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import numpy
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def hildebrand_sekhon(data, navg):
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"""
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This method is for the objective determination of de noise level in Doppler spectra. This
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implementation technique is based on the fact that the standard deviation of the spectral
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densities is equal to the mean spectral density for white Gaussian noise
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Inputs:
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Data : heights
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navg : numbers of averages
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Return:
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-1 : any error
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anoise : noise's level
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"""
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dataflat = data.reshape(-1)
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dataflat.sort()
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npts = dataflat.size #numbers of points of the data
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if npts < 32:
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print "error in noise - requires at least 32 points"
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return -1.0
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dataflat2 = numpy.power(dataflat,2)
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cs = numpy.cumsum(dataflat)
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cs2 = numpy.cumsum(dataflat2)
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# data sorted in ascending order
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nmin = int((npts + 7.)/8)
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for i in range(nmin, npts):
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s = cs[i]
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s2 = cs2[i]
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p = s / float(i);
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p2 = p**2;
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q = s2 / float(i) - p2;
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leftc = p2;
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rightc = q * float(navg);
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R2 = leftc/rightc
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# Signal detect: R2 < 1 (R2 = leftc/rightc)
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if R2 < 1:
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npts_noise = i
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break
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anoise = numpy.average(dataflat[0:npts_noise])
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return anoise;
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def sorting_bruce(Data, navg):
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sortdata = numpy.sort(Data)
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lenOfData = len(Data)
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nums_min = lenOfData/10
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if (lenOfData/10) > 0:
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nums_min = lenOfData/10
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else:
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nums_min = 0
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rtest = 1.0 + 1.0/navg
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sum = 0.
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sumq = 0.
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j = 0
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cont = 1
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while((cont==1)and(j<lenOfData)):
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sum += sortdata[j]
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sumq += sortdata[j]**2
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j += 1
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if j > nums_min:
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if ((sumq*j) <= (rtest*sum**2)):
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lnoise = sum / j
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else:
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j = j - 1
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sum = sum - sordata[j]
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sumq = sumq - sordata[j]**2
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cont = 0
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if j == nums_min:
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lnoise = sum /j
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return lnoise
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class Noise:
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"""
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Clase que implementa los metodos necesarios para deternimar el nivel de ruido en un Spectro Doppler
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"""
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data = None
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noise = None
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dim = None
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def __init__(self, data=None):
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"""
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Inicializador de la clase Noise para la la determinacion del nivel de ruido en un Spectro Doppler.
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Inputs:
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data: Numpy array de la forma nChan x nHeis x nProfiles
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Affected:
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self.noise
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Return:
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None
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"""
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self.data = data
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self.dim = None
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self.nChannels = None
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self.noise = None
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def setNoise(self, data):
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"""
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Inicializador de la clase Noise para la la determinacion del nivel de ruido en un Spectro Doppler.
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Inputs:
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data: Numpy array de la forma nChan x nHeis x nProfiles
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Affected:
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self.noise
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Return:
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None
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"""
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if data == None:
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raise ValueError, "The data value is not defined"
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shape = data.shape
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self.dim = len(shape)
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if self.dim == 3:
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nChan, nProfiles, nHeis = shape
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elif self.dim == 2:
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nChan, nHeis = shape
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else:
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raise ValueError, ""
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self.nChannels = nChan
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self.data = data.copy()
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self.noise = numpy.zeros(nChan)
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return 1
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def byHildebrand(self, navg=1):
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"""
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Determino el nivel de ruido usando el metodo Hildebrand-Sekhon
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Return:
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noiselevel
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"""
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daux = None
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for channel in range(self.nChannels):
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daux = self.data[channel,:,:]
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self.noise[channel] = hildebrand_sekhon(daux, navg)
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return self.noise
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def byWindow(self, heiIndexMin, heiIndexMax, freqIndexMin, freqIndexMax):
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"""
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Determina el ruido del canal utilizando la ventana indicada con las coordenadas:
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(heiIndexMIn, freqIndexMin) hasta (heiIndexMax, freqIndexMAx)
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Inputs:
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heiIndexMin: Limite inferior del eje de alturas
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heiIndexMax: Limite superior del eje de alturas
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freqIndexMin: Limite inferior del eje de frecuencia
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freqIndexMax: Limite supoerior del eje de frecuencia
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"""
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data = self.data[:, heiIndexMin:heiIndexMax, freqIndexMin:freqIndexMax]
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for channel in range(self.nChannels):
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daux = data[channel,:,:]
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self.noise[channel] = numpy.average(daux)
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return self.noise
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def bySort(self,navg = 1):
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daux = None
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for channel in range(self.nChannels):
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daux = self.data[channel,:,:]
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self.noise[channel] = sorting_bruce(daux, navg)
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return self.noise
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