Invited Seminar at CES on 3 October 2017 at 3:00 pm titled "Texture Analysis of Very High Spatial Resolution Optical Images as a Way to Monitor Vegetation and Forest Biomass in the Tropics" by Prof Pierre Couteron from IRD-UMR AMAP, Montpellier, France
Space observation is acknowledged as quintessential for providing reliable monitoring strategies for vegetation at multiple scales over extensive territories with a low population and limited accessibility. Optical satellite imagery represents the major source of data and covers an ample continuum of image resolution and swath. Yet vegetation monitoring in both the dry and wet tropics has long been hampered by insufficient pixel resolution that renders the well-mastered, pixel-wise classification techniques inefficient. The increasing availability of images with high spatial resolution (HSR, pixels of 10 m or less) to very high spatial resolution (VHSR, pixels of less than 2 m) has opened up new prospects by allowing the inference of vegetation properties from image texture features (i.e., inter-pixel variability with respect to distance). In the present talk, we aim to illustrate this potential through published case studies dealing with semiarid vegetation monitoring and baseline above ground biomass assessment in moist tropical forests. In both cases, we applied variants of a method called FOTO (Fourier-based textural ordination) to obtain textural features from the images and relate them to meaningful vegetation properties, such as patterns of vegetation vs. bare ground in drylands, or crown and gap size distribution in forest canopy images. Textural ordination based on Fourier spectra provides a powerful and consistent framework for identifying prominent scales of landscape patterns and comparing scaling properties across landscapes. In the case of forest landscapes, texture features relate to crown size distribution and sometimes to inter-crown gaps and therefore are often good predictors of stand structure and biomass. We also use the radiative transfer model DART as to generate canopy images from three-dimensional forest stand mockups parametrized from pantropical field plots. Simulated canopy images allowed us testing the relevance of texture approaches to retrieve stand characteristics and to explore the complementary with FOTO of features provided by Gabor and continuous wavelet transforms.
Keywords: above ground biomass, canopy grain, FOTO method, patterned semiarid vegetation, tropical moist and wet forest, continuous wavelet transform