Distanciometría Laser a Satélite (SLR)

En el marco de las actividades programadas para la Escuela Regional “Nuevas técnicas geodésicas para América Latina y el Caribe” , realizada entre el 5 y el 10 de abril de 2021, se dictó un módulo teórico-práctico acerca de la técnica Satellite Laser Ranging (SLR). El programa incluyó la puesta en contexto de la técnica SLR junto a las demás técnicas fundamentales de la Geodesia Espacial (es decir, GNSS, VLBI y DORIS) así como la descripción detallada de los parámetros que permite observar (incluyendo la longitud del día, las órbitas satelitales, las coordenadas de las estaciones, las coordenadas del geocentro, el campo de gravedad, etc.). Así mismo, se desarrolló en profundidad la aplicación del método de cuadrados mínimos a la estimación de parámetros de interés a partir de observaciones multianuales SLR, incluyendo la técnica de apilado de ecuaciones normales, la introducción de condicionamientos absolutos y relativos a los valores a priori y la preeliminación de parámetros al nivel de las ecuaciones normales a fin de optimizar los tiempos de cómputo. Se realizó una detallada descripción de la técnica SLR, incluyendo su ecuación de observación, el segmento espacial específico (LAGEOS, Etalon, Starlette & Stella, GNSS, etc.) y el segmento terrestre (las estaciones de rastreo).Facultad de Ciencias Astronómicas y Geofísica

Near-real-time VTEC maps: new contribution for Latin America Space Weather

The development of regional services able to provide ionospheric vertical total electron content (VTEC) maps and ionospheric indexes with a high spatial resolution, and in near-real-time, are of great importance for both civilian applications and the research community. We provide here the methodologies, and an assessment, of such a system. It relies on the public Global Navigational Satellite Systems (GNSS) infrastructure in South America, incorporates data from multiple constellations (currently GPS, GLONASS, Galileo and BeiDou), employs multiple frequencies, and produces continental wide VTEC maps with a latency of just a few minutes. To assess the ability of our system to model the ionospheric behavior we performed a yearround intercomparison between our near-real-time regional VTEC maps, and VTEC maps of veri ed quality produced by several referent analysis centers, resulting in mean biases lower than 1 TEC units (TECU). Also, the evaluation of our products against direct and independent GNSS-based slant TEC measurements shows RMS values better than 1 TECU. In turn, ionospheric weather W-index maps were generated, for calm and disturbed geomagnetic scenarios, solely employing our quality veri ed VTEC maps. The spatial representation of these W-index maps re ects the state of the ionosphere, with a resolution of 0:5 0:5 degrees. Finally, we conclude that our products, computed every 15 minutes, do provide an excellent spatial representation of the regional TEC, and are able to provide the bases for the possible computation of ionospheric W-index maps, also in near-real-time.Facultad de Ciencias Astronómicas y Geofísica

Near-real-time VTEC maps: New contribution for Latin America Space Weather

The development of regional services able to provide ionospheric vertical total electron content (VTEC) maps and ionospheric indexes with a high spatial resolution, and in near-real-time, are of great importance for both civilian applications and the research community. We provide here the methodologies, and an assessment, of such a system. It relies on the public Global Navigational Satellite Systems (GNSS) infrastructure in South America, incorporates data from multiple constellations (currently GPS, GLONASS, Galileo and BeiDou), employs multiple frequencies, and produces continental wide VTEC maps with a latency of just a few minutes. To assess the ability of our system to model the ionospheric behavior we performed a year-round intercomparison between our near-real-time regional VTEC maps, and VTEC maps of verified quality produced by several referent analysis centers, resulting in mean biases lower than 1 TEC units (TECU). Also, the evaluation of our products against direct and independent GNSS-based slant TEC measurements shows RMS values better than 1 TECU. In turn, ionospheric weather W-index maps were generated, for calm and disturbed geomagnetic scenarios, solely employing our quality verified VTEC maps. The spatial representation of these W-index maps reflects the state of the ionosphere, with a resolution of 0.5×0.5 degrees. Finally, we conclude that our products, computed every 15 min, do provide an excellent spatial representation of the regional TEC, and are able to provide the bases for the possible computation of ionospheric W-index maps, also in near-real-time.Fil: Mendoza, Luciano Pedro Oscar. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Meza, Amalia Margarita. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Aragón Paz, Juan Manuel. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentin

Implementation of a GNSS meteorological model to the estimation of the Haines Index

Background: The objective of this study was to look for a replacement to the radiosonde measurements that are necessary for the construction of an index of potential wildfire severity (i.e., Haines Index, HI) in areas of South America that have had few to no radiosonde launches. To this end, we tested the application of GPT2w, an empirical model originally developed for Global Navigation Satellite System (GNSS) meteorology. By using the GPT2w model, and starting from measured surface meteorological data (air pressure, temperature, and relative humidity), estimators of air temperature and dew-point air temperature at different pressure levels were generated. The selected testing area was a region of South America that included most of the Río de la Plata drainage basin, along with two hazardous areas: Sierras de Córdoba in Argentina and Serra da Canastra in Brazil. This region was chosen due to the availability of the radiosonde launches required for comparison during 2016. Results: To characterize the regional performance of HI, we used data from the European Centre for Medium-Range Weather Forecast’s (ECMWF) reanalysis model (ERA Interim; Dee et al., Quarterly Journal of the Royal Meteorological Society 137: 553–597, 2011) for the period 2000 to 2016. A statistical analysis of the differences between the simulated HI from GPT2w (HI_GPT2w) and the HI values derived from radiosonde measurements (HI_R) was performed. The results showed that HI_GPT2w reproduced HI_R values about 50% of the time, most accurately for low-severity HI values (2 to 3, on a scale of 2 to 6). In general, HI_GPT2w exhibited an underestimation of HI that increased as the index value increased. We analyzed how this underestimation affected the different HI variants calculated. To this end, we recall that each HI variant results from the sum of the stability and moisture terms. The stability term resulted from the temperature difference at different pressure levels while the moisture term is represented by the dew-point depression. Thus, the pressure level limits in the stability term define the HI variant. In this study, we used the Low-variant HI (950 and 850 hPa) and the Mid-variant HI (850 and 700 hPa). If we analyze this underestimation according to the HI variants, the moisture term is responsible for the Low variant underestimation and the stability term is responsible for the Mid variant. Conclusion: The simple application of GPT2w to extrapolate the vertical values of temperature and its dew-point depression is not enough to reproduce the Haines Index as it was measured from radiosonde measurements. Nevertheless, an improved application of GPT2w and the extrapolated saturation water vapor pressure by using the Integrated Water Vapor from Global Navigation Satellite System (GNSS-IWV) values could improve the results.Fil: Fernandez, Laura Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Cs.astronomicas y Geofisicas. Laboratorio Maggia; ArgentinaFil: Aragón Paz, Juan Manuel. Universidad Nacional de la Plata. Facultad de Cs.astronomicas y Geofisicas. Laboratorio Maggia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Meza, Amalia Margarita. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Cs.astronomicas y Geofisicas. Laboratorio Maggia; ArgentinaFil: Mendoza, Luciano Pedro Oscar. Universidad Nacional de la Plata. Facultad de Cs.astronomicas y Geofisicas. Laboratorio Maggia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Diurnal variation of precipitable water vapor over Central and South America

Annual and seasonal diurnal precipitable water vapor (PWV) variations over Central and South America are analyzed for the period 2007–2013. PWV values were obtained from Global Navigation Satellite Systems (GNSS) observations of sixty-nine GNSS tracking stations. Histograms by climate categories show that PWV values for temperate, polar and cold dry climate have a positive skewed distribution and for tropical climates (except for monsoon subtype) show a negative skewed distribution. The diurnal PWV and surface temperatures (T) anomaly datasets are analyzed by using principal components analysis (PCA). The first two modes represent more than 90% of the PWV variability. The first PCA mode of PWV variability shows a maximum amplitude value in the late afternoon few hours later than the respective values for surface temperature (T), therefore the temperature and the surface conditions (to yield evaporation) could be the main agents producing this variability; PWV variability in inland stations are mainly represented by this mode. The second mode of PWV variability shows a maximum amplitude at midnight, a possible explanation of this behavior is the effect of the sea/valley breeze. The coastal and valley stations are affected by this mode in most cases. Finally, the “undefined” stations, surrounded by several water bodies, are mainly affected by the second mode with negative eigenvectors. In the seasonal analysis, both the undefined and valley stations constitute the main cases that show a sea or valley breeze only during some seasons, while the rest of the year they present a behavior according to their temperature and the surface conditions. As a result, the PCA proves to be a useful numerical tool to represent the main sub-daily PWV variabilities.Fil: Meza, Amalia Margarita. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Laboratorio Maggia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Mendoza, Luciano Pedro Oscar. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Laboratorio Maggia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Natali, Maria Paula. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Laboratorio Maggia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Bianchi, Clara Eugenia. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Laboratorio Maggia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Fernandez, Laura Isabel. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Laboratorio Maggia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentin

A Multi-GNSS, Multifrequency, and Near-Real-Time Ionospheric TEC Monitoring System for South America

Taking advantage of the public Global Navigational Satellite Systems (GNSS) infrastructure in South America, an operational monitoring system for the total electron content (TEC) in the ionosphere has been developed. It incorporates data in near real time, from more than 90 GNSS satellites tracked by more than 200 ground stations. In turn, the system produces every 15 min a snapshot, that is a map, of the current state of the regional ionosphere, which is immediately available online. These maps could be employed, for example, to augment positioning with single-frequency GNSS receivers. They could also be combined with similar products in order to obtain weighted and reliable regional TEC maps, even in near real time. Most importantly, these products could be employed as data input in space environment forecasting and nowcasting models, given their very short latency of just a few minutes. In order to assess the response of the whole system to severe geomagnetic disturbances, the performance of the whole monitoring system during an actual geomagnetic storm has been investigated. The results suggest that the near-real-time system should be quite capable to monitor the regional TEC at a high temporal rate even under such conditions.Facultad de Ciencias Astronómicas y GeofísicasConsejo Nacional de Investigaciones Científicas y Técnica

Sistema GPS de guiado autónomo corregido

La Agricultura de Precisión (AP) utiliza un conjunto de herramientas técnicas e informáticas a fin de optimizar el manejo específico del sitio de cultivo. Estas herramientas incluyen software SIG y estadístico, sensores remotos, registros en el terreno, la aplicación controlada de agroquímicos y sistemas para el guiado preciso de la maquinaria agrícola. Se desarrolla aquí un software original para guiado autónomo que satisface los requerimientos de precisión para algunas aplicaciones de la AP.The Precision Agriculture (PA) uses many technical and computational tools to optimize the site-specific management of the land. These tools include GIS and statistical software, remote sensors instruments, records on the field, variable agrochemicals dose, and precise guiding systems. We describe here an original software for an autonomous guiding system which satisfies many PA requirements.Material digitalizado en SEDICI gracias a la colaboración de la Facultad de Ciencias Astronómicas y Geofísicas (UNLP).Asociación Argentina de Geofísicos y Geodesta

Aplicación del modelo de transformación de alturas de la Provincia de Buenos Aires, en el partido de General Madariaga

Durante el año 2005 se repitió una experiencia realizada en el partido de Gral. Lavalie (Perdomo etal., 2004), que consistió en el relevamiento de cotas a lo largo de toda la red de caminos rurales del partido y el posicionamiento de alcantarillas, puentes y cruces de agua. La metodología empleada consistió en el posicionamiento GPS cinemático con estaciones de control vinculadas a la red GEOBA98. De esta manera, se recorrieron unos 600 km. obteniendo cotas para unos 20000 puntos y 485 obras de arte (alcantarillas y puentes) en 5 días de campaña. Las alturas así obtenidas son elipsóidicas. La aplicación del modelo de transformación de alturas FCAG98 (Perdomo y Del Cogliano, 1999) sobre este conjunto de puntos permitió obtener una primera aproximación de las cotas sobre el nivel medio del mar. En esta oportunidad, se realizó un control del modelo existente eligiendo como puntos de control cuatro mojones IGM con cota conocida ubicados en zonas de borde del partido. En cada uno de ellos se puede estimar la ondulación del geoide (N) como la diferencia entre la altura elipsóidica y la cota IGM y comparar este resultado con el producido por el modelo existente (FCAG98). Dos de los cuatro puntos mostraron desvíos de 4 y 9 cm. Se incorporó ambos puntos a un nuevo modelo zonal mejorando la calidad del modelo FCAG98 en dicha región. Con esta corrección se estima que la transformación de alturas elipsoidales en alturas sobre el nivel medio del mar (cotas) en la zona es mejor que 5 cm. Los relevamientos se realizaron con una antena sujetada a un vehículo en movimiento. En consecuencia, es necesario considerar los errores que esto introduce en la realización de cada punto observado. Para obtener una estimación objetiva se tuvieron en cuenta 210 puntos de control en las cuales se midió dos o más veces en forma independiente y desde distintas bases. Los resultados permiten estimar errores típicos del orden de los 6 cm (desviación estándar).During 2005, an experience previously developed in the Gral. Lavalie district (Perdomo et al., 2004) was carried out. It consisted in surveying of heights on the rural roads and positioning of bridges and water flows. Kinematic GPS was used with control stations related to Buenos Aires GPS network GEOBA98. In this way, almost 600 km were surveyed and heights were obtained for about 20000 points, 485 bridges and waters flows, during a survey of only 5 days. The heightsw were ellipsoidal. The application ofthe height transformation model FCAG98 (Perdomo y Del Cogliano, 1999) on these points allowed to obtein a first approximation to mean sea level heights for all of them. In this case, the existing model was monitored using four IGM pillars with known heights as control points. These points are located on the limits ofthe district. In each ofthem, the geoid undulation (N) is calculated as the difference between the ellipsoidal height and the IGM mean sea level heigh and these results are compared with the predicted values from the existing model (FCAG98). Two ofthe points showed discrepancies of4 and 9 cm. So both points were incorporated to a new local model improving the FCAG98 model for this region. With these local corrections, the height transformations should be at least more accurate than 5 cm. The survey was run with an antenna located on a moving truck. This procedure introduces new errors. To monitor them 210 points were measured twice, during independent trajectories and using different bases. The comparison of the heights for these 210 points is typically 6 cm (standard deviation).Material digitalizado en SEDICI gracias a la colaboración de la Facultad de Ciencias Astronómicas y Geofísicas (UNLP).Asociación Argentina de Geofísicos y Geodesta

Multi-year GNSS monitoring of atmospheric IWV over Central and South America for climate studies

Atmospheric water vapour has been acknowledged as an essential climate variable. Weather prediction and hazard assessment systems benefit from real-time observations, whereas long-term records contribute to climate studies. Nowadays, ground-based global navigation satellite system (GNSS) products have become widely employed, complementing satellite observations over the oceans. Although the past decade has seen a significant development of the GNSS infrastructure in Central and South America, its potential for atmospheric water vapour monitoring has not been fully exploited. With this in mind, we have performed a regional, 7-year-long and homogeneous analysis, comprising 136 GNSS tracking stations, obtaining high-rate and continuous observations of column-integrated water vapour and troposphere zenith total delay. As a preliminary application for this data set, we have estimated local water vapour trends, their significance, and their relation with specific climate regimes. We have found evidence of drying at temperate regions in South America, at a rate of about 2 % per decade, while a slow moistening of the troposphere over tropical regions is also weakly suggested by our results. Furthermore, we have assessed the regional performance of the empirical model GPT2w to blindly estimate troposphere delays. The model reproduces the observed mean delays fairly well, including their annual and semi-annual variations. Nevertheless, a long-term evaluation has shown systematical biases, up to 20 mm, probably inherited from the underlying atmospheric reanalysis. Additionally, the complete data set has been made openly available as supplementary material.Fil: Bianchi, Clara Eugenia. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Mendoza, Luciano Pedro Oscar. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Fernandez, Laura Isabel. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Natali, Maria Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Departamento de Georreferenciación Satelitaria; ArgentinaFil: Meza, Amalia Margarita. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Área Física Teórica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Moirano, Juan Francisco. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentin

Implementation of a GNSS meteorological model to the estimation of the Haines Index

Background: The objective of this study was to look for a replacement to the radiosonde measurements that are necessary for the construction of an index of potential wildfire severity (i.e., Haines Index, HI) in areas of South America that have had few to no radiosonde launches. To this end, we tested the application of GPT2w, an empirical model originally developed for Global Navigation Satellite System (GNSS) meteorology. By using the GPT2w model, and starting from measured surface meteorological data (air pressure, temperature, and relative humidity), estimators of air temperature and dew-point air temperature at different pressure levels were generated. The selected testing area was a region of South America that included most of the Río de la Plata drainage basin, along with two hazardous areas: Sierras de Córdoba in Argentina and Serra da Canastra in Brazil. This region was chosen due to the availability of the radiosonde launches required for comparison during 2016. Results: To characterize the regional performance of HI, we used data from the European Centre for Medium-Range Weather Forecast’s (ECMWF) reanalysis model (ERA Interim; Dee et al., Quarterly Journal of the Royal Meteorological Society 137: 553–597, 2011) for the period 2000 to 2016. A statistical analysis of the differences between the simulated HI from GPT2w (HI_GPT2w) and the HI values derived from radiosonde measurements (HI_R) was performed. The results showed that HI_GPT2w reproduced HI_R values about 50% of the time, most accurately for lowseverity HI values (2 to 3, on a scale of 2 to 6). In general, HI_GPT2w exhibited an underestimation of HI that increased as the index value increased. We analyzed how this underestimation affected the different HI variants calculated. To this end, we recall that each HI variant results from the sum of the stability and moisture terms. The stability term resulted from the temperature difference at different pressure levels while the moisture term is represented by the dew-point depression. Thus, the pressure level limits in the stability term define the HI variant. In this study, we used the Low-variant HI (950 and 850 hPa) and the Mid-variant HI (850 and 700 hPa). If we analyze this underestimation according to the HI variants, the moisture term is responsible for the Low variant underestimation and the stability term is responsible for the Mid variant. Conclusion: The simple application of GPT2w to extrapolate the vertical values of temperature and its dew-point depression is not enough to reproduce the Haines Index as it was measured from radiosonde measurements. Nevertheless, an improved application of GPT2w and the extrapolated saturation water vapor pressure by using the Integrated Water Vapor from Global Navigation Satellite System (GNSS-IWV) values could improve the resultsLaboratorio de Meteorología espacial, Atmósfera terrestre, Geodesia, Geodinámica, diseño de Instrumental y Astrometrí