Estimating Shrub Cover in Arctic Tundra from Structural Metrics and Effects on Albedo
Mark
James
Chopping, Montclair State University, chopping@pegasus.montclair.edu
(Presenting)
Kenneth
Tape, University of Alaska, Fairbanks, fnkdt@uaf.edu
Sawahiko
Shimada, Montclair State University/Tokyo University of Agriculture, shimadas@mail.montclair.edu
Rocio
Raquel
Duchesne, Montclair State University, duchesneonr1@mail.montclair.edu
Zhuosen
Wang, Boston University, wangzhs@bu.edu
Crystal
Schaaf, Boston University, schaaf@bu.edu
Increasing shrub abundance has been observed in Arctic tundra over the last 60 years and this is ecologically significant as - unlike trees - shrubs are present over a very large area and able to expand rapidly, with consequences in terms of ecosystem structure and function, albedo, and feedbacks to climate. Cover remains relatively low but future expansion may be more important as a result of rapid warming since the 1970s. However the rate of expansion and increase in shrub abundance are not known over large areas. It should be possible to exploit the structural signal (i.e., reflectance anisotropy) in moderate resolution remote sensing data from MISR and MODIS to detect woody plants and estimate cover over large areas and through time, since they protrude from the surface and cast shadows that are especially long at high latitudes. Measures of surface physical structure are encapsulated in the kernel weights of linear, semi-empirical kernel-driven models of the bidirectional reflectance distribution function (BRDF) and have been exploited elsewhere to map structure, e.g., using indices such as the Structural Scattering Index. In order to assess how well woody plant cover is reflected in BRDF model kernel weights and the effects of shrubs on albedo in Arctic tundra, in the summer of 2009 we acquired aerial and field photographs for a number of selected sites along the Chandler River. Estimates of shrub cover were then obtained from geometrically-corrected versions of the aerial photographs and checked against the field photographs. These estimates were used to make preliminary assessments of spatial patterns in kernel weight maps from inversion of a Li-Ross BRDF model against MISR and MODIS red band data, in cover and height retrievals from inversion of a geometric-optical model, and against albedo estimates from MODIS.
Presentation Type: Poster
Poster Session: Ecosystems Science
NASA TE Funded Awards Represented:
Chopping, Mark
Mapping Changes in Shrub Abundance and Biomass in Arctic Tundra using NASA Earth Observing System Data: A Structural Approach