Intercomparison of airborne multi-angle polarimeter observations from the Polarimeter Definition Experiment

Area of Science:

• Atmospheric Science
• Remote Sensing
• Instrument Calibration

Background:

• The Polarimeter Definition Experiment (PODEX) supported the NASA Aerosol-Cloud-Ecosystem (ACE) mission, aiming for advanced remote sensing of aerosols, oceans, and clouds.
• Airborne polarimeters, including the Airborne Multiangle Spectropolarimetric Imager (AirMSPI) and Research Scanning Polarimeter (RSP), were tested during PODEX.
• Level 1 data products from these instruments are crucial for validating subsequent geophysical product (Level 2) generation.

Purpose of the Study:

• To compare Level 1 data from AirMSPI and RSP to assess agreement within stated uncertainties.
• To identify and address discrepancies in radiometric and polarimetric measurements.
• To establish confidence in the data for future remote sensing applications and intercomparisons.

Main Methods:

• Georegistered observations from AirMSPI and RSP were compared for various scene types.
• Initial comparisons focused on radiometric and polarimetric agreement.
• Subsequent analysis involved updates to calibration, georegistration, and measurement uncertainty models.

Main Results:

• Initial comparisons showed radiometric agreement but revealed polarimetric biases beyond uncertainties.
• After calibration and model updates, most observations agreed within stated uncertainties.
• A ~6% bias in AirMSPI's 470 nm reflectance channels relative to RSP persists; dark ocean scenes showed polarimetric disagreement.

Conclusions:

• The PODEX intercomparison largely validates the consistency of AirMSPI and RSP Level 1 data, supporting Level 2 data product creation.
• The established comparison methodology can be applied to other polarimetric campaigns, such as ACEPOL.
• Further investigation is needed for persistent biases in specific channels and dark scene observations.