5  SPEXone L2 Validation (V3)

This page summarizes validation results for aerosol and ocean products retrieved from the PACE multi-angle polarimeters using the FastMAPOL algorithm, with emphasis on SPEXone aerosol optical properties and ocean remote-sensing reflectance (\(R_{rs}\)).

FastMAPOL performs coupled aerosol–surface retrievals using an optimal-estimation framework accelerated by deep neural network forward models. This page focuses on the validation results and their interpretation for Version 3 (V3) data. Version 4 (V4) data show generally similar performance, as summarized in the V4 data release notes. More detailed V4 validation is ongoing.

Additional quantified validation results are available in Gao et al. (2026) and will be updated on the PACE FastMAPOL validation page.

5.1 Summary Information

  • FastMAPOL version: v3.0
  • Data period: 2024/03–2025/12
  • Reference: AERONET v3, Level 1.5

5.2 Retrieval Products Evaluated

Aerosol - Total, fine-mode, and coarse-mode aerosol optical depth (AOD) - Total, fine-mode, and coarse-mode single-scattering albedo (SSA)

Ocean - Ocean remote-sensing reflectance (\(R_{rs}\))

5.3 Validation Strategy

Validation is organized into three levels:

  1. Global Level-3 assessment
    Evaluate large-scale spatial and seasonal patterns as shown below.

  2. Global aerosol validation
    Compare retrievals with AERONET observations

  3. Joint aerosol–ocean validation
    Evaluate aerosol and \(R_{rs}\) simultaneously using AERONET-OC matchups, study the mutual dependencies on the retrieval uncertainties.

The objective is to assess both the physical realism of the retrieved fields and the consistency of aerosol and ocean products.

5.4 Global Level-3 Products

Aerosol Products (556 nm)

Global distributions of total, fine-mode, and coarse-mode AOD and SSA at 556 nm:

Figure 5.1: Global aerosol products from SPEXone. Adapted from Gao et al. (2026).

Ocean Products

Global distributions of \(R_{rs}\) (443, 556, 667 nm) and chlorophyll-a:

Figure 5.2: Global ocean products from SPEXone. Adapted from Gao et al. (2026)

The retrieved \(R_{rs}\) contains spectral and angular dimensions. The results shown here represent the BRDF-corrected angular mean.

Key result:
The global distributions show realistic spatial and seasonal patterns, indicating effective separation of atmospheric and oceanic retrieval components.