Carlos Alexandre Gomes Costa

Spatial behaviour of soil moisture in the root zone of the Caatinga biome

The purpose of this study was to represent the soil moisture in the profile corresponding to the root zone from TDR sensors in a preserved area of the Caatinga biome and analyze the spatialized moisture adjustment equations under different layers of the soil profile. For that, we analyzed three classes of soil (red yellow Ultisol; Hypochromic Luvisol; Udorthent) in the Aiuaba Experimental Watershed, located in the semiarid zone of northeastern Brazil. The hydro-physical parameters representing the soil water retention (field capacity, wilting point and residual moisture) were collected in four campaigns, in six points and in the profiles corresponding to the effective root depth, totaling 216 samples. For the evaluation of the regression models, we used the coefficient of determination, the Pearson correlation and the performance index. The results indicate that the analyzed parameters are homogeneous for the studied soil profiles. The Pearson correlation coefficient indicates a moderate performance for all regression equations. However, the confidence index was determined as very bad for the Red-Yellow Ultisol, passable for the Hypochromic Luvisol and bad for the Udorthent, for the rainy season, and very bad for all classes, for the dry season. Therefore, the use of the regression models is more indicated for periods of higher soil moisture.

Análise da influência vegetacional na altimetria dos dados SRTM em bacias hidrográficas no semiárido

Topography is a major factor for understanding hydrological and environmental dynamics. Therefore, validation of the altimetric data obtained by remote sensing is required. SRTM data are a result of an orbital mission by interferometer RADAR, corresponding to the Earth surface topography, also considering the influence of vegetation in the signal. The objective of this work is to validate SRTM data for the semi-arid conditions in Northeast Brazil. The methodology used consists in the comparison and statistical analysis of field data obtained with a differential GPS (DGPS) and other existing data bases such as the DSG/SUDENE topographic maps and level reference points from IBGE in the Jaguaribe basin, located in the semi-arid region of Ceara Federal State. Results present an elevation error of approximately 7 m in relation to the level reference points in the basin. The use of DGPS on a plan relief with very low slopes and vegetation with low height, resulted on an elevation error of approximately 1.7 m. It can be concluded that, despite the influence of the vegetation cover on the altimetric variation, SRTM data are reliable for regions with vegetation type typical of semi-arid regions.