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Impact of Orbital Drift on NDVI Derived from AVHRR

Jyoteshwar R Nagol, University of Maryland College Park, jnagol@umd.edu (Presenting)
Eric F Vermote, University of Maryland College Park, eric@ltdri.org
Stephen D Prince, University of Maryland College Park, sprince@umd.edu



Data derived from the AVHRR (Advanced Very High Resolution Radiometer) series of instruments have been extensively used for monitoring global and regional vegetation dynamics for last 25+ years. Past studies have shown that the influence of systematic change in satellite overpass time during the course of satellite’s life due to orbital drift remains, even after sensor calibration. This is due to change in sun-sensor geometry. In order to assess the impacts of orbital drift on NDVI (Normalized Difference Vegetation Index), simulated AVHRR time series data created with actual AVHRR viewing and illumination geometry was analyzed. To facilitate investigation of the impacts of orbital drift alone, interannual variations in phenology were not introduced in the simulations. One representative site each in tropical forest, savanna, and semi-arid landcover were utilized.



BRDF (Bidirectinal Reflection Distribution Function) database derived from POLDER (POLarisation and Directionality of the Earth’s Reflectance) was employed to model the impact of solar zenith angle drift on NDVI at top of the canopy level. Further investigations into impacts of atmosphere on directional signature were carried out using 6s (Second Simulation of the Satellite Signal in the Solar Spectrum), an atmospheric radiative transfer model. The results show that atmosphere was a more dominant contributor to the impact of orbital drift on AVHRR-NDVI timeseries data.



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