remote sensing Article Functional Phenology of a Texas Post Oak Savanna from a CHRIS PROBA Time Series Michael J. Hill 1,2,* , Andrew Millington 2 , Rebecca Lemons 1 and Cherie New 1 1 Department of Earth System Science and Policy, University of North Dakota, Grand Forks, ND 58202, USA;
[email protected] (R.L.);
[email protected] (C.N.) 2 College of Science and Engineering, Flinders University, Sturt Road, Bedford Park, South Australia 5042, Australia; andrew.millington@flinders.edu.au * Correspondence:
[email protected]; Tel.: +61-413161853 Received: 19 September 2019; Accepted: 13 October 2019; Published: 15 October 2019 Abstract: Remnant midwestern oak savannas in the USA have been altered by fire suppression and the encroachment of woody evergreen trees and shrubs. The Gus Engeling Wildlife Management Area (GEWMA) near Palestine, Texas represents a relatively intact southern example of thickening and evergreen encroachment in oak savannas. In this study, 18 images from the CHRIS/PROBA (Compact High-Resolution Imaging Spectrometer/Project for On-Board Autonomy) sensor were acquired between June 2009 and October 2010 and used to explore variation in canopy dynamics among deciduous and evergreen trees and shrubs, and savanna grassland in seasonal leaf-on and leaf-off conditions. Nadir CHRIS images from the 11 useable dates were processed to surface reflectance and a selection of vegetation indices (VIs) sensitive to pigments, photosynthetic efficiency, and canopy water content were calculated. An analysis of temporal VI phenology was undertaken using a fishnet polygon at 90 m resolution incorporating tree densities from a classified aerial photo and soil type polygons.