System and method for characterizing polarimetric response of a remote sensing instrument
View Patent ↗Measuring the polarimetric response of an optical instrument includes the steps of: emitting light along an optical axis; receiving the light through first and second polarizers; and detecting the light received through the first and second polarizers, using a filter and a detector. A first set of measurements is obtained by measuring the intensity of light received through the first and second polarizers. A second set of measurements is obtained by placing an optical instrument along the optical axis in lieu of the filter and detector; and measuring the intensity of light received through the first polarizer, after the second polarizer has been removed. A third set of measurements is obtained using the optical instrument but having the second polarizer replace the first polarizer. The optical instrument may be characterized using the first, second and third sets of measurements. The characterization is completed without having to know the extinction ratios and the transmittance parameters of the polarizers.
1. A method of calibrating a polarimeter comprising the steps of:
passing light through a first and a second polarizer disposed sequentially along an optical axis:
measuring an intensity of light output from the second polarizer by a detector coupled to a data collection system;
collecting the measured an intensity of light by a data collection system as first measured data:
placing the polarimeter along the optical axis;
removing the first polarizer from the optical axis;
measuring an intensity of light output from the second polarizer, using the polarimeter coupled to a data collection system, after removing the first polarizer;
collecting by the data collection system the intensity measured by the polarimeter as second measured data;
replacing the second polarizer with the first polarizer along the optical axis; and
measuring intensity of light output from the first polarizer after replacing the second polarizer with the first polarizer, using the polarimeter coupled to the data collection system;
collecting by the data collection system the intensities measured by the polarimeter after replacing the second polarizer with the first polarizer as third measured data;
using the first, second and third measured data to determine an extinction ratio of the polarimeter, calibrating the polarimeter;
calibrating the polarimeter based on the determined extinction ratio.
2. The method of claim 1 wherein measuring intensity of light output from the second polarizer includes:
positioning along the optical axis a spectral filter and a detector in sequence after the second polarizer;
detecting by the detector the intensity of light output from the spectral filter,
wherein the spectral filter has a spectral response similar to a spectral response of the polarimeter and the detector is coupled to the data collection system.
3. The method of claim 2 wherein measuring intensities of light output from first and second polarizers further includes:
angularly rotating the first polarizer with respect to the second polarizer,
recording an angle of a polarization axis of the first polarizer as the first polarizer is rotated, and
measuring, by the data collection system, an intensity of light output at the recorded angle of the polarization axis of the first polarizer from the first polarizer, second polarizer, and the spectral filter; and
collecting the recorded angle and measured intensity by the data collection system.
4. The method of claim 1 wherein calibrating the polarimeter includes:
determining the extinction ratio of the optical instrument independently of transmittance values and extinction ratio values of the first and second polarizers based on the first, second and third measured data.
5. The method of claim 1 , further comprising wherein the second and third measuring steps include:
obtaining from the second and third measured data measurement data having (a) peak-to-peak variations of intensities of light and (b) mean values of the intensities of light at the output of the polarimeter, and
using the obtained measurement value to calibrate the polarimeter.
6. The method of claim 1 wherein the first, second and third measuring steps include:
calculating intensity values versus phase response of the polarimeter.