Relativistic geodesy

Quantum metrology enables new applications in geodesy, including relativistic geodesy. The recent progress in optical atomic clocks and in long-distance frequency transfer by optical fiber together pave the way for using measurements of the gravitational frequency redshift for geodesy. The remote comparison of frequencies generated by calibrated clocks will allow for a purely relativistic determination of differences in gravitational potential and height between stations on Earth surface (chronometric leveling). The long-term perspective is to tie potential and height differences to atomic standards in order to overcome the weaknesses and inhomogeneity of height systems determined by classical spirit leveling. Complementarily, gravity measurements with atom interferometric setups, and satellite gravimetry with space borne laser interferometers allow for new sensitivities in the measurement of the Earth's gravity field.DFG/SFB/112

Residual ocean tide signal in GRACE(-FO) range-rate post-fit residuals

Ocean tide model imperfections are one of the major uncertainty factors in gravity field recovery. Unmodeled signal can alias into level-2 gravity field products and be interpreted as real signal, e.g. as ice mass loss. An accurate understanding of the ocean tide model imperfections (on spectral and spatial level) is therefore not only important for current, but also for future gravity field missions. For this contribution, we analyzed 20+ years of GRACE(-FO) K-band range-rate post-fit residuals for residual ocean tide signal. The post-fit residuals are obtained as part of the gravity field estimation of monthly solutions. We low pass filter and differentiate range-rate post-fit residuals to obtain residual range-accelerations. Obtained residual range-accelerations are assigned to 5x5 degree grid cells and Lomb-Scargle periodograms for each cell are computed. An analysis of the periodograms reveals peaks at frequencies of ocean tide constituents. The peaks with the largest spectral amplitude can be found at frequencies of the major constituents (O1, M2, K1). In total around 30 constituents are detectable, among them also compound tides and degree-3 tides

Influence of accelerometer parametrizations on GRACE post-fit residuals

Accelerometers onboard of satellites can be regarded as a key improvement in gravity field recovery. These instruments are located in the center of mass of the satellite and are precisely measuring non-gravitational forces acting on the satellite surfaces. Accelerometer measurements are distorted in their magnitude and amplitude, so an accelerometer calibration has to be carried out. Usually, in orbit determination and gravity field parameter estimation, a priori values are introduced and corresponding numeric corrections are estimated iteratively. Within the gravity field recovery community various accelerometer calibration parametrizations are applied. We have tested several parametrization scenarios within our in-house developed GRACE-SIGMA gravity field recovery software. In this contribution, we present the impact of these scenarios on post- fit KBRR residuals

Spectral analysis of residual GRACE and GRACE-FO range accelerations

GRACE and GRACE-FO K-band range-rate post-fit residuals obtained after a common estimation of monthly gravity field coefficients and ancillary satellite parameters represent a complex superposition of different effects. In this contribution, we analyze the component of the residuals that is related to geophysical effects. We low pass filter and differentiate range-rate post-fit residuals to obtain residual range-accelerations. A spectral analysis of globaly gridded residual range-accelerations reveals unmodeled signal related to (ocean) tides and hydrology. The time series with approximately 100 millions of data records allows us to identify main periodic contributors in different bands. Diurnal and semi-diurnal signal can be resolved on a 5x5 degree grid, while periods of 5 and 3 hours can be resolved on a 7.5x7.5 and 10x10 degree grid

GRACE-FO monthly solutions using the GRACE-SIGMA software

In this contribution we present gravity field monthly solutions from GRACE Follow-On (GRACE-FO) Level-1B sensor data. The monthly solutions are computed with the GRACE-SIGMA software developed at the Institute of Geodesy, Leibniz University Hannover. The solutions are obtained using a two-step approach. In a first step, the orbits of the two satellites are pre-adjusted by estimating local arc parameters. In a second step, the monthly gravity field potential in terms of normalized spherical harmonic coefficients is recovered. Several parametrization scenarios are tested and the obtained solutions are compared with solutions of other processing centers. Furthermore, K-band range-rate (KBRR) post-fit residuals are analyzed in time, frequency and space domain and are compared to the typical post-fit residuals of the GRACE mission

Antarctic Time-Variable Regional Gravity Field Model Derived from Satellite Line-of-Sight Gravity Differences and Spherical Cap Harmonic Analysis

This study focuses on the development of a time-variable regional geo-potential model for Antarctica using the spherical cap harmonic analysis (SCHA) basis functions. The model is derived from line-of-sight gravity difference (LGD) measurements obtained from the GRACE-Follow-On (GFO) mission. The solution of a Laplace equation for the boundary values over a spherical cap is used to expand the geo-potential coefficients in terms of Legendre functions with a real degree and integer order suitable for regional modelling, which is used to constrain the geo-potential coefficients using LGD measurements. To validate the performance of the SCHA, it is first utilized with LGD data derived from a L2 JPL (Level 2 product of the Jet Propulsion Laboratory). The obtained LGD data are used to compute the local geo-potential model up to Kmax = 20, corresponding to the SH degree and order up to 60. The comparison of the radial gravity on the Earth’s surface map across Antarctica with the corresponding radial gravity components of the L2 JPL is carried out using local geo-potential coefficients. The results of this comparison provide evidence that these basis functions for Kmax = 20 are valid across the entirety of Antarctica. Subsequently, the analysis proceeds using LGD data obtained from the Level 1B product of GFO by transforming these LGD data into the SCHA coordinate system and applying them to constrain the SCHA harmonic coefficients up to Kmax = 20. In this case, several independent LGD profiles along the trajectories of the satellites are devised to verify the accuracy of the local model. These LGD profiles are not employed in the inverse problem of determining harmonic coefficients. The results indicate that using regional harmonic basis functions, specifically spherical cap harmonic analysis (SCHA) functions, leads to a close estimation of LGD compared to the L2 JPL. The regional harmonic basis function exhibits a root mean square error (RMSE) of 3.71 × 10−4 mGal. This represents a substantial improvement over the RMSE of the L2 JPL, which is 6.36 × 10−4 mGal. Thus, it can be concluded that the use of local geo-potential coefficients obtained from SCHA is a reliable method for extracting nearly the full gravitational signal within a spherical cap region, after validation of this method. The SCHA model provides significant realistic information as it addresses the mass gain and loss across various regions in Antarctica

GRACE-FO processing at IfE/LUH

Processing strategy of the LUH-GRACE-FO-2020 monthly gravity field time series is presented. The spectral noise, spatial noise and signal content of the time series (2018-06 - 2020-08) is evaluated

GRACE and GRACE-FO processing at IfE/LUH

Updates on gravity field recovery from GRACE and GRACE Follow-On data at IfE/LUH

Signals of Geophysical Nature in GRACE and GRACE-FO Post-Fit Range-Rate Residuals

Post-fit residuals of satellite-to-satellite tracking measurements of the GRACE and GRACE-FO missions obtained after a common estimation of orbit and gravity field parameters should ideally contain measurement noise with a behavior that meets expectations for the involved sensors. In reality, obtained GRACE and GRACE-FO post-fit range-rate residuals represent a complex superposition of different effects, e.g. of instrumental, environmental and geophysical nature. In this contribution, we focus on the geophysical signals in the post-fit residuals of the LUH GRACE and GRACE-FO time series. We apply band-pass filtering to extract the geophysical signal buried in the residuals and analyze the most distinctive signatures for their spatial and temporal behavior

Marssonina: Ab Ende April Infektionen möglich

Kahle Apfelbäume im August, Früchte, die an winterlich anmutenden Ästen hängen: ein Bild, das immer öfter anzutreffen ist. Vor allem Streuobstwiesen und Einzelbäume in Hausgärten sind betroffen, aber auch Produktionsanlagen mit reduziertem Fungizideinsatz. Ursache ist die Marssonina-Blattfallkrankheit, die in China und Indien eine der ökonomisch wichtigsten Apfelkrankheiten ist