MATLAB tools for the post-processing of GRACE temporal gravity field solutions

2020 ◽  
Author(s):  
Dimitrios Piretzidis ◽  
Michael Sideris
Keyword(s):  
Gravity Field ◽  
Land Surface ◽  
Optimal Strategies ◽  
Post Processing ◽  
Satellite Mission ◽  
Surface Mass ◽  
Isostatic Adjustment ◽  
Processing Strategies ◽  
Grace Data ◽  
Temporal Gravity

<p>We present a collection of MATLAB tools for the post-processing of temporal gravity field solutions from the Gravity Recovery and Climate Experiment (GRACE) satellite mission. GRACE final products are in the form of monthly sets of spherical harmonic coefficients and have been extensively used by the scientific community to study the land surface mass redistribution that is predominantly due to ice melting, glacial isostatic adjustment, seismic activity and hydrological phenomena. Since the launch of GRACE satellites, a substantial effort has been made to develop processing strategies and improve the surface mass change estimates.</p><p>The MATAB software presented in this work is developed and used by the Gravity and Earth Observation group at the department of Geomatics Engineering, University of Calgary. A variety of techniques and tools for the processing of GRACE data are implemented, tested and analyzed. Some of the software capabilities are: filtering of GRACE data using decorrelation and smoothing techniques, conversion of gravity changes into mass changes on the Earth’s spherical, ellipsoidal and topographical surface, implementation of forward modeling techniques for the estimation and removal of long-term trends due to ice mass melting, basin-specific spatial averaging in the spatial and spectral domain, time series smoothing and decomposition techniques, and data visualization.</p><p>All tools use different levels of parameterization in order to assist both expert users and non-specialists. Such a software makes the comparison between different GRACE processing methods and parameters used easier, leading to optimal strategies for the estimation of surface mass changes and to the standardization of GRACE data post-processing. It could also facilitate the use of GRACE data to non-geodesists.</p>

An analysis of terrestrial water and groundwater storage changes in North America using recent GRACE products

2020 ◽  
Author(s):  
Michael Sideris ◽  
Dimitrios Piretzidis
Keyword(s):  
North America ◽  
Satellite Mission ◽  
Groundwater Storage ◽  
Surface Mass ◽  
Isostatic Adjustment ◽  
Grace Data ◽  
Combination Scheme ◽  
Terrestrial Water ◽  
Annual Signal

<p>In this study, we use temporal solutions of the Gravity Recovery and Climate Experiment (GRACE) satellite mission to study the surface mass variations of hydrological origin in North America. The most recent release (RL06) of GRACE Level 2 data from three processing centers (CSR, JPL, GFZ) and mascon products are used in a combination scheme to produce estimates of terrestrial water storage (TWS) changes for the period 2002–2016. The land hydrology signal is isolated from GRACE data by removing the contribution of two major non-hydrologic processes, i.e., the glacial isostatic adjustment (GIA) and the ice mass melting from the glaciated areas of Alaska, Greenland and the Canadian Arctic.</p><p>The examination of long-term TWS trends revealed strong signatures of the 2011–2015 droughts in California and Texas, as well as accumulation of TWS in the central part of North America. Negative long-term TWS trends associated with ice melting were found around the Hudson Bay region. The TWS changes are dominated by a strong annual and semi-annual signal with higher magnitude in Alaska and along the west coast of North America.</p><p>An additional study on the estimation of groundwater storage (GWS) changes is performed using the Global Land Data Assimilation System (GLDAS) model. The GLDAS data are pre-filtered using the same strategy as GRACE data to ensure spectral consistency between them. The general behavior of GWS agrees well with the TWS, especially in terms of positive long-term GWS trends in central North America and strong annual signal in Alaska. Positive GWS trends are also identified in the east US coast.</p>

scholarly journals Impact of Different Kinematic Empirical Parameters Processing Strategies on Temporal Gravity Field Model Determination

2018 ◽  
Vol 123 (11) ◽  
pp. 10,252-10,276 ◽  
Author(s):  
Hao Zhou ◽  
Zhicai Luo ◽  
Zebing Zhou ◽  
Qiong Li ◽  
Bo Zhong ◽  
...  
Keyword(s):  
Gravity Field ◽  
Field Model ◽  
Gravity Field Model ◽  
Processing Strategies ◽  
Model Determination ◽  
Temporal Gravity

Simulation study on gravity field determination with small satellites in NGGM 

2021 ◽  
Author(s):  
Nikolas Pfaffenzeller ◽  
Roland Pail
Keyword(s):  
Gravity Field ◽  
Cost Effective ◽  
Transport Processes ◽  
Ocean Tide ◽  
Satellite Mission ◽  
Spatiotemporal Resolution ◽  
Small Satellites ◽  
Gravity Fields ◽  
Ocean Tide Models ◽  
Temporal Gravity

<p>In the context of an increased public interest in climate-relevant processes, a number of studies on Next Generation Gravity Missions (NGGMs) have been commissioned to better map mass transport processes on Earth. On the basis of the successfully completed gravity field missions CHAMP, GOCE and GRACE as well as the current satellite mission GRACE-FO, different concepts were examined for their feasibility and economic efficiency. The focus is on increasing the spatiotemporal resolution while simultaneously reducing the known error effects such as the aliasing of temporal gravity fields due to under-sampling of signals and uncertainties in ocean tide models. An additional inclined pair to a GRACE-like satellite pair (Bender constellation) is the most promising solution. Since the costs for a realization of the Bender constellation are very high, this contribution focuses on alternative concepts in the form of different constellations and formations of small satellites. The latter includes both satellite pairs and chains consisting of trailing satellites. The aim is to provide a cost-effective alternative to the previous gravity field satellites while simultaneously increasing the spatiotemporal resolution and minimizing the above mentioned error effects. In numerical closed-loop simulations, various scenarios will be conducted which differ in orbit parameters like shape and number of orbits, the number of satellites per orbit and instrument performances. Additionally, the impacts from the co-parametrization of non-tidal temporal gravity field signal and ocean tides on the gravity field solutions, obtained by the different concepts, will be investigated. In particular the possibilities and limits with multiple satellites pairs for achieving the highest possible spatial and temporal resolution in (sub-)daily temporal gravity fields shall be analysed in detail.</p>

scholarly journals Post-Glacial Land Uplift Rate in Fennoscandia and Laurentia Determined by GRACE Data

2019 ◽  
Author(s):  
Mehdi S. Shafiei Joud ◽  
Lars Erik Sjöberg ◽  
Mohammad Bagherbandi
Keyword(s):  
Gravity Field ◽  
Signal To Noise Ratio ◽  
Principal Component ◽  
Complete Agreement ◽  
Uplift Rate ◽  
Mathematical Methods ◽  
Land Uplift ◽  
Forward Models ◽  
Isostatic Adjustment ◽  
Grace Data

The mantle mass flow interconnected with the process of Glacial Isostatic Adjustment (GIA) and the reformation of the Earth’s crust constantly perturbs the observed gravity field towards a hypothetic isostatic state. We analyse the temporal changes of the gravity field from the GRACE data, using different mathematical and/or statistical methods to detect the GIA amidst other gravity signals. A number of gravimetric post-glacial land uplift rate (LUR) modelling methods are investigated and compared with the data from a total number of 515 GPS stations and preferred GIA forward models in Fennoscandia and North America. We investigate three mathematical methods, namely regression, principal component, and independent component analysis (ICA) to extracting the GIA signal from the GRACE monthly geoid heights. We use some regularization techniques to exploit the GRACE monthly data to their maximum spatial resolution and to increase the Signal to Noise Ratio of their short wavelengths. Near the centres of the study areas the gravimetric LUR model using the fast-ICA algorithm of Hyvärinen and Oja (2000) is shown to be in a complete agreement with the GPS data and the predictions of the GIA forward models, and for the whole areas, subject to epeirogeny movement of the two regions, their discrepancies reach to the extrema at -1.8 and +3.3, and -4.5 and +7.5 mm/a, respectively. We show that the largest discrepancies between the gravimetric model using the ICA method and the GIA forward model, occur for the sub-regions likely collocated with strong ice mass change signals.

Simulation study on future gravity missions with constellations and formations of small satellites

2020 ◽  
Author(s):  
Nikolas Pfaffenzeller ◽  
Roland Pail ◽  
Tom Yunck
Keyword(s):  
Gravity Field ◽  
Cost Effective ◽  
Transport Processes ◽  
Ocean Tide ◽  
Satellite Mission ◽  
Spatiotemporal Resolution ◽  
Small Satellites ◽  
Under Sampling ◽  
Ocean Tide Models ◽  
Temporal Gravity

<p>In the context of an increased public interest in climate-relevant processes, a number of studies on Next Generation Gravity Missions (NGGMs) have been commissioned to better map mass transport processes on Earth. On the basis of the successfully completed gravity field missions CHAMP, GOCE and GRACE as well as the current satellite mission GRACE-FO, different concepts were examined for their feasibility and economic efficiency. The focus is on increasing the spatiotemporal resolution while simultaneously reducing the known error effects such as the aliasing of temporal gravity fields due to under-sampling of signals and uncertainties in ocean tide models. An additional inclined pair to a GRACE-like satellite pair (Bender constellation) is the most promising solution. Since the costs for a realization of the Bender constellation are very high, this contribution focuses on alternative concepts in the form of different constellations and formations of small satellites. The latter includes both satellite pairs and chains consisting of trailing satellites. The aim is to provide a cost-effective alternative to the previous gravity field satellites while simultaneously increasing the spatiotemporal resolution and minimizing the above mentioned error effects. In numerical closed-loop simulations, different scenarios will be performed which differ in orbit parameters like shape and number of orbits, the number of satellites per orbit and their distance to each other as well as the number of inter-satellite links. Additionally, the impacts from the co-parametrization of non-tidal temporal gravity field signal and ocean tides on the gravity field solutions, obtained by the different concepts, will be investigated. </p>

Temporal gravity variations in GOCE release 6 gravitational gradients

2020 ◽  
Author(s):  
Betty Heller ◽  
Frank Siegismund ◽  
Roland Pail ◽  
Thomas Gruber
Keyword(s):  
Gravity Field ◽  
Spatial Scales ◽  
Low Frequency ◽  
Frequency Range ◽  
Gravitational Gradient ◽  
Grace Data ◽  
Gravitational Gradients ◽  
Gravity Variations ◽  
Temporal Gravity ◽  
Gravity Field Models

<p>As opposed to the level 1B release 5 GOCE gravitational gradient data, the newly reprocessed release 6 gradients provide reduced noise amplitudes in the low frequency-range, leading to reduced noise amplitudes of the derived gravity field models at large spatial scales, where temporal variations of the Earth’s gravity field have their highest amplitudes. This is the motivation to test the release 6 gradients for their ability to resolve temporal gravity variations.</p><p>For the gravity field processing, we apply a conventional spherical harmonics approach using the time-wise (TIM) processing method as well as a mass concentration (mascon) approach using point masses as base elements, which are grouped to land or ocean mascons by taking into account the coastlines.</p><p>By means of a closed-loop simulation study, we find that the colored instrument noise of the GOCE gravitational gradiometer introduces noise amplitudes into the derived gravity field models that lie above the amplitude of the gravity trend signal accumulated over 5 years. This indicates that detecting gravity variations taking place during the four-year GOCE data period from GOCE gradients only is challenging.</p><p>Using real GOCE data, we test bimonthly gradiometry-only gravity field models computed by both the spherical harmonic and the mascon approach for gravity signals that are resolved by GRACE data, being the temporal signals due to the ice mass trends in Greenland and Antarctica and the 2011 earthquake in Japan. Besides, corresponding GRACE/GOCE combination models are used to test whether the incorporation of GOCE data increases the resolution of temporal gravity signals.</p><p>We found that high-amplitude long-wavelength noise prevented the detection of temporal gravity variations among the bimonthly GOCE-only models. Using the SH approach, it was possible to detect the mean trend signal contained in the data by averaging multiple bimonthly models and considering their difference to a reference model. Using the mascon approach, trend signals contained in GOCE data could be recovered by including a GRACE model truncated to d/o 45 in a GRACE/GOCE combination model and thus let the GOCE data determine the short-scale signal structures instead of GRACE.</p><p>Finally, compared to the temporal gravity signal as resolved by GRACE data, no significant benefit of using or incorporating GOCE gravitational gradient data was found. The reason are the still rather high noise amplitudes in the derived models at large spatial scales, where the considered signal is strongest.</p><p>In order to detect temporal gravity variations in satellite gravitational gradiometry data, the measurement noise amplitudes in the low-frequency range would need to be reduced.</p>

Constellations and formations of small satellites in NGGM concepts

2020 ◽  
Author(s):  
Nikolas Pfaffenzeller ◽  
Roland Pail
Keyword(s):  
Gravity Field ◽  
Cost Effective ◽  
Transport Processes ◽  
Ocean Tide ◽  
Satellite Mission ◽  
Spatiotemporal Resolution ◽  
Small Satellites ◽  
Gravity Fields ◽  
Ocean Tide Models ◽  
Temporal Gravity

<p>In the context of an increased public interest in climate-relevant processes, a number of studies on Next Generation Gravity Missions (NGGMs) have been commissioned to better map mass transport processes on Earth. On the basis of the successfully completed gravity field missions CHAMP, GOCE and GRACE as well as the current satellite mission GRACE-FO, different concepts were examined for their feasibility and economic efficiency. The focus is on increasing the spatiotemporal resolution while simultaneously reducing the known error effects such as the aliasing of temporal gravity fields due to under-sampling of signals and uncertainties in ocean tide models. An additional inclined pair to a GRACE-like satellite pair (Bender constellation) is the most promising solution. Since the costs for a realization of the Bender constellation are very high, this contribution focuses on alternative concepts in the form of different constellations and formations of small satellites. The latter includes both satellite pairs and chains consisting of trailing satellites. The aim is to provide a cost-effective alternative to the previous gravity field satellites while simultaneously increasing the spatiotemporal resolution and minimizing the above mentioned error effects. In numerical closed-loop simulations, various scenarios will be conducted which differ in orbit parameters like shape and number of orbits and the number of satellites per orbit and instrument performances. Additionally, the impacts from the co-parametrization of non-tidal short periodic temporal gravity field signal on the gravity field solutions (so-called Wiese approach), obtained by the different concepts, will be investigated. In particular the possibilities and limits with multiple satellites pairs for achieving the highest possible spatial and temporal resolution in (sub-)daily temporal gravity fields shall be analyzed in detail which is crucial for macrosocial tasks in water balance estimation and water management.</p>

scholarly journals Estimation of regional mass anomalies from Gravity Recovery and Climate Experiment (GRACE) over Himalayan region

2014 ◽  
Vol XL-8 ◽  
pp. 329-332 ◽  
Author(s):  
R. Agrawal ◽  
S. K. Singh ◽  
A. S. Rajawat ◽  
Ajai
Keyword(s):  
Gravity Field ◽  
Spherical Harmonic ◽  
Regional Scale ◽  
Indus Basin ◽  
Time Variability ◽  
Annual Change ◽  
Large Area ◽  
Satellite Mission ◽  
Grace Data ◽  
Gravity Recovery

Time-variable gravity changes are caused by a combination of postglacial rebound, redistribution of water and snow/ice on land and as well as in the ocean. The Gravity Recovery and Climate Experiment (GRACE) satellite mission, launched in 2002, provides monthly average of the spherical harmonic co-efficient. These spherical harmonic co-efficient describe earth’s gravity field with a resolution of few hundred kilometers. Time-variability of gravity field represents the change in mass over regional level with accuracies in cm in terms of Water Equivalent Height (WEH). The WEH reflects the changes in the integrated vertically store water including snow cover, surface water, ground water and soil moisture at regional scale. GRACE data are also sensitive towards interior strain variation, surface uplift and surface subsidence cover over a large area. <br><br> GRACE data was extracted over the three major Indian River basins, Indus, Ganga and Brahmaputra, in the Himalayas which are perennial source of fresh water throughout the year in Northern Indian Plain. Time series analysis of the GRACE data was carried out from 2003&ndash;2012 over the study area. Trends and amplitudes of the regional mass anomalies in the region were estimated using level 3 GRACE data product with a spatial resolution at 10 by 10 grid provided by Center for Space Research (CSR), University of Texas at Austin. Indus basin has shown a subtle decreasing trend from 2003&ndash;2012 however it was observed to be statistically insignificant at 95 % confidence level. Ganga and Brahmaputra basins have shown a clear decreasing trend in WEH which was also observed to be statistically significant. The trend analysis over Ganga and Brahamputra basins have shown an average annual change of &minus;1.28 cm and &minus;1.06 cm in terms of WEH whereas Indus basin has shown a slight annual change of &minus;0.07 cm. This analysis will be helpful to understand the loss of mass in terms of WEH over Indian Himalayas and will be crucial for hydrological and climate applications at regional scale.

scholarly journals Instrument Data Simulations for GRACE Follow-on: Observation and Noise Models

2017 ◽  
Author(s):  
Neda Darbeheshti ◽  
Henry Wegener ◽  
Vitali Müller ◽  
Majid Naeimi ◽  
Gerhard Heinzel ◽  
...  
Keyword(s):  
Gravity Field ◽  
Simulated Data ◽  
Laser Interferometry ◽  
Scientific Basis ◽  
Satellite Mission ◽  
Earth’S Gravity Field ◽  
Gravity Field Recovery ◽  
Grace Data ◽  
Data Files ◽  
Grace Mission

Abstract. The Gravity Recovery and Climate Experiment (GRACE) mission has yielded data on the Earth's gravity field to monitor temporal changes for more than fifteen years now. The GRACE twin satellites use microwave ranging with micrometer precision to measure distance variations between two satellites caused by the Earth's global gravitational field. GRACE Follow-on (GRACE-FO) will be the first satellite mission to use inter-satellite laser interferometry in space. The laser ranging instrument (LRI) will provide two additional measurements compared to the GRACE mission: interferometric inter-satellite ranging with nanometer precision and inter-satellite pointing information. We have designed a set of simulated GRACE-FO data, which include LRI measurements, apart from all other GRACE instrument data needed for the Earth's gravity field recovery. The simulated data files are publicly available via https://doi.org/10.22027/AMDC2 and can be used to derive gravity field solutions like from GRACE data. This paper describes the scientific basis and technical approaches used to simulate the GRACE-FO instrument data.

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