Inversion method of deflection of the vertical based on SWOT wide-swath altimeter data

The deflection of the vertical(DOV)is the key information in the study of ocean gravity field.However,in most areas,the precision of the prime component of DoV is significantly lower than that of the meridian component.To obtain higher accuracy and resolution of ocean gravity information,researchers have proposed a novel altimeter called the wide-swath altimeter.This altimeter allows for the simultaneous acquisition of high-precision and high-resolution two-dimensional measurements of sea surface height(SSH).In this paper,the Surface Water and Ocean Topography(SWOT)mission with a wide-swath altimeter on board is selected for research.One cycle of swoT sea surface height data is simulated to inverse the DOV in the Arabian Sea(45°E—80°E,0°-30°N),and the inversion results are compared with those of conventional altimeter data.The results demonstrate that the difference between the meridian and prime components derived from the inversion of swoT wide-swath data is minimal,significantly outperforming the inversion results of conventional nadir altimeter data.The advantage of swoT wide-swath altimeter lies in its ability to use the multi-directional geoid slope at any sea surface measurement point to invert the components in the meridian and prime directions.To investigate the impact of this advantage on inversion precision,this paper employs a method to calculate the gradient of the geoid in multiple directions to invert DoV components.The improvement effect of calculating the gradient of the geoid in multiple directions on the precision of DoV component is analyzed.It is found that the accuracy of DoV inversion has significantly improved with the increase of geodetic gradient calculation direction.In addition,the effects of various errors and grid spacing in SwoT wide sea surface height data on the precision of Dov inversion are also analyzed.

Gravity anomalies determined from mean sea surface model data over the Gulf of Mexico

With the improvements in the density and quality of satellite altimetry data,a high-precision and high-resolution mean sea surface model containing abundant information regarding a marine gravity field can be calculated from long-time series multi-satellite altimeter data.Therefore,in this study,a method was proposed for determining marine gravity anomalies from a mean sea surface model.Taking the Gulf of Mexico(15°–32°N,80°–100°W)as the study area and using a removal-recovery method,the residual gridded deflections of the vertical(DOVs)are calculated by combining the mean sea surface,mean dynamic topography,and XGM2019e_2159 geoid,and then using the inverse Vening-Meinesz method to determine the residual marine gravity anomalies from the residual gridded DOVs.Finally,residual gravity anomalies are added to the XGM2019e_2159 gravity anomalies to derive marine gravity anomaly models.In this study,the marine gravity anomalies were estimated with mean sea surface models CNES_CLS15MSS,DTU21MSS,and SDUST2020MSS and the mean dynamic topography models CNES_CLS18MDT and DTU22MDT.The accuracy of the marine gravity anomalies derived by the mean sea surface model was assessed based on ship-borne gravity data.The results show that the difference between the gravity anomalies derived by DTU21MSS and CNES_CLS18MDT and those of the ship-borne gravity data is optimal.With an increase in the distance from the coast,the difference between the gravity anomalies derived by mean sea surface models and ship-borne gravity data gradually decreases.The accuracy of the difference between the gravity anomalies derived by mean sea surface models and those from ship-borne gravity data are optimal at a depth of 3–4 km.The accuracy of the gravity anomalies derived by the mean sea surface model is high.

Height connection across sea by using satellite altimetry data sets,ellipsoidal heights,astrogeodetic deflections of the vertical,and an Earth Gravity Model

Islands and the mainland are separated by seas,and the distances between them might be so long that the height on the mainland cannot be exactly translated to the islands,resulting in different height systems on the mainland and the islands.In this study,we used astrogeodetic deflections of the vertical and ellipsoidal heights of points on the mainland and island near their coastlines to implement height connection across sea areas.First,the modeled gravity and modeled astrogeodetic vertical deflections of segmentation points along connecting routes over the sea between the mainland and the island were determined by Earth Gravity Model(EGM),and the ellipsoidal heights of segmentation points were determined by the satellite altimetry data sets.Second,we used a linear interpolation model to increase the precision of the vertical deflections of segmentation points.Third,we computed the geopotential difference of points between the mainland and the island using a method derived from geopotential theory and the astronomical leveling principle.Finally,we estimated the normal height of the point on the island using the geopotential-difference iterative computation approach.Using observed data of normal heights,ellipsoidal heights,and astrogeodetic vertical deflections referring to height sites in Qingdao,Shandong Province,we conducted a numerical experiment involving the normal height connection across sea regions.We determined the data of the ellipsoidal heights and gravity of segmentation points along the connecting route across the water in the numerical experiment using DTU10.The distance of the height connection across the sea was approximately 10.5 km.According to China's official leveling specifications,the experimental results met the criterion of third-class leveling precision.

Influence of higher-order ionospheric delay correction on GPS precise orbit determination and precise positioning

At present, Global Navigation Satellite Systems（GNSS） users usually eliminate the influence of ionospheric delay of the first order items by dual-frequency ionosphere-free combination. But there is still residual ionospheric delay error of higher order term. The influence of the higher-order ionospheric corrections on both GPS precision orbit determination and static Precise Point Positioning（PPP） are studied in this paper. The influence of higher-order corrections on GPS precision orbit determination, GPS observations and static PPP are analyzed by neglecting or considering the higher-order ionospheric corrections by using a globally distributed network which is composed of International GNSS Service（IGS） tracking stations. Numerical experimental results show that, the root mean square（RMS） in three dimensions of satellite orbit is 36.6 mme35.5 mm. The maximal second-order ionospheric correction is 9 cm, and the maximal third-order ionospheric correction is 1 cm. Higher-order corrections are influenced by latitude and station distribution. PPP is within 3 mm in the directions of east and up. Furthermore, the impact is mainly visible in the direction of north, showing a southward migration trend, especially at the lower latitudes where the influence value is likely to be bigger than 3 mm.

Lunar deflections of the vertical and their distribution

The deflection of the vertical reflects the mass distribution and density anomaly of celestial bodies. Lunar deflections of the vertical include directional information of the Moon’s gravity field. SGM90d, recovered from SELENE mission, revealed the lunar far side gravity field for the first time in history owes to 4-way Doppler data. Lunar deflections of the vertical and their meridional and prime vertical components are calculated from SGM90d, and then their global distributions are also given in the paper. The gradients of lunar deflections of the vertical are defined and computed as well. The correlations between the lunar deflections of the vertical and the lunar terrain have been fully discussed. Many different characteristics of lunar deflections of vertical have been found between the near side and the far side of the Moon, which may be caused from the lithospheric compensation and the uplifting of mantle.

Study on ionosphere change over Shandong based from SDCORS in 2012

Temporal and spatial variation of ionosphere can influence our daily communication activities. By solving the one-year global positioning system （GPS） data of Shandong Continuous Operational Reference System （SDCORS） in 2012, we modeled the single-layer spherical harmonic model of vertical total electron content （TEC） over Shandong Province, China, and analyzed the time series of TEC in 2012. The ionosphere over Shandong in 2012 was in the peak year of solar activity. The ionospheric model over Shandong was calibrated and verified using data of the Center for Orbit Determination in Europe （CODE） and the Crustal Movement Observation Network of China （CMONOC）, respectively. The ionosphere is greatly influenced by latitude and solar activity and has the phenomenon of Winter anomaly and semiannual anomaly as well as the session change, diurnal variation, monthly change and seasonal variations. So we can grasp the regularity of temporal and spatial distribution of ionosphere over Shandong, China.

Digital zenith telescope prototype of China

Classical optical astronomy measures the direction of the local plumb line on the stellar background,and is influenced by variations of the earth gravity field.Therefore,classical optical astrometry can be used to measure and study variations of plumb line.This endows classical optical astrometric technologies special significance for the interdisciplinary researches of astronomy and geoscience,and makes them irreplaceable by technologies like very long baseline interferometry,satellite laser ranging.However,classical astrometric instruments have a major drawback of low efficiency,such as the low automaticity,more operating observers,and even operative error which makes it very difficult to reduce the random observation error in some visual instruments.To overcome this drawback,we have successfully developed the digital zenith telescope prototype(DZT-1)with the aperture of200 mm,using charge coupled device and other advanced technologies and new equipments.As proved by test observations,DZT-1 can observe thousands of stars over one night,which significantly reduces the random observation error and increases the observation accuracy.In addition,DZT-1 has a high degree of automation,even allowing unattended observation by remote control.Besides,DZT-1 has a small-size and is easy to move,making it convenient for mobile measurement of the deflection of the vertical.In summary,DZT can be widely used in the geoscience and astronomy fields.

n-平移代数、平凡扩张与预投射代数

Koszul稳定n-平移代数的对偶τ-切片代数是一类拟(n-1)-Fano代数.本文给出一个分次代数成为稳定n-平移代数的对偶τ-切片代数的判别法,并证明Koszul稳定n-平移代数的齐次对偶τ-切片代数的预投射代数等于其二次对偶的扭平凡扩张的二次对偶,作为其推论,本文得到对偶切片代数的导出范畴与其预投射代数的非交换射影概型的导出范畴等价.