Estimation of the Gravity Field and Sea Surface Heights from Heterogeneous Data in the Central Mediterranean

1991 ◽  
pp. 63-74
Author(s):  
D. Arabelos ◽  
I. N. Tziavos
Keyword(s):  
Gravity Field ◽  
Heterogeneous Data ◽  
Sea Surface ◽  
Central Mediterranean ◽  
Sea Surface Heights

scholarly journals Recovering Marine Gravity Over the Gulf of Guinea From Multi-Satellite Sea Surface Heights

2021 ◽  
Vol 9 ◽  
Author(s):  
Richard Fiifi Annan ◽  
Xiaoyun Wan
Keyword(s):  
Gravity Field ◽  
Gravity Anomalies ◽  
Sea Surface ◽  
Shallow Waters ◽  
Gulf Of Guinea ◽  
Gravity Field Model ◽  
The North ◽  
Marine Gravity ◽  
Sea Surface Heights ◽  
East Component

A regional gravity field product, comprising vertical deflections and gravity anomalies, of the Gulf of Guinea (15°W to 5°E, 4°S to 4°N) has been developed from sea surface heights (SSH) of five altimetry missions. Though the remove-restore technique was adopted, the deflections of the vertical were computed directly from the SSH without the influence of a global geopotential model. The north-component of vertical deflections was more accurate than the east-component by almost three times. Analysis of results showed each satellite can contribute almost equally in resolving the north-component. This is attributable to the nearly northern inclinations of the various satellites. However, Cryosat-2, Jason-1/GM, and SARAL/AltiKa contributed the most in resolving the east-component. We attribute this to the superior spatial resolution of Cryosat-2, the lower inclination of Jason-1/GM, and the high range accuracy of the Ka-band of SARAL/AltiKa. Weights of 0.687 and 0.313 were, respectively, assigned to the north and east components in order to minimize their non-uniform accuracy effect on the resultant gravity anomaly model. Histogram of computed gravity anomalies compared well with those from renowned models: DTU13, SIOv28, and EGM2008. It averagely deviates from the reference models by −0.33 mGal. Further assessment was done by comparing it with a quadratically adjusted shipborne free-air gravity anomalies. After some data cleaning, observations in shallow waters, as well as some ship tracks were still unreliable. By excluding the observations in shallow waters, the derived gravity field model compares well in ocean depths deeper than 2,000 m.

scholarly journals CHARACTERIZATION OF THE RIO GRANDE RISE FROM ELEMENTS OF THE TERRESTRIAL GRAVITY FIELD

2018 ◽  
Vol 36 (3) ◽  
pp. 1
Author(s):  
Marília T. Dicezare ◽  
Eder C. Molina
Keyword(s):  
Gravity Field ◽  
Structural Characteristics ◽  
Rio Grande ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Entire Area ◽  
Terrestrial Gravity ◽  
Surface Gradient ◽  
Adjacent Structures ◽  
Sea Surface Heights

ABSTRACT. The aim of this paper is to investigate the structural characteristics of the Rio Grande Rise, South Atlantic, through the analysis of the elements of the terrestrial gravity field. We used sea surface height (SSH) data and calculated sea surface gradients (SSG) from the ERS1-GM, Geosat-GM and Seasat satellite missions. By analyzing the sea surface heights it was possible to identify larger structures, such as the rift of the rise, some fractures and large seamounts. Sea surface gradients provided greater details of the features characterized by the SSH and, additionally, of the entire area, also revealing several other structures related to short wavelengths. The positioning of the features identified by both SSH and SSG is fairly accurate. Factors such as the direction and the orientation of the satellite tracks and the presence of adjacent structures may influence the SSG response to a given tectonic feature, making it important to analyze both ascending and descending sets of tracks from several missions to obtain better results. The study also allowed us to identify possible structures with a characteristic response of seamounts on SSH descending tracks, which were not previously characterized in the literature and do not have a similar correspondent in topographic/bathymetric models.Keywords: Sea Surface Height (SSH), Sea Surface Gradient (SSG), Rio Grande Rise (RGR), Satellite Altimetry.RESUMO. Este trabalho teve como objetivo investigar as características estruturais da Elevação do Rio Grande, no Atlântico Sul, através de elementos do campo de gravidade terrestre. Para isso, foram utilizados dados de altura da superfície do mar (SSH) e gradientes da superfície do mar (SSG) provenientes dos satélites das missões ERS1-GM, Geosat-GM e Seasat. Através da SSH foi possível identificar estruturas de maior porte, como o rift da elevação, algumas fraturas e montes submarinos maiores. A SSG forneceu maiores detalhes sobre as feições já caracterizadas pela SSH e de toda a região, revelando também diversas outras estruturas relacionadas aos comprimentos de onda curtos. O posicionamento das feições identificadas por ambas as grandezas é bastante preciso. Fatores como a direção e a orientação das trilhas dos satélites e a presença de estruturas adjacentes podem influenciar a resposta da SSG para uma determinada feição tectônica, sendo importante analisar os dois conjuntos de trilhas, ascendentes e descendentes, de várias missões para obter melhores resultados. O estudo também permitiu identificar possíveis estruturas com uma resposta característica de montes submarinos, nas trilhas descendentes de SSH, que não foram caracterizados anteriormente na literatura e não possuem correspondente nos modelos topográficos/batimétricos.Palavras-chave: Altura da Superfície do Mar (SSH), Gradiente da Superfície do Mar (SSG), Elevação do Rio Grande (RGR), Altimetria por Satélite.

Sea Surface Heights and Marine Gravity Determined from SARAL/AltiKa Ka-band Altimeter Over South China Sea

2021 ◽  
Author(s):  
Chengcheng Zhu ◽  
Xin Liu ◽  
Jinyun Guo ◽  
Shengwen Yu ◽  
Yupeng Niu ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Sea Surface ◽  
Ka Band ◽  
China Sea ◽  
Marine Gravity ◽  
Sea Surface Heights

Airborne measurement of absolute sea-surface heights

1993 ◽  
Vol 20 (9) ◽  
pp. 875-878 ◽  
Author(s):  
John M. Brozena ◽  
Mary F. Peters ◽  
Rene Forsberg
Keyword(s):  
Sea Surface ◽  
Airborne Measurement ◽  
Sea Surface Heights

scholarly journals Vertical Deflections and Gravity Disturbances Derived from HY-2A Data

2020 ◽  
Vol 12 (14) ◽  
pp. 2287
Author(s):  
Xiaoyun Wan ◽  
Richard Fiifi Annan ◽  
Shuanggen Jin ◽  
Xiaoqi Gong
Keyword(s):  
Gravity Field ◽  
Systematic Errors ◽  
Mean Value ◽  
Gravity Disturbance ◽  
Long Wavelength ◽  
The North ◽  
Marine Gravity ◽  
Gravity Disturbances ◽  
Sea Surface Heights ◽  
East Component

The first Chinese altimetry satellite, Haiyang-2A (HY-2A), which was launched in 2011, has provided a large amount of sea surface heights which can be used to derive marine gravity field. This paper derived the vertical deflections and gravity disturbances using HY-2A observations for the major area of the whole Earth’s ocean from 60°S and 60°N. The results showed that the standard deviations (STD) of vertical deflections differences were 1.1 s and 3.5 s for the north component and the east component between HY-2A’s observations and those from EGM2008 and EIGEN-6C4, respectively. This indicates the accuracy of the east component was poorer than that of the north component. In order to clearly demonstrate contribution of HY-2A’s observations to gravity disturbances, reference models and the commonly used remove-restore method were not adopted in this study. Therefore, the results can be seen as ‘pure’ signals from HY-2A. Assuming the values from EGM2008 were the true values, the accuracy of the gravity disturbances was about −1.1 mGal in terms of mean value of the errors and 8.0 mGal in terms of the STD. This shows systematic errors if only HY-2A observations were used. An index of STD showed that the accuracy of HY-2A was close to the theoretical accuracy according to the vertical deflection products. To verify whether the systematic errors of gravity field were from the long wavelengths, the long-wavelength parts of HY-2A’s gravity disturbance with wavelengths larger than 500 km were replaced by those from EGM2008. By comparing with ‘pure’ HY-2A version of gravity disturbance, the accuracy of the new version products was improved largely. The systematic errors no longer existed and the error STD was reduced to 6.1 mGal.

scholarly journals Improving the GNSS-R Specular Reflection Point Positioning Accuracy Using the Gravity Field Normal Projection Reflection Reference Surface Combination Correction Method

2018 ◽  
Vol 11 (1) ◽  
pp. 33 ◽  
Author(s):  
Fan Wu ◽  
Wei Zheng ◽  
Zhaowei Li ◽  
Zongqiang Liu
Keyword(s):  
Gravity Field ◽  
Specular Reflection ◽  
Correction Method ◽  
Sea Surface ◽  
Reference Surface ◽  
Reflection Point ◽  
Positioning Accuracy ◽  
Normal Projection ◽  
Point Positioning ◽  
Surface Correction

Global Navigation Satellite System Reflectometry (GNSS-R) is of great significance for the extraction and research of precise information of sea surface topography. Improving measurement accuracy is necessary for realizing spaceborne GNSS-R sea surface altimetry application. The main error source of GNSS-R distance measurement is the error of the specular reflection point positioning, which directly affects the sea surface altimetry accuracy on the reference datum. There is an elevation error of several tens of meters between the reflection reference surface used by the existing specular reflection point geometric positioning methods and the sea surface elevation, which is importantly influenced by the earth’s gravity field. Therefore, the gravity field reflection reference surface correction is the key to improving the specular reflection point positioning accuracy. In this study, based on the correction of the GNSS-R reflection reference surface, research on improving the positioning accuracy of the specular reflection point is carried out. Firstly, in order to reduce the positioning error caused by the elevation difference between the reflection reference surface and the sea surface, the gravity field reflection reference surface correction method (GFRRSCM) which corrects the reflection reference surface from the WGS-84 ellipsoid to geoid is proposed, and the positioning accuracy is improved by 25.15 m. Secondly, the normal projection reflection reference surface correction method (NPRRSCM) is proposed to correct the specular reflection point determined by the GFRRSCM from the reflection reference plane of the radial to that of the normal. Additionally, in the process of solving the spatial geometric relationship of the reflection path, the approximate substitution error is reduced by directly solving the normal projection on the plane, and the positioning accuracy is further improved by 13.05 m towards the normal. Thirdly, based on the gravity field normal projection reflection reference surface combination correction method (GF-NPRRSCCM), the specular reflection point positioning accuracy is synthetically improved by 28.66 m.

Determining sea surface heights using small footprint airborne laser scanning

2013 ◽  
Author(s):  
A. Gruno ◽  
A. Liibusk ◽  
A. Ellmann ◽  
T. Oja ◽  
A. Vain ◽  
...  
Keyword(s):  
Laser Scanning ◽  
Airborne Laser Scanning ◽  
Sea Surface ◽  
Airborne Laser ◽  
Sea Surface Heights ◽  
Small Footprint

Comparison of Sea Surface Heights Derived from Satellite Altimetry and from Ocean Bottom Pressure Gauges: The SW Pacific MOTEVAS Project

2004 ◽  
Vol 27 (3-4) ◽  
pp. 597-613 ◽  
Author(s):  
S. CALMANT ◽  
K. CHENG ◽  
G. JAN ◽  
C. KUO ◽  
C. SHUM ◽  
...  
Keyword(s):  
Satellite Altimetry ◽  
Sea Surface ◽  
Ocean Bottom ◽  
Bottom Pressure ◽  
Ocean Bottom Pressure ◽  
Sw Pacific ◽  
Sea Surface Heights
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