ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Publication Date: 2021-10-25
    Description: In this manuscript, we present a new analysis tool, called space-time-accuracy grid (STAG) analysis, to simultaneously assess the performance of an observing system architecture across space and time. Such an analysis tool is useful to directly link science objectives (typically expressed via a targeted spatial resolution, temporal resolution, and accuracy) to the expected performance of the observing system architecture. As a proof of concept, we apply STAG analysis to analyze three potential future observing systems for mass change in the Earth system: a single pair of polar orbiting satellites (heritage Gravity Recovery and Climate Experiment and Gravity Recovery and Climate Experiment Follow-On), two polar pairs of satellites, and a polar pair of satellites coupled with an inclined (70°) pair of satellites. Here, we demonstrate the use of STAG analysis to quantify the relative performance of each architecture across space (200–1,800 km) and time (1–30 days), offering a significantly more comprehensive assessment of performance than previous studies. Results show that the polar pair coupled with the inclined pair reduces errors (after state-of-the-art post-processing for each architecture is accounted for) relative to the single pair of satellites by 40–60% in medium spatial scales (500–1,200 km), with the greatest benefit being for longer solution (monthly) timespans. Overall, the results from this case study highlight the importance of increasing the isotropy of the observable over simply increasing the sampling frequency. Some demonstrated benefits of STAG analysis include the ability to incorporate state-of-the-art post-processing methods into the analysis and also tailor the analysis to specific geographic regions to address targeted scientific objectives.
    Keywords: 526.7 ; geophysical mass flux signals ; future satellite gravity field mission concept ; space vs. time vs. accuracy grid ; GRACE Follow-On ; GRACE
    Language: English
    Type: map
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Publication Date: 2018-01-17
    Print ISSN: 0949-7714
    Electronic ISSN: 1432-1394
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Published by Springer
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Publication Date: 2020-03-01
    Electronic ISSN: 2333-5084
    Topics: Geosciences , Physics
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2022-12-02
    Description: Temporal aliasing errors resulting from the undersampling of non-tidal atmospheric as well as oceanic mass variations constitute the largest limitation towards the retrieval of monthly gravity solutions based on GRACE and GRACE-FO satellite gravity missions. Their mitigation is thus a primary goal of current research. Unfortunately, the two-step co-parametrization approach proposed for application in Bender-type gravity retrieval scenario in Wiese et al. yields no added value for a single satellite pair. A detailed study of this parametrization strategy is carried out and it is shown that the reason for this is the flawed central assumption of the proposed method, that is that signals of different spatial wavelengths can be perfectly captured and separated with respect to their temporal extent. Based on this finding, we derive a multi-step self-de-aliasing approach (DMD) which aims to rectify the shortcoming of the Wiese et al. method specifically for the single-pair case while retaining its independence from background-model-based de-aliasing of non-tidal atmosphere and ocean (AO) signal components. The functionality and added value of this novel approach is validated within a set of numerical closed-loop simulations as well as in real GRACE and GRACE-FO data processing. The simulation results show that the DMD may improve the gravity retrieval performance in the high-degree spectrum by more than one order of magnitude if one aims to retrieve the full AOHIS (i.e. atmosphere, ocean, hydrology, ice, solid earth) signal, and by at least a factor 5 if a priori AO de-aliasing is applied. Simultaneously, the DMD is shown to degrade the retrieval of the low degrees, but it is also demonstrated that this issue can be mitigated by introducing a constraint into the processing scheme. The simulation results are widely confirmed by results obtained from applying the DMD to real GRACE/GRACE-FO data of the test years 2007, 2014 and 2019. The applicability of the DMD is further shown for Bender-type gravity retrieval. It is demonstrated that in case of a double-pair-based gravity retrieval this approach is at least equivalent to the Wiese et al. method.
    Type: info:eu-repo/semantics/article
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2023-08-30
    Description: Based on the large success of GRACE and GRACE-FO and their contributions to climate change research, there is a large interest in Germany to continue mass change measurements. Since 2020 GFZ and the German Space Agency at DLR have investigated a mission concept together with NASA based on a GRACE-like concept with a fully redundant Laser Ranging Interferometer (LRI). A Phase A study was successfully performed in 2022 with significant support of JPL. In October 2022 the German Parliament secured funds for the German mission elements Launcher, LRI optical components, Mission Operations and Science Data System (SDS). MPG and GFZ will additionally provide significant funding for LRI development and testing, SDS and Mission Operations after launch. To realize the GRACE-FO successor with launch not later than 2028 DLR is currently in close contact with NASA for the implementation of the next joint US/German Gravity mission. The GRACE-FO successor could be the first pair (P1) of a hybrid “Bender” constellation if combined with a second inclined pair (P2). The realization of this Mass-change And Geoscience International Constellation is currently discussed between ESA and NASA. P2 will fly lower than P1 and will be based on advanced instrumentation. Therefore, Phase A also investigated the option to add adapted MicroStar accelerometers to the baseline GRACE-FO like accelerometer on each P1 satellite as technology demonstrator for P2. We will present the current P1 mission status from a German view and discuss further steps towards realization.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2023-06-28
    Description: The GRACE and GRACE-FO missions have been fundamental in establishing a near-continuous time series of global mass transport since 2002. However, gravity field recovery using these mission data includes errors limiting the spatial and temporal resolution of gravity field solutions. The primary error contributions arise from instrument noise, temporal aliasing errors, uncertainties in the de-aliasing models, and imperfect ocean tide models. Particularly the latter will remain a limiting factor in determining high-resolution gravity fields from Next-Generation Gravity Missions.The topic has been investigated within the DFG research unit NEROGRAV and ESA´s Third Party Mission Program. One of the projects concerns stochastic modeling of ocean tide background models utilizing covariance information for eight major tidal constituents. The repeatable pattern of the tidal signal enables the extraction of uncertainty information by an ensemble of different ocean tide models. This information is introduced into the gravity field recovery process as a covariance matrix while expanding the parameter space by additional tidal parameters.An overview is provided of the recovered monthly gravity fields from GRACE/GRACE-FO when applying this covariance information. Additionally, realistic simulations have been performed for GRACE-like and MAGIC constellations to assess the impact that covariance information has on tidal errors and tidal constituents which have been co-estimated over one year and used to generate an improved ocean tide model for gravity field recovery. It is shown that the application of ocean tide covariance information contributes to the reduction of temporal aliasing caused by the mismodeling of ocean tide background models.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2023-03-10
    Description: The Gravity Recovery and Climate Experiment (GRACE) satellite mission has provided global long-term observations of mass transport in the Earth system with applications in numerous geophysical fields. In this paper, we targeted the in-orbit performance of the GRACE key instruments, the ACCelerometers (ACC) and the MicroWave ranging Instrument (MWI). For the ACC data, we followed a transplant approach analyzing the residual accelerations from transplanted accelerations of one of the two satellites to the other. For the MWI data, we analyzed the post-fit residuals of the monthly GFZ GRACE RL06 solutions with a focus on stationarity. Based on the analyses for the two test years 2007 and 2014, we derived stochastic models for the two instruments and a combined ACC+MWI stochastic model. While all three ACC axes showed worse performance than their preflight specifications, in 2007, a better ACC performance than in 2014 was observed by a factor of 3.6 due to switched-off satellite thermal control. The GRACE MWI noise showed white noise behavior for frequencies above 10 mHz around the level of 1.5×10−6 m/Hz−−−√. In the combined ACC+MWI noise model, the ACC part dominated the frequencies below 10 mHz, while the MWI part dominated above 10 mHz. We applied the combined ACC+MWI stochastic models for 2007 and 2014 to the monthly GFZ GRACE RL06 processing. This improved the formal errors and resulted in a comparable noise level of the estimated gravity field parameters. Furthermore, the need for co-estimating empirical parameters was reduced.
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Publication Date: 2023-01-30
    Description: The GRACE Follow-On satellite mission measures distance variations between its two satellites in order to derive monthly gravity field maps, indicating mass variability on Earth on a scale of a few 100 km originating from hydrology, seismology, climatology and other sources. This mission hosts two ranging instruments, a conventional microwave system based on K(a)-band ranging (KBR) and a novel laser ranging instrument (LRI), both relying on interferometric phase readout. In this paper, we show how the phase measurements can be converted into range data using a time-dependent carrier frequency (or wavelength) that takes into account potential intraday variability in the microwave or laser frequency. Moreover, we analyze the KBR-LRI residuals and discuss which error and noise contributors limit the residuals at high and low Fourier frequencies. It turns out that the agreement between KBR and LRI biased range observations can be slightly improved by considering intraday carrier frequency variations in the processing. Although the effect is probably small enough to have little relevance for gravity field determination at the current precision level, this analysis is of relevance for detailed instrument characterization and potentially for future more precise missions.
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2023-12-11
    Description: Being part of the GRACE/GRACE-FO Science Data System, the GFZ German Research Centre for Geosciences is one of the official Level-2 processing centers routinely providing monthly gravity models. These models are used by a wide variety of geoscientists to infer mass changes mainly at the Earth’s surface. Currently, the operationally processed monthly gravity fields are still based on release 6 (RL06) standards, but developments in view of a reprocessed and improved GFZ RL07 time series are already ongoing. Most of these improvements have been developed within the Research Unit “New Refined Observations of Climate Change from Spaceborne Gravity Missions” (NEROGRAV) funded by the German Research Foundation DFG. After a successful first phase, the second three years phase of NEROGRAV has started at the beginning of this year. Regarding an advanced gravity field processing strategy for RL07, the main focus is on an optimized stochastic modelling of: (1) instrument errors for the main observations (K-band/LRI ranging, GPS, and accelerometer), and (2) background model errors for ocean tides and non-tidal atmosphere and ocean de-aliasing (AOD), making use of respective variance-covariance matrices. This presentation provides an overview of the main outcomes of the advanced processing strategies. Details on the applied stochastic modelling approaches will be discussed. Preliminary monthly gravity field results will be presented and compared to current GFZ RL06 solutions.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2024-03-07
    Description: Monthly gravity field recovery using data from the GRACE and GRACE Follow-On missions includes errors limiting the spatial and temporal resolution of the estimated gravity fields. The major error contributions, besides the noise of the accelerometer instruments, arise from temporal aliasing errors due to imperfections in the non-tidal atmospheric and oceanic de-aliasing models and ocean tide models. We derive uncertainty information for the eight major tidal constituents from five different ocean tide models and introduce it into the gravity field recovery process in terms of a constrained normal equation system while expanding the parameter space by additional tidal parameters to be adjusted. We prove the effectiveness of the ocean tide variance-covariance information through realistic simulations and we assess its potential based on microwave and laser interferometer observations from the GRACE Follow-On mission. We show that errors are reduced by more than 20% ocean wRMS for a Gaussian filter radius of 300 km if uncertainty information for ocean tides is considered and stochastic modeling of instrument errors is applied, compared to the latest GFZ release 6.1. Our results also show the limited visibility of the effectiveness of the ocean tide variance-covariance information due to the dominating error contribution of non-tidal atmospheric and oceanic mass variations. Additionally, we investigate the option of estimating ocean tide parameters over a 1-year period while including ocean tide uncertainty information in order to improve ocean tide background modeling.
    Type: info:eu-repo/semantics/article
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...