scholarly journals Temporal Gravity Signals in Reprocessed GOCE Gravitational Gradients

2020 ◽  
Vol 12 (21) ◽  
pp. 3483
Author(s):  
Betty Heller ◽  
Frank Siegismund ◽  
Roland Pail ◽  
Thomas Gruber ◽  
Roger Haagmans
Keyword(s):  
Gravity Field ◽  
Ocean Circulation ◽  
Signal To Noise Ratio ◽  
Spatial Scales ◽  
Low Frequency ◽  
Temporal Variations ◽  
Normal Equation ◽  
Frequency Noise ◽  
Satellite Mission ◽  
Gravitational Gradients

The reprocessing of the satellite gravitational gradiometry (SGG) data from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission in 2018/2019 considerably reduced the low-frequency noise in the data, leading to reduced noise amplitudes in derived gravity field models at large spatial scales, at which temporal variations of the Earth’s gravity field have their highest amplitudes. This is the motivation to test the reprocessed GOCE SGG data for their ability to resolve time-variable gravity signals. For the gravity field processing, we apply and compare a spherical harmonics (SH) approach and a mass concentration (mascon) approach. Although their global signal-to-noise ratio is <1, SH GOCE SGG-only models resolve the strong regional signals of glacier melting in Greenland and Antarctica, and the 2011 moment magnitude 9.0 earthquake in Japan, providing an estimation of gravity variations independent of Gravity Recovery and Climate Experiment (GRACE) data. The benefit of combined GRACE/GOCE SGG models is evaluated based on the ice mass trend signals in Greenland and Antarctica. While no signal contribution from GOCE SGG data additional to the GRACE models could be observed, we show that the incorporation of GOCE SGG data numerically stabilizes the related normal equation systems.

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

&lt;p&gt;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&amp;#8217;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.&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;

scholarly journals Ultrasonic frogs call at a higher pitch in noisier ambiance

2015 ◽  
Vol 61 (6) ◽  
pp. 996-1003 ◽  
Author(s):  
Fang Zhang ◽  
Pan Chen ◽  
Zhuqing Chen ◽  
Juan Zhao
Keyword(s):  
Fundamental Frequency ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Environmental Noise ◽  
Central China ◽  
Signal Frequency ◽  
Frequency Noise ◽  
Acoustic Adaptation ◽  
Adaptation Hypothesis ◽  
Acoustic Adaptation Hypothesis

Abstract The ultrasonic communication in Concave-eared torrent frogs Odorrana tormota is believed to be an adaptation to avoid masking by the intense low-frequency noise of the rushing stream in their habitat. The acoustic adaptation hypothesis for ultrasonic origin predicts that some organisms subjecting to persistent acoustic interference from broadband, low-frequency environmental noise, might shift their signal frequency upward into frequency bands with lower noise energy. In other words, low-frequency environmental noise might cause upward shifts of species’ vocalization frequencies making their signals more conspicuous. Presently, it is unclear whether male O. tormota adjust their signal features in response to a change in the ambient noise level. We tested the prediction of the acoustic adaptation hypothesis by recording the vocalizations of male O. tormota inhabiting two streams with different background noise levels in Huangshan in central China and comparing their call features including the fundamental frequency (F0). Results showed that the spectrotemporal characteristics of the vocal signals of males in the two habitats were indifferent, except the duration of the call harmonic segments and three parameters related to the call fundamental frequency (F0). In terms of the F0, the pooled and individual frog data showed that frogs inhabiting the noisier habitat tended to emit calls having higher F0. The higher F0 increases the signal-to-noise ratio, thus benefiting the detection of vocalization. Thus, similar to several anuran species, concave-eared torrent frogs also display noise-dependent adjustment of vocal pitch in their vocalizations for making them more audible.

scholarly journals Daily GRACE gravity field solutions track major flood events in the Ganges–Brahmaputra Delta

2018 ◽  
Vol 22 (5) ◽  
pp. 2867-2880 ◽  
Author(s):  
Ben T. Gouweleeuw ◽  
Andreas Kvas ◽  
Christian Gruber ◽  
Animesh K. Gain ◽  
Thorsten Mayer-Gürr ◽  
...  
Keyword(s):  
Gravity Field ◽  
River Runoff ◽  
Large Scale ◽  
High Volume ◽  
Temporal Variations ◽  
Flood Events ◽  
Satellite Mission ◽  
Flood Level ◽  
Flood Monitoring ◽  
The Ganges

Abstract. Two daily gravity field solutions based on observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission are evaluated against daily river runoff data for major flood events in the Ganges–Brahmaputra Delta (GBD) in 2004 and 2007. The trends over periods of a few days of the daily GRACE data reflect temporal variations in daily river runoff during major flood events. This is especially true for the larger flood in 2007, which featured two distinct periods of critical flood level exceedance in the Brahmaputra River. This first hydrological evaluation of daily GRACE gravity field solutions based on a Kalman filter approach confirms their potential for gravity-based large-scale flood monitoring. This particularly applies to short-lived, high-volume floods, as they occur in the GBD with a 4–5-year return period. The release of daily GRACE gravity field solutions in near-real time may enable flood monitoring for large events.

THE ELUSIVE FIRST ARRIVAL

Geophysics ◽  
1964 ◽  
Vol 29 (5) ◽  
pp. 806-813 ◽  
Author(s):  
J. G. Hagedoorn
Keyword(s):  
Frequency Response ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Dominant Frequency ◽  
Recording System ◽  
Transmission Curve ◽  
Frequency Noise ◽  
Signal To Noise ◽  
First Arrival ◽  
Noise Ratio

In first‐arrival refraction work, the initial deflection of the first loop of the signal arriving from the shotpoint must be readily recognised against a background of seismic disturbances due to sources other than the explosion. The accuracy of timing a first arrival is determined by this signal‐to‐noise ratio. It depends primarily on the location of shot and receivers, the size of the charge, and the existing ground unrest at the time of registration. Experiments carried out with these variables kept constant, by recording at the same location from the same shot, show how much the signal‐to‐noise ratio also depends on the characteristics of the recording equipment used. The best signal‐to‐noise ratio is certainly not obtained when the transmission curve of the entire system, comprising geophone, amplifier, and galvanometer, peaks at the apparent dominant frequency of the refraction signal. Practical examples show that the signal‐to‐noise ratio can be improved considerably by using recording systems that transmit a band of frequencies extending many octaves below the observed dominant frequency. The inception of an oscillatory signal was found to be particularly sensitive to the characteristics of a recording system. A seismometer, for example, will transform a starting sine wave with a frequency equal to the natural frequency of the seismometer into a signal with a first loop that is about half as high and half as long as the succeeding loops, the latter moreover being advanced by one‐quarter period. This relative constriction of the initial part of a signal is called the “cramping” effect. Such an effect will weaken a refraction first arrival relative to simultaneously arriving later parts of noise signals. This explains why a cramping effect will impair the signal‐to‐noise ratio. A cramping effect can, of course, be avoided by using a recording system with a flat frequency response. The opposite effect, which can be expected to improve the signal‐to‐noise ratio, could obviously be achieved by using systems with relatively increased low‐frequency response. The practical limit to this improvement would be set by the low‐frequency noise that is enhanced by this procedure.

scholarly journals Constraining parameters in marine pelagic ecosystem models – is it actually feasible with typical observations of standing stocks?

Ocean Science ◽  
2015 ◽  
Vol 11 (4) ◽  
pp. 573-590 ◽  
Author(s):  
U. Löptien ◽  
H. Dietze
Keyword(s):  
Ocean Circulation ◽  
Carbon Assimilation ◽  
Low Frequency ◽  
Biogeochemical Model ◽  
Model Parameters ◽  
Frequency Noise ◽  
Standing Stocks ◽  
Estimation Of Model Parameters ◽  
Model Components ◽  
Parameter Retrieval

Abstract. In a changing climate, marine pelagic biogeochemistry may modulate the atmospheric concentrations of climate-relevant species such as CO2 and N2O. To date, projections rely on earth system models, featuring simple pelagic biogeochemical model components, embedded into 3-D ocean circulation models. Most of these biogeochemical model components rely on the hyperbolic Michaelis–Menten (MM) formulation which specifies the limiting effect of light and nutrients on carbon assimilation by autotrophic phytoplankton. The respective MM constants, along with other model parameters, of 3-D coupled biogeochemical ocean-circulation models are usually tuned; the parameters are changed until a "reasonable" similarity to observed standing stocks is achieved. Here, we explore with twin experiments (or synthetic "observations") the demands on observations that allow for a more objective estimation of model parameters. We start with parameter retrieval experiments based on "perfect" (synthetic) observations which we distort, step by step, by low-frequency noise to approach realistic conditions. Finally, we confirm our findings with real-world observations. In summary, we find that MM constants are especially hard to constrain because even modest noise (10 %) inherent to observations may hinder the parameter retrieval already. This is of concern since the MM parameters are key to the model's sensitivity to anticipated changes in the external conditions. Furthermore, we illustrate problems caused by high-order parameter dependencies when parameter estimation is based on sparse observations of standing stocks. Somewhat counter to intuition, we find that more observational data can sometimes degrade the ability to constrain certain parameters.

scholarly journals Downscaling GRACE total water storage change using partial least squares regression

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Bramha Dutt Vishwakarma ◽  
Jinwei Zhang ◽  
Nico Sneeuw
Keyword(s):  
Water Mass ◽  
Spatial Scales ◽  
Water Storage ◽  
Temporal Variations ◽  
Least Squares Regression ◽  
Total Water ◽  
Satellite Mission ◽  
Grace Data ◽  
Gravity Recovery ◽  
Storage Change

AbstractThe Gravity Recovery And Climate Experiment (GRACE) satellite mission recorded temporal variations in the Earth’s gravity field, which are then converted to Total Water Storage Change (TWSC) fields representing an anomaly in the water mass stored in all three physical states, on and below the surface of the Earth. GRACE provided a first global observational record of water mass redistribution at spatial scales greater than 63000 km2. This limits their usability in regional hydrological applications. In this study, we implement a statistical downscaling approach that assimilates 0.5° × 0.5° water storage fields from the WaterGAP hydrology model (WGHM), precipitation fields from 3 models, evapotranspiration and runoff from 2 models, with GRACE data to obtain TWSC at a 0.5° × 0.5° grid. The downscaled product exploits dominant common statistical modes between all the hydrological datasets to improve the spatial resolution of GRACE. We also provide open access to scripts that researchers can use to produce downscaled TWSC fields with input observations and models of their own choice.

scholarly journals Daily GRACE gravity field solutions track major flood events in the Ganges-Brahmaputra Delta

2017 ◽  
Author(s):  
Ben T. Gouweleeuw ◽  
Andreas Kvas ◽  
Christian Grüber ◽  
Animesh K. Gain ◽  
Thorsten Mayer-Gürr ◽  
...  
Keyword(s):  
Gravity Field ◽  
River Runoff ◽  
Large Scale ◽  
High Volume ◽  
Temporal Variations ◽  
Flood Events ◽  
Satellite Mission ◽  
Flood Level ◽  
Flood Monitoring ◽  
The Ganges

Abstract. Two daily gravity field solutions based on observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission are evaluated against daily river runoff data for major flood events in the Ganges-Brahmaputra Delta (GBD) in 2004 and 2007. The trends over periods of a few days of the daily GRACE data reflect temporal variations in daily river runoff during major flood events. This is especially true for the larger flood in 2007, which featured two distinct periods of critical flood level exceedance in the Brahmaputra River. This first hydrological evaluation of daily GRACE gravity field solutions based on a Kalman filter approach confirms their potential for gravity-based large-scale flood monitoring. This particularly applies to short-lived, high-volume floods, as they occur in the GBD with a 4–5 year return period. The release of daily GRACE gravity field solutions in near real-time may enable flood monitoring for large events.

scholarly journals Electrical Characteristics and pH Response of a Parylene-H Sensing Membrane in a Si-Nanonet Ion-Sensitive Field-Effect Transistor

Sensors ◽  
2018 ◽  
Vol 18 (11) ◽  
pp. 3892 ◽  
Author(s):  
Bo Jin ◽  
Ga-Yeon Lee ◽  
ChanOh Park ◽  
Donghoon Kim ◽  
Wonyeong Choi ◽  
...  
Keyword(s):  
Field Effect ◽  
Field Effect Transistor ◽  
Ph Value ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Frequency Noise ◽  
Electrical Characteristics ◽  
Ph Sensing ◽  
Effect Transistor ◽  
Sensing Membrane

We report the electrical characteristics and pH responses of a Si-nanonet ion-sensitive field-effect transistor with ultra-thin parylene-H as a gate sensing membrane. The fabricated device shows excellent DC characteristics: a low subthreshold swing of 85 mV/dec, a high current on/off ratio of ~107 and a low gate leakage current of ~10−10 A. The low interface trap density of 1.04 × 1012 cm−2 and high field-effect mobility of 510 cm2V−1s−1 were obtained. The pH responses of the devices were evaluated in various pH buffer solutions. A high pH sensitivity of 48.1 ± 0.5 mV/pH with a device-to-device variation of ~6.1% was achieved. From the low-frequency noise characterization, the signal-to-noise ratio was extracted as high as ~3400 A/A with the lowest noise equivalent pH value of ~0.002 pH. These excellent intrinsic electrical and pH sensing performances suggest that parylene-H can be promising as a sensing membrane in an ISFET-based biosensor platform.

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