scholarly journals High frequency variations in Earth rotation

1988 ◽  
Vol 128 ◽  
pp. 181-186 ◽  
Author(s):  
W. E. Carter ◽  
D. S. Robertson ◽  
F. W. Fallon
Keyword(s):  
Time Series ◽  
Earth Orientation ◽  
Continuous Coverage ◽  
Standard Product ◽  
Orientation Time ◽  
Monitoring Service ◽  
Cross Track ◽  
Along Track ◽  
Frequency Variations ◽  
Nearly Continuous

The combined POLARIS-IRIS Earth orientation time series now span nearly a full cycle of the Chandler-annual beat period, beginning in late 1980. Since April 1985 there is also a nearly continuous coverage of UT1 at daily intervals. We have fit a simple model, consisting of circular 14-month and annual components and a linear drift to the polar motion series, then computed the “along-track” and “cross-track” residuals. Both sets of residuals display structure with amplitudes of tens of milliseconds of arc on time scales of months, but Fourier analysis reveals no significant peaks at shorter periods, including the 40-60 day period found in the UT1 time series.During September, 1986, we introduced a new “quick-look” UT1 time series. The values are typically available within 7 days. The accuracy, which depends strongly on the accuracy of the X and Y pole coordinates used in the computations, ranged from 0.3 to 0.7 milliseconds during the first two weeks, but improved to about 0.1 milliseconds during the latter two weeks of the month. We plan to continue the quick-look UT1 series as a standard product of the IRIS Earth orientation monitoring service.

scholarly journals GLACIER VOLUME CHANGE ESTIMATION USING TIME SERIES OF IMPROVED ASTER DEMS

2016 ◽  
Vol XLI-B8 ◽  
pp. 489-494 ◽  
Author(s):  
Luc Girod ◽  
Christopher Nuth ◽  
Andreas Kääb
Keyword(s):  
Climate Change ◽  
Time Series ◽  
Volume Change ◽  
Thermal Emission ◽  
Aster Data ◽  
Rational Polynomial ◽  
The Cross ◽  
Cross Track ◽  
Along Track

Volume change data is critical to the understanding of glacier response to climate change. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) system embarked on the Terra (EOS AM-1) satellite has been a unique source of systematic stereoscopic images covering the whole globe at 15m resolution and at a consistent quality for over 15 years. While satellite stereo sensors with significantly improved radiometric and spatial resolution are available to date, the potential of ASTER data lies in its long consistent time series that is unrivaled, though not fully exploited for change analysis due to lack of data accuracy and precision. Here, we developed an improved method for ASTER DEM generation and implemented it in the open source photogrammetric library and software suite MicMac. The method relies on the computation of a rational polynomial coefficients (RPC) model and the detection and correction of cross-track sensor jitter in order to compute DEMs. ASTER data are strongly affected by attitude jitter, mainly of approximately 4 km and 30 km wavelength, and improving the generation of ASTER DEMs requires removal of this effect. Our sensor modeling does not require ground control points and allows thus potentially for the automatic processing of large data volumes. <br><br> As a proof of concept, we chose a set of glaciers with reference DEMs available to assess the quality of our measurements. We use time series of ASTER scenes from which we extracted DEMs with a ground sampling distance of 15m. Our method directly measures and accounts for the cross-track component of jitter so that the resulting DEMs are not contaminated by this process. Since the along-track component of jitter has the same direction as the stereo parallaxes, the two cannot be separated and the elevations extracted are thus contaminated by along-track jitter. Initial tests reveal no clear relation between the cross-track and along-track components so that the latter seems not to be easily modeled analytically from the first one. We thus remove the remaining along-track jitter effects in the DEMs statistically through temporal DEM stacks to finally compute the glacier volume changes over time. Our method yields cleaner and spatially more complete elevation data, which also proved to be more in accordance to reference DEMs, compared to NASA’s AST14DMO DEM standard products. <br><br> The quality of the demonstrated measurements promises to further unlock the underused potential of ASTER DEMs for glacier volume change time series on a global scale. The data produced by our method will help to better understand the response of glaciers to climate change and their influence on runoff and sea level.

scholarly journals GLACIER VOLUME CHANGE ESTIMATION USING TIME SERIES OF IMPROVED ASTER DEMS

2016 ◽  
Vol XLI-B8 ◽  
pp. 489-494
Author(s):  
Luc Girod ◽  
Christopher Nuth ◽  
Andreas Kääb
Keyword(s):  
Climate Change ◽  
Time Series ◽  
Volume Change ◽  
Thermal Emission ◽  
Aster Data ◽  
Rational Polynomial ◽  
The Cross ◽  
Cross Track ◽  
Along Track

Volume change data is critical to the understanding of glacier response to climate change. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) system embarked on the Terra (EOS AM-1) satellite has been a unique source of systematic stereoscopic images covering the whole globe at 15m resolution and at a consistent quality for over 15 years. While satellite stereo sensors with significantly improved radiometric and spatial resolution are available to date, the potential of ASTER data lies in its long consistent time series that is unrivaled, though not fully exploited for change analysis due to lack of data accuracy and precision. Here, we developed an improved method for ASTER DEM generation and implemented it in the open source photogrammetric library and software suite MicMac. The method relies on the computation of a rational polynomial coefficients (RPC) model and the detection and correction of cross-track sensor jitter in order to compute DEMs. ASTER data are strongly affected by attitude jitter, mainly of approximately 4 km and 30 km wavelength, and improving the generation of ASTER DEMs requires removal of this effect. Our sensor modeling does not require ground control points and allows thus potentially for the automatic processing of large data volumes. <br><br> As a proof of concept, we chose a set of glaciers with reference DEMs available to assess the quality of our measurements. We use time series of ASTER scenes from which we extracted DEMs with a ground sampling distance of 15m. Our method directly measures and accounts for the cross-track component of jitter so that the resulting DEMs are not contaminated by this process. Since the along-track component of jitter has the same direction as the stereo parallaxes, the two cannot be separated and the elevations extracted are thus contaminated by along-track jitter. Initial tests reveal no clear relation between the cross-track and along-track components so that the latter seems not to be easily modeled analytically from the first one. We thus remove the remaining along-track jitter effects in the DEMs statistically through temporal DEM stacks to finally compute the glacier volume changes over time. Our method yields cleaner and spatially more complete elevation data, which also proved to be more in accordance to reference DEMs, compared to NASA’s AST14DMO DEM standard products. <br><br> The quality of the demonstrated measurements promises to further unlock the underused potential of ASTER DEMs for glacier volume change time series on a global scale. The data produced by our method will help to better understand the response of glaciers to climate change and their influence on runoff and sea level.

scholarly journals A Simple Model for Simulating Tornado Damage in Forests

2006 ◽  
Vol 45 (12) ◽  
pp. 1597-1611 ◽  
Author(s):  
Andrew P. Holland ◽  
Allen J. Riordan ◽  
E. C. Franklin
Keyword(s):  
Simple Model ◽  
Loblolly Pine ◽  
Forward Speed ◽  
Forward Motion ◽  
Tree Resistance ◽  
Forested Areas ◽  
Storm Characteristics ◽  
Tornado Damage ◽  
Cross Track ◽  
Along Track

Abstract An analytical model is presented to describe patterns of downed trees produced by tornadic winds. The model uses a combined Rankine vortex of specified tangential and radial components to describe a simple tornado circulation. A total wind field is then computed by adding the forward motion of the vortex. The lateral and vertical forces on modeled tree stands are then computed and are compared with physical characteristics of Scots and loblolly pine. From this model, patterns of windfall are computed and are compared to reveal three basic damage patterns: cross-track symmetric, along-track asymmetric, and crisscross asymmetric. These patterns are shown to depend on forward speed, radial speed, and tree resistance. It is anticipated that this model will prove to be useful in assessing storm characteristics from damage patterns observed in forested areas.

scholarly journals A two-dimensional Stockwell transform for gravity wave analysis of AIRS measurements

2016 ◽  
Vol 9 (6) ◽  
pp. 2545-2565 ◽  
Author(s):  
Neil P. Hindley ◽  
Nathan D. Smith ◽  
Corwin J. Wright ◽  
D. Andrew S. Rees ◽  
Nicholas J. Mitchell
Keyword(s):  
General Circulation ◽  
Drake Passage ◽  
General Circulation Models ◽  
Two Dimensional ◽  
Atmospheric Infrared Sounder ◽  
Spectral Window ◽  
Energy And Momentum ◽  
Stockwell Transform ◽  
Cross Track ◽  
Along Track

Abstract. Gravity waves (GWs) play a crucial role in the dynamics of the earth's atmosphere. These waves couple lower, middle and upper atmospheric layers by transporting and depositing energy and momentum from their sources to great heights. The accurate parameterisation of GW momentum flux is of key importance to general circulation models but requires accurate measurement of GW properties, which has proved challenging. For more than a decade, the nadir-viewing Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite has made global, two-dimensional (2-D) measurements of stratospheric radiances in which GWs can be detected. However, one problem with current one-dimensional methods for GW analysis of these data is that they can introduce significant unwanted biases. Here, we present a new analysis method that resolves this problem. Our method uses a 2-D Stockwell transform (2DST) to measure GW amplitudes, horizontal wavelengths and directions of propagation using both the along-track and cross-track dimensions simultaneously. We first test our new method and demonstrate that it can accurately measure GW properties in a specified wave field. We then show that by using a new elliptical spectral window in the 2DST, in place of the traditional Gaussian, we can dramatically improve the recovery of wave amplitude over the standard approach. We then use our improved method to measure GW properties and momentum fluxes in AIRS measurements over two regions known to be intense hotspots of GW activity: (i) the Drake Passage/Antarctic Peninsula and (ii) the isolated mountainous island of South Georgia. The significance of our new 2DST method is that it provides more accurate, unbiased and better localised measurements of key GW properties compared to most current methods. The added flexibility offered by the scaling parameter and our new spectral window presented here extend the usefulness of our 2DST method to other areas of geophysical data analysis and beyond.

scholarly journals Dynamic Mapping of Along-Track Ocean Altimetry: Performance from Real Observations

2020 ◽  
Vol 37 (9) ◽  
pp. 1593-1601 ◽  
Author(s):  
Maxime Ballarotta ◽  
Clément Ubelmann ◽  
Marine Rogé ◽  
Florent Fournier ◽  
Yannice Faugère ◽  
...  
Keyword(s):  
Optimal Interpolation ◽  
Resolution Limit ◽  
Simulation Experiments ◽  
Qualitative And Quantitative ◽  
Dynamic Mapping ◽  
System Experiment ◽  
Ocean Altimetry ◽  
Marine Environment Monitoring ◽  
Monitoring Service ◽  
Along Track

AbstractThe dynamic optimal interpolation (DOI) method merges altimetric sea surface height (SSH) data into maps that are continuous in time and space. Unlike the traditional linear optimal interpolation (LOI) method, DOI has the advantage of considering a nonlinear temporal propagation of the SSH field. DOI has been successfully applied to along-track pseudo-observations in observing system simulation experiments (OSSEs), demonstrating a reduction in interpolation error in highly turbulent regions compared to LOI mapping. In the present study, we further extend the validation of the DOI method by an observing system experiment (OSE). We applied and validated the DOI approach with real nadir-altimetric observations in four regional configurations. Overall, the qualitative and quantitative assessments of these realistic SSH maps confirm the higher level of performance of the DOI approach in turbulent regions. It is more of a challenge to outperform the conventional LOI mapping in coastal and low-energy regions. Validations against LOI maps distributed by the Copernicus Marine Environment Monitoring Service indicate a 10%–15% increase in average performance and an improved resolution limit toward shorter wavelengths. The DOI method also shows improved mesoscale mapping of intense jets and fronts and reveals new eddies with smoother trajectories.

Evaluation of Pendulum NGGM Scenarios by Full Closed-Loop Simulation

2021 ◽  
Author(s):  
Florian Wöske ◽  
Benny Rievers
Keyword(s):  
Closed Loop ◽  
Variational Equation ◽  
Satellite Measurement ◽  
Observation Data ◽  
Near Surface ◽  
The Earth ◽  
Cross Track ◽  
Along Track ◽  
Grace Mission ◽  
Gravity Mission

&lt;p&gt;The GRACE mission (2002-2017) delivered temporal gravity field solutions of the Earth for 15 years. It's successor, GRACE follow-on (GRACE-FO) is continuing it's legacy since May 2018. The time series of monthly gravity fields revealed global mass redistribution in in the near surface layer of the Earth with unprecedented accuracy. This assessed a completely new observable in geoscience disciplines and has become a crucial data product for climate research.&lt;br&gt;Despite the groundbreaking success and relevance of the GRACE mission(s) for Earth observation and climate science, no further successor gravity mission is planned, yet. Summarized by the name Next Generation Gravity Mission (NGGM) concepts for future gravimetry missions have been proposed and analyzed for a while. As an outcome of these studies the so called Bender-configuration (two GRACE-like satellite pairs, one in a polar orbit and a second in an inclined orbit around 60&amp;#176; to 70&amp;#176;) is the concept currently favored by the scientific community for a candidate of the next gravity mission to be realized.&lt;/p&gt;&lt;p&gt;&lt;br&gt;However, an other concept still remains interesting due to specific advantages that might contribute to future improvements of gravity missions. In order to emphasize this, we present results of a full closed loop-simulation for a different ll-SST approach, the so called pendulum. It offers a quite similar overall performance with just two satellites. For this configuration the satellites are following each other in orbits with slightly different longitudes of the ascending nodes, thus the inter-satellite measurement direction is varying between along-track and cross-track. This configuration makes an interferometric laser ranging (LRI) quite challenging on the technical level. Nevertheless, the LRI accuracy is not necessarily needed. The relevance of the pendulum configuration has also been shifted into the focus of the French MARVEL mission proposal.&lt;/p&gt;&lt;p&gt;&lt;br&gt;In this contribution we analyze in detail the performance of the pendulum formation with the main parameters being the angle between along-track and cross-track component of the ranging direction at the equator, and the mean distance between the satellites. We conduct the angle variation for different mean ranges and assumed ranging accuracies. As reference, the GRACE and Bender concepts are simulated, as well. The orbit simulations are performed using a derivative of the ZARM/DLR XHPS mission simulator including high precision implementations of non-gravitational accelerations.&lt;br&gt;The different concepts and configurations include complete GRACE-FO like attitude control and realistic environment models. State-of-the-art instrument noise models based on GRACE/-FO are used to generate observation data for accelerometer (ACC), range dependent inter satellite ranging (KBR/LRI), kinematic orbit solution (KOS) and star camera (SCA). For the gravity recovery process we use the classical variational equation approach. As for real GRACE processing, ACC calibration parameter are estimated and KOS and KBR range-rate observations are weighted by VCE.&lt;/p&gt;

Large-scale, high-resolution maps of interseismic strain accumulation from Sentinel-1, and incorporation of along-track measurements

2021 ◽  
Author(s):  
Andy Hooper ◽  
Pawan Piromthong ◽  
Tim Wright ◽  
Jonathan Weiss ◽  
Milan Milan Lazecky ◽  
...  
Keyword(s):  
Time Series ◽  
High Resolution ◽  
Velocity Field ◽  
Reference Frame ◽  
Line Of Sight ◽  
Tectonic Deformation ◽  
Low Resolution ◽  
Gnss Measurements ◽  
Along Track ◽  
East West

&lt;p&gt;High-resolution geodetic measurements of crustal deformation from InSAR have the potential to provide crucial constraints on a region&amp;#8217;s tectonics, geodynamics and seismic hazard. Here, we present a high-resolution crustal velocity field for the Alpine-Himalayan Seismic Belt (AHSB) derived from Sentinel-1 InSAR and GNSS. We create time series and average velocities from ~220,000 interferograms covering an area of 15 million km&lt;sup&gt;2&lt;/sup&gt;, with an average of 170 acquisitions per measurement point. We tie the velocities to a Eurasian reference frame by jointly inverting the InSAR data with GNSS data to produce a low-resolution model of 3D surface velocities. We then use the referenced InSAR velocities to invert for high-resolution east-west and sub-vertical velocity fields for the entire region. The sub-vertical velocities, which also include a small component of north-south motion, are dominated by non-tectonic deformation, such as subsidence due to water extraction. The east-west velocity field, however, reveals the tectonics of the AHSB with an unprecedented level of detail.&lt;/p&gt;&lt;p&gt;The approach described above only provides good constraints on horizontal displacement in the east-west direction, with the north-south component provided by low-resolution GNSS measurements. Sentinel-1 does also have the potential to provide measurements that are sensitive to north-south motion, through exploitation of the burst overlap areas produced by the TOPS acquisition mode. These along-track measurements have lower precision than line-of-sight InSAR and are more effected by ionospheric noise, but have the advantage of being almost insensitive to tropospheric noise. We present a time series approach to tease out the subtle along-track signals associated with interseismic strain. Our approach includes improvements to the mitigation of ionospheric noise and we also investigate different filtering approaches to optimize the reduction of decorrelation noise. In contrast to the relative measurements of line-of-sight InSAR, these along-track measurements are automatically provided in a global reference frame. We present results from five years of data for the West-Lut Fault in eastern Iran and the Chaman Fault in Pakistan and Afghanistan. Our results agree well with independent GNSS measurements; however, the denser coverage of the technique allows us to also detect the variation in slip rate along the faults.&lt;/p&gt;&lt;p&gt;Finally, we demonstrate the improvement in the resolution of horizontal strain rates when including these along-track measurements, in addition to the conventional line-of-sight InSAR measurements.&lt;/p&gt;

scholarly journals Tropical Cyclone Center Fix Using CYGNSS Winds

2019 ◽  
Vol 58 (9) ◽  
pp. 1993-2003 ◽  
Author(s):  
David Mayers ◽  
Christopher Ruf
Keyword(s):  
Wind Speed ◽  
Tropical Cyclone ◽  
Satellite System ◽  
Center Location ◽  
Residual Difference ◽  
Measurement Results ◽  
Storm Center ◽  
Global Navigation Satellite ◽  
Cross Track ◽  
Along Track

AbstractA new method is described for determining the center location of a tropical cyclone (TC) using wind speed measurements by the NASA Cyclone Global Navigation Satellite System (CYGNSS). CYGNSS measurements made during TC overpasses are used to constrain a parametric wind speed model in which storm center location is varied. The “MTrack” storm center location is selected to minimize the residual difference between model and measurement. Results of the MTrack center fix are compared to the National Hurricane Center (NHC) Best Track, the Automated Rotational Center Hurricane Eye Retrieval (ARCHER), and aircraft reconnaissance fixes for category 1–category 3 TCs during the 2017 and 2018 hurricane seasons. MTrack produces storm center locations at intermediate times between NHC fixes with a factor of 5.6 overall reduction in sensitivity to uncertainties in the NHC fixes between which it interpolates. The MTrack uncertainty is found to be larger in the cross-track direction than the along-track direction, although this behavior and the absolute accuracy of position estimates require further investigation.

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