Establishing a Scale of Directional-Hemispherical Reflectance Factor I: The Van den Akker Method

Area of Science:

• Optical physics
• Metrology
• Materials science

Background:

• The Van den Akker method is crucial for establishing scales of directional-hemispherical reflectance factor.
• Accurate reflectance measurements are vital for various scientific and industrial applications.

Purpose of the Study:

• To conduct a thorough study and error analysis of the Van den Akker method.
• To develop a new, more accurate National Bureau of Standards (NBS) scale for directional-hemispherical reflectance factor.
• To incorporate the effects of non-Lambertian reflection, including retroreflection.

Main Methods:

• Detailed error analysis of the Van den Akker method.
• Measurement of three working standards to assess uncertainty.
• Development of a new NBS scale for 6°-hemispherical reflectance factor.

Main Results:

• Achieved an uncertainty in reflectance measurements of less than ±0.0015 for working standards.
• The new NBS scale demonstrates agreement with the 1965 NBS scale within ±0.005 uncertainty.
• Successfully included the effects of non-Lambertian radiation distribution in the analysis.

Conclusions:

• The refined Van den Akker method provides a basis for a more accurate scale of directional-hemispherical reflectance factor.
• The new scale offers improved precision for reflectance measurements.
• The study validates the accuracy and reliability of the new measurement scale.