Raimundo Alípio de Oliveira Leão

Hyperspectral Remote Sensing for Detecting Soil Salinization Using ProSpecTIR-VS Aerial Imagery and Sensor Simulation

Soil salinization due to irrigation affects agricultural productivity in the semi-arid region of Brazil. In this study, the performance of four computational models to estimate electrical conductivity (EC) (soil salinization) was evaluated using laboratory reflectance spectroscopy. To investigate the influence of bandwidth and band positioning on the EC estimates, we simulated the spectral resolution of two hyperspectral sensors (airborne ProSpecTIR-VS and orbital Hyperspectral Infrared Imager (HyspIRI)) and three multispectral instruments (RapidEye/REIS, High Resolution Geometric (HRG)/SPOT-5, and Operational Land Imager (OLI)/Landsat-8)). Principal component analysis (PCA) and the first-order derivative analysis were applied to the data to generate metrics associated with soil brightness and spectral features, respectively. The three sets of data (reflectance, PCA, and derivative) were tested as input variable for Extreme Learning Machine (ELM), Ordinary Least Square regression (OLS), Partial Least Squares Regression (PLSR), and Multilayer Perceptron (MLP). Finally, the laboratory models were inverted to a ProSpecTIR-VS image (400–2500 nm) acquired with 1-m spatial resolution in the northeast of Brazil. The objective was to estimate EC over exposed soils detected using the Normalized Difference Vegetation Index (NDVI). The results showed that the predictive ability of the linear models and ELM was better than that of the MLP, as indicated by higher values of the coefficient of determination (R2) and ratio of the performance to deviation (RPD), and lower values of the root mean square error (RMSE). Metrics associated with soil brightness (reflectance and PCA scores) were more efficient in detecting changes in the EC produced by soil salinization than metrics related to spectral features (derivative). When applied to the image, the PLSR model with reflectance had an RMSE of 1.22 dS·m−1 and an RPD of 2.21, and was more suitable for detecting salinization (10–20 dS·m−1) in exposed soils (NDVI < 0.30) than the other models. For all computational models, lower values of RMSE and higher values of RPD were observed for the narrowband-simulated sensors compared to the broadband-simulated instruments. The soil EC estimates improved from the RapidEye to the HRG and OLI spectral resolutions, showing the importance of shortwave intervals (SWIR-1 and SWIR-2) in detecting soil salinization when the reflectance of selected bands is used in data modelling.

Estimativa da evaporação no açude Banabuiú, no estado do Ceará, por diferentes métodos combinados, derivados da equação de Penman

O Estado do Ceara possui 75% do territorio abrangido pelo semiarido brasileiro, com suas caracteristicas peculiares. Nesse Estado, acudes constituem-se em estrutura hidrica de importância estrategica, garantindo, no tempo e no espaco, o desenvolvimento e o abastecimento hidrico das populacoes. No entanto, a construcao de reservatorios implica varios impactos que devem ser cuidadosamente observados no momento de decidir pela sua execucao. Um dos impactos apontados como negativo e o aumento da evaporacao, que se constitui em um dos principais componentes do balanco hidrico nos reservatorios, sobretudo em regioes aridas. Varios metodos de estimativa da evaporacao foram propostos ao longo do tempo, muitos deles derivados da equacao de Penman. Neste trabalho, foram avaliados seis diferentes metodos de estimativa da evaporacao a fim de determinar qual o mais adequado para utilizacao em modelos hidrologicos para o balanco hidrico em reservatorios no Estado do Ceara. Os metodos avaliados foram os propostos por Penman, Kohler-Nordenson-Fox, Priestley-Taylor, deBruim-Keijman, Brutsaert-Stricker e deBruim, os quais apresentaram otimo desempenho quando testados para o balanco hidrico durante a estacao seca, sendo o de Priestley-Taylor o mais adequado, uma vez que os dados do balanco hidrico simulado com a componente evaporacao estimada por este metodo foram os mais proximos dos dados do balanco hidrico observado a partir das medidas de nivel do reservatorio e da curva cota-volume fornecidos pela Companhia de Gestao dos Recursos Hidricos do Estado do Ceara - COGERH.

Use of capacitive sensors with the instantaneous profile method to determine hydraulic conductivity

Due to the need to monitor soil water tension continuously, the instantaneous profile method is considered laborious, requiring a lot of time, and especially manpower, to set up and maintain. The aim of this work was to evaluate the possibility of using capacitive sensors in place of tensiometers with the instantaneous profile method in an area of the Lower Acarau Irrigated Perimeter. The experiment was carried out in a Eutrophic Red-Yellow Argisol. The sensors were installed 15, 30, 45 and 60 cm from the surface, and powered by photovoltaic panels, using a power manager to charge the battery and to supply power at night. Records from the capacitive sensors were collected every five minutes and stored on a data acquisition board. With the simultaneous measurement of soil moisture obtained by the sensors, and the total soil water potential from the soil water retention curve, it was possible to determine the hydraulic conductivity as a function of the volumetric water content for each period using the Richards equation. At the end of the experiment, the advantage of using capacitive sensors with the instantaneous profile method was confirmed as an alternative to using a tensiometer. The main advantages of using capacitive sensors were to make the method less laborious and to allow moisture readings at higher tensions in soils of a sandy texture.

Georeferenced database generation with the purpose of hydrologic molding in reservoirs of the hydrographic basin of Jaguaribe river in the state of Ceará, Brazil

The edafoclimatic conditions of the Brazilian semiarid region favor the water loss by surface runoff. The state of Ceara, almost completely covered by semiarid, has developed public policies for the construction of dams in order to attend the varied water demand. Several hydrological models were developed to support decisive processes in the complex management of reservoirs. This study aimed to establish a methodology for obtaining a georeferenced database suitable for use as input data in hydrological modeling in the semiarid of Ceara. It was used images of Landsat satellite and SRTM Mission, and soil maps of the state of Ceara. The Landsat images allowed the determination of the land cover and the SRTM Mission images, the automatic delineation of hydrographic basins. The soil type was obtained through the soil map. The database was obtained for Jaguaribe River hydrographic basin, in the state of Ceara, and is applicable to hydrological modeling based on the Curve Number method for estimating the surface runoff.