The code is also applicable to more than two overlaid echoes. The extension to echoes from the nth trip is straightforward. ![]() The same principles apply to cases in which the second-trip echo is stronger it suffices to interchange the indices to obtain the results. Therefore, the merit of the phase coding scheme is evaluated from its performance with respect to the recovery of υ 2. Of the six spectral moments, the recovery of the velocity of the weaker signal υ 2 is the most crucial and difficult all other moments can be recovered over a much larger dynamic range of the overlaid power ratios. Here, M is the number of samples in the time series available for estimating the spectral moments. In all the results presented, only the first- and second-trip signals are assumed to be overlaid, and the first-trip echo is assumed to be stronger. In this paper, we use the notations, p, υ, and w to represent the mean power, the mean velocity, and the spectrum width, respectively, with subscripts 1 and 2 signifying the first and the second trips. This basic concept is the same for all the phase coding schemes however, the relative merits of the phase codes differ and can be gauged by the accuracy of estimating the spectral moments over the widest dynamic range of the overlaid signal power ratios and spectrum widths. The phase coding scheme alters the spectra of the overlaid signals, enabling one to estimate the spectral moments of each with appropriate processing techniques. The phase coding scheme is similar to the random phase technique but uses a systematic code and a modified decoding procedure. In this paper, a new systematic phase code (SZ code) is proposed ( Sachidananda and Zrnic 1997 Zrnic and Sachidananda 1998), which, in the simulation studies, has performed better than the previously reported methods. The random phase coding ( Zrnic 1979 Laird 1981 Siggia 1983 Zrnic and Mahapatra 1985) and the systematic π/4 and π/2 phase coding ( Sachidananda and Zrnic 1986) techniques have been suggested for the recovery of spectral parameters of the first- and second-trip echoes if these echoes are overlaid. ![]() The other approach relies on variable PRTs that spread echoes in the time domain ( Zrnic and Mahapatra 1985). One uses the frequency domain to separate overlaid echoes and assign each to the correct range ( Zrnic 1979 Laird 1981 Siggia 1983). There are no solutions that can completely eradicate the range and velocity ambiguities of weather echoes the best that can be achieved is to reduce the effects. At pulse repetition times that allow reasonably large r a and υ a, echoes are not only ambiguous but are often overlaid that is, echoes from storms that are separated by r a arrive at the radar simultaneously. Meteorological scatterers are distributed continuously and produce semicoherent signals with a very large dynamic range (100 dB). Resolving range and velocity ambiguities of point scatterers (e.g., aircraft) is relatively easy because these objects are localized in space and produce coherent signals with a relatively modest dynamic range. Mean winds in storms can be greater than 50 m s −1, but meteorologists consider that a υ a = 50 m s −1 is sufficient for most applications. The earth’s curvature and maximum storm height (about 16 km) require that the unambiguous range be about 460 km, in which case all storms in the line of sight are within r a. Thus, even at the longest practical wavelength, a simultaneous large unambiguous range (>400 km) and velocity (>50 m s −1) cannot be achieved. Practical considerations such as the cost and the frequency allocation constrain the wavelength of weather surveillance radars to 10 cm or less. In terms of the pulse repetition time (PRT), T, r a = cT/2, and υ a = λ/(4 T). If you have outdoor plans, you may want to try to take advantage of the quiet weather at the beginning of the week before the clouds and rain roll in! Some spots in and around Houston could pick up anywhere from 1-3" of rain Friday through Monday.R a υ a cλ (1)where λ is the radar wavelength and c is the speed of light. Scattered showers and a few rumbles of thunder will come in waves Saturday and Sunday with slightly lower rain chances for Christmas on Monday. Isolated showers return Thursday with widespread rain expected Friday. Big pattern change builds in later in the week that will mean multiple rounds of rain and possibly soggy weather for Santa. We are officially just a week away from Christmas which is next Monday! Get ready for a few more super nice and quiet days of weather with cool temperatures in the morning and pleasant afternoons.
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