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Estimation of the chlorophyll content of the Monarch Butterfly reserve

Maria Luisa España(1), Omar Champo(1), Enrique Martínez(1), Philippe Lobit(1) and Fred Baret(2)

(1) UMSNH, Posta Veterinaria, 58240 Morelia, Michoacan, Mexico
(2) INRA, Site Agroparc, Avignon, France

Abstract

The annual arrival of the butterflies in the Monarch Biosphere Reserve in Michoacán (Mexico) is endangered by the degradation of the forest vegetation (Abies religiosa L.), due to illegal logging an plagues. The purpose of this project was to obtain a map of chlorophyll content in the Monarch Butterfly Biosphere Reserve, as a tool to improve the monitoring of the degraded area, since chlorophyll content in plant leaves indicates their photosynthetic capacity as well as the presence of stress or diseases. The map was calculated through a transfer function, adjusted by comparing measurements of chlorophyll content obtained from field data and vegetation indexes (VI) calculated from a MERIS image. During the field study, realized in July and August 2007, 12 300m x 300m sites distributed in the whole reserve area were identified. In each of these sites, 5 elementary sample units (ESU) of 20m x 20m were randomly selected. In each ESU, samples were taken on six Abies trees, corresponding to well exposed leaves of the previous year growth. Leaf chlorophyll content per leaf area was measured by DMSO extraction. Hemispherical photographs were taken for the calculation of the leaf area index (LAI), and used to estimate the chlorophyll content per soil area of each ESU and each site of each site. A MERIS image, taken on 2nd August 2007 was used to extract reflectance values of each site, and several VI based on the REP region were calculated. Using 2/3 of the sample points (data of 8 sites) different transfer functions were adjusted between chlorophyll content and VI; the other 1/3 of the sample points was used for validation. Finally, the transfer function that matched the best was applied to all the image pixels corresponding to Abies vegetation, in order to obtain a map.

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry