Temporal and spatial relationships between topography, atmospheric water vapor, liquid water and vegetation endmember fractions determined using AVIRIS

Temporal and spatial changes in water vapor, liquid water and endmember fractions were investigated using AVIRIS data collected in the vicinity of Jasper Ridge, CA, on three dates in 1992. Water vapor and liquid water were mapped using a Modtran-II based atmospheric model that accounts for spatially varying atmospheric properties. Spectral mixture analysis (SMA) was used to model vegetation as mixtures of green vegetation (GV), non-photosynthetic vegetation (NPV), soil, and shade. Atmospheric water vapor and elevation were negatively correlated for all three dates with anomalously high water vapor located over forested sites, equal in some places to over 100 meters in equivalent change in elevation. A local water vapor source was suggested, either as evapotranspired water by plants or entrained water vapor in canyons. Liquid water was negatively correlated to NPV and positively correlated to GV and shade. Anomalies occurred in which golf courses and forested wetland had a high GV fraction associated with low liquid water while redwoods had high liquid water yet low GV due to a high shade content. Qualitatively, liquid water absorption matched the expected pattern in changing leaf area, with low liquid water matching lower leaf areas and high liquid water matching high leaf areas, suggesting that SMA, when combined with the analysis of liquid water provides compatible, but distinct information about vegetation. SMA provides estimates of cover and architecture (through shade), while liquid water may provide an estimate of the ecological significant variable leaf area.<
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