The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Humberto C Godinez - One of the best experts on this subject based on the ideXlab platform.

  • dynamic data driven uncertainty quantification via polynomial chaos for space situational awareness
    Handbook of Dynamic Data Driven Applications Systems, 2018
    Co-Authors: Richard Linares, Vivek Vittaldev, Humberto C Godinez
    Abstract:

    Knowledge of all space objects in orbit and the space environment is collected and maintained by the Space Surveillance Network (SSN). This task is becoming more difficult as the number of objects currently tracked increases due to breakup events and improvements in sensor detection capabilities. The SSN is tasked with maintaining information on over 22,000 objects, 1,100 of which are active. In particular, low-Earth orbiting satellites are heavily influenced by Atmospheric drag which is difficult to model due to fluctuations in the upper Atmospheric Density. These fluctuations are caused by variations in the Solar energy flux which heats Earth’s atmosphere causing it to expand. This research uses probabilistic models to characterize and account for the fluctuations in the Earth’s atmosphere. By correctly estimating the fluctuations, our work contributes to improving the ability to determine the likelihood of satellite collisions in space.

  • new Density estimates derived using accelerometers on board the champ and grace satellites
    Social Work, 2017
    Co-Authors: Piyush M Mehta, Andrew Walker, E K Sutton, Humberto C Godinez
    Abstract:

    Atmospheric mass Density estimates derived from accelerometers onboard satellites such as CHAllenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) are crucial in gaining insight into open science questions about the dynamic coupling between space weather events and the upper atmosphere. Recent advances in physics-based satellite drag coefficient modeling allow derivation of new Density data sets. This paper uses physics-based satellite drag coefficient models for CHAMP and GRACE to derive new estimates for the neutral Atmospheric Density. Results show an average difference of 14–18% for CHAMP and 10–24% for GRACE between the new and existing data sets depending on the space weather conditions (i.e., solar and geomagnetic activity levels). The newly derived densities are also compared with existing models, and results are presented. These densities are expected to be useful to the wider scientific community for validating the development of physics-based models and helping to answer open scientific questions regarding our understanding of upper atmosphere dynamics such as the sensitivity of temporal and global Density variations to solar and geomagnetic forcing.

Hakan Kayal - One of the best experts on this subject based on the ideXlab platform.

  • propagating euv solar flux uncertainty to Atmospheric Density uncertainty
    Advances in Space Research, 2019
    Co-Authors: Fabian Schiemenz, Jens Utzmann, Hakan Kayal
    Abstract:

    Abstract The call for realistic covariances/uncertainties in orbit determination/estimation and propagation is becoming louder. The main reason for unrealistic uncertainties is, in most cases, a disregard of force model uncertainties, i.e. the calculated covariances are based only on the measurement uncertainties. For this reason the covariances are often scaled in practice to avoid misjudgment of orbit knowledge. J. Emmert has recently shown how solar flux uncertainties can be propagated to in-track orbit position errors in the case of long-term orbit propagation. In his method, the Density error resulting from solar flux errors is obtained via the underlying Atmospheric model. In this paper, a universal analytic approximation of Density uncertainty is presented, which is a fast, yet reliable, alternative to the case-based propagation via the Atmospheric model. The major benefit of the proposed analytic estimations is that they seamlessly integrate with orbit estimation/propagation. The uncertainty estimate can directly be computed without an additional call to the Atmospheric model.

  • least squares orbit estimation including Atmospheric Density uncertainty consideration
    Advances in Space Research, 2019
    Co-Authors: Fabian Schiemenz, Jens Utzmann, Hakan Kayal
    Abstract:

    Abstract Density uncertainty is the major driver of unrealistic covariances for objects in low Earth orbits. The analytic propagation of uncertainties in the neutral Atmospheric Density to resulting uncertainties in the orbital position and velocity has only received little attention in the literature so far. The main contribution of the paper at hand is the analytic development of an orbital state-vector error variance-covariance matrix that models the propagation of uncertainties in Atmospheric Density to the orbital state-vector error in the Geocentric Celestial Reference Frame (GCRF). Also extensions of the classical batch weighted least squares (WLS) and the sequential batch weighted least squares algorithms, which allow to incorporate this covariance matrix as process-noise, are presented. Numerical simulations with three different semi-empirical models are provided to validate the derivations. It is shown that the extension of the WLS-algorithm in combination with the Density uncertainty GCRF covariance matrix is able to consistently perform orbit and covariance estimation, which is not the case without Density uncertainty consideration in a classical WLS algorithm.

H Takahashi - One of the best experts on this subject based on the ideXlab platform.

  • Atmospheric Density and pressure inferred from the meteor diffusion coefficient and airglow o2b temperature in the mlt region
    Earth Planets and Space, 2004
    Co-Authors: H Takahashi, Takuji Nakamura, Toshitaka Tsuda, K Shiokawa, L M Lima, D Gobbi
    Abstract:

    Atmospheric Density and pressure in the upper mesosphere-lower thermosphere (MLT) region, around 90 km, are inferred from the meteor trail ambipolar diffusion coefficients, D, and simultaneously observed airglow O2b rotational temperatures. For the present study simultaneous observation data from the meteor radar and SATI imaging spectrometer taken at Shigaraki MU radar observatory (34.9°N, 136.1°E) were used. From the 18 winter nights of data, it is observed that in most of the cases nocturnal variation of the O2 temperature has a good correlation with D at 90 to 92 km. The inferred densities at 90 km showed a negative correlation with temperature variation, suggesting a constant pressure process. The O2 emission intensity shows a good correlation with the temperature, and negative correlation with the Density variation. The OH rotational temperature and D at 87 km also showed similar results to the case of the O2 temperature.

  • first measurement of Atmospheric Density and pressure by meteor diffusion coefficient and airglow oh temperature in the mesopause region
    Geophysical Research Letters, 2002
    Co-Authors: H Takahashi, Takuji Nakamura, Toshitaka Tsuda, R A Buriti, D Gobbi
    Abstract:

    [1] Atmospheric Density and pressure in the mesopause region, around 87 km, are inferred using meteor trail ambipolar diffusion coefficient, D, and simultaneously observed airglow OH rotational temperature, TOH. This is the first time to determine the Atmospheric Density, temperature and pressure by this method. From the 17 nights of data, we found that the number Density at around 87 km of altitude varied from 0.9 to 1.2 × 1014 cm−3, and the pressure varied from 0.27 to 0.35 Pascal. The Density variation is opposite to the temperature. The OH (6,2) band emission rates showed negative correlation with the Density, contrast to positive relation with the temperature. In order to explain temporal variation of the OH emission rate, therefore, it is necessary to assume change of atomic oxygen mixing ratio in the emission heights.

M Risse - One of the best experts on this subject based on the ideXlab platform.

  • impact of varying Atmospheric profiles on extensive air shower observation Atmospheric Density and primary mass reconstruction
    Astroparticle Physics, 2004
    Co-Authors: B Keilhauer, J Blumer, R Engel, H O Klages, M Risse
    Abstract:

    Abstract The longitudinal profile of extensive air showers is sensitive to the energy and type/mass of the primary particle. One of its characteristics, the Atmospheric depth of shower maximum, is often used to reconstruct the elemental composition of primary cosmic rays. In this article, the impact of the Atmospheric Density profile on the reconstruction of the depth of maximum, as observed in fluorescence light measurements, is investigated. We consider in detail the Atmospheric Density profile and its time variations at the site of the southern Pierre Auger Observatory, using data that were obtained from meteorological radio soundings. Similar Atmospheric effects are expected to be found also at other sites.

Saito A. - One of the best experts on this subject based on the ideXlab platform.

  • Potential for the measurement of mesosphere and lower thermosphere (MLT) wind, temperature, Density and geomagnetic field with Superconducting Submillimeter-Wave Limb-Emission Sounder 2 (SMILES-2)
    Copernicus Publications, 2020
    Co-Authors: Baron P., Ochiai S., Dupuy E., Larsson R., Liu H., Manago N., Murtagh D., Oyama S.-i., Sagawa H., Saito A.
    Abstract:

    Abstract Submillimeter-Wave Limb-Emission Sounder 2 (SMILES-2) is a satellite mission proposed in Japan to probe the middle and upper atmosphere (20–160 km). The main instrument is composed of 4 K cooled radiometers operating near 0.7 and 2 THz. It could measure the diurnal changes of the horizontal wind above 30 km, temperature above 20 km, ground-state atomic oxygen above 90 km and Atmospheric Density near the mesopause, as well as abundance of about 15 chemical species. In this study we have conducted simulations to assess the wind, temperature and Density retrieval performance in the mesosphere and lower thermosphere (60–110 km) using the radiometer at 760 GHz. It contains lines of water vapor (H₂O), molecular oxygen (O₂) and nitric oxide (NO) that are the strongest signals measured with SMILES-2 at these altitudes. The Zeeman effect on the O₂ line due to the geomagnetic field (B) is considered; otherwise, the retrieval errors would be underestimated by a factor of 2 above 90 km. The optimal configuration for the radiometer’s polarization is found to be vertical linear. Considering a retrieval vertical resolution of 2.5 km, the line-of-sight wind is retrieved with a precision of 2–5 m s−1 up to 90 km and 30 m s−1 at 110 km. Temperature and Atmospheric Density are retrieved with a precision better than 5 K and 7 % up to 90 km (30 K and 20 % at 110 km). Errors induced by uncertainties on the vector B are mitigated by retrieving it. The retrieval of B is described as a side-product of the mission. At high latitudes, precisions of 30–100 nT on the vertical component and 100–300 nT on the horizontal one could be obtained at 85 and 105 km (vertical resolution of 20 km). SMILES-2 could therefore provide the first measurements of B close to the electrojets' altitude, and the precision is enough to measure variations induced by solar storms in the auroral regions

  • Performance Assessment of Superconducting Submillimeter-Wave Limb-Emission Sounder-2 (SMILES-2)
    'Institute of Electrical and Electronics Engineers (IEEE)', 2019
    Co-Authors: Baron P., Ochiai S., Sagawa H., Saito A., Murtagh Donal, Shiotani M., Suzuki M.
    Abstract:

    \ua9 2019 IEEE. SMILES2 is a mission prepared for the next call-for-proposals for JAXA/ISAS M-class scientific satellite mission. It aims at scanning the Atmospheric limb from 20 to 160 km above the surface at frequencies near 700 GHz and 2 THz. It could provide the temperature and composition as well as, for the first time, the horizontal wind vector above 30 km, the atomic oxygen in its ground state above 90 km, and the Atmospheric Density and the geomagnetic field vector near the mesopause. The mission is proposed for the 2nd time and the instrument design has been improved for accounting for the recommendations of the review committee. In this publication, we discuss the measurement performances assessed from simulations including latest results showing the mission potential for measuring the geomagnetic field between 70-110 km