Characterization and absolute calibration of an AERONET-OC radiometer

Area of Science:

• Earth and Space Sciences
• Oceanography
• Atmospheric Science

Background:

• The Aerosol Robotic Network (AERONET-OC) provides crucial above-water radiometry for validating ocean color satellite data.
• CE-318 sun photometers are adapted for AERONET-OC measurements from fixed offshore platforms.
• Accurate calibration of these instruments is essential for reliable water-leaving radiance data.

Purpose of the Study:

• To assess the calibration of an AERONET-OC instrument (AERONET #080) using a novel laser-illuminated integrating sphere.
• To determine the linearity with flux and absolute radiance responsivity across multiple filter bands.
• To compare these results with existing AERONET calibration facilities.

Main Methods:

• A laser-illuminated integrating sphere with known radiance was used to calibrate AERONET #080.
• Measurements were conducted at multiple wavelengths within seven filter bands of the instrument.
• Results were compared against calibrations performed at NASA Goddard Space Flight Center and the European Commission's Joint Research Centre.

Main Results:

• The laser-sphere calibration results for AERONET #080 agreed with NASA and European Commission calibrations within an uncertainty of 1.88% (k=2).
• An assessment using lamp-illuminated spheres revealed an unexplained spectral dependence in the comparison results.
• The study confirmed the instrument's performance within expected parameters for key calibration metrics.

Conclusions:

• The laser-illuminated integrating sphere provides a reliable method for calibrating AERONET-OC instruments.
• The agreement between different calibration methods validates the accuracy of AERONET-OC data for satellite product validation.
• Further investigation is needed to understand the observed spectral dependence in comparison results.