A whole image approach using field measurements for transforming EO1 Hyperion hyperspectral data into canopy reflectance spectra

Abstract

To maximize the spectral distinctiveness (information) of the canopy reflectance, an atmospheric correction strategy was implemented to provide accurate estimates of the intrinsic reflectance from the Earth Observing 1 (EO1) satellite Hyperion sensor signal. In rendering the canopy reflectance, an estimate of optical depth derived from a measurement of downwelling irradiance was used to drive a radiative transfer simulation of atmospheric scattering and attenuation. During the atmospheric model simulation, the input whole‐terrain background reflectance estimate was changed to minimize the differences between the model predicted and the observed canopy reflectance spectra at 34 sites. Lacking appropriate spectrally invariant scene targets, inclusion of the field and predicted comparison maximized the model accuracy and, thereby, the detail and precision in the canopy reflectance necessary to detect low percentage occurrences of invasive plants. After accounting for artifacts surrounding prominent absorption features from about 400 nm to 1000 nm, the atmospheric adjustment strategy correctly explained 99% of the observed canopy reflectance spectra variance. Separately, model simulation explained an average of 88%±9% of the observed variance in the visible and 98%±1% in the near‐infrared wavelengths. In the 34 model simulations, maximum differences between the observed and predicted reflectances were typically less than ±1% in the visible; however, maximum reflectance differences higher than ±1.6% (<±2.3%) at more than a few wavelengths were observed at three sites. In the near‐infrared wavelengths, maximum reflectance differences remained less than ±3% for 68% of the comparisons (±1 standard deviation) and less than ±6% for 95% of the comparisons (±2 standard deviation). Higher reflectance differences in the visible and near‐infrared wavelengths were most likely associated with problems in the comparison, not in the model generation.

Acknowledgments

We thank Mr Jimmy Wimberly for access to the Wimberly Properties, Mr David Richard for access to the Gray Estate landholdings in Calcasieu and Cameron Parishes, and Mr Sam Bellafo for access to the Neumin Production Co. landholdings in Vinton Parish. We are grateful to Benjamin C. Seal Jr of Southern Helicopters Inc., Sunshine, Louisiana for the helicopter flights. Also, we would like to thank Johnson Controls Inc. personnel Ms Kristine Martella and Ms Amina Rangoonwala for the many hours of work on planning field logistics and data collections; US Geological Survey personnel Ms Beth Vairin for editing this manuscript; NASA personnel Tom Brakke and Lawrence Ong for tireless efforts to provide us with usable Hyperion data, and their technical advice; and the anonymous reviewers who greatly improved this manuscript. Partial funding for this work was provided through NASA grant number EO‐1‐0100‐0042. Mention of trade names or commercial products is not an endorsement or recommendation for use by the US Government.