Análise da distribuição espacial do índice de umidade do solo em regiões semiáridas a partir de dados de sensoriamento remoto

Abstract

Soil moisture represents a fraction of water that is at a surface level of the earth where there is interaction with the atmosphere through evapotranspiration. It is a fundamental variable in the functioning of several processes that act in the terrestrial system, besides characterizing the desertification of semiarid and arid regions. This course conclusion work aimed to evaluate the spatial distribution of the soil moisture index in a dry tropical forest area, in the city of Floresta/PE, through orbital images. The methodology was applied for four distinct dates (11/21/15, 11/23/16, 12/12/17 and 11/13/18) and data processing to obtain the Normalized Difference Vegetation Index (NDVI), Surface Temperature (Ts) and Soil Moisture Index (IUS) were performed using Qgis software. In addition, the time series of the annual precipitation of the municipality of Floresta / PE were classified into dry, normal or rainy years, using the quantile method and the monthly precipitation analysis in relation to the climatological normals from 2015 to 2018, using the data obtained from the APAC website. Finally, the point cloud distribution was distributed between IUSxNDVI and IUSxTs. The results showed that the classification from 1999 to 2018 eight years behaved as normal and six years as dry and rainy, where the values for dry years ranged from 149.50 to 349.20mm, the normal ones from 392.70 to 538.1mm and the rainy ones from 559.10 to 750.60mm. For the years 2015, 2016, 2017 and 2018, the accumulated monthly precipitation values were 223.00mm, 395.10mm, 399.20mm and 653.50mm, respectively. The NDVI values in exposed soil plus thin vegetation ranged from 0.124 to 0.323, in arboreal vegetation between 0.351 to 0.649 and in surrounding water bodies -0.072. At surface temperature, minimum values of 23.80 ° C and maximum values of 44.93 ° C were found. For the soil moisture index, 0.240 were found in exposed soil and thin vegetation, 0.417 to 0.746 in tree vegetation and 0.821 in water. In the distribution of the IUS point cloud with NDVI and Ts biophysical parameters, it was observed that 2015 and 2016 had no pixels in the negative NDVI region and Ts pixels were above 40 ° C. On the other hand, in 2017 and 2018 due to the presence of water there was a reduction in Ts, where most pixels were below 40 ° C. The Quantis method allowed to identify in an interval of twenty years an irregular pattern between years classified as dry, normal and rainy. The monthly precipitation of the four showed great variability in relation to the climatological normal of the municipality. The NDVI allowed to identify the presence of water bodies, exposed soil with herbaceous and arboreal vegetation in the farm Itapemirim / PE. The achievement of low surface temperature values on the imaged dates is associated with high NDVI and soil moisture values. IUS values were lower in exposed soil and more expressive in water and under tree vegetation, due to the rapid response of dry tropical forests during the rainy season during the imaging date. Point cloud distribution showed increasing behavior for IUSxNDVI and inverse for IUSxTs.