scholarly journals Phase-coded pulse aperiodic transmitter coding

2009 ◽  
Vol 27 (7) ◽  
pp. 2799-2811 ◽  
Author(s):  
I. I. Virtanen ◽  
J. Vierinen ◽  
M. S. Lehtinen
Keyword(s):  
Correlation Time ◽  
Pulse Repetition Frequency ◽  
Pulse Length ◽  
Simulated Data ◽  
Qualitative Evaluation ◽  
Weather Radar ◽  
Estimation Accuracy ◽  
Time Lags ◽  
F Region ◽  
D Region

Abstract. Both ionospheric and weather radar communities have already adopted the method of transmitting radar pulses in an aperiodic manner when measuring moderately overspread targets. Among the users of the ionospheric radars, this method is called Aperiodic Transmitter Coding (ATC), whereas the weather radar users have adopted the term Simultaneous Multiple Pulse-Repetition Frequency (SMPRF). When probing the ionosphere at the carrier frequencies of the EISCAT Incoherent Scatter Radar facilities, the range extent of the detectable target is typically of the order of one thousand kilometers – about seven milliseconds – whereas the characteristic correlation time of the scattered signal varies from a few milliseconds in the D-region to only tens of microseconds in the F-region. If one is interested in estimating the scattering autocorrelation function (ACF) at time lags shorter than the F-region correlation time, the D-region must be considered as a moderately overspread target, whereas the F-region is a severely overspread one. Given the technical restrictions of the radar hardware, a combination of ATC and phase-coded long pulses is advantageous for this kind of target. We evaluate such an experiment under infinitely low signal-to-noise ratio (SNR) conditions using lag profile inversion. In addition, a qualitative evaluation under high-SNR conditions is performed by analysing simulated data. The results show that an acceptable estimation accuracy and a very good lag resolution in the D-region can be achieved with a pulse length long enough for simultaneous E- and F-region measurements with a reasonable lag extent. The new experiment design is tested with the EISCAT Tromsø VHF (224 MHz) radar. An example of a full D/E/F-region ACF from the test run is shown at the end of the paper.

scholarly journals Towards multi-purpose IS radar experiments

2008 ◽  
Vol 26 (8) ◽  
pp. 2281-2289 ◽  
Author(s):  
I. I. Virtanen ◽  
M. S. Lehtinen ◽  
J. Vierinen
Keyword(s):  
Real Time ◽  
Data Storage ◽  
Large Range ◽  
Time Lag ◽  
Estimation Accuracy ◽  
Inversion Method ◽  
Real Time Monitoring ◽  
F Region ◽  
D Region ◽  
Profile Inversion

Abstract. The EISCAT incoherent scatter radars routinely perform simultaneous measurements of E- and F-regions of the ionosphere. In addition several experiments exist for measuring pulse-to-pulse correlations from the D-region. However, the D-region experiments have quite limited range extents and the short lags suffer from F-region echoes, which are difficult to properly handle with standard decoding methods. In this paper it is demonstrated with real data how D-region experiments can be designed to produce continuous lag profiles extending above the F-region maximum. The large range coverage is attained for all lags shorter than the longest transmission pulse and it allows one to properly include the F-region echoes in the analysis. The large coverage is not needed for pulse-to-pulse lags because E- and F-regions do not have this long correlation times. The lag profiles with large range extent also provide a useful measurement of the upper parts of the ionosphere. The experiments utilise new kind of phase coding technique, which has estimation accuracy comparable to that of alternating codes though the code sequence is very short. No special decoding method is applied to the codes, because the lag profile inversion method automatically adapts to any kind of transmission codes provided transmission samples are available. The computing resources needed for real-time lag profile inversion with two different kinds of goals are also discussed here: 1) real-time monitoring of the results and 2) use of inverted lag profiles as a way to permanently store the data. While it was possible to accomplish real-time monitoring with a standard high-end desktop workstation, the higher resolution requirement for permanent data storage purposes is a much more critical task, requiring the use of larger-scale parallel processing.

scholarly journals Mosaicking Weather Radar Retrievals from an Operational Heterogeneous Network at C and X Band for Precipitation Monitoring in Italian Central Apennines

2022 ◽  
Vol 14 (2) ◽  
pp. 248
Author(s):  
Stefano Barbieri ◽  
Saverio Di Fabio ◽  
Raffaele Lidori ◽  
Francesco L. Rossi ◽  
Frank S. Marzano ◽  
...  
Keyword(s):  
Atmospheric Precipitation ◽  
Weather Radar ◽  
Geographic Area ◽  
Single Frequency ◽  
Estimation Accuracy ◽  
Central Apennines ◽  
Data Set ◽  
Area Of Interest ◽  
Spatial Coverage ◽  
Network Pattern

Meteorological radar networks are suited to remotely provide atmospheric precipitation retrieval over a wide geographic area for severe weather monitoring and near-real-time nowcasting. However, blockage due to buildings, hills, and mountains can hamper the potential of an operational weather radar system. The Abruzzo region in central Italy’s Apennines, whose hydro-geological risks are further enhanced by its complex orography, is monitored by a heterogeneous system of three microwave radars at the C and X bands with different features. This work shows a systematic intercomparison of operational radar mosaicking methods, based on bi-dimensional rainfall products and dealing with both C and X bands as well as single- and dual-polarization systems. The considered mosaicking methods can take into account spatial radar-gauge adjustment as well as different spatial combination approaches. A data set of 16 precipitation events during the years 2018–2020 in the central Apennines is collected (with a total number of 32,750 samples) to show the potentials and limitations of the considered operational mosaicking approaches, using a geospatially-interpolated dense network of regional rain gauges as a benchmark. Results show that the radar-network pattern mosaicking, based on the anisotropic radar-gauge adjustment and spatial averaging of composite data, is better than the conventional maximum-value merging approach. The overall analysis confirms that heterogeneous weather radar mosaicking can overcome the issues of single-frequency fixed radars in mountainous areas, guaranteeing a better spatial coverage and a more uniform rainfall estimation accuracy over the area of interest.

Automatic scaling of polar ionograms

2011 ◽  
Vol 24 (1) ◽  
pp. 88-94 ◽  
Author(s):  
Carlo Scotto ◽  
Michael Pezzopane
Keyword(s):  
Automatic Scaling ◽  
Terra Nova Bay ◽  
F Region ◽  
D Region ◽  
Spread F ◽  
Terra Nova

AbstractThe Istituto Nazionale di Geosifica e Vulcanologia (INGV) software for automatic scaling of ionograms (Autoscala) was improved by introducing a system to identify D region absorption events, spread-F condition (frequency spreading in the F region), and Z-ray propagation. The algorithm was applied to a series of ionograms recorded by the AIS-INGV (Advanced Ionospheric Sounder-INGV) ionosonde installed at the Mario Zucchelli Station (74.7°S, 164.1°E), Terra Nova Bay, Antarctica. Critical cases are shown to illustrate the behaviour of the software.

scholarly journals Scan-to-Scan Correlation of Weather Radar Signals to Identify Ground Clutter

2013 ◽  
Vol 10 (4) ◽  
pp. 855-859 ◽  
Author(s):  
Yinguang Li ◽  
Guifu Zhang ◽  
Richard Doviak ◽  
Darcy Saxion
Keyword(s):  
Spatial Resolution ◽  
Correlation Time ◽  
Correlation Method ◽  
Weather Radar ◽  
Detection Algorithm ◽  
Weather Radars ◽  
Ground Clutter ◽  
Radar Echoes ◽  
Radar Signals

The scan-to-scan correlation method to discriminate weather signals from ground clutter, described in this letter, takes advantage of the fact that the correlation time of radar echoes from hydrometeors is typically much shorter than that from ground objects. In this letter, the scan-to-scan correlation method is applied to data from the WSR-88D, and its results are compared with those produced by the WSR-88D's ground clutter detector. A subjective comparison with an operational clutter detection algorithm used on the network of weather radars shows that the scan-to-scan correlation method produces a similar clutter field but presents clutter locations with higher spatial resolution.

scholarly journals On the factors controlling occurrence of F-region coherent echoes

2002 ◽  
Vol 20 (9) ◽  
pp. 1385-1397 ◽  
Author(s):  
D. W. Danskin ◽  
A. V. Koustov ◽  
T. Ogawa ◽  
N. Nishitani ◽  
S. Nozawa ◽  
...  
Keyword(s):  
Density Distribution ◽  
Radio Wave ◽  
Electron Density ◽  
Electron Density Distribution ◽  
Propagation Path ◽  
Occurrence Rate ◽  
Wave Refraction ◽  
F Region ◽  
D Region ◽  
Field Lines

Abstract. Several factors are known to control the HF echo occurrence rate, including electron density distribution in the ionosphere (affecting the propagation path of the radar wave), D-region radio wave absorption, and ionospheric irregularity intensity. In this study, we consider 4 days of CUTLASS Finland radar observations over an area where the EISCAT incoherent scatter radar has continuously monitored ionospheric parameters. We illustrate that for the event under consideration, the D-region absorption was not the major factor affecting the echo appearance. We show that the electron density distribution and the radar frequency selection were much more significant factors. The electron density magnitude affects the echo occurrence in two different ways. For small F-region densities, a minimum value of 1 × 1011 m-3 is required to have sufficient radio wave refraction so that the orthogonality (with the magnetic field lines) condition is met. For too large densities, radio wave strong "over-refraction" leads to the ionospheric echo disappearance. We estimate that the over-refraction is important for densities greater than 4 × 1011 m-3. We also investigated the backscatter power and the electric field magnitude relationship and found no obvious relationship contrary to the expectation that the gradient-drift plasma instability would lead to stronger irregularity intensity/echo power for larger electric fields.Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; auroral ionosphere)

scholarly journals A Novel Method to Identify the Physical Mechanism and Source Region of ELF/VLF Waves Generated by Beat-Wave Modulation Using Preheating Technique

Universe ◽  
2021 ◽  
Vol 7 (2) ◽  
pp. 43
Author(s):  
Zhe Guo ◽  
Hanxian Fang ◽  
Farideh Honary
Keyword(s):  
Physical Mechanism ◽  
Source Region ◽  
Low Frequency ◽  
Ionospheric Heating ◽  
F Region ◽  
D Region ◽  
Novel Method ◽  
Spatio Temporal ◽  
High Frequency Waves ◽  
Vlf Waves

One of the most important effects of ionospheric heating by HF (high-frequency) waves is the generation of ELF/VLF (extremely low-frequency/very low-frequency) waves by modulated heating. An important limitation of amplitude modulation (AM) is its dependence on ionospheric electrojet, which means to achieve better modulation effect, some strict spatio-temporal conditions must be met. To solve this problem, some possible methods have been proposed including beat-wave (BW) modulation. However, due to the controversy of its mechanism and the source region of the stimulated ELF/VLF waves, it is not clear whether it is an electrojet-independent method or not, which has become one of the hot topics in recent years. In this paper, we found that the effect of preheating on modulation efficiency of BW based on different theories is the opposite. We suppose the opposite character of the influence and effect on the efficiency of BW in D region and F region as a base for a novel method to identify the physical mechanism and source region of BW. This method can be feasible to solve the controversy of BW. The feasibility of this method is verified by simulation results in the paper.

Separating recruitment and mortality time lags for a delay-difference production model

2015 ◽  
Vol 72 (2) ◽  
pp. 161-165 ◽  
Author(s):  
Emilius A. Aalto ◽  
E.J. Dick ◽  
Alec D. MacCall
Keyword(s):  
Stock Assessment ◽  
Recovery Period ◽  
Time Lag ◽  
Simulated Data ◽  
Assessment Method ◽  
Production Model ◽  
Time Lags ◽  
Age At Maturity ◽  
Production Models ◽  
Pacific Rockfish

Many fishery production models implicitly incorporate a single time lag for both recruitment and mortality despite the fact that in populations of breeding adults, deaths occur yearly while the entry of new adults comes from juveniles born potentially many years prior to adulthood. Models that do not account for this difference in timing will overestimate abundance for a decreasing stock and underestimate increases during a recovery period. We investigated the effect of incorporating unequal recruitment and mortality time lags into depletion-based stock reduction analysis (DB-SRA), a stock assessment method for data-poor species. Using both simulated data and catch series of Pacific rockfish (Sebastes spp.), we found that for declining stocks with no mortality delay and a recruitment time lag equal to age-at-maturity, estimated overfishing limits were up to 40% lower than those from the model with both time lags equal to age-at-maturity. Deviation between the two models’ predictions increases with age-at-maturity and natural mortality rate, suggesting that time lag separation is most important for long-lived species. We propose a correction factor for net production models that eliminates stock overestimation due to implicitly equal time lags.

Evaluation of the Simultaneous Multiple Pulse Repetition Frequency Algorithm for Weather Radar

2008 ◽  
Vol 25 (7) ◽  
pp. 1166-1181 ◽  
Author(s):  
Evan Ruzanski ◽  
John C. Hubbert ◽  
V. Chandrasekar
Keyword(s):  
Pulse Repetition Frequency ◽  
Weather Radar ◽  
Interval Data ◽  
Radar Data ◽  
Repetition Frequency ◽  
Pulse Repetition ◽  
Doppler Velocity ◽  
Mean Power ◽  
Mean Velocity ◽  
Multiple Pulse

Abstract Performance of the simultaneous multiple pulse repetition frequency algorithm (SMPRF) for recovery of mean power and mean Doppler velocity is investigated using simulated weather radar data. Operation and functionality of the algorithm is described; methods to estimate mean power values using statistical inversion and to estimate mean velocity from unevenly spaced autocorrelation function samples are presented and analyzed. A simulation technique for constructing multiple pulse repetition interval data is described and the algorithm performance results are presented for an example SMPRF code using three weather profiles. This leads to the development of an error structure related to factors influencing moment recovery, including finite-length time series effects, the effects of overlaid echoes that create an effective signal-to-noise ratio that limits moment recovery performance, and the effects of spectrum width and radar frequency related to coherence time.

scholarly journals A Proposed Solution to the Range–Doppler Dilemma of Weather Radar Measurements by Using the SMPRF Codes, Practical Results, and a Comparison with Operational Measurements

2005 ◽  
Vol 44 (9) ◽  
pp. 1375-1390 ◽  
Author(s):  
Juha Pirttilä ◽  
Markku S. Lehtinen ◽  
Asko Huuskonen ◽  
Markku Markkanen
Keyword(s):  
High Resolution ◽  
Pulse Repetition Frequency ◽  
Weather Radar ◽  
Simplified Model ◽  
Measured Spectrum ◽  
Model Calculations ◽  
Incoherent Scatter ◽  
Incoherent Scatter Radars ◽  
Working Principle ◽  
Radar Measurements

Abstract Based on the measurement principles used on incoherent scatter radars, the authors have developed the Simultaneous Multiple Pulse Repetition Frequency (SMPRF) code that is intended to solve the range–Doppler dilemma and that can be used with modern magnetron radars. The working principle of the code is explained in mathematical terms and with the help of a simplified model. Results from the SMPRF and traditional fixed PRF weather radar measurements are compared, and the reasons for the differences are explained. The practical results show that the SMPRF code seems to work in the manner that is predicted by the theoretical and model calculations. The SMPRF code provides enough information to produce a high-resolution measured spectrum for each range gate. The shape of these measured spectra are seldom purely Gaussian. It is possible that more advanced raw products, other than just reflectivity, velocity, and width, can be produced with the help of these high-resolution spectra.

scholarly journals Sensitivity Enhancement System for Pulse Compression Weather Radar

2014 ◽  
Vol 31 (12) ◽  
pp. 2732-2748 ◽  
Author(s):  
Cuong M. Nguyen ◽  
V. Chandrasekar
Keyword(s):  
Pulse Compression ◽  
Doppler Radar ◽  
Matched Filter ◽  
Simulated Data ◽  
Weather Radar ◽  
Sensitivity Enhancement ◽  
Dual Frequency ◽  
Transmission Scheme ◽  
Compression Technique ◽  
System Sensitivity

Abstract The use of low-power solid-state transmitters in weather radar to keep costs down requires a pulse compression technique that maintains an adequate minimum detectable signal. However, wideband pulse compression filters will partly reduce the system’s sensitivity performance. In this paper, a sensitivity enhancement system (SES) for pulse compression weather radar is developed to mitigate this issue. SES uses a dual-waveform transmission scheme and an adaptive pulse compression filter. The waveforms’ diversity can be done in the frequency domain or the time domain. The adaptive filter is designed based on the self-consistency between signal returns from the two waveforms. Analysis based on radar-simulated data and observations from NASA’s dual-frequency dual-polarized Doppler radar (D3R) shows that by using SES, the system sensitivity can be improved by 7–10 dB when compared to that of the conventional matched filter.

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