Análise espaço-temporal da reflectância e estimativa de sedimentos em suspensão no reservatório Epitácio Pessoa

Abstract

Artificial reservoirs of water - regionally known as açudes (dams) - are essential sources for the supply of water, especially in semiarid climate regions, wich are susceptible to shortages, as is the case in the Cariri region. The Açude Epitácio Pessoa (or Boqueirão) is notably relevant in socio-economic and environmental context, supplying around a million inhabitants of 19 cities and 3 districts of the Paraíba state. Understand the quality of water requires robust and continuous monitoring, and usually is inconsonant with reality, creating spatial and temporal information gaps; these are shortages that are increasingly being overcome with the use of remote sensing and GIS technologies. In view of the above, the research objective was to analyse the space-time dynamic of the surface reflectance of water and to estimate the concentration of the variable Total Suspended Solids (TSS) in the Epitácio Pessoa Dam (PB) throughout 17 years (2000-2016), with the proposal of a methodology fitted to the conditions of the semiarid. Therefore, MOD09Q1 products of the MODIS/Terra sensor of 250 m spatial resolution were utilized, composition 8-days, for the red bands (RED, 645 nm) and approximated infrared (NIR, 859 nm), as well as complementary data to make the extraction of data and the removal of cloudiness in the historical series by means of programming. The main results, the reflectance variable demonstrated sensitivity to alterations in the pluviometric regime in the temporal perspective; the values of reflectance for the NIR band were almost always higher than those of the RED and when the opposite (2004 and 2008) indicating a alteration of the type of sediment as a reflex of the abrupt change of volume in the dam; the spatial interpolation of the data points to reduction of the reflectance of the entrance of the reservoir to the barrage for the majority of the years, notably for the RED band; among the three estimation models of SST - that of Robert al. (2017)/M3, a priori, was what demonstrated the highest performance in relation to the annual temporal analysis, varying between 270961 mg/L, with a correlation of 0,57 with data observed from SUDEMA. Regarding the to the proposed methodology, it demonstrated promising performance in the extraction of data in the temporal analysis and partially satisfactory performance in the spatial analysis due to the geometric conditions of the dam and considerable removal of pixels (longitudinal profile) in the face of the high coverage of clouds in some pixels, the comparison between the average values of reflectance by pixels shown in two distinct paths of extraction (longitudinal profile and sampling points) indicated strong correlation (r > 0,93).