# 1D FDEM and TDEM inversionsΒΆ

This example is used in the paper Heagy et al 2016 (in prep)

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 from SimPEG import (Mesh, Maps, Utils, DataMisfit, Regularization, Optimization, Inversion, InvProblem, Directives) import numpy as np from SimPEG.EM import FDEM, TDEM, mu_0 import matplotlib.pyplot as plt import matplotlib try: from pymatsolver import Pardiso as Solver except ImportError: from SimPEG import SolverLU as Solver def run(plotIt=True): """ 1D FDEM and TDEM inversions =========================== This example is used in the paper Heagy et al 2016 (in prep) """ # Set up cylindrically symmeric mesh cs, ncx, ncz, npad = 10., 15, 25, 13 # padded cyl mesh hx = [(cs, ncx), (cs, npad, 1.3)] hz = [(cs, npad, -1.3), (cs, ncz), (cs, npad, 1.3)] mesh = Mesh.CylMesh([hx, 1, hz], '00C') # Conductivity model layerz = np.r_[-200., -100.] layer = (mesh.vectorCCz >= layerz[0]) & (mesh.vectorCCz <= layerz[1]) active = mesh.vectorCCz < 0. sig_half = 1e-2 # Half-space conductivity sig_air = 1e-8 # Air conductivity sig_layer = 5e-2 # Layer conductivity sigma = np.ones(mesh.nCz)*sig_air sigma[active] = sig_half sigma[layer] = sig_layer # Mapping actMap = Maps.InjectActiveCells(mesh, active, np.log(1e-8), nC=mesh.nCz) mapping = Maps.ExpMap(mesh) * Maps.SurjectVertical1D(mesh) * actMap mtrue = np.log(sigma[active]) # ----- FDEM problem & survey ----- rxlocs = Utils.ndgrid([np.r_[50.], np.r_[0], np.r_[0.]]) bzi = FDEM.Rx.Point_bSecondary(rxlocs, 'z', 'real') bzr = FDEM.Rx.Point_bSecondary(rxlocs, 'z', 'imag') freqs = np.logspace(2, 3, 5) srcLoc = np.array([0., 0., 0.]) print('min skin depth = ', 500./np.sqrt(freqs.max() * sig_half), 'max skin depth = ', 500./np.sqrt(freqs.min() * sig_half)) print('max x ', mesh.vectorCCx.max(), 'min z ', mesh.vectorCCz.min(), 'max z ', mesh.vectorCCz.max()) srcList = [ FDEM.Src.MagDipole([bzr, bzi], freq, srcLoc, orientation='Z') for freq in freqs ] surveyFD = FDEM.Survey(srcList) prbFD = FDEM.Problem3D_b(mesh, sigmaMap=mapping, Solver=Solver) prbFD.pair(surveyFD) std = 0.03 surveyFD.makeSyntheticData(mtrue, std) surveyFD.eps = np.linalg.norm(surveyFD.dtrue)*1e-5 # FDEM inversion np.random.seed(1) dmisfit = DataMisfit.l2_DataMisfit(surveyFD) regMesh = Mesh.TensorMesh([mesh.hz[mapping.maps[-1].indActive]]) reg = Regularization.Simple(regMesh) opt = Optimization.InexactGaussNewton(maxIterCG=10) invProb = InvProblem.BaseInvProblem(dmisfit, reg, opt) # Inversion Directives beta = Directives.BetaSchedule(coolingFactor=4, coolingRate=3) betaest = Directives.BetaEstimate_ByEig(beta0_ratio=2.) target = Directives.TargetMisfit() directiveList = [beta, betaest, target] inv = Inversion.BaseInversion(invProb, directiveList=directiveList) m0 = np.log(np.ones(mtrue.size)*sig_half) reg.alpha_s = 5e-1 reg.alpha_x = 1. prbFD.counter = opt.counter = Utils.Counter() opt.remember('xc') moptFD = inv.run(m0) # TDEM problem times = np.logspace(-4, np.log10(2e-3), 10) print('min diffusion distance ', 1.28*np.sqrt(times.min()/(sig_half*mu_0)), 'max diffusion distance ', 1.28*np.sqrt(times.max()/(sig_half*mu_0))) rx = TDEM.Rx.Point_b(rxlocs, times, 'z') src = TDEM.Src.MagDipole( [rx], waveform=TDEM.Src.StepOffWaveform(), loc=srcLoc # same src location as FDEM problem ) surveyTD = TDEM.Survey([src]) prbTD = TDEM.Problem3D_b(mesh, sigmaMap=mapping, Solver=Solver) prbTD.timeSteps = [(5e-5, 10), (1e-4, 10), (5e-4, 10)] prbTD.pair(surveyTD) std = 0.03 surveyTD.makeSyntheticData(mtrue, std) surveyTD.std = std surveyTD.eps = np.linalg.norm(surveyTD.dtrue)*1e-5 # TDEM inversion dmisfit = DataMisfit.l2_DataMisfit(surveyTD) regMesh = Mesh.TensorMesh([mesh.hz[mapping.maps[-1].indActive]]) reg = Regularization.Simple(regMesh) opt = Optimization.InexactGaussNewton(maxIterCG=10) invProb = InvProblem.BaseInvProblem(dmisfit, reg, opt) inv = Inversion.BaseInversion(invProb, directiveList=directiveList) m0 = np.log(np.ones(mtrue.size)*sig_half) reg.alpha_s = 5e-1 reg.alpha_x = 1. prbTD.counter = opt.counter = Utils.Counter() opt.remember('xc') moptTD = inv.run(m0) if plotIt: plt.figure(figsize=(10, 8)) ax0 = plt.subplot2grid((2, 2), (0, 0), rowspan=2) ax1 = plt.subplot2grid((2, 2), (0, 1)) ax2 = plt.subplot2grid((2, 2), (1, 1)) fs = 13 # fontsize matplotlib.rcParams['font.size'] = fs # Plot the model ax0.semilogx(sigma[active], mesh.vectorCCz[active], 'k-', lw=2) ax0.semilogx(np.exp(moptFD), mesh.vectorCCz[active], 'bo', ms=6) ax0.semilogx(np.exp(moptTD), mesh.vectorCCz[active], 'r*', ms=10) ax0.set_ylim(-700, 0) ax0.set_xlim(5e-3, 1e-1) ax0.set_xlabel('Conductivity (S/m)', fontsize=fs) ax0.set_ylabel('Depth (m)', fontsize=fs) ax0.grid(which='both', color='k', alpha=0.5, linestyle='-', linewidth=0.2) ax0.legend(['True', 'FDEM', 'TDEM'], fontsize=fs, loc=4) # plot the data misfits - negative b/c we choose positive to be in the # direction of primary ax1.plot(freqs, -surveyFD.dobs[::2], 'k-', lw=2) ax1.plot(freqs, -surveyFD.dobs[1::2], 'k--', lw=2) dpredFD = surveyFD.dpred(moptTD) ax1.loglog(freqs, -dpredFD[::2], 'bo', ms=6) ax1.loglog(freqs, -dpredFD[1::2], 'b+', markeredgewidth=2., ms=10) ax2.loglog(times, surveyTD.dobs, 'k-', lw=2) ax2.loglog(times, surveyTD.dpred(moptTD), 'r*', ms=10) ax2.set_xlim(times.min(), times.max()) # Labels, gridlines, etc ax2.grid(which='both', alpha=0.5, linestyle='-', linewidth=0.2) ax1.grid(which='both', alpha=0.5, linestyle='-', linewidth=0.2) ax1.set_xlabel('Frequency (Hz)', fontsize=fs) ax1.set_ylabel('Vertical magnetic field (-T)', fontsize=fs) ax2.set_xlabel('Time (s)', fontsize=fs) ax2.set_ylabel('Vertical magnetic field (-T)', fontsize=fs) ax2.legend(("Obs", "Pred"), fontsize=fs) ax1.legend(("Obs (real)", "Obs (imag)", "Pred (real)", "Pred (imag)"), fontsize=fs) ax1.set_xlim(freqs.max(), freqs.min()) ax0.set_title("(a) Recovered Models", fontsize=fs) ax1.set_title("(b) FDEM observed vs. predicted", fontsize=fs) ax2.set_title("(c) TDEM observed vs. predicted", fontsize=fs) plt.tight_layout(pad=1.5) if __name__ == '__main__': run(plotIt=True) plt.show()