La Purisima Dam is a water body located south of Guanajuato City (Mexico) and it provides water to irrigate 4,500 hectares for Irapuato and Guanajuato municipalities. At this moment there aren’t studies about the relationship between the fluctuation of the water level and the physical and/or chemical characteristics of water. For this reason, the aim of this work is to establish relationships between the spectral responses linked to water level variation. To meet the goal, Landsat TM5 images were used in six different dates ranging from 1986 to 2009. The methodology included techniques such as radiometric corrections, segmentation image and spectral signature analysis for 3 points on a transect North-South. The results indicate that La Purisima Dam has a surface variation from 7.32 km2 in 2005 to 3.02 km2 in 2000 (reduction to 58%). The spectral responses for point 2 (midpoint) show a strong contrast between the visible and infrared regions for 2005, while the signature obtained for 2000 is flatter, showing less contrast between both regions of spectrum. The point 1 (north edge) shows a characteristic response of vegetation with high water content for 2000. This result is consistent with the variation of water level, since this year has the lowest level in the past 23 years. The spectral signatures for the point 3 (south edge) have a similar behavior to point 2. Future works include a project to acquire a field spectroradiometer and the chemical water analysis, to better understand the spectral and chemical behavior of water bodies.
