Facility for spectral radiance calibration at low light level.

Area of Science:

• Metrology
• Optical Engineering
• Radiometry

Background:

• Accurate spectral radiance measurements are vital for various applications.
• Nighttime spectral radiance calibration presents significant technical challenges compared to daytime levels.
• Existing calibration methods often lack the required precision for low-light conditions.

Purpose of the Study:

• To design and develop a spectral radiance calibration facility capable of high-accuracy measurements at nighttime levels.
• To enable the reproduction of spectral radiance across a wide dynamic range, specifically for low-light conditions.
• To reduce the calibration uncertainty for spectroradiometers operating in nighttime spectral radiance ranges.

Main Methods:

• Development of a spectral radiance calibration facility integrating a stable light source, precision aperture, and white diffuser.
• Characterization of the facility's spectral stability over multiple orders of magnitude.
• Utilization of the facility to calibrate a spectroradiometer at nighttime spectral radiance levels (380 nm to 780 nm).

Main Results:

• The developed facility exhibits an unchanged spectrum over 3 orders of magnitude and approximately unchanged spectrum over 6 orders of magnitude.
• The facility can reproduce spectral radiance at 380 nm from 4 × 10^-9 W/(m²·sr·nm) to 4 × 10^-3 W/(m²·sr·nm).
• Spectroradiometer calibration uncertainty was achieved at 0.87%–1.0% (k=1) for spectral radiance around 1 × 10^-7 W/(m²·sr·nm) between 380 nm and 780 nm.

Conclusions:

• The novel spectral radiance calibration facility effectively addresses the challenges of nighttime low-light measurements.
• The facility provides a reliable and accurate method for calibrating spectroradiometers, significantly improving measurement precision.
• This advancement is critical for applications requiring sensitive nighttime spectral radiance detection and analysis.