Validation Metrics¶
This page documents the validation metrics generated by SpectralBridge and recorded primarily in the QA JSON file. These metrics characterize reflectance quality, BRDF stability, harmonization accuracy, and mask distributions.
Reflectance metrics¶
- min/max/median per band
- out-of-range counts (>1.5 or <0)
- percent masked
- per-band histograms (in QA PNG/PDF)
High out-of-range values may indicate issues in BRDF correction or DEM artifacts.
Mask metrics¶
- cloud fraction
- cloud-shadow fraction
- snow fraction
- water fraction
- invalid/no-data fraction
These metrics help identify flights with adverse conditions or sensor anomalies.
BRDF metrics¶
- per-band BRDF model coefficients
- reconstruction RMSE
- flags for unstable or ill-conditioned fits
These diagnostics help identify pixels or bands where geometric normalization may be unreliable.
Convolution / harmonization metrics¶
- brightness adjustment coefficients
- per-band regression statistics (if applicable)
- spectral alignment differences
- RMSE for harmonized vs. reference spectra
These values help assess the quality of sensor harmonization.
Geometry and ancillary metrics¶
- solar zenith / azimuth
- view zenith / azimuth
- DEM slope/aspect summaries
These values allow interpretation of scene illumination conditions.
Using metrics for quality control¶
Typical red flags:
- Large brightness shifts (>0.1 reflectance)
- High invalid fraction (>20%)
- Poor BRDF fits (RMSE > threshold for the site/sensor)
- Unusual wavelength alignment differences
These indicators suggest reviewing the flight line before using it in ecological analyses.