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- 2. GPS: Global Positioning System
- 3. GPS: Segmento espacial Block I, Block II, Block IIA, Block IIR and Block IIF). Primero a comienzos de 1978. Formado por la constelación de satélites (nominalmente 24 activos). Cada satélite lleva a bordo varios relojes atómicos (5) para asegurar la exactitud de las marcas de tiempo y la estabilidad de la frecuencia de la señal emitida. GPS Block II/IIA: Original operational satellite design GPS Block IIR: R eplenishment satellite design GPS Block IIR-M: R eplenishment satellite design with M odernized features
- 4. GPS: Segmento de Control constituido por un conjunto de estaciones permanentes con coordenadas bien conocidas en un sistema terrestre de referencia internacionalmente aceptado. Su misión es la de rastrear a todos los satélites para calcular las órbitas (efemérides) y controlar sus relojes. NGA (National Geospatial-Intelligence Agency)
- 5. GPS: Segmento usuarios Los usuarios equipados con receptores de las señales satelitales reciben simultáneamente las componentes de la señal que sirven para medir la distancia receptor-satélite, y el mensaje de navegación (coordenadas de los satélites). Baderillero satelital: maquinaria agrícola, pulverizadores arrastre
- 6. Sistema de referencia terrestre
- 7. GPS: ¿Cómo funciona? Cada satélite que observa el navegador nos permite construir una ecuación de la forma Donde Son conocidas. Entonces necesito (por lo menos 4 ecuaciones como esta en el momento de observar para conocer la posición del navegador)
- 8. Errores: ¿P orque casi 10 metros? Fuentes de error: Valores aproximados, cerca de los 15 metros Efecto Ionoférico ± 5 metros Corrimientos orbitas satelitales ± 2.5 metros Falta de sincronía de los relojes (receptor-satélite) ± 2 metros Efecto de Multipath ± 1 meter Efecto troposférico (parte húmeda) ± 0.5 meter Además Errores de redondeo ± 1 metro
- 10. LUNA No hay atmósfera en la luna. (en realidad, muy delgada respecto a la de la Tierra). La mayoría de “ las colinas ” son cráteres , no volcanes. Se forman a partir de la caída de objetos masivos sobre la superficie.
- 17. Eclipse de Sol
- 18. Eclipses de Sol 1991 Jul 11 Total Solar Eclipse Eclipse parcial de Sol Eclipse anular
- 19. Eclipses de Sol Próximo eclipse de Sol que pasará por nuestro país: 11 de julio de 2010 http:// eclipse.gsfc.nasa.gov / SEmono /TSE2010/ TSE2010 . html CUIDADO: NUNCA observar directamente un eclipse de Sol !!!
- 20. Basura espacial, escombros NASA estima que existen no menos de 19,000 objetos mas grandes de 10 cm. en el espacio exterior y entre 500,000 y un millón de objetos entre 1 y 10 cm. Aproximadamente el 95 % de los objetos en estas ilustración son basura orbital, p. ej., satélites que no funcionan. Cada punto corresponde a su ubicación escalados según el tamaño. (around 35,785 km altitude) 200 km de altura Fuente: http://www.orbitaldebris.jsc.nasa.gov/
Notas del editor
- Selective Availability (SA) Selective Availability consists of two different components, first, an intentional manipulation of the satellite clock frequency resulting in the generation of the carrier waves and codes with varying wavelengths, and secondly, errors imposed within the description of the satellite orbit in the ephemeris data sent in the broadcast message. Typical error with SA imposed are +/- 100 m. Anti Spoofing (AS) Anti Spoofing alters GPS signals by changing the characteristics of the P code by mixing it with a so-called W code resulting in the Y code. It is the latter that is modulated onto the carriers and is thus designed to prevent the ability of the receiver to make P code measurements. many receiver manufacturers have developed techniques to still make P code measurements with only a small addition in added noise (cross correlation technique). Satellite errors These include errors in the modeling of the satellite clock offset and drift using a second order polynomial, and also errors that exist within the Keplerian representation of the satellite ephemeris information. Atmospheric propagation errors The satellite signals propagate through atmospheric layers as they travel from the satellite to the receiver. Two layers are generally considered when dealing with GPS: the ionosphere which extends from a height of 70 to 1000 km above the Earth, and the troposphere which extends from the ground level to 70 km. As the signal propagates through the ionosphere, the GPS code information is delayed resulting in the pseudoranges being measured too long as compared to the geometric distance to the satellite. The extent to which the measurements are delayed depends on the Total Electronic Content (TEC) along the signal path which is a measure of the electron density. Significantly larger delays occur for signals emitted from low elevation satellites, peaking during the daytime and subsiding during the night. In regions near the geomagnetic equator or near the poles, the delays are also larger. The ionospheric delay is frequency dependent and can therefore be eliminated using dual frequency GPS observations. Single frequency users, however, can partially model the effect of the ionosphere using standard models. The troposphere causes a delay in both the code and the carrier observations. Since it is not frequency dependent it cannot be canceled out by using dual frequency measurements but it can, however, be successfully modeled. The troposphere is split into two parts: the dry component which constitutes about 90% of the total refraction, and the wet part which constitutes the remaining 10%/ The wet component is the harder to modelize. Multipath Multipath is the phenomena by which the GPS signal is reflected by some object or surface before being detected by the antenna. Multipath is commonly considered to be the reflections due to surface surrounding the antenna and can cause errors as high as 15 cm for the L1 carrier and of the order of 15-20 m for the pseudorange. Receiver noise Errors which are due to the measurements processes used within the receiver are typically grouped together as receiver noise. These are dependent on the design of the antenna, the method used for the analogue to digital conversion, the correlation process, .... GPS receivers The GPS receivers can be divided in three categories, following their internal properties: Multi-channels receivers Sequential receivers Multiplex receivers The multi-channels receivers are the top level ones. Their are generally used in ultra precise applications or in dynamic positioning. These receivers have one channel for each satellite so that the satellite can be tracked without interruption. We can make a further distinction between SPS and PPS receivers. The SPS receivers measure only the C/A code and the L1/L2 carriers while the PPS receivers can also make measurements on the P code. The sequential receivers have one or two channels. The second channel is generally used for the tracking of an initial satellite and for the acquisition of the navigation message. The other channel tracks one satellite at a time with a typical window of 1 second. So, for each satellite, a small initialization is necessary. This method implies that the receiver can only determines a three dimensions position every 4 or 5 seconds. Furthermore, this position is less precise due to the fact that the measurements on the different satellites are not simultaneous. The multiplex receivers are a compromise between multi-channels and sequential receivers. They can, despite a principle similar to the sequential receiver, switch the acquisition between the different satellites in less that 20 milliseconds. Due to that high level of acquisition frequency, one can eliminate the initialization phase before each acquisition. For the sequential receivers as for the multiplex ones, the navigation messages are downloaded, for each satellite, in an asynchronous way, this is why the first computed position takes more time.
- Selective Availability (SA) Selective Availability consists of two different components, first, an intentional manipulation of the satellite clock frequency resulting in the generation of the carrier waves and codes with varying wavelengths, and secondly, errors imposed within the description of the satellite orbit in the ephemeris data sent in the broadcast message. Typical error with SA imposed are +/- 100 m. Anti Spoofing (AS) Anti Spoofing alters GPS signals by changing the characteristics of the P code by mixing it with a so-called W code resulting in the Y code. It is the latter that is modulated onto the carriers and is thus designed to prevent the ability of the receiver to make P code measurements. many receiver manufacturers have developed techniques to still make P code measurements with only a small addition in added noise (cross correlation technique). Satellite errors These include errors in the modeling of the satellite clock offset and drift using a second order polynomial, and also errors that exist within the Keplerian representation of the satellite ephemeris information. Atmospheric propagation errors The satellite signals propagate through atmospheric layers as they travel from the satellite to the receiver. Two layers are generally considered when dealing with GPS: the ionosphere which extends from a height of 70 to 1000 km above the Earth, and the troposphere which extends from the ground level to 70 km. As the signal propagates through the ionosphere, the GPS code information is delayed resulting in the pseudoranges being measured too long as compared to the geometric distance to the satellite. The extent to which the measurements are delayed depends on the Total Electronic Content (TEC) along the signal path which is a measure of the electron density. Significantly larger delays occur for signals emitted from low elevation satellites, peaking during the daytime and subsiding during the night. In regions near the geomagnetic equator or near the poles, the delays are also larger. The ionospheric delay is frequency dependent and can therefore be eliminated using dual frequency GPS observations. Single frequency users, however, can partially model the effect of the ionosphere using standard models. The troposphere causes a delay in both the code and the carrier observations. Since it is not frequency dependent it cannot be canceled out by using dual frequency measurements but it can, however, be successfully modeled. The troposphere is split into two parts: the dry component which constitutes about 90% of the total refraction, and the wet part which constitutes the remaining 10%/ The wet component is the harder to modelize. Multipath Multipath is the phenomena by which the GPS signal is reflected by some object or surface before being detected by the antenna. Multipath is commonly considered to be the reflections due to surface surrounding the antenna and can cause errors as high as 15 cm for the L1 carrier and of the order of 15-20 m for the pseudorange. Receiver noise Errors which are due to the measurements processes used within the receiver are typically grouped together as receiver noise. These are dependent on the design of the antenna, the method used for the analogue to digital conversion, the correlation process, .... GPS receivers The GPS receivers can be divided in three categories, following their internal properties: Multi-channels receivers Sequential receivers Multiplex receivers The multi-channels receivers are the top level ones. Their are generally used in ultra precise applications or in dynamic positioning. These receivers have one channel for each satellite so that the satellite can be tracked without interruption. We can make a further distinction between SPS and PPS receivers. The SPS receivers measure only the C/A code and the L1/L2 carriers while the PPS receivers can also make measurements on the P code. The sequential receivers have one or two channels. The second channel is generally used for the tracking of an initial satellite and for the acquisition of the navigation message. The other channel tracks one satellite at a time with a typical window of 1 second. So, for each satellite, a small initialization is necessary. This method implies that the receiver can only determines a three dimensions position every 4 or 5 seconds. Furthermore, this position is less precise due to the fact that the measurements on the different satellites are not simultaneous. The multiplex receivers are a compromise between multi-channels and sequential receivers. They can, despite a principle similar to the sequential receiver, switch the acquisition between the different satellites in less that 20 milliseconds. Due to that high level of acquisition frequency, one can eliminate the initialization phase before each acquisition. For the sequential receivers as for the multiplex ones, the navigation messages are downloaded, for each satellite, in an asynchronous way, this is why the first computed position takes more time.
- Para realizar el seguimiento de las fases debe partirse de la llamada Luna nueva o novilunio , que se da cuando la luna, entre el Sol y la Tierra, no es visible porque nos ofrece su cara no iluminada. A medida que pasan los días, la Luna aparece comenzando por una mínima lúnula que va creciendo hasta que los 7 días, 9 horas, 11 min. y 0.75 seg. Los tres astros forman un ángulo recto con lo cual la Luna se ve en cuarto creciente . En otro periodo igual de edad de la Luna (periodo que a transcurrido desde la Luna nueva), se llega hasta la fase de Luna llena o plenilunio ; a tardado 14 días, 18 horas, 22 min. y 1.5 seg.; desde la Tierra, entre la Luna y el Sol, se puede ver todo el disco lunar iluminado. Desde esta posición, el proceso inverso hará disminuir la parte iluminada hasta llegar al cuarto menguante en 22 días, 3 horas, 33 min. y 2.2 seg.; en esta fase, la parte iluminada es la que no se veía en el cuarto creciente, porque en el ángulo recto que los tres astros vuelven a formar la posición de la luna no es la misma. Finalmente, a los 29 días, 12 horas, 44 min. y 2.9 seg. se llega al final del mes sinódico y se inicia otra lunación.
- Pero, no vemos siempre exactamente la misma cara, aunque mucha gente desconoce este hecho. Como he mencionado antes, en total vemos alrededor del 60% de la superficie lunar, pero si siempre nos mostrarse la misma superficie sólo seríamos capaces de ver la mitad. ¿De dónde sale ese 10% “extra?” la culpa la tiene el hecho de que la órbita no es circular, sino elíptica. En primer lugar, puesto que la Luna no siempre está a igual distancia de la Tierra, su velocidad alrededor de nosotros no siempre es la misma: cuando está pasando cerca se mueve más rápido, y cuando está lejos lo hace más despacio. Pero su velocidad de rotación alrededor de su eje siempre es la misma… con lo que cuando está cerca va descubriendo a nuestros ojos un poquito de la superficie que normalmente oculta por un lado (pues se traslada más rápido de lo que rota), y cuando está lejos hace lo mismo por el otro lado (pues rota más rápido de lo que se traslada). Este fenómeno se conoce como libración longitudinal. Además, la órbita de la Luna no se encuentra sobre el plano de la eclíptica, sino que forma unos 5° con ella. Por lo tanto, según se mueve alrededor de la Tierra nos parece que su eje se bambolea hacia arriba y hacia abajo, lo que se conoce con el nombre de libración latitudinal. También hay un tercer tipo de libración, la libración diurna, que es una consecuencia de la rotación de la Tierra: nuestro planeta gira sobre su eje bastante más rápido que la Luna (un día comparado con casi un mes), de modo que a lo largo del día nos movemos respecto a la Luna, atisbando un poquito de superficie “extra” en ese movimiento. Aquí tienes una animación que te dará una idea del efecto combinado de todas las libraciones, y cómo nos descubren un 10% más de Luna del que veríamos de otro modo. De paso puedes ver las fases lunares “en acción”:
- Habrá eclipses lunares si la luna esta `` detrás del la tierra ". ¿Entonces, por qué nosotros no tenemos eclipse lunar cada mes? Es porque el plano de la órbita lunar no coincide con el plano de la órbita de laTierra. Así pues, para la mayoría de las Luna Llenas, está sur o norte del plano orbital de la Tierra. Por la misma razón, no vemos eclipse solar cada Luna Nueva.
- Los cielos por la noches en esta época de tecnología están actualmente amenazadas por la contaminación lumínica. La naturaleza está acostumbrada a un mundo de día y noche, y ha evolucionado como tal. Insectos, pájaros, incluso tortugas, por ejemplo, dependen de la oscuridad para varios mecanismos biológicos, ya sea para la navegación, patrones de apareamiento, y hasta en la selección de zonas de nidificación. Para llevar a cabo exitosamente estas observaciones, los astrónomos no sólo necesitan de grandes telescopios (para captar y concentrar la mayor cantidad posible de luz), y los detectores más sensibles, sino que también de los cielos más oscuros. Las estrellas y galaxias más tenues que es posible observar con un telescopio de 4 metros son cuarenta veces más débiles que la emisión natural del cielo nocturno. Por esta razón es de crítica importancia el minimizar las contribuciones lumínicas de ciudades vecinas con respecto a la emisión natural del cielo nocturno. El costo de un telescopio de 8 metros es de aproximadamente US$85 millones. De este modo, un incremento modesto de 25% en la luminosidad nocturna se transforma en una pérdida de casi US$20 millones para la astronomía.