author        = "Sanza Moral, Beatriz and Casterad Seral, Mª Auxiliadora
                       and Quílez, Dolores",
      title         = "{Posibilidad de uso de imágenes aéreas multiespectrales
                       y radiometría de campo en la evaluación de la
                       disponibilidad de nitrógeno en cereales}",
      year          = "2012",
      note          = "The importance of nitrogen in agricultural production
                       generates investigations in the search of a diagnosis of
                       appropriate nitrogen fertilization in order to improve the
                       recommendations of sub-scriber in the crops. This paper
                       deals with obtaining information from airborne platforms
                       and mul-tispectral images of radiometry, as field support
                       to the management of nitrogen fertilization in cereals. The
                       study has been carried out in two trials of strategies of
                       nitrogen fertilization located in the province of Huesca,
                       one of corn in the municipal term of Almudevar and another
                       of rice in the municipality of Villanueva de Sigena.
                       Multispectral aerial images of very high spatial resolution
                       have been used with the purpose of having information that
                       will help to diagnose the nutritional status of the crop.
                       In addition, this information has been completed with
                       radiometric measures and data on the chlorophyll content of
                       the plants, taken in the field to validate the information
                       derived from the images, and to be able to establish
                       relationships between the content of chlorophyll and
                       reflectivity. In order to achieve this aims the development
                       of the sampling equipment, the design of the field sampling
                       and the development of measurement protocols have been
                       implemented. However, the acquisition of the multispectral
                       images with a high resolution has yet a high cost. Through
                       the analysis of the influence of the variation of the pixel
                       size on the information, derived from the images of the
                       work (indexes and bands) the use of lower resolutions in
                       the images without changes to the information contained
                       herein has been determined, thereby reducing the costs of
                       acquisition.  Two models of radiometric calibration of the
                       images have been compared and information of the bands on
                       the green, red and infrared as well as two vegetation
                       indices, the NDVI and the GNDVI( information that relates
                       to the chlorophyll content of plants) has been extracted
                       from an image of the test of maize spectral. Some
                       preliminary results indicate the necessity to adjust
                       aspects in relation to the representativeness of the
                       samples and measurements performed, if you want to
                       characterize the behavior with the means in the plot of the
                       different variables studied. Moreover, the acquisition of
                       information has been plentiful even though it has to be
                       analysed in subsequent studies, and compared with different
                       parameters used in the line of research in which the work
                       is framed for the achievement of results.",