Soybean crops occupy most areas in Rio Grande do Sul State and are highly dependent on rainfall since most of them are non-irrigated. Rainfall during the harvest period is often insufficient to meet the water demand, making water indicators an important tool for the crops.
Given the need to search for robust indicators capable of representing the surface water condition in the various agricultural production regions in the state of Rio Grande do Sul, the objective of this study was to analyze the influence of different types of vegetation cover on the definition of Temperature Vegetation Dryness Index (TVDI) as an indicator of soil moisture in agricultural areas on a local scale. A Landsat 8-OLI image of February 7, 2015, and its Normalized Difference Vegetation Index (NDVI) product was used. The image was classified by the maximum likelihood method. The surface temperature (T S ) was obtained by the split-window algorithm and later the normalization of the TVDI model with the triangular characteristic dispersion was performed. With the data of TVDI, the different types of vegetation cover mapped were identified. Histograms of TVDI frequencies were also made for each of the targets The scatter plots between TVDI and NDVI and between TVDI and T S were made. The results showed that it was possible to differentiate the different types of soil use and cover, through the natural water condition of each target. With the scatter plots of the targets, it was possible to locate them with a certain overlap; the strong correlation between the index and T S was observed. TVDI has been shown to be effective for monitoring the variation of the water condition and can be used for monitoring and sustainable management purposes.
This work aimed at evaluating the TVDI (Temperature-Vegetation Dryness Index) as an indicator of water status and characterizing water spatial and temporal variability for the spring-summer crops in Rio Grande do Sul. For this purpose, the surface temperature MODIS products (MOD11A2) and vegetation index (MOD13A2) with spatial resolution of 1,000 m and temporal resolution of 8 and 16 days, respectively, were used to obtain the TVDI. Data from meteorological stations were also used to determine the water balance. The period of analysis corresponded to the spring-summer crops of 2011-12, 2012-13, 2013-14, 2014-15 and 2015-16. The results show that the TVDI is a good indicator of water surface status and represented well the water deficit occurrence in the spring-summer crops. The spatial and temporal resolution of the images used to calculate the index allowed obtaining reliable data, both during the development cycle and between Ecoclimatic Regions. These characteristics show that TVDI can be used as an indicator of water status and can, therefore, be part of the agrometeorological monitoring programs in Rio Grande do Sul.
O objetivo deste trabalho foi verificar o desempenho do índice TVDI (Temperature- Vegetation Dryness Index), obtido a partir de sensores espectrais de superfície, e compará-lo a dados de déficit hídrico determinado pelo balanço hídrico meteorológico, em lavoura de soja no noroeste do Estado do Rio Grande do Sul. O princípio de funcionamento do TVDI está ancorado na inclinação da reta de regressão linear entre o índice de vegetação e a temperatura de superfície, que representam o grau de deficiência da umidade do sistema solo/água/planta. Para o estudo foram utilizados sensores de superfície de índice de vegetação, no caso o NDVI (Normalized Difference Vegetation Index) e de temperatura radiométrica da superfície, conectados a dataloggers, registrando medidas a cada 15 minutos. O TVDI foi comparado frente a dados de déficit e excesso hídrico obtidos por balanço hídrico meteorológico diário. No período de maior déficit o TVDI apresentou os maiores valores, indicando a restrição hídrica, coerente com o armazenamento de água no solo. As temperaturas de superfície também foram altas neste período. O TVDI estimado a partir de sensores de superfície tem sensibilidade em representar a disponibilidade hídrica da cultura e permite acompanhar o desenvolvimento da soja durante a safra.
Resumo O objetivo do estudo foi analisar a variabilidade no TVDI (Temperature-Vegetation Dryness Index) obtido de sensores orbitais com resoluções distintas, em região agrícola no sul do Brasil. Utilizou-se três imagens OLI/TIRS (Operational Land Imager/Thermal Infrared Sensor) do satélite Landsat 8, e 12 imagens MODIS (Moderate Resolution Imaging Spectroradiometer) do satélite Terra. Dados coletados em campo serviram como base para classificação de imagem OLI/TIRS e mapeamento de áreas de arroz, soja, campos naturais, mata ciliar e solo exposto. O TVDI foi obtido por duas parametrizações em períodos distintos, utilizando as dispersões entre Temperatura de Superfície (TS) e NDVI (Normalized Difference Vegetation Index). O TVDI obtido para ambos sensores apresentou padrão similar possibilitando diferenciar os alvos. Na média de todas as datas e classes, o TVDI obtido das imagens MODIS foi superior em 0,128 unidades ao TVDI obtido com o OLI/TIRS. Quando utilizado OLI/TIRS há um melhor detalhamento espacial das condições hídricas, mas com menor repetição ao longo da safra; já utilizando o TVDI-MODIS é possível monitorar as condições hídricas em escala regional, com menor detalhamento espacial, mas com maior repetitividade no tempo. O TVDI estimado pelos sensores OLI/TIRS e MODIS, pode ser utilizado de forma conjunta, trazendo informações complementares.
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