Magnetometer data from the GRACE satellite duo

AbstractThis paper describes and discusses the preprocessing and calibration of the magnetic data taken by the navigational magnetometers onboard the two GRACE satellites, with focus on the almost 10 years period from January 2008 to the end of the GRACE mission in October 2017 for which 1-Hz magnetic data are available. A calibration of the magnetic data is performed by comparing the raw magnetometer sensor readings with model magnetic vector values as provided by the CHAOS-7 geomagnetic field model for the time and position of the GRACE data. The presented approach also accounts for magnetic disturbances produced by the satellite’s magnetorquer and for temperature effects, which are parametrized by the Sun incident angle. The root-mean-squared error of the difference between the calibrated data and CHAOS-7 model values is about 10 nT, which makes the GRACE magnetometer data relevant for geophysical investigations.

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Quantifying the resolution level where the GRACE satellites can separate Greenland's glacial mass balance from surface mass balance

The Cryosphere Discussions ◽

10.5194/tcd-9-1315-2015 ◽

2015 ◽

Vol 9 (1) ◽

pp. 1315-1343

Author(s):

J. A. Bonin ◽

D. P. Chambers

Keyword(s):

Mass Balance ◽

Gravity Measurement ◽

Surface Mass Balance ◽

Satellite Gravity ◽

Surface Mass ◽

Grace Data ◽

Resolution Level ◽

Grace Satellites ◽

Grace Satellite ◽

Gravity Mission

Abstract. Mass change over Greenland can be caused by either changes in the glacial mass balance (GMB) or the precipitation-based surface mass balance (SMB). The GRACE satellite gravity mission cannot directly separate the two physical causes because it measures the sum of the entire mass column with limited spatial resolution. We demonstrate one theoretical way to indirectly separate SMB from GMB with GRACE, using a least squares inversion technique with knowledge of the location of the glacier. However, we find that the limited 60 × 60 spherical harmonic representation of current GRACE data does not provide sufficient resolution to adequately accomplish the task. We determine that at a maximum degree/order of 90 × 90 or above, a noise-free gravity measurement could theoretically separate the SMB from GMB signals. However, current GRACE satellite errors are too large at present to separate the signals. A noise reduction of a factor of 9 at a resolution of 90 × 90 would provide the accuracy needed for the interannual SMB and GMB to be accurately separated.

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Quantifying the resolution level where the GRACE satellites can separate Greenland's glacial mass balance from surface mass balance

The Cryosphere ◽

10.5194/tc-9-1761-2015 ◽

2015 ◽

Vol 9 (5) ◽

pp. 1761-1772 ◽

Cited By ~ 2

Author(s):

J. A. Bonin ◽

D. P. Chambers

Keyword(s):

Mass Balance ◽

Gravity Measurement ◽

Surface Mass Balance ◽

Satellite Gravity ◽

Surface Mass ◽

Grace Data ◽

Resolution Level ◽

Grace Satellites ◽

Grace Satellite ◽

Gravity Mission

Abstract. Mass change over Greenland can be caused by either changes in the glacial dynamic mass balance (DMB) or the surface mass balance (SMB). The GRACE satellite gravity mission cannot directly separate the two physical causes because it measures the sum of the entire mass column with limited spatial resolution. We demonstrate one theoretical way to indirectly separate cumulative SMB from DMB with GRACE, using a least squares inversion technique with knowledge of the location of the glaciers. However, we find that the limited 60 × 60 spherical harmonic representation of current GRACE data does not provide sufficient resolution to adequately accomplish the task. We determine that at a maximum degree/order of 90 × 90 or above, a noise-free gravity measurement could theoretically separate the SMB from DMB signals. However, current GRACE satellite errors are too large at present to separate the signals. A noise reduction of a factor of 10 at a resolution of 90 × 90 would provide the accuracy needed for the interannual cumulative SMB and DMB to be accurately separated.

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Spatio-Temporal Patterns of Mass Changes in Himalayan Glaciated Region from EOF Analyses of GRACE Data

Remote Sensing ◽

10.3390/rs13020265 ◽

2021 ◽

Vol 13 (2) ◽

pp. 265

Author(s):

Harika Munagapati ◽

Virendra M. Tiwari

Keyword(s):

Temperature Anomaly ◽

Mass Gain ◽

Snow Accumulation ◽

Empirical Orthogonal Functions ◽

Total Water ◽

Orthogonal Functions ◽

Grace Data ◽

Grace Satellite ◽

Spatio Temporal ◽

Gravity Recovery

The nature of hydrological seasonality over the Himalayan Glaciated Region (HGR) is complex due to varied precipitation patterns. The present study attempts to exemplify the spatio-temporal variation of hydrological mass over the HGR using time-variable gravity from the Gravity Recovery and Climate Experiment (GRACE) satellite for the period of 2002–2016 on seasonal and interannual timescales. The mass signal derived from GRACE data is decomposed using empirical orthogonal functions (EOFs), allowing us to identify the three broad divisions of HGR, i.e., western, central, and eastern, based on the seasonal mass gain or loss that corresponds to prevailing climatic changes. Further, causative relationships between climatic variables and the EOF decomposed signals are explored using the Granger causality algorithm. It appears that a causal relationship exists between total precipitation and total water storage from GRACE. EOF modes also indicate certain regional anomalies such as the Karakoram mass gain, which represents ongoing snow accumulation. Our causality result suggests that the excessive snowfall in 2005–2008 has initiated this mass gain. However, as our results indicate, despite the dampening of snowfall rates after 2008, mass has been steadily increasing in the Karakorum, which is attributed to the flattening of the temperature anomaly curve and subsequent lower melting after 2008.

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THE STUDY OF LONGITUDINAL AND LATITUDINAL VARIATION OF EQUATORIAL ELECTROJET SIGNATURE AT STATIONS WITHIN THE 96°MM AND 210°MM AFRICAN AND ASIAN SECTORS RESPECTIVELY UNDER QUIET CONDITIONS.

FUDMA Journal of Sciences ◽

10.33003/fjs-2021-0502-662 ◽

2021 ◽

Vol 5 (2) ◽

pp. 511-532

Author(s):

Aniefiok Akpaneno ◽

Matthew Joshua ◽

K. R. Ekundayo

Keyword(s):

Seasonal Variation ◽

Geomagnetic Field ◽

Satellite Communication ◽

Equatorial Electrojet ◽

Latitudinal Variation ◽

Magnetic Data ◽

Horizontal Magnetic Field ◽

Baseline Values ◽

The Difference ◽

Current Systems

Solar quiet current (S_q) and Equatorial Electrojet (EEJ) are two current systems which are produced by electric current in the ionosphere. The enhancement of the horizontal magnetic field is the EEJ. This research is needed for monitoring equatorial geomagnetic current which causes atmospheric instabilities and affects high frequency and satellite communication. This study presents the longitudinal and latitudinal variation of equatorial electrojet signature at stations within the 96°mm and 210°mm African and Asian sectors respectively during quiet condition. Data from eleven observatories were used for this study. The objectives was to determine the longitudinal and latitudinal geomagnetic field variations during solar quiet conditions, Investigate monthly variation and diurnal transient seasonal variation; Measure the strength of the EEJ at stations within the same longitudinal sectors and find out the factors responsible for the longitudinal and latitudinal variation of EEJ. Horizontal (H) component of geomagnetic field for the year 2008 from Magnetic Data Acquisition System (MAGDAS) network were used for the study. The International Quiet Days (IQDs) were used to identify quiet days. Daily baseline values for each of the geomagnetic element H were obtained. The monthly average of the diurnal variation was found. The seasonal variation of dH was found. Results showed that: The longitudinal and latitudinal variation in the dH differs in magnitude from one station to another within the same longitude due to the difference in the influence of the EEJ on them.

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Joint assimilation of GRACE satellite and in-situ discharge observations into a global hydrological model

10.5194/egusphere-egu21-7511 ◽

2021 ◽

Author(s):

Kerstin Schulze ◽

Olga Engels ◽

Jürgen Kusche ◽

Helena Gerdener ◽

Hannes Müller Schmied ◽

...

Keyword(s):

Mississippi River ◽

Water Cycle ◽

Climate Forcing ◽

Model Parameters ◽

Multiple Observations ◽

Grace Data ◽

Freshwater System ◽

Grace Satellite ◽

Ocean Topography

Global hydrological models simulate water storages and fluxes of the water cycle which is important for e.g. water management decisions and drought/flood predictions. However, the models include many uncertainties due to the model inputs (e.g. climate forcing data), model parameters, and model structure resulting in disagreements with observations. To reduce these uncertainties, the models are typically calibrated against in-situ discharge observations or GRACE-derived total water storage anomalies (TWSA) are integrated into the model by data assimilation.In this study, we introduce a framework for jointly assimilating multiple observations into the WaterGAP 2.2d model over the Mississippi River Basin for 2003-2018. We do not only assimilate GRACE-derived TWSA but also in-situ discharge observations from gauge stations. In addition, we vary the number as well as the location of the considered discharge stations to derive information about e.g. the influence of assimilating down- or upstream stations.Our results show a strong influence of the GRACE data and that the assimilation of multiple discharge stations resembles the results of a traditional calibration approach. We expect the most downstream stations to have a larger impact on the assimilation results than the more upstream stations (as the downstream stations already include the information of the upstream stations). The gained insights of this study show a great potential to better assess and understand the global freshwater system and become even more relevant in view of the Surface Water and Ocean Topography (SWOT) satellite. SWOT will be launched in 2022 and is expected to allow the derivation of discharge observations globally for rivers wider than 50-100m.

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Multiscale techniques for 3D imaging of magnetic data for archaeo‐geophysical investigations in the Middle East: the case of Tell Barri (Syria)

Archaeological Prospection ◽

10.1002/arp.1751 ◽

2019 ◽

Vol 26 (4) ◽

pp. 379-395 ◽

Cited By ~ 2

Author(s):

Giovanni Florio ◽

Federico Cella ◽

Luca Speranza ◽

Raffaele Castaldo ◽

Raffaella Pierobon Benoit ◽

...

Keyword(s):

Middle East ◽

3D Imaging ◽

Magnetic Data ◽

Geophysical Investigations ◽

Multiscale Techniques

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An ice flow modeling perspective on bedrock adjustment patterns of the Greenland ice sheet

The Cryosphere ◽

10.5194/tc-6-1263-2012 ◽

2012 ◽

Vol 6 (6) ◽

pp. 1263-1274 ◽

Cited By ~ 3

Author(s):

M. Olaizola ◽

R. S. W. van de Wal ◽

M. M. Helsen ◽

B. de Boer

Keyword(s):

Mass Balance ◽

Maximum Yield ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Elastic Response ◽

Delayed Response ◽

Surface Mass ◽

Grace Data ◽

Grace Satellites ◽

Gravity Recovery

Abstract. Since the launch in 2002 of the Gravity Recovery and Climate Experiment (GRACE) satellites, several estimates of the mass balance of the Greenland ice sheet (GrIS) have been produced. To obtain ice mass changes, the GRACE data need to be corrected for the effect of deformation changes of the Earth's crust. Recently, a new method has been proposed where ice mass changes and bedrock changes are simultaneously solved. Results show bedrock subsidence over almost the entirety of Greenland in combination with ice mass loss which is only half of the currently standing estimates. This subsidence can be an elastic response, but it may however also be a delayed response to past changes. In this study we test whether these subsidence patterns are consistent with ice dynamical modeling results. We use a 3-D ice sheet–bedrock model with a surface mass balance forcing based on a mass balance gradient approach to study the pattern and magnitude of bedrock changes in Greenland. Different mass balance forcings are used. Simulations since the Last Glacial Maximum yield a bedrock delay with respect to the mass balance forcing of nearly 3000 yr and an average uplift at present of 0.3 mm yr−1. The spatial pattern of bedrock changes shows a small central subsidence as well as more intense uplift in the south. These results are not compatible with the gravity based reconstructions showing a subsidence with a maximum in central Greenland, thereby questioning whether the claim of halving of the ice mass change is justified.

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Efficient and robust coding in heterogeneous recurrent networks

10.1101/804864 ◽

2019 ◽

Author(s):

Fleur Zeldenrust ◽

Boris Gutkin ◽

Sophie Denéve

Keyword(s):

Mean Squared Error ◽

Predictive Coding ◽

Network Activity ◽

Inhibitory Neurons ◽

Correlated Noise ◽

Recurrent Networks ◽

Strong Correlations ◽

The Difference

Cortical networks show a large heterogeneity of neuronal properties. However, traditional coding models have focused on homogeneous populations of excitatory and inhibitory neurons. Here, we analytically derive a class of recurrent networks of spiking neurons that close to optimally track a continuously varying input online, based on two assumptions: 1) every spike is decoded linearly and 2) the network aims to reduce the mean-squared error between the input and the estimate. From this we derive a class of predictive coding networks, that unifies encoding and decoding and in which we can investigate the difference between homogeneous networks and heterogeneous networks, in which each neurons represents different features and has different spike-generating properties. We find that in this framework, ‘type 1’ and ‘type 2’ neurons arise naturally and networks consisting of a heterogeneous population of different neuron types are both more efficient and more robust against correlated noise. We make two experimental predictions: 1) we predict that integrators show strong correlations with other integrators and resonators are correlated with resonators, whereas the correlations are much weaker between neurons with different coding properties and 2) that ‘type 2’ neurons are more coherent with the overall network activity than ‘type 1’ neurons.

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Identifying the genetic and non-genetic factors associated with accelerated eye aging by using deep learning to predict age from fundus and optical coherence tomography images

10.1101/2021.06.24.21259471 ◽

2021 ◽

Author(s):

Alan Le Goallec ◽

Samuel Diai ◽

Sasha Collin ◽

Theo Vincent ◽

Chirag J Patel

Keyword(s):

Optical Coherence Tomography ◽

Genome Wide Association Study ◽

Mean Squared Error ◽

Optical Coherence ◽

Nucleotide Polymorphisms ◽

Age Related ◽

Genome Wide ◽

A Genome ◽

Eye Pigmentation ◽

The Difference

With age, eyesight declines and the vulnerability to age-related eye diseases such as glaucoma, cataract, macular degeneration and diabetic retinopathy increases. With the aging of the global population, the prevalence of these diseases is projected to increase, leading to reduced quality of life and increased healthcare cost. In the following, we built an eye age predictor by training convolutional neural networks to predict age from 175,000 eye fundus and optical coherence tomography images (R-Squared=83.6+/-0.6%; root mean squared error=3.34+/-0.07 years). We used attention maps to identify the features driving the eye age prediction. We defined accelerated eye aging as the difference between eye age and chronological age and performed a genome wide association study [GWAS] on this phenotype. Accelerated eye aging is 28.2+-1.2% GWAS-heritable, and is associated with 255 single nucleotide polymorphisms in 122 genes (e.g HERC2, associated with eye pigmentation). Similarly, we identified biomarkers (e.g blood pressure), clinical phenotypes (e.g chest pain), diseases (e.g cataract), environmental variables (e.g sleep deprivation) and socioeconomic variables (e.g income) associated with our newly defined phenotype. Our predictor could be used to detect premature eye aging in patients, and to evaluate the effect of emerging rejuvenation therapies on eye health.

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Monitoring Droughts From GRACE

Frontiers in Environmental Science ◽

10.3389/fenvs.2020.584690 ◽

2020 ◽

Vol 8 ◽

Author(s):

Bramha Dutt Vishwakarma

Keyword(s):

Satellite Remote Sensing ◽

Water Storage ◽

Economic Security ◽

Satellite Mission ◽

Near Surface ◽

The Earth ◽

Grace Data ◽

Near Future ◽

Grace Mission ◽

Storage Change

With ongoing climate change, we are staring at possibly longer and more severe droughts in the future. Therefore, monitoring and understanding duration and intensity of droughts, and how are they evolving in space and time is imperative for global socio-economic security. Satellite remote sensing has helped us a lot in this endeavor, but most of the satellite missions observe only near-surface properties of the Earth. A recent geodetic satellite mission, GRACE, measured the water storage change both on and beneath the surface, which makes it unique and valuable for drought research. This novel dataset comes with unique problems and characteristics that we should acknowledge before using it. In this perspective article, I elucidate important characteristics of various available GRACE products that are important for drought research. I also discuss limitations of GRACE mission that one should be aware of, and finally I shed some light on latest developments in GRACE data processing that may open numerous possibilities in near future.

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