Global Mapping Function (GMF): A new empirical mapping function based on numerical weather model data

Troposphere mapping functions are used in the analyses of Global Positioning System and Very Long Baseline Interferometry observations to map a priori zenith hydrostatic and wet delays to any elevation angle. Most analysts use the Niell Mapping Function (NMF) whose coefficients are determined from site coordinates and the day of year. Here we present the Global Mapping Function (GMF), based on data from the global ECMWF numerical weather model. The coefficients of the GMF were obtained from an expansion of the Vienna Mapping Function (VMF1) parameters into spherical harmonics on a global grid. Similar to NMF, the values of the coefficients require only the station coordinates and the day of year as input parameters. Compared to the 6-hourly values of the VMF1 a slight degradation in short-term precision occurs using the empirical GMF. However, the regional height biases and annual errors of NMF are significantly reduced with GMF

Results of the Australian geodetic VLBI experiment

The 250-2500 km baseline vectors between radio telescopes located at Tidbinbilla (DSS43) near Canberra, Parkes, Fleurs (X3) near Sydney, Hobart and Alice Springs were determined from radio interferometric observations of extragalactic sources. The observations were made during two 24-hour sessions on 26 April and 3 May 1982, and one 12-hour night-time session on 28 April 1982. The 275 km Tidbinbilla - Parkes baseline was measured with an accuracy of plus or minus 6 cm. The remaining baselines were measured with accuracies ranging from 15 cm to 6 m. The higher accuracies were achieved for the better instrumented sites of Tidbinbilla, Parkes and Fleurs. The data reduction technique and results of the experiment are discussed

Studies of Error Sources in Geodetic VLBI

Achieving the goal of millimeter uncertainty in three dimensional geodetic positioning on a global scale requires significant improvement in the precision and accuracy of both random and systematic error sources. For this investigation we proposed to study errors due to instrumentation in Very Long Base Interferometry (VLBI) and due to the atmosphere. After the inception of this work we expanded the scope to include assessment of error sources in GPS measurements, especially as they affect the vertical component of site position and the measurement of water vapor in the atmosphere. The atmosphere correction 'improvements described below are of benefit to both GPS and VLBI

Acerca de números palindrómicos o capicúas

El propósito de esta nota es hacer algunos comentarios y observaciones acerca de un tipo particular de números naturales que son considerados por mucha gente como un augurio de buena suerte; nos referimos por supuesto a los números capicúas o palindrómicos

Mobile radio interferometric geodetic systems

Operation of the Astronomical Radio Interferometric Earth Surveying (ARIES) in a proof of concept mode is discussed. Accuracy demonstrations over a short baseline, a 180 km baseline, and a 380 km baseline are documented. Use of ARIES in the Sea Slope Experiment of the National Geodetic Survey to study the apparent differences between oceanographic and geodetic leveling determinations of the sea surface along the Pacific Coast is described. Intergration of the NAVSTAR Global Positioning System and a concept called SERIES (Satellite Emission Radio Interferometric Earth Surveying) is briefly reviewed

Pioneer 10 Doppler data analysis: disentangling periodic and secular anomalies

This paper reports the results of an analysis of the Doppler tracking data of Pioneer probes which did show an anomalous behaviour. A software has been developed for the sake of performing a data analysis as independent as possible from that of J. Anderson et al. \citep{anderson}, using the same data set. A first output of this new analysis is a confirmation of the existence of a secular anomaly with an amplitude about 0.8 nms$^{-2}$ compatible with that reported by Anderson et al. A second output is the study of periodic variations of the anomaly, which we characterize as functions of the azimuthal angle $\varphi$ defined by the directions Sun-Earth Antenna and Sun-Pioneer. An improved fit is obtained with periodic variations written as the sum of a secular acceleration and two sinusoids of the angles $\varphi$ and $2\varphi$. The tests which have been performed for assessing the robustness of these results are presented.Comment: 13 pages, 6 figures, minor amendment

Análisis de componentes principales sobre datos multiespectrales “Landsat-TM” e interpretación de cubiertas vegetales en las Sierras de Tejeda y Almijara

The simultaneous consideration of all reflectance bands during image processing of multiespectral, remotely-sensed data, usually involves a very large volume of data to handle. However, this increase in data volume is not followed by a similar increment in the volume of additional information that is accounted for, which is due to the existence of a very high correlation between reflectance bands. In this paper we report the results of applying a multivariate statistical tool (Principal Component Analysis, PCA) to the first four reflectance bands of a LANDSAT «Thematic Mapper» image of Sierra de Tejeda and Sierra de Almijara (Southern Spain). The aim of this analysis was to achieve a reduction in the volume of data to handle during image processing while avoiding a significant loss of information. The first two principal components resulting from the analysis accounted for more than 99% of the total variance in the original data set. The image obtained through the first principal component transform could be interpreted as a weighed-sum image of all reflectance bands (thus similar to a black and white panchromatic photograph with an extension into the infrared wavelength). This image showed optimum feasibility for the interpretation of geological, hydrological and topographic features of the study area. The second principal component transform was able to extract the «green» signal of the vegetation canopy from the complex set of multiespectral data. Relief features (i.e., areas of shadow in north-facing slopes versus well-illuminated, south-facing slopes) did not appear in the resulting image (these features had already been accounted for by the first principal component), which is an advantage when studying vegetation cover in areas with steep relief. A strong possitive correlation was found between the second PCA image and those resulting from the application of standard spectral vegetation indexes (RVI and NDVI). The initial assesment of the images has shown that severe deaforestation is undergoing in the area. About 30% of the study area was occupied by bare soils. This figure went up to 85% if areas with scattered vegetation were also included. Multivariate analysis has confirmed as a valuable tool for the interpretation of multiespectral satellite data from the study area. Eventually, the obtention of a principal component transform based on the selective sampling of appropiate subsets of pixels from the area would provide of algorithms that applied to the entire set in multitemporal images could, for instance, be used to monitor long-term and large-scale deaforestation processes in the region.La consideración simultánea de todas las bandas de reflectancia en el análisis de imágenes multiespectrales teledetectadas, representa un incremento en el volumen de datos a procesar proporcionalmente mucho mayor que la ganancia real de información que se consigue, lo que se debe a la elevada correlación existente entre aquéllas. En este trabajo se aplica un análisis de componentes principales a datos multiespectrales Landsat TM de las Sierras de Tejeda y Almijara, con el objeto de sumarizar los mismos sin una pérdida significativa de información. Los dos primeros componentes principales obtenidos recogieron más del 99% de la varianza total original. La imagen que se obtuvo a partir del primer componente principal representaba, aproximadamente, una suma ponderada de todas las intensidades de reflectancia en las distintas bandas consideradas (análoga, por tanto, a una fotografía en blanco y negro con una extensión en el infrarrojo) y mostró una interpretabilidad óptima para aspectos de topografía-relieve, red de drenaje y tipos litológicos. La imagen resultante del segundo componente principal (ya sin efecto de relieve) mostró la intensidad de señal "verde" del dosel vegetal y se correlacionaba significativamente con las obtenidas de la aplicación de índices espectrales de vegetación (RVI, NDVI) a los datos originales. El análisis preliminar de las imagenes indica problemas de deforestación grave en la zona (casi un 30% de la superficie con suelos desnudos, y hasta un 85% si se incluyen areas con vegetación dispersa). El análisis multivariado se ha confirmado como una herramienta útil para la interpretación de imágenes teledetectadas de la zona de estudio. Eventualmente, la obtención de la transformación de componentes principales por medio de un muestreo selectivo, proveería de algoritmos de transformación para los datos multiespectrales con los que se podría, por ejemplo, hacer un seguimiento de cambios en procesos tales como la deforestación