Space science and Engineering

Boulder City, CO, United States

Space science and Engineering

Boulder City, CO, United States
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Liu C.L.,Chinese Academy of Sciences | Liu C.L.,University of Graz | Kirchengast G.,Chinese Academy of Sciences | Kirchengast G.,University of Graz | And 8 more authors.
Advances in Space Research | Year: 2016

Global Navigation Satellite System radio occultation (GNSS RO, or in short GRO) has become a major method to observe the Earth's atmospheric thermodynamic state variables, i.e., pressure, temperature, and humidity as retrieved from refraction measurements using the GNSS radio wave signals. The GRO data products, such as bending angle and refractivity, are widely used for numerical weather prediction and global climate monitoring. Practically, in GRO, the temperature and humidity variables in the troposphere can only be retrieved separately from refractivity by co-using a priori humidity and/or temperature information.Fortunately, as an advanced technique beyond GRO, developed over the past two decades, future microwave occultation using centimeter and millimeter wave signals between low Earth orbit satellites (LEO-LEO microwave occultation, LMO), can exploit both the refraction and absorption of the signals to solve the temperature-humidity ambiguity in the troposphere. Thus, LMO promises to retrieve the pressure, temperature, and humidity profiles without auxiliary background information. Furthermore, it is anticipated that ozone profiles can be retrieved by absorption measurements near the 195. GHz ozone line, and line-of-sight wind speed in the upper stratosphere into the mesosphere. Liquid water and ice cloud variables as well as turbulence strength can be retrieved as by-products.Additionally, the novel concept of LEO-LEO infrared-laser occultation (LIO), using laser signals in the short-wave infrared band 2-2.5μm between LEO satellites, has been designed to accurately observe key trace gas species for chemistry and climate (i.e., greenhouse gases H2O, CO2, CH4, N2O, O3, CO, including key isotopes), line-of-sight wind speed, and also profiles of cloud layers and aerosols as by-products.In 2010, a new occultation mission concept was proposed, named ACCURATE-climate benchmark profiling of greenhouse gases and thermodynamic variables and wind from space, which combines the highly synergetic LMO and LIO techniques into LEO-LEO microwave and infrared-laser occultation (LMIO). Focusing on the LMO technique only, several other missions were proposed before, in particular ATOMMS (Active Temperature Ozone and Moisture Microwave Spectrometer) and ACE+ (Atmosphere and Climate Explorer-Plus).In this paper, a review of the LEO-LEO occultation techniques (LMO, LIO, and LMIO) in aspects of measurement principle, retrieval algorithms, atmospheric profiling performance and demonstration experiments is performed based on available literature. As part of the conclusions, discussions of outstanding issues, on-going activities, and recommendations for the future are given. © 2017 COSPAR.

Brogniez H.,French National Center for Scientific Research | English S.,ECMWF | Mahfouf J.-F.,Meteo - France | Behrendt A.,University of Hohenheim | And 14 more authors.
Atmospheric Measurement Techniques | Year: 2016

Several recent studies have observed systematic differences between measurements in the 183.31 GHz water vapor line by space-borne sounders and calculations using radiative transfer models, with inputs from either radiosondes (radiosonde observations, RAOBs) or short-range forecasts by numerical weather prediction (NWP) models. This paper discusses all the relevant categories of observation-based or model-based data, quantifies their uncertainties and separates biases that could be common to all causes from those attributable to a particular cause. Reference observations from radiosondes, Global Navigation Satellite System (GNSS) receivers, differential absorption lidar (DIAL) and Raman lidar are thus overviewed. Biases arising from their calibration procedures, NWP models and data assimilation, instrument biases and radiative transfer models (both the models themselves and the underlying spectroscopy) are presented and discussed. Although presently no single process in the comparisons seems capable of explaining the observed structure of bias, recommendations are made in order to better understand the causes. © Author(s) 2016.

Valek P.W.,Space Science and Engineering | Goldstein J.,Space Science and Engineering | McComas D.J.,Space Science and Engineering | Fok M.-C.,NASA | Mitchell D.G.,Applied Physics Laboratory
Journal of Geophysical Research: Space Physics | Year: 2014

During large geomagnetic storms (Dst ≤-100 nT), oxygen can become a significant component of the energetic particles of the inner magnetosphere. Until recently, there were no available global observations of the medium energy (<50 keV) oxygen populations. Using observations from the Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) Energetic Neutral Atom (ENA) imagers we present a study of nine large storms of solar cycle 24 as a function of storm phase. For these storms we observe that the H and O ENA fluxes and their temperatures increase in tandem during the storm's initial phase. However, there is no increase in the O+/H+ ratio in the inner magnetosphere until the storm main phase. Also seen during the main phase is an energy dispersion with higher-energy (32 keV) H ENAs seen before the arrival of O ENAs of the same energy. The O ENAs take longer to return to prestorm levels during the recovery phases. This longer recovery time is likely because of the large difference between the storm time and prestorm O populations compared to H (i.e., there is always some prestorm H in the inner magnetosphere, but effectively no O prestorm). These results imply that medium-energy O ENAs evolve over long time scales (hours to days) as opposed to the shorter substorm time scales of the higher-energy (>52 keV) O ENAs. Key Points The first global observations of the medium energy H and O ENAs during storms The energy distribution and concentrations evolved over the storm phases For these storms a pattern has emerged in the medium energy ENA observations ©2014. American Geophysical Union. All Rights Reserved.

Griggs E.,University of Colorado at Boulder | Kursinski E.R.,Space science and Engineering | Akos D.,University of Colorado at Boulder
Radio Science | Year: 2015

Global Navigation Satellite System (GNSS) clock stability is characterized via the modified Allan deviation using active hydrogen masers as the receiver frequency reference. The high stability of the maser reference allows the GNSS clock contribution to the GNSS carrier phase variance to be determined quite accurately. Satellite clock stability for four different GNSS constellations are presented, highlighting the similarities and differences between the constellations as well as satellite blocks and clock types. Impact on high-rate applications, such as GNSS radio occultation (RO), is assessed through the calculation of the maximum carrier phase error due to clock instability. White phase noise appears to dominate at subsecond time scales. However, while we derived the theoretical contribution of white phase modulation to the modified Allan deviation, our analysis of the GNSS satellite clocks was limited to 1-200 s time scales because of inconsistencies between the subsecond results from the commercial and software-defined receivers. The rubidium frequency standards on board the Global Positioning System (GPS) Block IIF, BeiDou, and Galileo satellites show improved stability results in comparison to previous GPS blocks for time scales relevant to RO. The Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS) satellites are the least stable of the GNSS constellations in the short term and will need high-rate corrections to produce RO results comparable to those from the other GNSS constellations. Key Points Stability of GNSS satellite clocks for time intervals less than 200 s Development and validation of data collection and processing techniques Effect of clock instabilities on radio occultation atmospheric products ©2015. American Geophysical Union. All Rights Reserved.

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