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Tropical forests are key components of the biogeochemical cycles, complex in structure, diversity and dynamics, also, tropical regions have been deforested and modified by human activities particularly for agriculture. Understanding the inter-annual and intra-annual variation dynamics of tropical regions could give valuable information on temporal characteristics of ecosystems behavior which is important for mapping and monitoring. This dissertation assesses seasonal and inter-annual changes in the tropical land cover that may be related to changes in the natural environment and/or human activities. Research was focused on the Mayan forest located in southern Mexico and Northwest Guatemala, one of the northern-most important tropical areas in the continent. Using vegetation index products from the Moderate Resolution Imaging Spectroradiometer (MODIS) from 2001 to 2005, the vegetation condition “greenness” was modeled through temporal profiles. The higher spatial resolution data and the availability of two vegetation indices: the standard Normalized Difference Vegetation Index (NDVI), and the Enhanced Vegetation Index (EVI), designed to improve sensitivity to differences in vegetation from sparse to dense vegetation conditions, offer a great opportunity to model vegetation dynamics in tropical areas. Additionally, the Wide Dynamic Range Vegetation Index (WDRVI) which is derived from the NDVI and designed to enhance the spectral response where the NDVI saturates, is included. Comparison between the different vegetation indices is analyzed by means of cross-plots and a wavelet analysis. Then a Fourier series approximation calculation was applied to extract the main seasonal components (high harmonics amplitude and phase) of the biweekly greenness profiles in order to input to an unsupervised classification to obtain a land use/land cover map and to compare mean amplitude and phase parameters value between years.
Results show differences between indices in terms of seasonal and vegetation response. In terms of mapping the WDRVI was the index with better performance. Fourier parameters mapping, particularly the first harmonic phase, was sensitive to annual variation of environmental conditions (precipitation). The use of multitemporal observations through remote sensing observations, provide a continuous and dynamic view of tropical regions to support monitoring and sustainable development and management of environmental policies.
Advisor: James W. Merchant