Calibration And Characterization

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Calibration converts the raw CCD/ADC stream into a more useful spectrum. Characterization measures how well that calibrated result matches known optical inputs. The project uses CIE 233:2019 and ASTM E275 as technical references for array spectroradiometer calibration and UV-Vis spectrometer performance measurement.

Calibration Pipeline

The host app’s processing order is:

  1. Convert raw ADC counts to floating-point values.

  2. Remove stored master bias B_p when configured.

  3. Estimate a frame-wise dark reference from shielded pixels 16 through 28 when dark subtraction is enabled.

  4. Convert the inverted CCD readout into light-tracking counts.

  5. Apply stored master-dark offsets if configured.

  6. Apply flat-field or PRNU multiplicative correction when enabled.

  7. Apply wavelength-dependent QE/response correction when enabled.

  8. Build wavelengths from stored polynomial coefficients.

  9. Normalize the display by absolute saturation reference or per-frame peak.

Characterization Tests

The characterization plan should record:

  • Wavelength-map fit residuals using laser diodes or known emission lines.

  • FWHM of narrow lines at multiple wavelengths.

  • SNR versus wavelength, especially near 850-1000 nm where detector response is expected to be lower.

  • Linearity versus input level and integration time.

  • Repeatability over repeated acquisitions without realignment.

  • Stray-light and second-order diffraction behavior with and without filtering.

  • Comparison against a reference source or commercial spectrometer.

Calibration and characterization are coupled. Wavelength error depends on optical alignment, grating angle, CCD placement, and the pixel-to-wavelength curve. Intensity error depends on the CCD response, mirror and grating efficiency, filter transmission, analog acquisition chain, integration time, and the software correction factors.

Verification Methods And Evidence

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Calibration and characterization results remain planned until their method, criterion, measurement conditions, uncertainty context, evidence artifacts, and review disposition are recorded. The requirements-linked methods and evidence-package rules are defined in Test and Verification.