scholarly journals Comparison of accelerometer data calibration methods used in thermospheric neutral density estimation

2018 ◽  
Vol 36 (3) ◽  
pp. 761-779 ◽  
Author(s):  
Kristin Vielberg ◽  
Ehsan Forootan ◽  
Christina Lück ◽  
Anno Löcher ◽  
Jürgen Kusche ◽  
...  
Keyword(s):  
Solar Activity ◽  
Radiation Pressure ◽  
Precise Orbit Determination ◽  
High Solar Activity ◽  
Neutral Density ◽  
Accelerometer Data ◽  
The Earth ◽  
Calibration Methods ◽  
Leo Satellites ◽  
Gravity Recovery

Abstract. Ultra-sensitive space-borne accelerometers on board of low Earth orbit (LEO) satellites are used to measure non-gravitational forces acting on the surface of these satellites. These forces consist of the Earth radiation pressure, the solar radiation pressure and the atmospheric drag, where the first two are caused by the radiation emitted from the Earth and the Sun, respectively, and the latter is related to the thermospheric density. On-board accelerometer measurements contain systematic errors, which need to be mitigated by applying a calibration before their use in gravity recovery or thermospheric neutral density estimations. Therefore, we improve, apply and compare three calibration procedures: (1) a multi-step numerical estimation approach, which is based on the numerical differentiation of the kinematic orbits of LEO satellites; (2) a calibration of accelerometer observations within the dynamic precise orbit determination procedure and (3) a comparison of observed to modeled forces acting on the surface of LEO satellites. Here, accelerometer measurements obtained by the Gravity Recovery And Climate Experiment (GRACE) are used. Time series of bias and scale factor derived from the three calibration procedures are found to be different in timescales of a few days to months. Results are more similar (statistically significant) when considering longer timescales, from which the results of approach (1) and (2) show better agreement to those of approach (3) during medium and high solar activity. Calibrated accelerometer observations are then applied to estimate thermospheric neutral densities. Differences between accelerometer-based density estimations and those from empirical neutral density models, e.g., NRLMSISE-00, are observed to be significant during quiet periods, on average 22 % of the simulated densities (during low solar activity), and up to 28 % during high solar activity. Therefore, daily corrections are estimated for neutral densities derived from NRLMSISE-00. Our results indicate that these corrections improve model-based density simulations in order to provide density estimates at locations outside the vicinity of the GRACE satellites, in particular during the period of high solar/magnetic activity, e.g., during the St. Patrick's Day storm on 17 March 2015.

Scale factors of the thermospheric neutral density – a comparison of SLR and accelerometer solutions

2021 ◽  
Author(s):  
Lea Zeitler ◽  
Armin Corbin ◽  
Kristin Vielberg ◽  
Sergei Rudenko ◽  
Anno Löcher ◽  
...  
Keyword(s):  
Time Resolution ◽  
Aerodynamic Drag ◽  
Precise Orbit Determination ◽  
Neutral Density ◽  
Observation Data ◽  
Accelerometer Data ◽  
Scale Factors ◽  
Weather Events ◽  
Leo Satellites ◽  
Gravity Recovery

<p>The aerodynamic drag depending on the neutral density of the thermosphere is the largest non-gravitational force that decelerates Low Earth Orbiting (LEO) satellites with altitudes lower than 1000 km.  Consequently, the knowledge of the thermospheric neutral density is of crucial importance for many applications in geo-scientific investigations, such as precise orbit determination (POD), re-entry prediction, manoeuvre planning or satellite lifetime predictions. The accuracy of existing thermosphere models depends on observation data of the thermosphere, which are quite sparse. Evaluations of different thermosphere models indicate considerable differences, especially for time epochs of severe space weather events. Hence, an improvement of thermosphere models is absolutely necessary.</p><p>In this study, discrepancies between the empirical thermosphere model NRLMSISE-00 and the results of two geodetic observation techniques are discussed. For this purpose, two approaches are applied to calculate scale factors between the modelled density from the NRLMSISE-00 model and those from geodetic techniques. The first approach applies the POD of LEO satellites to estimate scale factors with a time resolution of 12 hours derived from Satellite Laser Ranging (SLR) tracking measurements. The SLR missions used here include the spherical satellites Starlette, Westpac, Blits, Stella and Larets. As our second approach, scale factors are computed by evaluating the aerodynamic acceleration using the on-board accelerometer data of the Challenging Mini-satellite Payload (CHAMP) mission and the Gravity Recovery and Climate Experiment (GRACE) mission. Here, the time resolution of scale factors is fixed to be 12 hours to be comparable with the first approach. Finally, we investigate the resulting scale factors from the above mentioned satellites at various altitudes, e.g. 960 km for Starlette and 400 km for GRACE. Especially, the temporal variation as well as the altitude dependency of the scale factors will be discussed.</p>

GRACE and GRACE-FO Level-1 V04 Data Processing Status

2020 ◽  
Author(s):  
Christopher Mccullough ◽  
Tamara Bandikova ◽  
William Bertiger ◽  
Carmen Boening ◽  
Sung Byun ◽  
...  
Keyword(s):  
Data Processing ◽  
Attitude Determination ◽  
Precise Orbit Determination ◽  
Mass Change ◽  
Sensor Data ◽  
The Earth ◽  
Analysis Center ◽  
Level 1 ◽  
Gravity Recovery

<p>The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO), launched in May 2018, provides invaluable information about mass change in the Earth system, continuing the legacy of GRACE. Fundamental requirements for successful mass change recovery are precise orbit determination and inter-satellite ranging, determination of the relative clock alignment of the ultra-stable oscillators (USOs), precise attitude determination, and accelerometry. NASA/Caltech Jet Propulsion Laboratory is the official Level-1 data processing and analysis center, and is currently processing software version 04. Here we present analysis of the aforementioned GRACE-FO sensor data, as well a preview of an upcoming GRACE reprocessing, and a discussion of measurement performance.</p>

How can Thermospheric Neutral Density (TND) estimates from CHAMP and GRACE accelerometer observations be used to improve empirical models?

2020 ◽  
Author(s):  
Ehsan Forootan ◽  
Saeed Farzaneh ◽  
Mona Kosary ◽  
Maike Schumacher
Keyword(s):  
Kalman Filter ◽  
Data Assimilation ◽  
Orbit Determination ◽  
Ensemble Kalman Filter ◽  
Precise Orbit Determination ◽  
Accurate Estimation ◽  
Neutral Density ◽  
Square Root ◽  
Precise Orbit ◽  
Leo Satellites

<p>An accurate estimation of the Thermospheric Neutral Density (TND) is important to compute drag forces acting on Low-Earth-Orbit (LEO) satellites and debris. Empirical thermospheric models are often used to compute TNDs (along-track of LEO satellites) for the Precise Orbit Determination (POD) experiments. However, recent studies indicate that the TNDs of available models do not perfectly reproduce TNDs derived from accelerometer observations. In this study, we use TND estimates from the Challenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) missions and merge them with the NRLMSISE00 from the Mass Spectrometer and Incoherent Scatter family. The integration is implemented by applying a simultaneous Calibration and Data Assimilation (C/DA) technique. The application of C/DA is advantageous since it uses model equation to interpolate and extrapolate TNDs that are not covered by CHAMP and GRACE. It also modifies the model's selected parameters to simulate TNDs that are closer to those of CHAMP and GRACE. The C/DA of this study is implemented daily using CHAMP- and/or GRACE-TNDs, while using the Ensemble Kalman Filter (EnKF) and Ensemble Square-Root Kalman Filter (EnSRF) as merger. Compared to the original model, on average, we found 27% (in the range of 2% to 56%) improvements in the estimation of TNDs. In addition, the results of the C/DA are compared with the TND outputs of the JB2008 model along the CHAMP and GRACE orbits, whose results indicate that the daily C/DA outputs are 60% closer to the observed TNDs (that are not used for the C/DA). Overall, our assessment indicates that EnSRF results in more realistic TND simulation and prediction compared to those derived from EnKF. We show that the improved TND estimates of this study will be beneficial for Precise Orbit Determination (POD) studies.  </p><p><strong>Keywords: </strong>Thermosphere, Calibration and Data Assimilation (C/DA), NRLMSISE00, Ensemble Kalman Filter (EnKF), Ensemble Square-Root Kalman Filter (EnSRF)</p>

A simultaneous calibration and data assimilation (C/DA) to improve NRLMSISE00 using thermospheric neutral density (TND) from space-borne accelerometer measurements

2020 ◽  
Vol 224 (2) ◽  
pp. 1096-1115
Author(s):  
E Forootan ◽  
S Farzaneh ◽  
M Kosary ◽  
M Schmidt ◽  
M Schumacher
Keyword(s):  
Kalman Filter ◽  
Data Assimilation ◽  
Precise Orbit Determination ◽  
Low Earth Orbit ◽  
Model Parameters ◽  
Neutral Density ◽  
Incoherent Scatter ◽  
Drag Forces ◽  
Gravity Recovery ◽  
Limited Accuracy

SUMMARY Improving thermospheric neutral density (TND) estimates is important for computing drag forces acting on low-Earth-orbit (LEO) satellites and debris. Empirical thermospheric models are often used to compute TNDs for the precise orbit determination experiments. However, it is known that simulating TNDs are of limited accuracy due to simplification of model structure, coarse sampling of model inputs and dependencies to the calibration period. Here, we apply TND estimates from accelerometer measurements of the Challenging Minisatellite Payload (CHAMP) and the Gravity Recovery and Climate Experiment (GRACE) missions as observations to improve the NRLMSISE-00 model, which belongs to the mass spectrometer and incoherent scatter family of models. For this, a novel simultaneous calibration and data assimilation (C/DA) technique is implemented that uses the ensemble Kalman filter and the ensemble square-root Kalman filter as merger. The application of C/DA is unique because it modifies both model-derived TNDs, as well as the selected model parameters. The calibrated parameters derived from C/DA are then used to predict TNDs in locations that are not covered by CHAMP and GRACE orbits, and forecasting TNDs of the next day. The C/DA is implemented using daily CHAMP- and/or GRACE-TNDs, for which compared to the original model, we find 27 per cent and 62 per cent reduction of misfit between model and observations in terms of root mean square error and Nash coefficient, respectively. These validations are performed using the observations along the orbital track of the other satellite that is not used in the C/DA during 2003 with various solar activity. Comparisons with another empirical model, that is, Jacchia-Bowman, indicate that the C/DA results improve these quality measurements on an average range of 50 per cent and 60 per cent, respectively.

Estimation of Earth- and satellite-related parameters in radiation pressure modeling from space-borne accelerometry

2020 ◽  
Author(s):  
Kristin Vielberg ◽  
Jürgen Kusche
Keyword(s):  
Radiation Pressure ◽  
Precise Orbit Determination ◽  
Solar Radiation Pressure ◽  
Low Earth Orbit ◽  
Condition Numbers ◽  
Model Parameters ◽  
Accelerometer Data ◽  
Satellite Mission ◽  
Gravitational Forces ◽  
Earth Radiation

<p>Space-borne accelerometers measure the sum of all non-gravitational forces, which interact with the surface of a spacecraft. For low Earth orbit satellites, the atmospheric drag is the largest non-gravitational force. With increasing satellite altitude, the acceleration due to the Earth radiation pressure becomes less relevant, whereas the effect of the Solar radiation pressure becomes prevalent. Accurately modeled non-gravitational forces are necessary for precise orbit determination, satellite gravimetry, or thermospheric density estimation.</p><p>In this study, we apply an inverse procedure with the aim to overcome remaining limitations in state-of-the-art radiation pressure force models. We estimate corrections of limiting parameters such as the satellite’s thermo-optical material properties or systematic errors in Earth radiation data sets. We define different parameterizations and analyse their estimability in terms of rank deficiency and condition numbers. Correlation analyses between estimated parameters will help to detect and overcome multicollinearity. The results are expected to improve the estimation of certain physical radiation pressure model parameters from satellite accelerometer data. Here, the inverse modeling is based on calibrated accelerometer measurements from the satellite mission Gravity Recovery and Climate Experiment (GRACE).</p>

Optical GNSS Receiver for the ESA's NGGM-MAGIC Mission and for LEO Satellites with the Highest Orbit Accuracy

2021 ◽  
Author(s):  
Drazen Svehla
Keyword(s):  
Laser Beam ◽  
Gravity Field ◽  
Carrier Phase ◽  
Beam Steering ◽  
Precise Orbit Determination ◽  
Optical Carrier ◽  
Gnss Receiver ◽  
Cw Laser ◽  
Leo Satellites ◽  
Leo Satellite

<p>Precise orbit determination (POD) of LEO satellites is done with a geodetic grade GPS receiver measuring carrier-phase between a LEO and GPS satellites, and in some cases this is supported with a DORIS instrument measuring Doppler between LEO and ground DORIS stations. Over the last 20 years we have demonstrated 1-2 cm accurate LEO POD and about 1 mm for inter-satellite distance. In order to increase the accuracy of the single satellite POD or satellites in LEO formation we propose an “optical GNSS receiver”, a cw-laser on a LEO satellite to measure Doppler between a LEO and GNSS satellite(s) equipped with SLR arrays and to develop it for the next gravity field mission.      </p><p>The objective of the ESA mission NGGM-MAGIC (Next Generation Gravity Mission - Mass-change and Geosciences International Constellation) is the long-term monitoring of the temporal variations of Earth’s gravity field at high resolution in time (3 days) and space (100 km), complementing the GRACE-FO mission from NASA at 45° orbit inclination. Currently, the GRACE-type mission design is based on optical carrier-phase measurements between two LEO satellites flying in a formation and separated by 200 km.</p><p>We propose an extension of the GRACE-type LEO-LEO concept by the “optical GNSS receiver” to provide Doppler measurements between a LEO satellite and GNSS satellite(s) equipped with SLR corner cubes by means of a cw-laser onboard a LEO satellite. Such a “vertical” LEO-GNSS observable is missing in the classical GRACE-type LEO-LEO concept. If Doppler measurements are carried out from the two GRACE-type satellites in the LEO orbit to the same GNSS satellite and by forming single-differences to that GNSS satellite one can remove any GNSS-orbit related error in the measured LEO-GNSS Doppler. In this way, radial orbit difference can be obtained between the two GRACE-type satellites (free of all GNSS orbit errors) and complement “horizontal” LEO-LEO measurements between the two GRACE-type satellites in the LEO orbit.</p><p>The non-mechanical laser beam steering has been developed for an angle window of -40° to +40° and it does not require a rotating and a big telescope in LEO (no clouds and atmosphere turbulences in LEO). Therefore, in such a beam-steering window, one could always observe with a fiber cw-laser one GNSS satellite close to the zenith from both GRACE-type satellites. The non-mechanical beam steering concept in zenith direction can be supported by a small 10-cm like (fixed) Ritchey-Chrétien telescope (COTS), a Cassegrain reflector design widely used for LEO satellites, e.g., for James Webb Space Telescope or for an optical Earth imaging with Cubesats with the 50 cm resolution.</p><p>Considering that several GNSS satellites in the field of view could be observed from a LEO satellite with this approach (including LAGEOS-1/2 and Etalon satellites) and the non-mechanical laser beam steering could be extended towards the LEO horizon, an “optical” GNSS receiver is a new concept for POD of LEO satellites. Here, we provide simulations of this new concept for LEO POD with GNSS/SLR constellations equipped with SLR arrays and discuss all new applications this new concept could bring.</p>

Preliminary monthly gravity field models from kinematic orbits of SWARM Satellites

2021 ◽  
Author(s):  
Xingfu Zhang ◽  
Qiujie Chen ◽  
Yunzhong Shen
Keyword(s):  
Gravity Field ◽  
Large Scale ◽  
Earth System ◽  
The Earth ◽  
Swarm Satellites ◽  
Variable Gravity ◽  
Data Gap ◽  
One Year ◽  
Gravity Recovery ◽  
Gravity Field Models

<p>      Although the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE FO) satellite missions play an important role in monitoring global mass changes within the Earth system, there is a data gap of about one year spanning July 2017 to May 2018, which leads to discontinuous gravity observations for monitoring global mass changes. As an alternative mission, the SWARM satellites can provide gravity observations to close this data gap. In this paper, we are dedicated to developing alternative monthly time-variable gravity field solutions from SWARM data. Using kinematic orbits of SWARM from ITSG for the period January 2015 to September 2020, we have generated a preliminary time series of monthly gravity field models named Tongji-Swarm2019 up to degree and order 60. The comparisons between Tongji-Swarm2019 and GRACE/GRACE-FO monthly solutions show that Tongji-Swarm2019 solutions agree with GRACE/GRACE-FO models in terms of large-scale mass change signals over amazon, Greenland and other regions. We can conclude that Tongji-Swarm2019 monthly gravity field models are able to close the gap between GRACE and GRACE FO.</p>

MEDIUM-TERM OSCILLATIONS OF THE SOLAR ACTIVITY

2021 ◽  
Vol 44 ◽  
pp. 85-91
Author(s):  
V.N. Obridko ◽  
◽  
D.D. Sokoloff ◽  
V.V. Pipin ◽  
A.S. Shibalova ◽  
...  
Keyword(s):  
Solar Activity ◽  
Activity Cycle ◽  
Solar Interior ◽  
Local Fields ◽  
Lower Atmosphere ◽  
High Solar Activity ◽  
Dynamo Model ◽  
Sunspot Activity ◽  
Geomagnetic Variations ◽  
Near Surface

In addition to the well-known 11-year cycle, longer and shorter characteristic periods can be isolated in variations of the parameters of helio-geophysical activity. Periods of about 36 and 60 years were revealed in variations of the geomagnetic activity and an approximately 60-year periodicity, in the evolution of correlation between the pressure in the lower atmosphere and the solar activity. Similar periods are observed in the cyclonic activity. Such periods in the parameters of the solar activity are difficult to identify because of a limited database available; however, they are clearly visible in variations of the asymmetry of the sunspot activity in the northern and southern solar hemispheres. In geomagnetic variations, one can also isolate oscillations with the characteristic periods of 5-6 years (QSO) and 2-3 years (QBO). We have considered 5-6-year periodicities (about half the main cycle) observed in variations of the sunspot numbers and the intensity of the dipole component of the solar magnetic field. A comparison with different magnetic dynamo models allowed us to determine the possible origin of these oscillations. A similar result can be reproduced in a dynamo model with nonlinear parameter variations. In this case, the activity cycle turns out to be anharmonic and contains other periodicities in addition to the main one. As a result of the study, we conclude that the 5-6-year activity variations are related to the processes of nonlinear saturation of the dynamo in the solar interior. Quasi-biennial oscillations are actually separate pulses related little to each other. Therefore, the methods of the spectral analysis do not reveal them over large time intervals. They are a direct product of local fields, are generated in the near-surface layers, and are reliably recorded only in the epochs of high solar activity.

Sign in / Sign up

Export Citation Format

Share Document