Recommended background reading

Chave, A.D. and Thomson, D.J. (1989) Some comments on magnetotelluric response function estimation. Journal of Geophysical Research 94: 14,215-14,255.

Holcomb, L.G. (1989) A direct method for calculating instrument noise levels in side-by-side seismometer evaluations. USGS Open-File Report 89-214.

Pavlis, G.L. and Vernon, F.L. (1994) Calibration of seismometers using ground noise. Bulletin of the Seismological Society of America 84: 1243-1255.

Ringler, A.T., Hutt, C.R., Aster, R., Bolton, H., Gee, L.S., Storm, T. (2012) Estimating pole-zero errors in GSN-IRIS/USGS network calibration metadata. Bulletin of the Seismological Society of America 102: 836-841.

Sleeman, R., van Wettum, A., Trampert, J. (2006) Three-channel correlation analysis: A new technique to measure instrumental noise of digitizers and seismic sensors. Bulletin of the Seismological Society of America 96: 258-271.

http://en.wikipedia.org/wiki/Polynomial_and_rational_function_modeling#Rational_function_models

http://en.wikipedia.org/wiki/Levenberg%E2%80%93Marquardt_algorithm

“Understanding Poles and Zeros”, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2.14 Analysis and Design of Feedback Control Systems