ICESat Lidar and Global Digital Elevation Models: Application to DESDynI

Geodetic control is extremely important in the production and quality control of topographic data sets, enabling elevation results to be referenced to an absolute vertical datum. Global topographic data with improved geodetic accuracy achieved using global Ground Control Point (GCP) databases enable more accurate characterization of land topography and its change related to solid Earth processes, natural hazards and climate change. The multiple-beam lidar instrument that will be part of the NASA Deformation, Ecosystem Structure and Dynamics of Ice (DESDynI) mission will provide a comprehensive, global data set that can be used for geodetic control purposes. Here we illustrate that potential using data acquired by NASA's Ice, Cloud and land Elevation Satellite (ICEsat) that has acquired single-beam, globally distributed laser altimeter profiles (+/-86deg) since February of 2003 [1, 2]. The profiles provide a consistently referenced elevation data set with unprecedented accuracy and quantified measurement errors that can be used to generate GCPs with sub-decimeter vertical accuracy and better than 10 m horizontal accuracy. Like the planned capability for DESDynI, ICESat records a waveform that is the elevation distribution of energy reflected within the laser footprint from vegetation, where present, and the ground where illuminated through gaps in any vegetation cover [3]. The waveform enables assessment of Digital Elevation Models (DEMs) with respect to the highest, centroid, and lowest elevations observed by ICESat and in some cases with respect to the ground identified beneath vegetation cover. Using the ICESat altimetry data we are developing a comprehensive database of consistent, global, geodetic ground control that will enhance the quality of a variety of regional to global DEMs. Here we illustrate the accuracy assessment of the Shuttle Radar Topography Mission (SRTM) DEM produced for Australia, documenting spatially varying elevation biases of several meters in magnitude

ICESat Observations of Topographic Change in the Northern Segment of the 2004 Sumatra-Andaman Islands Earthquake Rupture Zone

The Andaman Islands are located 120 km east of the Sunda trench in the northern quarter of the 1300 km long rupture zone of the 2004 Sumatra-Andaman Islands earthquake inferred from the distribution of aftershocks. Initial field reports indicate that several meters of uplift and up to a meter of submergence occurred on the western and eastern shorelines of the Andaman Islands, respectively, associated with the earthquake (Bilham, 2005). Satellite images also document uplift of western shoreline coral reef platforms above sea level. Body-wave (Ji, 2005; Yamamaka, 2005) and tide-gauge (Ortiz, 2005) slip inversions only resolve coseismic slip in the southern one-third to one-half of the rupture zone. The amount of coseismic slip in the Andaman Islands region is poorly constrained by these inversions. The Ice, Cloud, and land Elevation Satellite (ICESat), a part of the NASA Earth Observing System, is being used to document the spatial pattern of Andaman Islands vertical displacements in order to constrain models of slip distribution in the northern part of the rupture zone. ICESat carries the Geoscience Laser Altimeter System (GLAS) that obtains elevation measurements from 80 m diameter footprints spaced 175 m apart along profiles. For surfaces of low slope, single-footprint absolute elevation and horizontal accuracies of 10 cm and 6 m (1 sigma), respectively, referenced to the ITRF 2002 TOPEX/Poseidon ellipsoid are being obtained. Laser pulse backscatter waveforms enable separation of ground topography and overlying vegetation cover. During each 33-day observing period ICESat acquires three profiles crossing the Andaman Islands. A NNE-SSW oriented track consists of 1600 laser footprints along the western side of North, Middle, and South Andaman Islands and 240 laser footprints across the center of Great Andaman Island. Two NNW-SSE tracks consist of 440 footprints across Middle Andaman Island and 25 footprints across the west side of Sentinel Island. Cloud-free profiles were acquired in the fall of 2003 and 2004. During February-March, 2005 ICESat's precise pointing capability will be used to exactly repeat these three profiles, with a cross-track accuracy of better than 100 m, providing trench- parallel and -perpendicular observations of topographic change of the Andaman Islands that will compliment geodetic field surveys. The observed elevation changes will be compared to models of coseismic deformation associated with the mainshock and large aftershocks in the Andaman Islands region

The Digital Elevation Model Intercomparison eXperiment DEMIX, a community-based approach at global DEM benchmarking

This paper presents an initiative recently launched under the auspices of the Committee on Earth Observation Satellites (CEOS) aiming at providing harmonised terminology and methods, as well as practical guidelines and results allowing the intercomparison of continental or global Digital Elevation Models (DEM). As the work is still ongoing the main purpose of this article is not the dissemination of the outcome but rather to inform the wider community about the initiative, communicate the chosen approach to raise awareness, and attract possible further participants. Nevertheless, some preliminary results are included and an outlook on planned next steps is provided

LAS “LLAVES” PARA FORMAR UN MEJOR INGENIERO AGRONOMO.

La sociedad valora a aquellos profesionales que hacen aportes para la solución de sus problemas. El saber “hacer cosas” y hacerlas bien dignifica la profesión, eleva la autoestima y la autoconfianza de los profesionales. Este trabajo refleja un estudio retrospectivo de 25 años de docencia en donde he buscado la excelencia en la docencia, tratando de enseñar – haciendo para formar profesionales que la sociedad requiere, con la optimización de recursos, adaptación a los cambios emergentes, y satisfacer las necesidades de los productores de grandes especies y agricultores pequeños y grandes. Por lo que propongo ¨llaves¨ para la reflexión

Hypogammaglobulinaemia secondary to cow-milk allergy in children under 2 years of age

Symptomatic hypogammaglobulinaemia in children younger than 2 years of age was studied to rule out a primary immunodeficiency. Thirty-four patients were referred to the Immunology Service to study the hypogammaglobulinaemia- associated clinical picture. Food allergy was documented in 10 patients by personal and familial history, presence of specific immunoglobulin E (IgE) and elevated total serum IgE levels. Coeliac disease and human immunodeficiency virus infection were also ruled out. Protein loss through stools was assessed by clearance of α1-antitrypsin (AAT). Serum immunoglobulin levels were determined by nephelometry and functional antibodies were studied by enzyme-linked immunosorbent assay. The cellular immune response was assessed by in vitro lymphocyte proliferation in response to mitogens and cell subsets were analysed by flow cytometry. In five patients of the 10 patients we suspected a protein loss through the mucosa. Four of these five patients showed an increased AAT and the other showed an extensive cutaneous lesion. Immunological studies revealed normal antibody function, in vitro lymphoproliferative responses and cell numbers in four of the 5 patients. One patient showed abnormally low numbers of CD4+ T cells as well as a defective proliferative response to mitogens. After diagnosis of cow milk allergy, milk was replaced with infant milk formula containing hydrolysed proteins. Recovery of immunoglobulin values and clinical resolution were achieved. Hypogammaglobulinaemia during early childhood in some children may be secondary to cow milk allergy, and immunoglobulins and cells may leak through the inflamed mucosa. Resolution of symptoms as well as normalization of immunoglobulin values may be easily achieved by avoidance of the offending allergen.Laboratorio de Investigaciones del Sistema Inmun

Compensación reactiva estática de generadores eólicos a inducción

El artículo describe las dificultades de control reactivo encontradas en la aplicación de generadores eólicos a inducción a sistemas eléctricos aislados de media tensión. Un compensador estático compuesto de capacitores desconectables y reactores controlables por tiristores es propuesto como solución. La metodología y programa de diseño paramétrico introducidos, formulados en dominios de variable compleja de Laplace y frecuencia, incluyen un modelo dinámico de impedancia del inductor. La inestabilidad de la ganancia de realimentación del sistema para variaciones del atraso de fase de disparo de tiristores, obligó a la adopción de un algoritmo adaptivo para obtención de las ganancias límite instantáneas por Routh-Hurwitz. Su operación –para una aplicación típica sujeta a respuesta a escalón- se encontró satisfactoria.The article describes the difficulties found in the application of eolic induction generators to isolated midvoltage electrical systems. A static compensator consisting of a combination of thyristor-switched capacitors and thyristorcontrolled reactors is proposed as a solution. The introduced parametric-sizing methodology and program, formulated in Laplace complex-variable and frequency domains, include a dynamic model of the inductor’s impedance. The system proportional-gain feedback instability for changing thyristor-firing phase-lag angles, compels to the use of an adaptivecontrol algorithm drawing instantaneous Routh-Hurwitz limit gains. Its operation –for a typical application subject to a stepresponse test- was found satisfactory.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES

Estabilidad dinámica de generadores eólicos por el trazo inverso de Nyquist

El típico análisis de estabilidad para máquinas sincrónicas por simulación de las excursiones angulares rotóricas post-falla no es directamente aplicable a generadores a inducción por carecer éstos del marco de referencia de ejes d-q. Continuando con un trabajo previo que introduce un diseño de compensador estático al control de tensión terminal de generadores eólicos a inducción, el presente artículo desarrolla un análisis dinámico en dominio frecuencial para evaluar la conectabilidad de estas máquinas a redes sincrónicas. El algoritmo inverso de Nyquist introducido, de aplicación extensiva a generadores sincrónicos e inclusive a motores, confirma la inclinación a inestabilidad de la máquina para mayores impedancias de transferencia. La conexión de un compensador a terminales del generador estabiliza adicionalmente –merced a la resonancia en paralelo de aquél con la línea de interconexión- al sistema con baja impedancia de transferencia.The typical stability analysis for synchronous machines by simulation of post-fault rotor angle excursions is not directly applicable to induction generators for the lack of a d-q axes reference frame in these machines. Following a previous work introducing a static compensator design for the control of wind induction generators’ terminal voltage, the present article develops a dynamic analysis in frequency domain to evaluate the connectivity of these machines to synchronous networks. The introduced inverse-Nyquist algorithm, also applicable to synchronous generators and also to motors, confirms the tendency to instability of the machine for higher transfer impedances. A compensator connected to the wind generator’s terminals introduces additional stability –by its parallel resonance with the interconnection line- to the low transfer-impedance system.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES

Compensación reactiva estática de generadores eólicos a inducción

El artículo describe las dificultades de control reactivo encontradas en la aplicación de generadores eólicos a inducción a sistemas eléctricos aislados de media tensión. Un compensador estático compuesto de capacitores desconectables y reactores controlables por tiristores es propuesto como solución. La metodología y programa de diseño paramétrico introducidos, formulados en dominios de variable compleja de Laplace y frecuencia, incluyen un modelo dinámico de impedancia del inductor. La inestabilidad de la ganancia de realimentación del sistema para variaciones del atraso de fase de disparo de tiristores, obligó a la adopción de un algoritmo adaptivo para obtención de las ganancias límite instantáneas por Routh-Hurwitz. Su operación –para una aplicación típica sujeta a respuesta a escalón- se encontró satisfactoria.The article describes the difficulties found in the application of eolic induction generators to isolated midvoltage electrical systems. A static compensator consisting of a combination of thyristor-switched capacitors and thyristorcontrolled reactors is proposed as a solution. The introduced parametric-sizing methodology and program, formulated in Laplace complex-variable and frequency domains, include a dynamic model of the inductor’s impedance. The system proportional-gain feedback instability for changing thyristor-firing phase-lag angles, compels to the use of an adaptivecontrol algorithm drawing instantaneous Routh-Hurwitz limit gains. Its operation –for a typical application subject to a stepresponse test- was found satisfactory.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES

Compensación reactiva estática de generadores eólicos a inducción

El artículo describe las dificultades de control reactivo encontradas en la aplicación de generadores eólicos a inducción a sistemas eléctricos aislados de media tensión. Un compensador estático compuesto de capacitores desconectables y reactores controlables por tiristores es propuesto como solución. La metodología y programa de diseño paramétrico introducidos, formulados en dominios de variable compleja de Laplace y frecuencia, incluyen un modelo dinámico de impedancia del inductor. La inestabilidad de la ganancia de realimentación del sistema para variaciones del atraso de fase de disparo de tiristores, obligó a la adopción de un algoritmo adaptivo para obtención de las ganancias límite instantáneas por Routh-Hurwitz. Su operación –para una aplicación típica sujeta a respuesta a escalón- se encontró satisfactoria.The article describes the difficulties found in the application of eolic induction generators to isolated midvoltage electrical systems. A static compensator consisting of a combination of thyristor-switched capacitors and thyristorcontrolled reactors is proposed as a solution. The introduced parametric-sizing methodology and program, formulated in Laplace complex-variable and frequency domains, include a dynamic model of the inductor’s impedance. The system proportional-gain feedback instability for changing thyristor-firing phase-lag angles, compels to the use of an adaptivecontrol algorithm drawing instantaneous Routh-Hurwitz limit gains. Its operation –for a typical application subject to a stepresponse test- was found satisfactory.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES

Evaluation of the Global Multi-Resolution Terrain Elevation Data 2010 (GMTED2010) Using ICESat Geodetic Control

Supported by NASA's Earth Surface and Interior (ESI) Program, we are producing a global set of Ground Control Points (GCPs) derived from the Ice, Cloud and land Elevation Satellite (ICESat) altimetry data. From February of 2003, to October of 2009, ICESat obtained nearly global measurements of land topography (+/- 86deg latitudes) with unprecedented accuracy, sampling the Earth's surface at discrete approx.50 m diameter laser footprints spaced 170 m along the altimetry profiles. We apply stringent editing to select the highest quality elevations, and use these GCPs to characterize and quantify spatially varying elevation biases in Digital Elevation Models (DEMs). In this paper, we present an evaluation of the soon to be released Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010). Elevation biases and error statistics have been analyzed as a function of land cover and relief. The GMTED2010 products are a large improvement over previous sources of elevation data at comparable resolutions. RMSEs for all products and terrain conditions are below 7 m and typically are about 4 m. The GMTED2010 products are biased upward with respect to the ICESat GCPs on average by approximately 3 m