Stray light correction

Spectral stray-light correction

Spectral stray light in a spectroradiometer can be described by the instrument's spectral line spread function (SLSF). An example of a SLSF of a CCD array spectroradiometer is shown in the figure at the top right.

We have developed a correction method to obtain spectral stray-light corrected signal, Y_IB, by using a simple matrix multiplication of the raw measured signals, Y_meas, by a spectral stray-light correction matrix, C_spec, (Equation 1)

Only a one-time characterization of the instrument for a set of SLSFs is required to derive the correction matrix, C_spec. A correction, which can be done in real time, can reduce errors due to stray light by more than one order of magnitude. Thus, the application of this method could lead to significant reductions in the overall measurement uncertainties in applications where spectral components of the source have a large dynamic range. An example of stray-light correction results for a CCD-array spectroradiometer is shown in Figure 1, where the light source is an incandescent lamp with a green bandpass filter. The residues of the stray light signals are at least one order smaller than the original stray-light signals.

For more technical information, see Simple spectral stray light correction method for array spectroradiometers and New NIST method improves accuracy of spectrometers.

Spatial stray-light correction

Spatial stray light in an imaging instrument can be described by the instrument's point spread function (PSF). An example of a PSF of a CCD imaging radiometer is shown in the figure at the bottom right.

We have also developed a correction method to acquire spatial stray-light corrected signals (transposed to a column vector (CV)), Y_IR,cv, involving simple matrix multiplication of the raw measured signals (transposed to a CV), Y_meas,cv, by a spatial stray-light correction matrix, C_spat, (Equation 2).

Only a one-time characterization of the instrument for a set of PSFs is required to derive the correction matrix, C_spat. A correction, which minimally impacts data acquisition time, can reduce errors due to stray light by more than one order of magnitude. Thus, application of this method could lead to significant reductions in the overall measurement uncertainties in applications where images have high contrast ratios. An example of stray-light correction results for a CCD imaging radiometer is shown in Figure 2, where the light source is an integrating sphere with the center of exit port covered by an opaque black sheet, The plot is a 1 dimensional image signals along the center line across the sphere port. The residues of the stray-light signals are at least one order of magnitude smaller than the original stray light signals.

For more technical information, see Characterization and correction of stray light in optical instruments.