No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Simulation and analysis of pulse compression for weather radars
Abstract
Wideband waveform techniques, such as pulse compression, allow for
accurate weather measurements in a short data acquisition time. However,
for extended targets such as precipitation systems, range sidelobes mask
and corrupt observations of weak phenomena occurring near areas of
strong echoes. Therefore, sidelobe suppression is extremely important in
precisely determining the echo scattering region. A simulation procedure
is developed to describe the signal returns from distributed targets
with pulse compression. The simulation procedure is capable of
generating signals from test targets with sharp gradients with different
velocities and spectral widths at each range location. The results from
the simulation are used to evaluate the performance of range sidelobe
suppression techniques for distributed targets. The evaluation shows the
effect of Doppler velocity estimates in the presence of reflectivity
gradients. Comparative analysis of the sidelobe suppression procedures
with Doppler tolerant procedures is presented in the context of
fluctuating weather targets
... We demonstrate the application of the matched and inverse filters by analyzing four profiles generated by the new simulation procedure described in Section II. A more detailed discussion on the results from the first three profiles described below can be found in Mudukutore et al. [19], [20]. ...
Wideband waveform techniques, such as pulse compression, allow for
accurate weather radar measurements in a short data acquisition time.
However, for extended targets such as precipitation systems, range
sidelobes mask and corrupt observations of weak phenomena occurring near
areas of strong echoes. Therefore, sidelobe suppression is extremely
important in precisely determining the echo scattering region. A
simulation procedure has been developed to accurately describe the
signal returns from distributed weather targets, with pulse compression;
waveform coding. This procedure is unique and improves on earlier work
by taking into account the effect of target reshuffling during the pulse
propagation time which is especially important for long duration pulses.
The simulation procedure is capable of generating time series from
various input range profiles of reflectivity, mean velocity, spectrum
width, and SNR. Results from the simulation are used to evaluate the
performance of phase coded pulse compression in conjunction with matched
and inverse compression filters. The evaluation is based on comparative
analysis of the integrated sidelobe level and Doppler sensitivity after
the compression process. Pulse compression data from the CSU-CHILL radar
is analyzed. The results from simulation and the data analysis show that
pulse-compression techniques indeed provide a viable option for faster
scanning rates while still retaining good accuracy in the estimates of
various parameters that can be measured using a pulsed-Doppler radar.
Also, it is established that with suitable sidelobe suppression filters,
the range-time sidelobes can be suppressed to levels that are acceptable
for operational and research applications
Coded orthogonal frequency division multiplexing (OFDM), like several other coded waveforms, exhibits inherent high range sidelobes after matched filtering. Consequently special processing at the receiver is required that can serve for sidelobe suppression in order to avoid target masking. However unmasking is not the only concern. It is crucial to evaluate the filtering scheme both in terms of sidelobe suppression capability and in terms of output signal-to-noise ratio (SNR). This last criterion is essential when aiming at detecting weaker reflections also. The theoretical performance of the reiterated filtering technique based on the linear minimum mean square error (LMMSE), as implemented in the adaptive pulse compression (APC) scheme, is derived and compared with the matched filter (MF). The analysis of the performance is done for a multi-target scenario where targets are close enough for the sidelobes of a target to interfere with the mainlobe of another target. Consequently the unmasking capabilities are relevant, but also output power figures. Complex-valued filter output peaks are also evaluated and compared with the MF output peaks. Moreover the performance of the method is evaluated for OFDM communication-encoded radar waveforms and compared with linear frequency modulated waveforms aiming at simultaneous use of the radar signal for both communication and radar.
This paper addresses the blind-zone problem associated with pulse compression techniques used to overcome the low peak power of solid-state transmitters, as well as interpulse coding techniques that take advantage of high duty cycles to mitigate range-velocity ambiguities. The implementation of these techniques on the CSU Wideband Experimental X-band (WiBEX) radar is presented.
Adequate sensitivity of weather radars using low-powered solid-state transmitter is achieved by using pulse compression waveforms. However, pulse compression waveforms have drawbacks of blind zone and range side lobes. In this paper, we present a methodology to address the major challenges in designing the waveforms for an X-band dual polarization Doppler radar operating with a solid-state transmitter. Here, frequency diversity wideband waveforms are proposed to mitigate low sensitivity of solid-state transmitters and the range eclipsing problem associated with pulse compression. An analysis of the performance of pulse compression using mismatched compression filters is reported. The performance of the proposed system is also quantified using signal and system simulations.
Seismic recordings made with standard filters often afford insufficient resolution for overlapping reflected events. In this treatment we apply least squares Wiener theory to the design of high-resolution digital time-domain filters. Under the assumption that estimates of the seismic pulse shape are available, we present techniques that allow one to calculate digital filters which transform this pulse into one which is sufficiently sharp so that it can be distinguished against a background of noise. The two design criteria governing filter performance are filter lag and filter memory function duration. The performance of a Wiener filter is numerically measurable by a quantity which we call the filter performance parameter P, where 0 ¿ P ¿ 1. The quality of the filter output improves as P approaches unity. We thus seek that combination of lag and memory function duration that maximizes P. This goal can be accomplished by the study of a two-dimensional display of P vs. lag and memory function duration. The proposed design techniques are illustrated by means of numerical examples.
Thesis (M.S.)--Drexel University, 1991. Includes bibliographical references (leaf 147).
The next century's advanced weather radars will be able to
accommodate pulse compression waveforms and phased array electronically
scanned antennas to meet higher time and space resolution requirements.
We have investigated several coded waveforms and compression filters for
weather radar applications. Candidate waveforms include Barker bi-phase
coded as well as linear and non-linear FM coded waveforms. Minimum
integrated sidelobe (inverse) filters are demonstrated to be superior to
matched filters for compression processing of distributed weather
echoes. We describe the Doppler sensitivity of the waveform and filters
by plotting the integrated and peak sidelobe ratios vs. Doppler shift.
We demonstrate these effects on both ground clutter and 50 dB
reflectivity transition weather data taken with the 3 cm ELDORA testbed
radar
This paper discusses the application of least-mean-squares approximate inverse filtering techniques to radar range sidelobe reduction. The method is illustrated by application to the 13-element Barker code. The performance of the least-mean-square inverse filter is compared with the matched filter and with the simplified sidelobereducing filters of Rihaczek and Golden. A filter which completely suppresses the range sidelobes of a 13-element Barker sequence is only 0.2 dB worse than a matched filter in noise.
A method of side-lobe suppression in phase-coded pulse compression systems
- E L Key
- E N Fowle
- R D Haggarty
Statistical Properties of Dual-Polarized Radar Signals
- V Chandrasekar
- V N Bringi
- P J Brockwell