Attitude Determination for GRACE-FO: Reprocessing the Level-1A SC and IMU Data

The satellite gravity mission GRACE(-FO) has not yet reached its designed baseline accuracy. Previous studies demonstrated that the deficiency in the sensor system or the related signal processing might be responsible, which in turn motivates us to keep revising the sensor data processing, typically the spacecraft’s attitude. Many efforts in the past have been made to enhance the attitude modeling for GRACE, for instance, the latest release reprocesses the attitude by fusing the angular acceleration with the star camera/tracker (SC) measurements, which helps to reduce the error in Level-2 temporal gravity fields. Therefore, in addition to GRACE, revising GRACE-FO attitude determination might make sense as well. This study starts with the most original raw GRACE-FO Level-1A data including those from three SCs and one IMU (Inertial Measurement Unit) sensors, and manage to generate a new publicly available Level-1B attitude product called HUGG-01 covering from June 2018 to December 2020, using our independently-developed software. The detailed treatment of individual payload is present in this study, and an indirect Kalman filter method is introduced to fuse the multiple sensors to acquire a relatively stable and precise attitude estimation. Unlike the direct SC combination method with a predefined weight as recommended in previous work, we propose an involvement of each SC measurement in the Kalman filter to enable a dynamic weight adjustment. Intensive experiments are further carried out to assess the HUGG-01, which demonstrate that the error level of HUGG-01 is entirely within the design requirement, i.e., the resulting KBR pointing variations are well controlled within 1 mrad (pitch), 5 mrad (roll) and 1 mrad (yaw). Moreover, comparisons with the official JPL-V04 attitude product demonstrate an equivalent performance in the low-to-middle spectrum, with even a slightly lower noise level (in the high spectrum) than JPL-V04. Further analysis on KBR range-rate residuals and gravity recovery on Jan 2019 indicates that, i.e., RMS of the difference (HUGG-01 minus JPL-V04) for the range rate is less than 3.234×10−8 m/s, and the amplitude of geoid height difference is approximately 0.5 cm. Both differences are below the sensitivity of the state-of-the-art satellite gravity mission, demonstrating a good agreement between HUGG-01 and JPL-V04.

Geological interpretation of offshore Central Sumatra basin using topex satellite gravity data

Topex is a geodetic satellite to map earth surface topography with very high precision. Two types of data can be obtained from Topex satellite, namely topographic and free-air gravity field data. Then, it is processed to produce Bouguer anomaly which will be used to interpret the subsurface geology of a specific study area. The purpose of this study was to delineate sedimentary basin and basement configurations. The methods used in this research are spectral analysis, band-pass filter and 2D forward modeling. The spectral analysis results show the average thickness of the sedimentary rocks is 2.1 km. Sub-basin patterns based on the band-pass filter are 7 sedimentary sub-basins and the structural patterns found in this area comprise basement height, graben and fault. The 2D modeling results show that the bedrock in the eastern part of the Central Sumatra basin is granitic with a mass density value of 2.67 gr/cc and the layer above the bedrock is interpreted as a sedimentary rock with a mass density value of 2.35 gr/cc. Analysis of the gravity data shows significant results as initial information to delineate sedimentary sub-basin and regional structure to enhance information to the next stage of hydrocarbon exploration.

The Wishbone Ridge at the Chatham Rise Intersection: Structural Characteristics and Tectonic Implications

<p>Geophysical data show that the West Wishbone Ridge, offshore of eastern New Zealand, is best described as having previously been a crustal transform fault, which first propagated along the eastern margin of the Hikurangi Plateau as subduction along the New Zealand sector of the Gondwana margin began to slow and reorientate between 105 and 101 Ma. Variation in the strike of the West Wishbone Ridge has resulted in contrasting compressional and extensional zones along the ridge. These regimes reflect the direction of strike offset from the direction of fault propagation, and constrain the sense of motion along the West Wishbone Ridge as having been dextral. We find evidence that Cretaceous subduction along the Chatham Rise margin extended east of the margin offset at 174°W that marks the edge of Hikurangi Plateau subduction beneath the margin. Rotation of the Chatham Rise margin between 105 and 101 Ma was accommodated by westward broadening of the extensional zone of deformation associated with the West Wishbone Ridge near its intersection with the Chatham Rise. The amount of offset along the ridge indicates that significant transform motion along the West Wishbone Ridge south of ~40.5°S ceased ca. 101 Ma, coeval with the cessation of spreading of the Osbourn Trough, and of subduction of the Hikurangi Plateau. Additionally, we find anomalously thick oceanic crust adjacent to the WWR and north of the Hikurangi Plateau (>12 km thick). This is attributed to the proximity of this crust to the Hikurangi Plateau Large Igneous Province. The results of this study are based on seismic reflection and magnetic data recently collected during the 2016 R/V Sonne survey SO-246, as well as previously collected seismic reflection profiles and satellite gravity data.</p>

Analysis of gravity anomaly and seismicity in Bali region

This study aims to determine the value of the gravity anomaly in the Bali region, identify the fault structure in the Bali region using gravity interpretation and analyze the relationship between gravity anomaly and seismicity in the Bali region. The data used is secondary data, namely satellite gravity anomaly data obtained from the topex website and earthquake data obtained from the Indonesian Agency for Meteorological, Climatological, and Geophysics (BMKG) catalog. Data processing in this study was done using gravity and Second Vertical Derivative (SVD) methods. We used Surfer15 software, Oasis Montaj, and the Generic Mapping Tool (GMT). The results of the complete Bouguer anomaly map show the anomalous value of the study area between 10-220 mGal, regional anomaly 40-190 mGal, and the residual anomaly between (-120)-60 mGal. Judging from the SVD contour map that has included earthquake data in the Bali region for the 2008-2020 period, the type of fault in the Seririt Fault, Tejakula Fault, and Fault around Mount Agung is a thrust fault. Judging from the value of the coefficient of determination, it shows that 99% of the seismicity value is influenced by gravity anomaly. The higher the value of the gravity anomaly, the higher the seismicity value.

ADAPTATION OF THE GLOBAL GEOID MODEL EGM2008 ON CAMPANIA REGION (ITALY) BASED ON GEODETIC NETWORK POINTS

The knowledge of the geoid undulation, the height of the geoid relative to a given ellipsoid of reference, is fundamental to transform the ellipsoidal heights into orthometric heights. Global geoid undulation models developed from satellite gravity measurements appropriately integrated with other data, are free accessible in internet, but their accuracy may be inadequate for specific applications. Earth Gravitational Model 2008 (EGM2008) is one of those: usually available in grid form 2.5’ × 2.5’ (a geotif is developed by Agisoft with resolution 1’ × 1’), it defines the difference between the WGS84 ellipsoid height and the mean sea level, but in some areas the discrepancies between these geoid undulations and local correspondent measured values are on the order of various decimetres. For consequence, more accurate models are necessary. This article aims to determine a geoid undulation model suitable for Campania Region (Italy), starting from the global model EGM2008 (1’ × 1’) that is locally adjusted by using geodetic network points (GNPs) and GIS interpolation functions. Three different datasets are considered including respectively 20, 40 and 60 GNPs and three deterministic interpolators are applied in global way to generate geoid undulation grids: Inverse Distance Weight (IDW), Global Polynomial 1st order (GP1), Global Polynomial 2nd order (GP2). The resultant 9 models are tested on 20 additional GNPs. The experiments demonstrate that local geoid can be produced on a little area adapting global geoid by means of GNPs: the model obtained using GP2 and 60 GNPs, the most accurate one, fits the data with ±3.2 cm root mean square error (RMSE).

Utilization of Gravity Satellite Data to Imaging Subsurface Conditions, Case Study: Lake Toba, North Sumatera

The purpose of this study is to utilize satellite gravity data for free to interpret subsurface conditions. The data can be obtained from the topex site with a latitude range is +/-80,738. The author tries to interpret the gravity data for Lake Toba, North Sumatra. The area is attractive because it has a sizeable geological object in the form of a large lake and a fault called the Sumatran fault. This gravity data is processed like ordinary gravity processing so that Complete Bouguer Anomaly (CBA) is obtained, then regional-residual separation is carried out using a moving average. From CBA, it can be seen that there are two closures just below Lake Toba. There are two possible chambers under Lake Toba, namely the central and southern parts. In addition, it is also clear that the lineament of the Sumatran fault is also visible, as well as three other lineaments which may be faults that are not identified from the surface. So, we can take advantage of this free gravity satellite data for interpretation of sizeable geological objects that can be applied to other areas. It is helpful to know the general picture of regional geology before conducting a more detailed survey.

Analysis of the interannual variability in satellite gravity solutions: detection of climate modes fingerprints in water mass displacements across continents and oceans

This study analyzes the interannual variability of the water mass transport measured by satellite gravity missions in regard to eight major climate modes known to influence the Earth’s climate from regional to global scales. Using sparsity promoting techniques (i.e., LASSO), we automatically select the most relevant predictors of the climate variability among the eight candidates considered. The El Niño–Southern Oscillation, Southern Annular Mode and Arctic Oscillation are shown to account for a large part the interannual variability of the water mass transport observed in extratropical ocean basins (up to 40%) and shallow seas (up to 70%). A combination of three Pacific and one Atlantic modes is needed to account for most (up to 60%) of the interannual variability of the terrestrial water storage observed in the North Amazon, Parana and Zambezi basins. With our technique, the impact of climate modes on water mass changes can be tracked across distinct water reservoirs (oceans, continents and ice-covered regions) and we show that a combination of climate modes is necessary to explain at best the natural variability in water mass transport. The climate modes predictions based on LASSO inversions can be used to reduce the inter-annual variability in satellite gravity measurements and detect processes unrelated with the natural variability of climate but with similar spatio-temporal signatures. However, significant residuals in the satellite gravity measurements remain unexplained at inter-annual time scales and more complex models solving the water mass balance should be employed to better predict the variability of water mass distributions.