The Intriguing Structure of Stripes in GRACE Geopotential Models

Geopotential models derived from Gravity Recovery and Climate Experiment (GRACE) mission measurements are significantly obscured by the presence of a systematic artifact, known as longitudinal stripes. Based on our previous work (Peidou and Pagiatakis, 2020) we provide an in-depth analysis of the latitudinal sampling characteristics of GRACE and we reveal the intriguing sampling mechanism that creates sub-Nyquist artifacts (stripes). Because the sub-Nyquist artifacts are poorly understood, we provide a simple simulation example to elucidate the mechanism of the sub-Nyquist artifact generation. Subsequently, we randomly select June 2009 daily GPS precise science orbits for GRACE-A to produce ground tracks to sample the low frequency disturbing potential (geoid) along the parallel of ϕ=10° N. The sampled geoid is then deinterlaced in space to produce a monthly data sequence whose detailed analysis shows that the sub-Nyquist artifacts (stripes) are produced from a critical sampling rate of the low degree gravitational field that is related to the ratio m/n of two mutually prime integers, where m is the number of days it takes to have a nearly repeat orbit and n is the number of complete orbits in one day. We perform extensive analyses of GRACE Level-2 data over a period of eight years to show the variability in the orbital characteristics that are directly linked to the orbit resonances (via integers m and n). It turns out that during short repeat cycle resonances the stripes are amplified. Finally, to minimize the presence of stripes in Level-2 data products, it is recommended that orbits of future missions should be designed to avoid the critical m/n ratios while appropriately monitoring and adjusting them during the mission. For completed missions, or missions that are already active, force modelling the latitudinal low frequency disturbing potential may be a viable and most preferred approach to filtering.

Download Full-text

Introducing an Improved GRACE Global Point-Mass Solution—A Case Study in Antarctica

Remote Sensing ◽

10.3390/rs12193197 ◽

2020 ◽

Vol 12 (19) ◽

pp. 3197 ◽

Cited By ~ 1

Author(s):

Vagner G. Ferreira ◽

Bin Yong ◽

Kurt Seitz ◽

Bernhard Heck ◽

Thomas Grombein

Keyword(s):

Noise Level ◽

Order Approximation ◽

Statistical Tests ◽

Taylor Series Expansion ◽

Point Mass ◽

Surface Integral ◽

Goddard Space Flight Center ◽

Gravity Recovery ◽

Grace Mission ◽

Level 2

In the so-called point-mass modeling, surface densities are represented by point masses, providing only an approximated solution of the surface integral for the gravitational potential. Here, we propose a refinement for the point-mass modeling based on Taylor series expansion in which the zeroth-order approximation is equivalent to the point-mass solution. Simulations show that adding higher-order terms neglected in the point-mass modeling reduces the error of inverted mass changes of up to 90% on global and Antarctica scales. The method provides an alternative to the processing of the Level-2 data from the Gravity Recovery and Climate Experiment (GRACE) mission. While the evaluation of the surface densities based on improved point-mass modeling using ITSG-Grace2018 Level-2 data as observations reveals noise level of approximately 5.77 mm, this figure is 5.02, 6.05, and 5.81 mm for Center for Space Research (CSR), Goddard Space Flight Center (GSFC), and Jet Propulsion Laboratory (JPL) mascon solutions, respectively. Statistical tests demonstrate that the four solutions are not significant different (95% confidence) over Antarctica Ice Sheet (AIS), despite the slight differences seen in the noises. Therefore, the estimated noise level for the four solutions indicates the quality of GRACE mass changes over AIS. Overall, AIS shows a mass loss of −7.58 mm/year during 2003–2015 based on the improved point-mass solution, which agrees with the values derived from mascon solutions.

Download Full-text

Preliminary GRACE-FO gravity field solutions from Tongji University

10.5194/egusphere-egu2020-7707 ◽

2020 ◽

Author(s):

Qiujie Chen ◽

Yunzhong Shen ◽

Xingfu Zhang ◽

Jürgen Kusche

Keyword(s):

Mass Transport ◽

Gravity Field ◽

Sampling Rate ◽

Laser Ranging ◽

University Of Technology ◽

Gravity Field Determination ◽

New Feature ◽

Gravity Recovery ◽

Grace Mission ◽

Tongji University

<p>Due to the battery issue, the Gravity Recovery and Climate Experiment (GRACE) mission unfortunately came to an end in October 2017 after providing more than 15 years of mass transport information of our changing planet. To continue to monitoring the mass transport in the Earth system, the GRACE Follow-On (GRACE-FO) was launched in May 2018. As a new feature of GRACE-FO, a Laser Ranging Interferometer (LRI) was equipped to measure the inter-satellite range at a nanometer level. Since May 2019, GRACE-FO Level-1B observations have been made available to our community. Using the GRACE-FO Level-1B observations without laser ranging information, preliminary GRACE-FO gravity field solutions from Center for Space Research (CSR), GeoForschungsZentrum (GFZ), Jet Propulsion Laboratory (JPL) and Graz University of Technology have been released. Incorporating laser ranging observations into gravity field determination, a preliminary time series of GRACE-FO gravity field solutions has been derived from Tongji University in collaboration with University of Bonn. In this paper, the signal and noise of our gravity field solutions are analyzed and compared to those from other research groups. Our results show that the laser ranging observations with a sampling rate of 2s are able to improve gravity field solutions by about 7% in terms of geoid degree variances up to degree and order 96 as compared to the K-Band ranging data with a sampling rate of 5s.</p>

Download Full-text

The Attenuation of Very Low Frequency Brain Oscillations in Transitions from a Rest State to Active Attention

Journal of Psychophysiology ◽

10.1027/0269-8803.23.4.191 ◽

2009 ◽

Vol 23 (4) ◽

pp. 191-198 ◽

Cited By ~ 26

Author(s):

Suzannah K. Helps ◽

Samantha J. Broyd ◽

Christopher J. James ◽

Anke Karl ◽

Edmund J. S. Sonuga-Barke

Keyword(s):

Brain Activity ◽

Sampling Rate ◽

Low Frequency ◽

Future Research ◽

Adhd Symptoms ◽

Default Mode ◽

Very Low Frequency ◽

Wide Range ◽

Interference Hypothesis ◽

Mode Interference

Background: The default mode interference hypothesis ( Sonuga-Barke & Castellanos, 2007 ) predicts (1) the attenuation of very low frequency oscillations (VLFO; e.g., .05 Hz) in brain activity within the default mode network during the transition from rest to task, and (2) that failures to attenuate in this way will lead to an increased likelihood of periodic attention lapses that are synchronized to the VLFO pattern. Here, we tested these predictions using DC-EEG recordings within and outside of a previously identified network of electrode locations hypothesized to reflect DMN activity (i.e., S3 network; Helps et al., 2008 ). Method: 24 young adults (mean age 22.3 years; 8 male), sampled to include a wide range of ADHD symptoms, took part in a study of rest to task transitions. Two conditions were compared: 5 min of rest (eyes open) and a 10-min simple 2-choice RT task with a relatively high sampling rate (ISI 1 s). DC-EEG was recorded during both conditions, and the low-frequency spectrum was decomposed and measures of the power within specific bands extracted. Results: Shift from rest to task led to an attenuation of VLFO activity within the S3 network which was inversely associated with ADHD symptoms. RT during task also showed a VLFO signature. During task there was a small but significant degree of synchronization between EEG and RT in the VLFO band. Attenuators showed a lower degree of synchrony than nonattenuators. Discussion: The results provide some initial EEG-based support for the default mode interference hypothesis and suggest that failure to attenuate VLFO in the S3 network is associated with higher synchrony between low-frequency brain activity and RT fluctuations during a simple RT task. Although significant, the effects were small and future research should employ tasks with a higher sampling rate to increase the possibility of extracting robust and stable signals.

Download Full-text

Study of water storage variations at the Pantanal wetlands area from GRACE monthly mass grids

Journal of Geodetic Science ◽

10.1515/jogs-2019-0013 ◽

2019 ◽

Vol 9 (1) ◽

pp. 133-143

Author(s):

Ayelen Pereira ◽

Cecilia Cornero ◽

Ana C. O. C. Matos ◽

M. Cristina Pacino ◽

Denizar Blitzkow

Keyword(s):

Water Mass ◽

Spatial Scales ◽

Water Storage ◽

Transport Processes ◽

Satellite Gravity ◽

The North ◽

Paraguay River ◽

Gravity Recovery ◽

Grace Mission ◽

Phase Differences

Abstract The continental water storage is significantly in-fluenced by wetlands, which are highly affected by climate change and anthropogenic influences. The Pantanal, located in the Paraguay river basin, is one of the world’s largest and most important wetlands because of the environmental biodiversity that represents. The satellite gravity mission GRACE (Gravity Recovery And Climate Experiment) provided until 2017 time-variable Earth’s gravity field models that reflected the variations due to mass transport processes-like continental water storage changes-which allowed to study environments such as wetlands, at large spatial scales. The water storage variations for the period 2002-2016, by using monthly land water mass grids of Total Water Storage (TWS) derived from GRACE solutions, were evaluated in the Pantanal area. The capability of the GRACE mission for monitoring this particular environment is analyzed, and the comparison of the water mass changes with rainfall and hydrometric heights data at different stations distributed over the Pantanal region was carried out. Additionally, the correlation between the TWS and river gauge measurements, and the phase differences for these variables, were also evaluated. Results show two distinct zones: high correlations and low phase shifts at the north, and smaller correlation values and consequently significant phase differences towards the south. This situation is mainly related to the hydrogeological domains of the area.

Download Full-text

Determination of the Distribution of Relaxation Times by Means of Pulse Evaluation for Offline and Online Diagnosis of Lithium-Ion Batteries

Batteries ◽

10.3390/batteries7020036 ◽

2021 ◽

Vol 7 (2) ◽

pp. 36

Author(s):

Erik Goldammer ◽

Julia Kowal

Keyword(s):

Lithium Ion Batteries ◽

Electrochemical Impedance ◽

Sampling Rate ◽

Relaxation Times ◽

Low Frequency ◽

Lithium Ion ◽

Battery Management ◽

Time Constants ◽

Time Domain Data ◽

Aging Study

The distribution of relaxation times (DRT) analysis of impedance spectra is a proven method to determine the number of occurring polarization processes in lithium-ion batteries (LIBs), their polarization contributions and characteristic time constants. Direct measurement of a spectrum by means of electrochemical impedance spectroscopy (EIS), however, suffers from a high expenditure of time for low-frequency impedances and a lack of general availability in most online applications. In this study, a method is presented to derive the DRT by evaluating the relaxation voltage after a current pulse. The method was experimentally validated using both EIS and the proposed pulse evaluation to determine the DRT of automotive pouch-cells and an aging study was carried out. The DRT derived from time domain data provided improved resolution of processes with large time constants and therefore enabled changes in low-frequency impedance and the correlated degradation mechanisms to be identified. One of the polarization contributions identified could be determined as an indicator for the potential risk of plating. The novel, general approach for batteries was tested with a sampling rate of 10 Hz and only requires relaxation periods. Therefore, the method is applicable in battery management systems and contributes to improving the reliability and safety of LIBs.

Download Full-text

Results of the infrasonic array on the Valaam Island primary data processing

Российский сейсмологический журнал [Russian Journal of Seismology] ◽

10.35540/2686-7907.2020.1.08 ◽

2020 ◽

Vol 2 (1) ◽

pp. 85-91

Author(s):

Vladimir Karpinsky ◽

Vladimir Asming

Keyword(s):

Data Processing ◽

Seismic Station ◽

Sampling Rate ◽

Low Frequency ◽

Primary Data ◽

Joint Analysis ◽

Main Task ◽

Significant Difference ◽

Infrasound Signal ◽

Short Time

The infrasound array VALS developed in Kola Branch GS RAS has been installed in June 2016 on the Valaam Island in addition to the continuously operating seismic station VALR. The array consists of 3 spaced low-frequency microphones. The data with a sampling rate of 100 Hz is stored continuously at the acquisition computer; the timing is carried out using GPS. In addition to the acquisition system, an infrasound signal detector is installed on the computer. It works in near real-time mode and enables us to find signals and compute their back azimuths. At the end of 2018, a new version of the detector was developed at the Kola Branch GS RAS. The detector began to work much faster, which enabled us to carry out data processing for 2.5 years in two frequency ranges in a short time. The main task of the array is acoustic monitoring, the detection of infrasound events, the determination of their parameters, and the selection of events of natural origin. The data are also used (in combination with the VALR seismic station data) to locate near seismic events, especially weak ones. The analysis of the obtained data revealed the prevailing directions to the signal sources. The change of directions to sources in time was investigated, seasonal features were revealed. Acoustic events were detected in the frequency bands 1–5 Hz and 10–20 Hz, and a significant difference was found in the azimuthal distribution of events for these ranges. A joint analysis of acoustic and seismic data showed that the part of events with both acoustic and seismic components is low – it is almost completely exhausted by career explosions. It was also noted that in addition to explosions in nearby quarries (Kuznechnoye, Pitkäranta) located at a distance of 50–60 km, according to acoustic data, events corresponding to explosions at quarries located at a distance of 100 km or more were repeatedly identified.

Download Full-text

Behavioral evidence for post-pause reduced responsiveness in the electrosensory system ofGymnotus carapo

Journal of Experimental Biology ◽

10.1242/jeb.205.16.2525 ◽

2002 ◽

Vol 205 (16) ◽

pp. 2525-2533 ◽

Cited By ~ 1

Author(s):

Stefan Schuster

Keyword(s):

High Frequency ◽

Sampling Rate ◽

Sensory System ◽

Low Frequency ◽

Electric Organ ◽

Weakly Electric Fish ◽

Sensory Stimuli ◽

Novelty Response ◽

Electric Organ Discharges ◽

Electrical Stimuli

SUMMARYGymnotiform weakly electric fish find their way in the dark using a continuously operating active sensory system. An electric organ generates a continuous train of discharges (electric organ discharges, EODs), and tuberous high-frequency electroreceptors monitor the pattern of transcutaneous current flow associated with each EOD. Here, I report that a prior interruption to the continuous train of EODs dramatically affects a response shown by many pulse-type gymnotids. In this so-called novelty response, fish normally raise their electrosensory sampling rate in response to novel sensory stimuli. The gymnotid Gymnotus carapo was induced to pause its EODs briefly, and the novelty response to sensory stimuli given post-pause was analyzed. Mechanosensory stimuli given as early as 20 EODs after a pause elicited clear novelty responses, but strong high-frequency electrical stimuli were ineffective at this time. Moreover, high-frequency electrical stimuli remained less efficient in eliciting normal-sized responses until approximately 2000 EODs, or 40s, after a pause. The post-pause inefficiency of high-frequency stimuli was not due to an inappropriate choice of intensity or their temporal patterning and did not result from the stimulation that caused the pausing. Low-frequency stimuli that also recruited ampullary electroreceptors were more efficient than high-frequency stimuli in eliciting post-pause responses. These findings show that continuous activity is required either to maintain sensitivity to high-frequency electrical stimuli or to ensure that such stimuli are able to modulate efficiently the pacemaker that sets the discharge frequency.

Download Full-text

Evaluation of the latest GOCE GGMs in support of regional geoid modeling over Greece

10.5194/egusphere-egu21-1648 ◽

2021 ◽

Author(s):

Georgios S. Vergos ◽

Ilias N. Tziavos ◽

Dimitrios A. Natsiopoulos ◽

Elisavet G. Mamagiannou ◽

Eleftherios A. Pitenis

Keyword(s):

Maximum Degree ◽

Gravity Data ◽

Ground Truth ◽

Satellite Gravity ◽

Disturbing Potential ◽

Geopotential Models ◽

Potential Functionals ◽

Geoid Computation ◽

Goce Satellite

<p>In the frame of the GeoGravGOCE project, funded by the Hellenic Foundation for Research Innovation, GOCE Satellite Gravity Gradiometry (SGG) data are to be used for regional geoid and gravity field refinement as well as for potential determination in the frame of the International Height Reference Frame (IHRF). An inherent step in the geoid computation with either stochastic or spectral methods is the reduction of the related disturbing potential functionals within the well-known Remove-Compute-Restore (RCR) procedure. In this work we evaluate the latest, Release 6 (R6), satellite only and combined Global Geopotential Models (GGMs) which rely solely on GOCE and on land gravity data. The evaluation is performed over the established network of 1542 GPS/Levelling benchmarks over Greece mainland (BMs), which have been used in the past for the evaluation of GOCE GGMs. We employ the spectral enhancement approach, during which the GOCE-based GGMs are evaluated every one degree to the maximum degree of expansion coupled by EGM2008 and high-frequency RTM effects. This synthesis resolves wavelengths corresponding to maximum degree 216,000, hence the omission error is at the few mm-level. TIM-R6, DIR-R6, GOCO06s and XGM2019e are evaluated using EGM2008 residuals to the GPS/Levelling as the ground truth. From the results achieved, the optimal combination degree of a GOCE-only GGM augmented with EGM2008 is selected to be used in the sequel as reference field for the practical determination of the gravimetric geoid over Greece.</p>

Download Full-text

Sclerosing vulva lichen: a modern overview of the clinical symptoms,diagnostics and treatment methods (Analytical survey and actual expertise)

HEALTH OF WOMAN ◽

10.15574/hw.2020.154.76 ◽

2020 ◽

pp. 76-82

Author(s):

T.F. Tatarchuk ◽

◽

T.V. Protsenko ◽

V.V. Dunaevskaya ◽

D.O. Tzerkovsky ◽

...

Keyword(s):

Photodynamic Therapy ◽

Clinical Symptoms ◽

Low Frequency ◽

Disease Diagnosis ◽

Laser Coagulation ◽

Physical Factors ◽

Effective Prevention ◽

Depth Analysis ◽

Modern Classification ◽

Methods Analytical

Sclerosing lichen is one of the most common pathophysiological conditions observed in the peri-and postmenopausal periods. This problem is relevant because the clinical symptoms of the disease associated with atrophy (dryness, itching in the vagina and vulva, dyspareunia, dysuria) occur in more than 40% of patients aged over 50 years old. Nowadays the problem of maintaining health and preventing diseases caused by aging has become a central one. An in-depth analysis and systematization of key issues related to the precancerous pathology of the vulva have been conducted in this article. The first part of the publication covers main issues of epidemiology, etiology, pathogenesis and modern classification of sclerotic lichen, the second part presents the main aspects of the clinical picture, differential diagnosis and methods of disease diagnosis. The most effective and relevant treatments are under consideration in the third part of the article. Particular emphasis is made on the use of destructive techniques based on the use of laser technology and other approaches based on the use of physical factors (laser therapy, laser coagulation, cryodestruction). An important role among them is played by such an option as photodynamic therapy – a method of treatment based on the combined use of special substances (photosensitizers) and laser radiation with a certain wavelength. The authors report that only a comprehensive approach in this pathology treatment is the key to success in combating the main symptoms of the disease, and such an approach is a solution to the issue of effective prevention of vulvar cancer. The detailed information presented in the article is relevant, it can be extremely important for gynecologists, as well as professionals involved in solving problems related to sclerotic lichen. Keywords: sclerosing lichen, vulva, low-frequency ultrasound cavitation, photodynamic therapy.

Download Full-text

Feedforward Control Based on Error and Disturbance Observation for the CCD and Fiber-Optic Gyroscope-Based Mobile Optoelectronic Tracking System

Electronics ◽

10.3390/electronics7100223 ◽

2018 ◽

Vol 7 (10) ◽

pp. 223 ◽

Cited By ~ 3

Author(s):

Yong Luo ◽

Wei Ren ◽

Yongmei Huang ◽

Qiunong He ◽

Qiongyan Wu ◽

...

Keyword(s):

Fiber Optic ◽

Control Method ◽

Feedforward Control ◽

Tracking System ◽

Sampling Rate ◽

Low Frequency ◽

Integration Time ◽

Fiber Optic Gyroscope ◽

Loop Control ◽

Boresight Error

In the mobile optoelectronic tracking system (MOTS) based on charge-coupled device (CCD) and fiber-optic gyroscope (FOG), the tracking performance (TP) and anti-disturbance ability (ADA) characterized by boresight error are of equal importance. Generally, the position tracking loop, limited by the image integration time of CCD, would be subject to a non-negligible delay and low-sampling rate, which could not minimize the boresight error. Although the FOG-based velocity loop could enhance the ADA of the system, it is still insufficient in the case of some uncertain disturbances. In this paper, a feedforward control method based on the results of error and disturbance observation was proposed. The error observer (EOB) based on the CCD data and model output essentially combined the low-frequency tracking feedforward and closed-loop disturbance observer (DOB), which could simultaneously enhance the low-frequency TP and ADA. In addition, in view of the poor low-frequency performance of the FOG due to drift and noise that may result in the inaccuracy of the observed low-frequency disturbance, the FOG-based DOB was used to improve the relatively high-frequency ADA. The proposed method could make EOB and DOB complementary and help to obtain a high-precision MOTS, for in practical engineering, we give more attention to the low-frequency TP and full-band ADA. Simulations and experiments demonstrated that the proposed method was valid and had a much better performance than the traditional velocity and position double-loop control (VPDC).

Download Full-text