GNSS transpolar earth reflectometry exploriNg system (G-TERN): mission concept

The global navigation satellite system (GNSS) Transpolar Earth Reflectometry exploriNg system (G-TERN) was proposed in response to ESA's Earth Explorer 9 revised call by a team of 33 multi-disciplinary scientists. The primary objective of the mission is to quantify at high spatio-temporal resolution crucial characteristics, processes and interactions between sea ice, and other Earth system components in order to advance the understanding and prediction of climate change and its impacts on the environment and society. The objective is articulated through three key questions. 1) In a rapidly changing Arctic regime and under the resilient Antarctic sea ice trend, how will highly dynamic forcings and couplings between the various components of the ocean, atmosphere, and cryosphere modify or influence the processes governing the characteristics of the sea ice cover (ice production, growth, deformation, and melt)? 2) What are the impacts of extreme events and feedback mechanisms on sea ice evolution? 3) What are the effects of the cryosphere behaviors, either rapidly changing or resiliently stable, on the global oceanic and atmospheric circulation and mid-latitude extreme events? To contribute answering these questions, G-TERN will measure key parameters of the sea ice, the oceans, and the atmosphere with frequent and dense coverage over polar areas, becoming a “dynamic mapper”of the ice conditions, the ice production, and the loss in multiple time and space scales, and surrounding environment. Over polar areas, the G-TERN will measure sea ice surface elevation (<;10 cm precision), roughness, and polarimetry aspects at 30-km resolution and 3-days full coverage. G-TERN will implement the interferometric GNSS reflectometry concept, from a single satellite in near-polar orbit with capability for 12 simultaneous observations. Unlike currently orbiting GNSS reflectometry missions, the G-TERN uses the full GNSS available bandwidth to improve its ranging measurements. The lifetime would be 2025-2030 or optimally 2025-2035, covering key stages of the transition toward a nearly ice-free Arctic Ocean in summer. This paper describes the mission objectives, it reviews its measurement techniques, summarizes the suggested implementation, and finally, it estimates the expected performance.Peer ReviewedPostprint (published version

Aeronautics and space report of the President, 1980 activities

The year's achievements in the areas of communication, Earth resources, environment, space sciences, transportation, and space energy are summarized and current and planned activities in these areas at the various departments and agencies of the Federal Government are summarized. Tables show U.S. and world spacecraft records, spacecraft launchings for 1980, and scientific payload anf probes launched 1975-1980. Budget data are included

A chemical survey of exoplanets with ARIEL

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio

An Earth-system prediction initiative for the twenty-first century

International audienceSome scientists have proposed the Earth-System Prediction Initiative (EPI) at the 2007 GEO Summit in Cape Town, South Africa. EPI will draw upon coordination between international programs for Earth system observations, prediction, and warning, such as the WCRP, WWRP, GCOS, and hence contribute to GEO and the GEOSS. It will link with international organizations, such as the International Council for Science (ICSU), Intergovernmental Oceanographic Commission (IOC), UNEP, WMO, and World Health Organization (WHO). The proposed initiative will provide high-resolution climate models that capture the properties of regional high-impact weather events, such as tropical cyclones, heat wave, and sand and dust storms associated within multi-decadal climate projections of climate variability and change. Unprecedented international collaboration and goodwill are necessary for the success of EPI

The role of the research simulator in the systems development of rotorcraft

The potential application of the research simulator to future rotorcraft systems design, development, product improvement evaluations, and safety analysis is examined. Current simulation capabilities for fixed-wing aircraft are reviewed and the requirements of a rotorcraft simulator are defined. The visual system components, vertical motion simulator, cab, and computation system for a research simulator under development are described

Aeronautics and space report of the President, 1982 activities

Achievements of the space program are summerized in the area of communication, Earth resources, environment, space sciences, transportation, aeronautics, and space energy. Space program activities of the various deprtments and agencies of the Federal Government are discussed in relation to the agencies' goals and policies. Records of U.S. and world spacecraft launchings, successful U.S. launches for 1982, U.S. launched applications and scientific satellites and space probes since 1975, U.S. and Soviet manned spaceflights since 1961, data on U.S. space launch vehicles, and budget summaries are provided. The national space policy and the aeronautical research and technology policy statements are included

Impact of Atmospheric Propagation Effects on the Performance of Pulse Compression Techniques for Radar Systems

Currently, more than three tons of space debris are an integrate part of the low earth orbit, and exhibit a trend to increase, due to collisions and the constant inoperability of older satellite systems. The technological era that we are living, in which satellites are a major element of any Telecommunications service, it is necessary to make a sustainable use of Space, so that technology can keep improving. The European Space Surveillance and Tracking support framework has as its main objective the catalogue and prediction of space debris’ orbits, as a nonactive approach to the space debris problem. The rAdio TeLescope pAmpilhosa Serra (ATLAS) is incorporated on this framework, giving Portugal the capability of performing space debris detection and tracking. The main objective of this thesis was the creation of an Earth-space propagation simulator with frequency agility, so that it would be possible to simulate the propagation of many radar signals originated through pulse compression techniques and thus be able to quantify the impact of atmospheric propagation on its efficiency. To prove the profitability of using these techniques, two types of tests were carried out: a test using the ATLAS radar receiver circuit, providing a familiarization with this type of systems and afterwards, the obtainment of True Positive Rate curves, where it was demonstrated the high target detention capability when using pulse compression techniques compared to unmodulated radar pulses, mainly with very low SNR around -20dBAtualmente, mais de três toneladas de detritos espaciais são parte integrante da órbita baixa da Terra, apresentando uma tendência de aumento, devido à constante obsolescência de satélites mais antigos e possíveis colisões entre os mesmos. Na era tecnológica em que vivemos, em que os satélites são um elemento importante de qualquer serviço de telecomunicações, torna-se necessário fazer um uso sustentável do espaço, para que a tecnologia continue a evoluir. A estrutura europeia de apoio à vigilância e rastreamento espacial (EUSST) tem como principal objetivo a catalogação e previsão das órbitas dos detritos espaciais, sendo por isso considerada com uma abordagem não ativa de combate aos detritos espaciais. O rAdio TeLescope pAmpilhosa Serra (ATLAS) está incorporado nesta estrutura, proporcionando a Portugal a capacidade de realizar deteção e rastreamento de detritos espaciais. O principal objetivo desta tese passa pela criação de um simulador de propagação Terra-espaço, com agilidade em frequência, de forma a ser possível simular a propagação de vários sinais radar originados a partir de técnicas de compressão de impulsos, sendo assim capaz de quantificar o impacto da propagação atmosférica na eficiência dos mesmos. Para comprovar a rentabilidade do uso destas técnicas, foram realizados dois tipos de testes: um teste utilizando o circuito recetor do radar ATLAS, proporcionando uma familiarização com este tipo de sistemas e, posteriormente, a obtenção das curvas de percentagem de verdadeiros positivos, onde foi demonstrado a elevada capacidade de deteção de alvos ao utilizar técnicas de compressão de impulsos em comparação com impulsos de radar não modulados, principalmente para valores de SNR muito baixos, sensivelmente em torno de -20dB