Using SeaWiFS Measurements to Evaluate Radiometric Stability of Pseudo-Invariant Calibration Sites at Top of Atmosphere

The Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) data from 1997 to 2001 are adopted to monitor the radiometric stability of six pseudo-invariant calibration sites (PICSs) at the top of atmosphere (TOA). Cloud-free and homogeneous observations of the spectral TOA reflectance ρ^TOA at eight SeaWiFS channels over these sites are fitted to the Ross-Li bidirectional reflectance distribution function (BRDF) model, and the time series of BRDF-normalized spectral TOA reflectance R^TOA is presented and analyzed afterward. Overall, good stability during the evaluated period is exhibited as more than half of the derived trends are statistically insignificant, whereas root mean square (RMS) of the BRDF modeling residuals reveal spectral dependence of the PICSs´ stability at TOA, i.e., the uncertainty of R^TOA appears to be larger at shortwave visible (SV) channels (~2.5%) compared with that of red/NIR bands (~1%). In addition, the early mission data adopted in our study shows favorable reliability thus is recommended to be applied for similar purposes.