I used an fminsearch function to fit the SRM and ITMY actuator response magnitudes. The testfunction was just that for a single second order pole, but it gave what I consider to be good fits for the following reasons:

*for 3 of the 4 fits the residuals were less than 0.5% of the summed input data points. The worst one (ITMY pitch) was about 2.7%, which I think is due to the resonance happening to be right in the middle of two data points.

*the tolerance of 1 part in 10^9 was reached quickly from not very finely tuned starting points.

The test function was: G=abs(Gp./(1+1i.*f./fp./Qp-(f./fp).^2)), where G(f) is the actuator response magnitude, Gp is the pole gain, fp is the pole frequency, and Qp is the pole Q factor.

In the end I just fitted the response magnitude. I was initially fitting the complex response function, but ran into problems which I think were cased by overall phase offsets between the data and test function. Can I canvass for opinion if fitting the magnitude is OK, or should I try again fitting the phase too?

Anyway, here are the results of the fits, and I've attached plots of each too (each one in linear and log y axis because each on its own might be misleading for fits):

EDIT - I added more points to the otherwise sparse looking fitted curves

ITMY PITCH actuator response fit

-- Fit completed after 190 iterations--

 Started with: Gain = 3e-06,

 Q factor = 5,

 Pole frequency = 1,

 Fit results:  Gain = 1.32047e-06,

 Q factor = 4.34542,

 Pole frequency = 0.676676

 Residual (normalised against the sum of input datapoints) = 0.0268321

ITMY YAW actuator response fit

-- Fit completed after 156 iterations--

 Started with: Gain = 3e-06,

 Q factor = 5,

 Pole frequency = 1,

 Fit results:  Gain = 1.14456e-06,

 Q factor = 8.49875,

 Pole frequency = 0.730028

 Residual (normalised against the sum of input datapoints) = 0.00468077

SRM PITCH actuator response fit

 -- Fit completed after 192 iterations--

 Started with: Gain = 3e-06,

 Q factor = 5,

 Pole frequency = 1,

 Fit results:  Gain = 7.94675e-06,

 Q factor = 7.16458,

 Pole frequency = 0.57313

 Residual (normalised against the sum of input datapoints) = 0.00301265

SRM YAW actuator response fit

 -- Fit completed after 156 iterations--

 Started with: Gain = 3e-06,

 Q factor = 5,

 Pole frequency = 1,

 Fit results:  Gain = 3.34179e-06,

 Q factor = 9.57601,

 Pole frequency = 0.855322

 Residual (normalised against the sum of input datapoints) = 0.000840468