ABSTRACT
Plant community succession is generally approached with phytosociological methods, but field surveys are time-consuming, expensive, and limited to several of sites. Remote sensing offers an efficient and economical way to analyze vegetation on large extensions and in inaccessible areas. Most studies addressing remote sensing and tree community succession refer to forest physiognomies. We investigated whether structural changes that occur in non-forest physiognomies are identified by multispectral sensor images (OLI-Landsat). Thirteen 0.1-ha plots were set up in Caatinga fragments aging 10-15, 20-25, 30-35, 40-45 and >50 years to calculate the total density of individuals (TD), mean canopy height (H), total basal area (G) and total aboveground biomass (AGB). We performed correlation analyses between these structural descriptors and eight remote sensing variables (reflectance data and spectral indices) obtained from Landsat images at the end of the rainy season and during the dry season. Blue and short-wave infrared reflectances were negatively correlated with mean height, basal area and biomass, regardless of the analyzed scene (coefficients between -0.58 and -0.79). The litter layer (a non-photosynthetic vegetation component) and the soil exposure are important factors influencing the spectral data.
Subject(s)
Forests , Trees , Humans , BiomassABSTRACT
Utilizar inversores no controle de vazão de sistemas de bombeamento por meio da variação de sua velocidade pode ter uma maior viabilidade, caso o custo de sensores seja minimizado. Este trabalho investiga, por intermédio de análise multivariada, uma variável adequada ao pseudocontrole da vazão de um sistema de irrigação que economize o uso de sensores e simplifique o sistema de controle. Uma bancada de ensaio para coleta dados foi montada no laboratório e os dados foram processados no Statistical Package for the Social Sciences (SPSS). A análise de agrupamento hierárquico utilizando o método de Ward com base na distância euclidiana quadrática mostrou um grupo composto de quatro variáveis, estando presente nesse grupo a vazão, voltas no registro, altura do nível de água da calha parshall e a corrente elétrica, indicativo de que a corrente elétrica pode ser usada para o pseudocontrole, pois o inversor mede essa variável. A análise fatorial também indicou uma forte correlação da corrente elétrica com a vazão do sistema. A pressão foi o parâmetro da primeira componente da análise fatorial que apresentou a maior correlação com a vazão, no entanto o uso dessa variável para o controle automático demanda o uso de sensores.
Using inverters to control flow of pumping systems by means of changes in speed may be more viable if the cost of sensors is minimized. This work investigates through multivariate analysis an adequate variable for the pseudo control of the flow of an irrigation system that saves the use of sensors and simplifies the control system. A bench test to collect data was mounted in the laboratory and the data were processed using Statistical Package for the Social Sciences (SPSS). The hierarchical cluster analysis using the Ward method based on the squared Euclidean distance showed a group composed of four variables, being present in that group flow, turns on the register, water level of the Parshall weir and electric current, indicating that the electric current can be used for pseudo control because the inverter measures this variable. The factor analysis also indicated a strong correlation between the electric current and the system flow. In the first Principal Component, the pressure showed the highest correlation with the flow, although the use of this variable for automated control requires the use of sensors.
