Suomi NPP VIIRS solar diffuser screen transmittance model and its applications.
Applied Optics
|November 2, 2017
Summary
Accurate calibration of the Suomi National Polar-orbiting Partnership satellite relies on precise solar diffuser (SD) screen transmittance measurements. This study develops a model to correct prelaunch transmittance errors caused by alignment issues, ensuring better on-orbit calibration quality.
Area of Science:
- Earth Observation
- Satellite Calibration
- Radiometry
Background:
- The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership satellite uses a solar diffuser (SD) panel for calibrating reflective solar bands.
- Sunlight passes through an SD screen before reaching the SD panel, making accurate transmittance measurements crucial for on-orbit calibration.
Purpose of the Study:
- To develop a mathematical model to assess the accuracy of prelaunch SD screen transmittance measurements.
- To identify and model the impact of alignment errors on transmittance measurements.
- To retrieve the true transmittance and evaluate the accuracy of prelaunch SD bidirectional reflectance distribution function (BRDF) values.
Main Methods:
- Developed a mathematical model for transmittance as a function of incident light angles.
- Applied the model to fit prelaunch measured transmittance data.
- Modeled orientation alignment errors for the SD panel and measurement apparatus.
- Examined the finite source size effect on transmittance.
- Compared retrieved "true" transmittance multiplied by prelaunch SD BRDF with on-orbit data.
Main Results:
- The initial model did not reproduce measured transmittance without assuming significantly different aperture sizes.
- Alignment errors in the SD panel and measurement apparatus were identified as the cause of discrepancies.
- The developed model successfully retrieved the "true" transmittance by accounting for alignment errors.
- Comparison of retrieved "true" transmittance and prelaunch SD BRDF with on-orbit data indicated relative accuracy.
Conclusions:
- Prelaunch SD screen transmittance measurements can be inaccurate due to alignment errors.
- The developed model provides a method to evaluate transmittance accuracy and retrieve true transmittance.
- Accurate transmittance and BRDF values lead to improved on-orbit calibration and more reliable sensor data products.
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