Return to Answer

fix: remembered 2nd example incorrectly => corrected now

Source Link

edited Mar 21, 2015 at 15:13

Here are two examples from my experience (chemometrics, optical/vibrational/Raman spectroscopy):

I recently had optical spectroscopy data, where > 99% of the total variance of the raw data was due to changes in the background light (spotlight more or less intense on the measured point, fluorescent lamps switched on/off, more or less clouds before the sun). After background correction with the optical spectra of known influencing factors (extracted by PCA on the raw data; extra measurements taken in order to cover those variations), the effect we were interested in showed up in PCs 4 and 5.
PCs 1 and 3 where due to other effects in the measured sample, and PC 2 correlates with the instrument tip heating up during the measurements.
In another measurement, a lens without color correction for the measured spectral range was used. The chromatic aberration lead to distortions in the spectra that accounted for ca. 9590 % of total variance of the pre-processed data (captured mostly in PC 1).
For this data it took us quite a while to realize what exactly had happened, but switching to a better objective solved the problem for later experiments.

(I cannot show details as these studies are still unpublished)

Here are two examples from my experience (chemometrics, optical/vibrational/Raman spectroscopy):

I recently had optical spectroscopy data, where > 99% of the total variance of the raw data was due to changes in the background light (spotlight more or less intense on the measured point, fluorescent lamps switched on/off, more or less clouds before the sun). After background correction with the optical spectra of known influencing factors (extracted by PCA on the raw data; extra measurements taken in order to cover those variations), the effect we were interested in showed up in PCs 4 and 5.
PCs 1 and 3 where due to other effects in the measured sample, and PC 2 correlates with the instrument tip heating up during the measurements.
In another measurement, a lens without color correction for the measured spectral range was used. The chromatic aberration lead to distortions in the spectra that accounted for ca. 95 % of total variance of the pre-processed data (captured mostly in PC 1).
For this data it took us quite a while to realize what exactly had happened, but switching to a better objective solved the problem for later experiments.

(I cannot show details as these studies are still unpublished)

Here are two examples from my experience (chemometrics, optical/vibrational/Raman spectroscopy):

I recently had optical spectroscopy data, where > 99% of the total variance of the raw data was due to changes in the background light (spotlight more or less intense on the measured point, fluorescent lamps switched on/off, more or less clouds before the sun). After background correction with the optical spectra of known influencing factors (extracted by PCA on the raw data; extra measurements taken in order to cover those variations), the effect we were interested in showed up in PCs 4 and 5.
PCs 1 and 3 where due to other effects in the measured sample, and PC 2 correlates with the instrument tip heating up during the measurements.
In another measurement, a lens without color correction for the measured spectral range was used. The chromatic aberration lead to distortions in the spectra that accounted for ca. 90 % of total variance of the pre-processed data (captured mostly in PC 1).
For this data it took us quite a while to realize what exactly had happened, but switching to a better objective solved the problem for later experiments.

(I cannot show details as these studies are still unpublished)

Source Link

created Dec 22, 2014 at 12:35

Here are two examples from my experience (chemometrics, optical/vibrational/Raman spectroscopy):

I recently had optical spectroscopy data, where > 99% of the total variance of the raw data was due to changes in the background light (spotlight more or less intense on the measured point, fluorescent lamps switched on/off, more or less clouds before the sun). After background correction with the optical spectra of known influencing factors (extracted by PCA on the raw data; extra measurements taken in order to cover those variations), the effect we were interested in showed up in PCs 4 and 5.
PCs 1 and 3 where due to other effects in the measured sample, and PC 2 correlates with the instrument tip heating up during the measurements.
In another measurement, a lens without color correction for the measured spectral range was used. The chromatic aberration lead to distortions in the spectra that accounted for ca. 95 % of total variance of the pre-processed data (captured mostly in PC 1).
For this data it took us quite a while to realize what exactly had happened, but switching to a better objective solved the problem for later experiments.

(I cannot show details as these studies are still unpublished)