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Abstract
Agriculture is a dynamic activity that causes yearly and seasonal changes in cultivated landscapes. These changes depend on meteorological variations and on the exploitation of annual or perennial crops. Sensor technology including the Advanced Very High Resolution Radiometer (AVHRR) in NOAA satellites constitutes a useful tool to assess changes in cultivated landscapes, as well as to measure crop density and vigour throughout an agricultural cycle. This study analyses relationships among variables, such as precipitation, growth stage and vegetation index values, for crops during the 1996 and 1997 agricultural cycles. The study area was the physiographic province known as ‘Mesa Central’ located in the state of Guanajuato, Mexico, which, in general, has homogeneous features such as topography and soil type, and a marked precipitation season. Corn and bean are two of the most widely cultivated crops in this region. The methodology used included the following aspects: registering, geometrical correction, calculation of the Normalized Difference Vegetation Index (NDVI) and time-series composites. Additionally, fieldwork assessment was conducted at cultivated areas, where data for daily precipitation, sowing time, crop variety, and duration of vegetative, reproductive and maturity periods were gathered. The correlation analysis between NDVI and precipitation resulted in r=0.9087 and 0.8935 for the analysed regions in 1996 and r=0.8812 and 0.8600 in 1997. The vegetation growth and NDVI also showed a qualitative positive relationship. Therefore these satellite images represent a useful tool in the analysis of crop-related phenological phenomena.
Acknowledgments
We gratefully acknowledge the assistance of Laboratorio de Sistemas de Información Geográfica y Precepción Remota of the UNAM's Institute of Geography. Thanks are due to Dr Raúl Aguirre Gómez for comments on an earlier version of this manuscript. Also we wish to acknowledge the financial support given by the Mexican Council of Science and Technology (CONACYT).
Notes
*Currently at: Geography Department, University of Edinburgh, Drummond Street, Edinburgh, EH8 9XP, UK
