RESUMO
Spaceborne spectrometers require spectral-temporal stability characterization to aid validation of derived data products. EO-1 began orbital precession in 2011 after exhausting onboard fuel resources. In the Libya-4 Pseudo Invariant Calibration Site (PICS) this resulted in a progressive shift from a mean local equatorial crossing time of ~10:00 AM in 2011 to ~8:30 AM in late 2015. Here, we studied precession impacts to Hyperion surface reflectance products using three atmospheric correction approaches from 2004 to 2015. Combined difference estimates of surface reflectance were < 5% in the visible near infrared (VNIR) and < 10% for most of the shortwave infrared (SWIR). Combined coefficient of variation (CV) estimates in the VNIR ranged from 0.025 - 0.095, and in the SWIR ranged from 0.025 - 0.06, excluding bands near atmospheric absorption features. Reflectances produced with different atmospheric models were correlated (R 2) in VNIR from 0.25 - 0.94 and SWIR from 0.12 - 0.88 (p < 0.01). The uncertainties in all models increased with terrain slope up to 15° and selecting dune flats could reduce errors. We conclude that these data remain a useful resource over this period.
