 to 2.5 m s−1 and percentage error is about 9.68%–12.73% in four-beam configuration, whereas in other beam configurations the standard deviation is about 1.65–3.9 m s−1 and the percentage error is about 11.29%–15.16% with reference to GPS sonde balloon–measured winds.

A Study on Optimum Tilt Angle for Wind Estimation Using Indian MST Radar

Abstract The effect of tilt angle on horizontal wind estimation is studied using Indian mesosphere–stratosphere–troposphere (MST) radar located at Gadanki (13.45°N, 79.18°E). It operates in Doppler beam swinging (DBS) mode with a beamwidth of 3°. Horizontal winds are computed for different tilt angles from 3° to 15° with an increment of 3° from a height range of 3.6–18 km. The effective beam pointing angle (θeff) is calculated to determine the effect of aspect sensitivity on the determination of horizontal wind components. For different tilt angles radar-derived winds are compared with simultaneous GPS sonde wind measurements, which were launched from a nearby site. The first method utilizes direct comparison of radar-derived winds with those of GPS sondes using the actual beam pointing angle; the second method uses the effective beam pointing angle derived from the ratios of two oblique beams. For this study a variety of statistics were explored in terms of standard deviation, correlation coefficient, and percentage error. From the results it is observed that in agreement with previous studies, the effective beam pointing angle deviates from the actual beam pointing angle, which results in the underestimation of horizontal wind components, and also when tilt angle is close to zenith and far from zenith, the estimation of horizontal winds is found to be far from true values at different heights. Radar wind estimation has better agreement with GPS sonde measurement when the off-zenith angle is around 10°. It is also found that correction to the actual beam pointing angle provides 3%–6% improved agreement between the radar and GPS wind measurements.

Variance of wind estimates using spaced antenna techniques with the MU radar

Abstract. Variance of horizontal wind estimates in conditions of anisotropic scattering are obtained for the Spaced Antenna (SA) Full Correlation Analysis (FCA) method of Holloway et al. (1997b) and Doviak et al. (1996), but are equally applicable to the Briggs method of FCA. Variance and covariance of cross-correlation magnitudes are theoretically estimated, and the standard theory of error propagation is used to estimate the variance of the wind components for the infinite SNR case. The effect of baseline orientation is investigated, and experimental data from the MU radar in Japan is presented.

Comparison of wind estimation errors for the spaced antenna technique: A case study for the MU radar

[1] In this paper we estimate the random errors in the spaced antenna (SA) winds by two techniques and compare them with measurements made by the Doppler technique. With a one spatial dimension computer simulation, we apply typical parameters for the middle and upper atmosphere (MU) radar without noise. Briggs [1984] full correlation analysis (FCA) is commonly applied to the SA technique, while Doviak et al. [1996] and Holloway et al. [1997] used another simple analytic form based on scattering theory to derive generalized expressions. This simple analytic form should have equivalent results to the Briggs FCA for the horizontal wind estimation. With our simulation results, this form generally shows similar results to the FCA, and sometimes shows better performance than the FCA although it needs simpler calculation than the FCA. The estimation error of this simple analytic form is better than that of the Doppler for large wind, and better than that of the FCA for small antenna spacing. MU radar observations are compared with these two analyses for the SA technique, and the simple analytic form also shows similar performance to the FCA.

Investigation on horizontal wind estimation around high aspect sensitivity

In the present paper, simultaneous radar observations in the Doppler beam swinging (DBS), spatial interferometry (SI), and spaced antenna (SA) modes with the middle and upper atmosphere (MU) radar are shown. High aspect sensitivities were found after a passage of a cutoff low and an incidental trough owing to observations in the DBS mode. Because it is known that tilted aspect sensitivities introduce a bias in radial velocity measurements, we corrected the horizontal wind directly measured by oblique beams in the DBS mode by taking account of the arrival angle of the oblique beams estimated by the SI technique. On the other hand, the aspect angle is derived from the echo power ratio of the vertical to the oblique beams with the DBS mode, which allows us to estimate an effective pointing angle, and the Doppler wind is corrected by using this effective angle. In addition, the SA technique is performed simultaneously for estimating the horizontal wind. The above four estimating processes are used to determine the horizontal wind and compared for the aspect sensitivity. Finally, a simple computer simulation is performed for the SA technique for constant and variable wind conditions during incoherent integrations.

Distortion of gravity wave spectra of imaging Doppler interferometry horizontal winds

We elsewhere suggest (Rastogi et al., this issue) that an analytic model for spectral distortion in the Doppler beam steering (DBS) horizontal wind estimates should also qualitatively hold for the imaging Doppler interferometry (IDI) and spaced antenna (SA) methods. Here we give further support for this suggestion through a statistical model for spectral distortion in the IDI horizontal wind estimates. In IDI the signals observed with a single or multiple receivers at ground are used to identify the locations and radial velocities of virtual atmospheric targets; wind components are then estimated by regression. The statistical model includes the effect of isotropic target configurations as a spatial filter on an isotropic ensemble of atmospheric gravity waves. It shows that the frequency spectrum of IDI horizontal wind estimates is enhanced beyond a knee, located at a ∼0.7‐hour period in the upper mesosphere, and then drops near the buoyancy frequency. The occurrence of the knee and its location is similar to the spectral distortion in the DBS horizontal wind estimates modelled earlier.

Weighted imaging Doppler interferometry

Development of a simplified, multiple‐receiver, wind estimation scheme is presented. The new algorithm is a modification of the three‐receiver, imaging Doppler interferometry (IDI3) technique, which estimates the location of scattering centers and their corresponding radial velocities. Using the estimated location of the scattering centers, a solution for the three components of the wind vector is obtained. The modification presented is based on a weighted least squares solution of the radial velocity equation. Many IDI3‐like analyses are hampered by the use of a threshold that determines whether a scattering center is “good” or “bad.” Using the weighted least squares solution simplifies the IDI3 procedure by eliminating the need for a threshold. It should be noted that the results obtained by IDI3 are extremely sensitive to the thresholding scheme used. In addition to eliminating the need for the thresholding procedure, the new algorithm greatly reduces the measurement variance in the horizontal wind estimates. Data collected from the Middle and Upper (MU) Atmosphere radar are used to substantiate the technique.

A note on oblique spaced antenna method

Biases in oblique spaced antenna (OSA) horizontal wind estimates due to flow field inhomogeneities are shown to preclude reliable estimation of the vertical component of wind vorticity with the OSA method.

Development of Wind Profiling Sodar

Abstract The present study group has developed a new wind profiling sodar with a phased array antenna. This system is superior to usual ones with parabolic reflectors in its portability. Preliminary experiments have shown the expected acoustic performance by theoretical estimations. A new simplified homodyne complex covariance method has been introduced and tested to estimate the Doppler frequency shifts. Doppler wind measurement based on the five-beam system was used to get free from acoustic refraction effect and contamination of vertical component on the horizontal wind estimates. The test observations were successful but the data are too small in number at this stage to discuss the instrumentation error or the error due to inhomogeneity.

Effects of Precipitation on UHF Wind Profiler Measurements

Abstract Horizontal winds in the presence of precipitation were measured routinely with a UHF (405 MHz) Wind Profiler. The profiler had five beam-pointing positions so independent measurements of horizontal winds could be compared to determine relative accuracy and precision. Large precipitation fall speeds are shown to cause very large errors (on the order of tens of meters per second) in the horizontal wind estimates when those fall speeds are not properly included in the estimates. But when the precipitation fall speeds are properly included, the errors are much smaller (2–4 m s−1), approaching those of clear air (1 m s−1). The decrease in the precision in precipitation is attributed largely to horizontal nonuniformity in precipitation from one antenna beam to another. A 4- or 5-beam profiler can detect conditions of horizontal inhomogeneity by virtue of its ability to make independent measurements of the winds from horizontally separated scattering volumes.