Ángel Marqués-Mateu

Grey Level and Noise Evaluation of a Foveon X3 Image Sensor: A Statistical and Experimental Approach

Radiometric values on digital imagery are affected by several sources of uncertainty. A practical, comprehensive and flexible procedure to analyze the radiometric values and the uncertainty effects due to the camera sensor system is described in this paper. The procedure is performed on the grey level output signal using image raw units with digital numbers ranging from 0 to 212-1. The procedure is entirely based on statistical and experimental techniques. Design of Experiments (DoE) for Linear Models (LM) are derived to analyze the radiometric values and estimate the uncertainty. The presented linear model integrates all the individual sensor noise sources in one global component and characterizes the radiometric values and the uncertainty effects according to the influential factors such as the scene reflectance, wavelength range and time. The experiments are carried out under laboratory conditions to minimize the rest of uncertainty sources that might affect the radiometric values. It is confirmed the flexibility of the procedure to model and characterize the radiometric values, as well as to determine the behaviour of two phenomena when dealing with image sensors: the noise of a single image and the stability (trend and noise) of a sequence of images.

Wetland soils under rice management and seawater intrusion: Characterization and classification

Wetlands started to gain attention when the scientific community began investigating these resources in the eighties. Water, wildlife, and vegetation attracted most of the interest and funding, whereas soils were relegated from research efforts. Despite this situation, US researchers started developing a specific terminology and methodologies for hydric soils in order to unveil a new soil class that could offer great agricultural and environmental opportunities. In Spain, similar studies are practically nonexistent, and so we carried out a study of wetland soils examining 19 profiles and 133 pits in the Albufera of Valencia, a marsh area cultivated with rice. The aim of this paper was to define the morphology and physico-chemical properties of these hydric soils in order to classify them and to correlate those properties with three topographic variables: distance to the sea, distance to the lagoon and height above the sea level. The soils showed an alluvial character with moderate carbonate content and a high variation in organic matter content due to the management of paddy fields. The proximity to the sea and the different intrusion processes revealed salinity as the most important factor in these soils, which were classified as Entisols and Aridisols.

Significance of Soil Lightness Versus Physicochemical Soil Properties in Semiarid Areas

Modern agriculture aims to encompass all soil attributes to optimize soil use and minimize environmental impacts. One of those attributes is soil color, which allows determining important soil variables for crop management and soil conservation. In this study, the relationships between lightness and several pedologic, topographic, and soil management variables were determined. One hundred and ten topsoil points were sampled in an area where the Mediterranean climate is the only homogeneous soil forming factor. Soil samples were air dried, crushed, and sieved, and lightness measurements were made using a trichromatic colorimeter. The relationships between lightness and soil-related parameters were carried out by means of bivariate linear correlation, and Mann-Witney and Kruskal-Wallis tests. Soil textural fractions (sand and silt), electrical conductivity and carbonates were statistically significant (p < 0.001) and exhibited moderate correlation coefficients (0.32–0.45). Topographic variables (slope and aspect), soil organic carbon, iron, nitrogen, pH, and parent material (marls) exhibited lower effect on lightness. The response of lightness to clay content was highly conditioned by iron content. Stoniness, phosphorous, elevation, and soil management variables (irrigation and land use) were not statistically significant. The results obtained with calcareous samples from semiarid areas showed that soil lightness behavior agree with findings in developed soils, despite of the large differences in soil composition and the heterogeneity of the study area.