RECEPTORES DE SINAIS DO SISTEMA GLOBAL DE NAVEGAÇÃO POR SATÉLITE SUBMETIDOS A INTERFERÊNCIAS FÍSICAS

RECEPTORES DE SINAIS DO SISTEMA GLOBAL DE NAVEGAÇÃO POR SATÉLITE SUBMETIDOS A INTERFERÊNCIAS FÍSICAS JOÃO LUIZ JACINTHO1, GABRIEL ARAÚJO E SILVA FERRAZ2, LUCAS SANTOS SANTANA3, PATRÍCIA FERREIRA PONCIANO FERRAZ4 1 Instituto Federal do Norte de Minas Gerais - IFNMG, Campus Araçuaí BR 367, km 278, s/n - Zona Rural, 39600-000, Araçuaí - MG, Brasil. [email protected]. 2 Departamento de Engenharia Agrícola, Universidade Federal de Lavras – UFLA, Aquenta Sol, 3037, 37200900, Lavras - MG, Brasil. [email protected]. 3Departamento de Engenharia Agrícola, Universidade Federal de Lavras – UFLA, Aquenta Sol, 3037, 37200900, Lavras - MG, Brasil. [email protected]. 4 Departamento de Engenharia Agrícola, Universidade Federal de Lavras – UFLA, Aquenta Sol, 3037, 37200900, Lavras - MG, Brasil. [email protected]. RESUMO: Incertezas são encontradas em trabalhos com receptores do Sistemas Global de Navegação por Satélite GNSS. Diante disso, objetivou-se com este estudo investigar a influência de obstáculos físicos nos erros de acurácia e precisão em levantamentos com receptores GNSS e suas aplicações agrícolas. Foram implantados quatros pontos de controle rastreados no modo estático (base) e oito pontos de estudos rastreados no modo cinemático em tempo real (RTK) e Estático Rápido (ER), utilizando um par de receptores GNSS e um par de receptores GNSS-RTK. Os níveis de acurácia e precisão foram avaliados em oito pontos obtidos por rastreios do tipo ER e RTK. Combinados com quatro bases fixas, alocados de três formas: mínima, média e alta interferência física. Pontos provenientes do levantamento RTK, apresentaram diferenças na ordem de milímetros a centímetros, quando comparados às coordenadas obtidas do levantamento (ER). Para os níveis de obstrução, a mínima interferência apresentou erro dentro dos limites estipulados pelo equipamento, a máxima interferência apresentou menor acurácia. O efeito do multipercurso do sinal foi o fator mais determinante para a redução da acurácia das coordenadas dos pontos. Recomenda-se a aplicação do levantamento RTK para trabalhos onde a precisão das coordenadas seja mais relevante que a acurácia. Palavras-chaves: Geodésia, levantamento planialtimétrico, acurácia, precisão. GLOBAL SATELLITE NAVIGATION SYSTEM RECEIVERS SUBMITTED TO PHYSICAL INTERFERENCES ABSTRACT: Uncertainties are found in works with Global Navigation Satellite System receivers (GNSS). Therefore, this study aimed to investigate influence physical obstacles on accuracy and precision errors in surveys with GNSS receivers and their agricultural applications. Four control points tracked in static (base) mode and eight study points tracked in a kinematic mode in real-time (RTK) and Fast Static (ER) were implemented, using a pair of GNSS receivers and pair of GNSS-RTK receivers. Accuracy levels and precision were evaluated at eight points obtained by ER and RTK, combined with four fixed bases, allocated in three ways: minimal, medium and high physical interference. RTK survey points showed differences order millimeters to centimeters when compared to the survey (ER) coordinates. The obstruction levels, interference minimum, had an error within limits stipulated by equipment, interference maximum showed low accuracy. RTK survey is recommended for jobs where the coordinate precision is more relevant than accuracy. Keywords: Geodesy, planialtimetric survey, accuracy, precision.

Polarized-Light Interferometry of Calcium Carbonate Deposition in Moss from a Waterfall on the Niagara Escarpment

Deposition of calcium carbonate from groundwater was examined on a moss, Didymodon tophaceus, from a Niagara Escarpment waterfall. A spectrophotometer on a polarizing microscope was used for interferometry. A second-order blue interference with an interference minimum around 620 nm was found when moss cell spaces were fully calcified. Filled cell spaces were often surrounded by empty cell spaces. Complete calcification of whole leaflets resulted in progressively higher orders of interference colors and a positive shift in interference minima. Calcified leaflets finally became cemented together, but each retained a weak extinction when rotated. Small calcareous spherulites (mean diameter 15.7 ± 2.1 μm) were found between leaflets. Spherulites exhibited first-order white interference with a Maltese cross that rotated when the polarizer and analyzer were rotated in tandem. A Nikitin-Berek compensator was tilted at 5.5° to give an interference minimum at 600 nm in the optical axis. Quadrants of spherulites with radii more or less in line with the tilting axis of the compensator had lower (P < 0.001) interference minima (535 ± 27 nm) than quadrants with radii more or less perpendicular to the compensator (659 ± 15 nm), thus indicating a radial internal structure. Spherulites were tentatively identified as vaterite.

Intercollisional Interference in the S Lines of H2–He Mixtures

Further experimental results on the pressure induced spectrum of normal H2–He in the region of the S(1) branch of the fundamental band are presented. These results show a well-defined minimum at the transition frequency of the free molecule. The S line is found to be the sum of two components. One of these is of essentially the same nature as the Q branch and should therefore show a pronounced intercollisional interference minimum. The second component shows the usual quadrupolar line shape without a minimum. Finally, a value for the strength parameter characterizing the short range component of the induced dipole moment is determined.