24,473 research outputs found
Robust seismic velocity change estimation using ambient noise recordings
We consider the problem of seismic velocity change estimation using ambient
noise recordings. Motivated by [23] we study how the velocity change estimation
is affected by seasonal fluctuations in the noise sources. More precisely, we
consider a numerical model and introduce spatio-temporal seasonal fluctuations
in the noise sources. We show that indeed, as pointed out in [23], the
stretching method is affected by these fluctuations and produces misleading
apparent velocity variations which reduce dramatically the signal to noise
ratio of the method. We also show that these apparent velocity variations can
be eliminated by an adequate normalization of the cross-correlation functions.
Theoretically we expect our approach to work as long as the seasonal
fluctuations in the noise sources are uniform, an assumption which holds for
closely located seismic stations. We illustrate with numerical simulations and
real measurements that the proposed normalization significantly improves the
accuracy of the velocity change estimation
Ego-motion estimation using rectified stereo and bilateral transfer function
We describe an ego-motion algorithm based on dense spatio-temporal correspondences, using
semi-global stereo matching (SGM) and bilateral image warping in time.
The main contribution is an improvement in accuracy and robustness of such techniques, by taking care of
speed and numerical stability, while employing twice the structure and data for the motion estimation task,
in a symmetric way.
In our approach we keep the tasks of structure and motion estimation separated, respectively solved by the SGM
and by our pose estimation algorithm. Concerning the latter, we show the benefits introduced by our rectified, bilateral formulation, that provides at the same time more robustness to noise and disparity errors, at the price of a moderate increase in computational complexity, further reduced by an improved Gauss-Newton descent
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