Bergson Guedes Bezerra

ESTIMATIVA DA EVAPOTRANSPIRAÇÃO REAL DIÁRIA UTILIZANDO-SE IMAGENS DIGITAIS TM - LANDSAT 5

Quantification of evapotranspiration is of great importance for hydrological and meteorological modeling and indispensable for water management of irrigated crops. In this sense the main objective of this study was the estimation of actual daily evapotranspiration (Etr), in local and regional scale, utilizing the SEBAL (Surface Energy Balance Algorithm for Land). The TM - Landsat 5 images and weather data were used in order to assess the energy balance components. The studied area is located in Cariri region, Ceara State, and is composed by irrigated areas, native vegetation and part of the Chapada do Araripe Reserve. Four TM - Landsat 5 images of September 29th, October 15th, October 31st and November 16th of 2005, were used. Daily ETr was estimated based on the density of latent heat flux, obtained as residue of the energy balance equation. The application of the SEBAL algorithm includes some steps as radiometric calibration, estimation of the reflectance and albedo, emissivity and vegetation index, based on the reflective bands of the orbital sensors and further on the surface temperature (thermal band) for the TM - Ladsat 5. Two irrigated fields of castor bean and cotton were used do validated the ETr estimated values. The reference evapotranspiration was obtained by FAO-Penman-Monteith method. The mean daily ETr over the studied area presented values of 3.8, 3.7, 4.6 and 3.4 mm.dia-1 on 29/09, 15/10, 31/10 and 16/11, respectively. When compared to measured data in the castor bean (Ricinus communis L.) and cotton (Gossypium hirsutum) irrigated crops, the ETr values obtained with SEBAL present differences smaller than 1,0 mm day-1, showing its importance and accuracy.

Assessment of daily actual evapotranspiration with SEBAL and S-SEBI algorithms in cotton crop

The main objective of this study is to assess the daily ET accuracy obtained by remote sensing algorithms in comparison with measurements in situ. The experiment was conducted in the State of Ceara, Brazil, in a cotton experimental field of EMBRAPA using Bowen ratio measurements to obtain the energy balance components. SEBAL and S-SEBI algorithms were used with four TM Landsat – 5 images of 2005, in order to determine the actual evapotranspiration of cotton crop. The comparison between the estimated values by remote sensing algorithms and the measured values in situ showed that the methods (SEBAL and S-SEBI) presented satisfactory results. The S-SEBI algorithm is an important tool to be applied in ET analysis of semi-arid regions, due its practicability to solve the energy balance and its processing is simpler than SEBAL algorithm which needs the solution of an iterative process.

Estimation of soil moisture in the root-zone from remote sensing data

Field-based soil moisture measurements are cumbersome. Thus, remote sensing techniques are needed because allows field and landscape-scale mapping of soil moisture depth-averaged through the root zone of existing vegetation. The objective of the study was to evaluate the accuracy of an empirical relationship to calculate soil moisture from remote sensing data of irrigated soils of the Apodi Plateau, in the Brazilian semiarid region. The empirical relationship had previously been tested for irrigated soils in Mexico, Egypt, and Pakistan, with promising results. In this study, the relationship was evaluated from experimental data collected from a cotton field. The experiment was carried out in an area of 5 ha with irrigated cotton. The energy balance and evaporative fraction (Λ) were measured by the Bowen ratio method. Soil moisture (θ) data were collected using a PR2 - Profile Probe (Delta-T Devices Ltd). The empirical relationship was tested using experimentally collected Λ and θ values and was applied using the Λ values obtained from the Surface Energy Balance Algorithm for Land (SEBAL) and three TM - Landsat 5 images. There was a close correlation between measured and estimated θ values (p<0.05, R2 = 0.84) and there were no significant differences according to the Student t-test (p<0.01). The statistical analyses showed that the empirical relationship can be applied to estimate the root-zone soil moisture of irrigated soils, i.e. when the evaporative fraction is greater than 0.45.

Avaliação dos efeitos atmosféricos no albedo e NDVI obtidos com imagens de satélite

O albedo e um elemento importante em estudos relacionados aos balancos de radiacao e energia. Por conseguinte, alteracoes ocorridas em diversos biomas trazem grandes implicacoes ao conforto humano e animal. Neste sentido, o monitoramento do albedo atraves de imagens orbitais possibilita identificar a antropizacao de grandes areas e seus impactos ambientais. O presente trabalho foi desenvolvido com o objetivo de avaliar o impacto da correcao atmosferica na estimativa do albedo da superficie e do NDVI, utilizando-se a metodologia tradicional do SEBAL (Bastiaanssen, 2000) e a correcao atmosferica no computo da refletância, banda a banda (Allen et al., 2007b), para quatro imagens Landsat 5 - TM da regiao do Cariri cearense. Os resultados mostraram diminuicao no albedo da superficie e acrescimo no NDVI, corrigidos os efeitos atmosfericos para todas as areas amostrais. De acordo com o teste de Student as diferencas entre os albedos e NDVIs, obtidas segundo os dois procedimentos considerados, sao significativas a nivel de significância de 0,01.

Zoneamento agroclimático da palma forrageira (Opuntia sp.) para o estado da Paraíba

A palma forrageira tornou-se, ao longo dos anos, uma importante alternativa forrageira no semiarido brasileiro (SAB) principalmente em longos periodos de estiagens. Apesar de sua magnitude para a agropecuaria, seu cultivo tem dispensando tratos culturais basicos e embasamento tecnico-cientifico quanto as suas exigencias climaticas. Assim, o principal objetivo deste estudo foi elaborar o zoneamento agroclimatico da cultura da palma forrageira (Opuntia sp.) para o estado da Paraiba. O zoneamento agroclimatico da palma forrageira foi elaborado com base nos indicadores climaticos delineados na literatura e nos dados climatologicos de precipitacao e temperatura (media, maxima e minima) de 97 localidades do estado da Paraiba. De acordo com os resultados obtidos, a mesorregiao da Borborema e a que apresenta as condicoes climaticas mais favoraveis para o cultivo da palma forrageira. As mesorregioes do Agreste, Sertao e a parte do Litoral, sao aptas porem com restricoes. No entanto, recomenda-se o cultivo da palma forrageira em todo o territorio do estado da Paraiba, exceto para a parte costeira da mesorregiao do Litoral e regiao em torno de Areia. Em ambos os casos a inaptidao ocorre em funcao do excesso de precipitacao.

Evapotranspiração real obtida através da relação entre o coeficiente dual de cultura da FAO-56 e o NDVI

REAL ACTUAL EVAPOTRANSPIRATION OBTAINED THROUGH THE RELATIONSHIP BETWEEN THE FAO-56 CROP DUAL COEFFICIENT AND NDVI A fundamental requirement for adoption of irrigation management is to determine the crop daily evapotranspiration (ET). On an operational basis the crop coefficient method proposed by the Food and Agriculture Organization (FAO) through its report 56 (Irrigation and Drainage Paper) is widely used in the determination of ET and due to its accurate estimative, it has been globally accepted. The ET-based crop coefficient (Kc) obtained from vegetation indices, particularly the Vegetation Index Normalized Difference (NDVI) has been measured in several studies and various crops showing great accuracy when compared to field observations. The objective of this study was to calculate the daily and seasonal ET of cotton crop using the method of dual Kc obtained as a function of the NDVI obtained from TM - Landsat 5 images clouds free. The obtained results are reliable, because less than 10% differences were found when comparing to the Bowen ratio technique observations, corroborating to the method performance achieved in other experiments conducted in other regions

Refinamento de imagens termais do Landsat 5 - TM com base em classes de NDVI

The objective of this study was to use a simplified method based on NDVI classes for the sharpening of the Landsat 5 - TM surface temperature images (Ts) obtained during the years of 2005 and 2006. Thus, three sharpening models, based on the linear regression method, were proposed and compared. The relative and the root mean square errors obtained through the suggested models were of 0.37% and 1.38 oC, respectively, while the original model presented root mean square error of 1.32 oC. It was verified that the errors obtained with the accomplished calibrations did not significantly influence in the average values of the thermal images and the results contributed substantially to the improvement of their spatial resolution. The sharpening allowed the precise identification of the targets and features undetectable at the original spatial resolution. This evidences that the simplified method, suggested in this study, allows an accurate sharpening more easily applicable than the original model.