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Unification of the global vertical datum has been a key problem to be solved for geodesy over a long period, and the main challenge for unifying the global vertical datum system is to determine the geopotential value W0 of the geoid and to calculate the vertical offset between the local vertical datum and the global vertical datum W0. The geopotential value W0 can be calculated using the grid mean sea surface (GMSS) data and the global geopotential model (GGM). In this study, this GMSS data was measured with adjustment methods and 24 years of merged multi-satellite altimetry data. The data of HaiYang-2A (HY-2A) and Jason-3 were first used to calculate W0. The geopotential value W0 was determined to be 62,636,856.82 m2s−2 by combining the EIGEN-6C4 (European Improved Gravity Model of the Earth by New Techniques) and the GMSS data. Then, the geopotential difference approach and geodetic boundary value problem (GBVP) approach were used to determine the vertical datum parameters in this study. To compensate for the omission error of the GGM, this study utilized the remove–compute–restore (RCR) technique and the residual terrain model (RTM)-recovered high-frequency gravity signals. Finally, as a result of the GBVP solution, the geopotential value of the Australian Height Datum (AHD) was 62,636,851.935 m2s−2, and the vertical offset of the AHD relative to the global vertical datum W0 was 0.4885 m. As a result of the geopotential difference approach, the geopotential value of the Chinese Height datum was 62636861.412 m2s−2, and the vertical offset of the Chinese Height datum was −0.4592 m.

To address the limitations in global seafloor topography model construction, a scheme is proposed that takes into account the efficiency of seafloor topography prediction, the applicability of inversion methods, the heterogeneity of seafloor environments, and the inversion advantages of sea surface gravity field element. Using the South China Sea as a study area, we analyzed and developed the methodology in modeling the seafloor topography, and then evaluated the feasibility and effectiveness of the modeling strategy. Based on the proposed modeling approach, the STO_IEU2020 global bathymetry model was constructed using various input data, including the SIO V29.1 gravity anomaly (GA) and vertical gravity gradient anomaly (VGG), as well as bathymetric data from multiple sources (single beam, multi-beam, seismic, Electronic Navigation Chart, and radar sensor). Five evaluation areas located in the Atlantic and Indian Oceans were used to assess the performance of the generated model. The results showed that 79%, 89%, 72%, 92% and 93% of the checkpoints were within the ±100 m range for the five evaluation areas, and with average relative accuracy better than 6%. The generated STO_IEU2020 model correlates well with the SIO V20.1 model, indicating that the proposed construction strategy for global seafloor topography is feasible.

One of the key constraints for the accelerometer of GRACE-type gravity satellites to accurately measure the non-gravitational accelerations acting on the satellite is that the center of mass of the satellite and the proof mass of the accelerometer should maintain a coincidence. In addition, the accuracy requirement is that the center of mass offset (CM-offset) in the three directions is less than 100 microns. Since the center of mass (CoM) of the satellite will change with the consumption of cold-gas fuel in the tanks, it is necessary to regularly carry out the CoM calibration maneuver. Firstly, the observation equations consisting of the accelerometer linear acceleration, angular acceleration, and the CM-offset vector are established in order to estimate the amount of CM-offset. Then, according to the estimated CM-offset, the satellite mass trim mechanisms are used to change the satellite’s CoM, so that the satellite’s CoM always approaches the proof mass of the accelerometer, with an accuracy of 100 μm per axis. The CM-offset of the satellite of GRACE-FO is estimated by using the accelerometer, star camera, magnetic torquer, magnetometer, and the precision orbit data during the GRACE-C CM-offset calibration period on 1 February 2020. Four kinds of CM-offset results are obtained by four different angular accelerations as follows: the angular acceleration based on the attitude dynamics (“MTQ angular acceleration”), the accelerometer angular acceleration calibrated by MTQ, the accelerometer angular acceleration, and the angular acceleration calculated by the star camera. By comparing the four kinds of CM-offset results that are estimated by the four different methods, all four of the results are shown to have the same level of accuracy. Based on the accelerometer (calibrated) angular acceleration, the difference with the JPL result is 0.5 μm, while the difference between the conventional method and the JPL result is 6.0 μm. All four of the methods can achieve the requirement of 50 μm accuracy and using four CM-offset estimation methods simultaneously can improve the integrity of the calibration results. Subsequently, the CM-offset results of GRACE-C since its launch are estimated here. The calibration algorithm that is proposed in this paper can be used as a reference in the calibration of gravity satellites carrying an accelerometer payload.

The coordinates of the KBR (K-band ranging system) antenna phase center of GRACE-type gravity satellites in the satellite Science Reference Frame should be precisely known, and the determination accuracy should reach 0.3 mrad in the Y (pitch) and Z (yaw) directions. Due to the precision limitation of ground measurement and the change of space environment during orbit, the KBR antenna phase center changes. In order to obtain more accurate KBR antenna phase center coordinates, it is necessary to maneuver the satellite to achieve the on-orbit calibration of the KBR antenna phase center. Based on the in-orbit calibration data of KBR of GRACE-FO satellites, a new method is proposed to estimate the antenna phase center of KBR using the inter-satellite range acceleration as the observation value. The antenna phase center of KBR is solved by the robust estimation method, and the obtained calibration results are better than 72 μm in the Y and Z directions and better than 1.3 mm in the X direction, which is 50% better than the least squares estimation algorithm. The accuracy of KBR calibration results obtained by using the data of positive maneuvers or mirror (negative) maneuvers, respectively, does not meet 0.3 mrad. It is shown that mirror maneuvers are required for KBR calibration of a GRACE-type gravity satellite to obtain antenna phase center estimation results that meet the accuracy requirements. The calibration algorithm proposed in this paper can provide reference for KBR antenna phase center calibration of Chinese GRACE-type gravity satellites.

According to the “theoretical admittance " and the "observation admittance" of the actual data, the theoretical value of effective elastic thickness in the study area was 10km. Combining the gravity anomalies and vertical gravity gradient anomalies, the admittance function is used to construct the 1'×1' bathymetry model over the Philippine Sea by using the adaptive weighting technique. It is found that the accuracy of the bathymetry model constructed is the highest when the ratio of inversion result of vertical gravity gradient anomalies and inversion result of gravity anomalies is 2∶3. At the same time, using multi-source gravity data to predict bathymetry could synthesize the superiority of gravity anomalies and vertical gravity gradient anomalies on the different seafloor topography, and the accuracy is better than bathymetry model that only used gravity anomalies or vertical gravity gradient anomalies. Taking the ship test data as the checking condition, the accuracy of predicting model is slightly lower than that of V18.1 model and improved by 27.17% and 39.02% respectively compared with the ETOPO1 model and the DTU10 model. Check points which the absolute value of the relative error of the predicting model is in the range of 5% accounted for 94.25% of the total.

Currently, seafloor topography inversion based on satellite altimetry gravity data provides the principal means to predict the global seafloor topography. Researchers often use sea surface geoid height or gravity anomaly to predict sea depth in the space domain. In this paper, a comprehensive discussion on seafloor topography inversion formulas in the space domain is presented using sea surface geoid height, gravity anomaly and introduces an approach that uses vertical gravity gradient. This would be the first study to estimate seafloor topography by vertical gravity gradient in the space domain. Further, a nonlinear iterative least-square inversion process is discussed. Using the search area for the Malaysia Airlines Flight MH370 as study site, we used the DTU17 gravity anomaly model and SIO V29.1 vertical gravity gradient to generate the seafloor topography. The results of the proposed bathymetric models were analyzed and compared with the DTU18 and SIO V20.1 bathymetric models. The experimental results show that the gravity anomaly and vertical gravity gradient in the study area are strongly correlated with the seafloor topography in the 20–200 km wavelength range. The optimal initial iteration values for seafloor topography variance and correlation length are 0.6365 km2 and 10.5′, respectively. Shipborne measurements from SONAR data were used as external checkpoints to evaluate the bathymetric models. The results show that the RMS for BAT_VGG_ILS (inversion model constructed by vertical gravity gradient) is smaller than for BAT_GA_ILS (inversion model constructed by gravity anomaly) and BAT_GA_VGG_ILS (inversion model constructed by gravity anomaly and vertical gravity gradient). The relative accuracy of the DTU18 bathymetry model was 9.27%, while the relative accuracy of the proposed seafloor models was higher than 4%. Within the 200 m difference range, the proportion of checkpoints for BAT_VGG_ILS was close to 95%, about 80% for BAT_GA_ILS and BAT_GA_VGG_ILS, and less than 50% for the DTU18. The results show that the nonlinear iterative least square method in the space domain is feasible.

Compared with airborne gravimetry, a technique frequently used to infer the seafloor topography at places inaccessible to ship soundings due to the presence of ice shelf or ice mélange, airborne gravity gradiometry inherently could achieve higher spatial resolution, thus it is promising for improved inference of seafloor topography. However, its estimation capability has not been demonstrated by real projects. Theoretical analysis through admittance shows that compared with gravity disturbance, gravity gradient is more sensitive to the short-wavelength seafloor topography but diminishes faster with the increase of the distance between the seafloor and airplane, indicating its superiority is recovering short-wavelength topographic features over shallow waters. We present the first numerical experiment that estimates seafloor topography from a 0.4-km resolution, real airborne gravity gradients. It is shown that airborne gravity gradiometry can recover smaller topographic features than typical airborne gravimetry, but the estimation accuracy is only ±17 m due to the presence of subsurface density variations. The long-wavelength effect of the subsurface density variations can be removed with the aid of constraining bathymetry inside the study area, whereas the short wavelengths cannot. This study expands the applications of airborne gravity gradiometry, and helps glaciologists understand its performance in seafloor topography estimation.

Selective catalytic reduction of nitrogen oxides (NOx) with C3H6 (C3H6‐SCR) was investigated over NiO catalysts supported on different metal‐oxides. A NiAlOx mixed oxide phase was formed over NiO/γ‐Al2O3 catalyst, inducing an immediate interaction between NiOx and AlOx species. Such interaction resulted in a charge transfer from Ni to Al site and the formation of Ni species in high oxidation state. In comparison to other NiO‐loaded catalysts, NiO/γ‐Al2O3 catalyst exhibited the highest NOx conversion at temperature higher than 450 °C, but a poor C3H6 oxidation activity due to the decreased nucleophilicity for surface oxygen species. By temperature‐programed NO oxidation, it is indicated that nitrate species were rapidly formed and stably maintained at high temperature over NiO/γ‐Al2O3 catalyst. In situ transient reactions further verified the Langmuir–Hinshelwood mechanism for C3H6‐SCR, where both gaseous NO and C3H6 were adsorbed and activated on catalyst surface and reacted to generate N2. Due to the strong metal‐support interaction over NiO/γ‐Al2O3 catalyst, both nitrate and CxHyOz intermediates were well preserved to attain high C3H6‐SCR activity. [ABSTRACT FROM AUTHOR]

Selective catalytic reduction of nitrogen oxides (NOx) with C3H6 (C3H6‐SCR) was investigated over NiO catalysts supported on different metal‐oxides. A NiAlOx mixed oxide phase was formed over NiO/γ‐Al2O3 catalyst, inducing an immediate interaction between NiOx and AlOx species. Such interaction resulted in a charge transfer from Ni to Al site and the formation of Ni species in high oxidation state. In comparison to other NiO‐loaded catalysts, NiO/γ‐Al2O3 catalyst exhibited the highest NOx conversion at temperature higher than 450 °C, but a poor C3H6 oxidation activity due to the decreased nucleophilicity for surface oxygen species. By temperature‐programed NO oxidation, it is indicated that nitrate species were rapidly formed and stably maintained at high temperature over NiO/γ‐Al2O3 catalyst. In situ transient reactions further verified the Langmuir–Hinshelwood mechanism for C3H6‐SCR, where both gaseous NO and C3H6 were adsorbed and activated on catalyst surface and reacted to generate N2. Due to the strong metal‐support interaction over NiO/γ‐Al2O3 catalyst, both nitrate and CxHyOz intermediates were well preserved to attain high C3H6‐SCR activity. [ABSTRACT FROM AUTHOR]

Based on the analysis of the natural gas component and its isotope，coupled with geochemical characteristics of source rocks and geological settings，the genetic type and distribution of natural gas of Langgu Sag were investigated. Analytical results show that great difference of geochemical characteristics exist between the shallow burial reservoirs （<1 900m）and deep burial reservoirs（>1 900m），displaying different genetic types.The shallow gas reservoirs are dominated by secondary biologic modification gas reservoirs with mixed secondary biogenic gas from biodegradation of thermogenic gas and residual thermogenic gas. And this type of gas is featured by high gas dry coefficient（>95%），but also relative high content of heavy gas（ΣC2+>0.5%）；significant increase of isoparaffin content and significant decrease of propane；the partially reversed carbon isotope order with anomalously heavy propane carbon isotope compositions；light stable carbon isotope (-60‰<δ13C1<-50‰) of methane. The deep gas is mainly humic-prone and generated from the primary cracking of kerogen. Maturity estimation combined with pyrolysis of the source rocks reveal that most deep gas samples are derived from E2sL3 source rock interval with low to moderate value of RO ranging from 0.5% to 0.8%，while four gas samples from deep depth in the area of Caojiawu and Gu’an as well as samples from Ordovician buried-hilled may be generated from the E2s4-Ek source rock with high value of RO varying from 1.1% to 1.5%. It is concluded that the kerogen type and maturity of the source rock control the distribution of deep gas and the activity of hydrocarbon-connecting faults may play an important role on the formation of shallow gas reservoirs. The secondary biologic modification gas reservoirs occur in the areas of Gu’an，Liuquan and Langdong. Also significant attention must be focused on the potential of deep natural gas resource and the Daxing conglomerate body in the Gu’an-Jiuzhou and the Bieguzhuang's buried hilled are the favorable targets zone of further exploration for the deep natural gas. [ABSTRACT FROM AUTHOR]

Selective catalytic reduction of nitrogen oxides (NO x ) with C 3 H 6 (C 3 H 6 -SCR) was investigated over NiO catalysts supported on different metal-oxides. A NiAlO x mixed oxide phase was formed over NiO/γ-Al 2 O 3 catalyst, inducing an immediate interaction between NiO x and AlO x species. Such interaction resulted in a charge transfer from Ni to Al site and the formation of Ni species in high oxidation state. In comparison to other NiO-loaded catalysts, NiO/γ-Al 2 O 3 catalyst exhibited the highest NO x conversion at temperature higher than 450 °C, but a poor C 3 H 6 oxidation activity due to the decreased nucleophilicity for surface oxygen species. By temperature-programed NO oxidation, it is indicated that nitrate species were rapidly formed and stably maintained at high temperature over NiO/γ-Al 2 O 3 catalyst. In situ transient reactions further verified the Langmuir-Hinshelwood mechanism for C 3 H 6 -SCR, where both gaseous NO and C 3 H 6 were adsorbed and activated on catalyst surface and reacted to generate N 2 . Due to the strong metal-support interaction over NiO/γ-Al 2 O 3 catalyst, both nitrate and C x H y O z intermediates were well preserved to attain high C 3 H 6 -SCR activity., (© 2022 Wiley-VCH GmbH.)