China
Africa
Explore chapters and articles related to this topic
X-Ray Fluorescence Analysis
Published in James P. Lodge, Methods of Air Sampling and Analysis, 2017
Scatter may involve a decrease in energy of the radiation (Compton or incoherent scatter), or no change in wavelength (Rayleigh or coherent scatter). Scattering of X-rays is important because the detection limit is defined in relation to the background radiation, which is primarily scattered excitation radiation.
Improved orbit prediction of LEO objects with calibrated atmospheric mass density model
Published in Journal of Spatial Science, 2019
Junyu Chen, Jianli Du, Jizhang Sang
NASA predicts that, by 2030, orbital collisions could become frequent enough to cause a collision cascade, which could potentially prevent the use of the LEO region (Kessler et al. 2010). One way to prevent a Kessler cascade is to more accurately predict orbits to better plan satellite collision-avoidance manoeuvres. A key component in OP of LEO objects is the knowledge of the mass density of the upper atmosphere, since the atmospheric drag is one of the main forces affecting the orbit of satellites and space debris. The atmosphere mass density models currently in use for OP are empirical, and typical ones include the US Naval Research Laboratory Mass Spectrometer and Incoherent Scatter radar Exosphere 2000 (NRLMSISE-00), the Jacchia Reference Atmosphere model series (J65, J70, J77, etc.), Jacchia-Bowman 2008, and the Drag Temperature Model series (DTM78, DTM2013, etc.). They are finely tuned, but when applied to satellite and space debris OP they can result in large uncertainties in the orbital parameters, often resulting in positional errors of the order of kilometres after a day (McLaughlin et al. 2011, Emmert et al. 2016).
Initial results of stimulated radiation measurements during the HAARP campaign of September 2017
Published in Radiation Effects and Defects in Solids, 2018
A.D. Yellu, W.A. Scales, A. Mahmoudian, C. Siefring, P. Bernhardt
The first observations of stimulated electromagnetic radiation, more commonly known as stimulated electromagnetic emission (SEE), in an ionospheric heating experiment using the ionosphere heating facility now called the European Incoherent Scatter (EISCAT) radar near Tromsø, Norway was reported in (1) and the first formal theoretical framework of SEE observed during ionospheric heating was postulated in (2). Since then, ionosphere scientists have leveraged on SEE as tool for ionospheric diagnostics. Useful diagnostics from SEE spectra include ionospheric plasma characteristics such electron temperature, ionospheric plasma dynamics and ionospheric plasma turbulence (3). Experimental observations of stimulated radiation and its theoretical foundation are well established in the field of Laser Plasma Interactions (4) and thus intellectual transfer from this field has provided invaluable insight into SEE generated during ionosphere heating experiments.
Simulation studies of strongly turbulent stimulated Brillouin backscattering during ionospheric heating
Published in Radiation Effects and Defects in Solids, 2020
A. D. Yellu, J. A. Frazier, W. A. Scales
The focus of this paper is on NSEE which result from stimulated Brillouin backscatter (SBS) instability. SBS is a parametric instability in which an electromagnetic EM wave () incident on a plasma decays into a backscatterd EM wave () and an ion acoustic (IA) wave (), where at the excitation threshold the three waves are coupled as follows [4]; and . Experimental observations of NSEE downshifted from by approximately 30 Hz possibly indicative of SBS was reported in [5], although the author noted that the attribution of the observed emissions to SBS was inconclusive. After the first definitive experimental observations of SBS during ionospheric heating at the High Frequency Active Auroral Research Program Facility HAARP in Gakone, Alaska were reported [6], an ‘SBS-like’ process, known as magnetized SBS (MSBS), which is similar to SBS except that the low frequency decay mode is an electrostatic ion cyclotron (EIC) wave instead of an IA wave, was reported in [7]. SBS has been used to diagnose electron temperature [8] and MSBS has been used to detect in the F-region ionosphere [7]. Results from studies conducted to assess the effects of transmit beam angle, offset from a harmonic of the electron gyrofrequency and measure NSEE thresholds have been reviewed in [2]. NSEE due to MSBS have recently being compared with the thermal ion line measured with an incoherent scatter radar [9]. SBS has also been linked with second harmonic generation [10]. Most recently, the rapid suppression of SBS and a decay line downshifted from observed during ionospheric heating at HAARP in which the ionosphere was irradiated with the maximum power available, was proposed to possibly be due to mechanisms other than the development of artificial field-aligned irregularities (AFAIs) at the upper hybrid (UH) layer [11].