The movement of mass on the Earth’s surface, including the atmosphere and oceans as well as hydrology and glacier melting, causes redistribution of loads on the Earth’s surface, changes in the solid Earth, and changes in the gravity field.
A research team led by Prof. Jin Shuanggen from the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences used space geodetic observations to reveal seasonal and intra-seasonal signal changes in Earth’s surface loads.
They analyzed displacements from the Global Navigation Satellite System (GNSS) and time-variable gravity from the Gravity Recovery and Climate Experiment (GRACE) to obtain surface loading signals and explore their geophysical applications. The results show that space geodesy offers an effective method for studying surface loads and the resulting crustal movements. The study was published in Satellite Navigation on July 24.
In the early days, the displacements generated by the loads on the Earth’s surface were not large enough to be detected by conventional methods of nonglobal measurement and thus were considered noise that disturbed the signals of tectonic movement. In the 1990s, however, geodesists began to observe crustal movements precisely, at high spatial and temporal resolution, using dense networks of continuous GNSS observation stations.
They found significant seasonal signals superimposed on secular tectonic movements, and such seasonal signals gradually gained their attention. The launch of the GRACE satellites in 2002 enabled scientists to directly observe Earth mass anomalies from space, and the combination of GRACE and GNSS observations contributed to making surface loading studies more convincing.
Previously, the research team studied seasonal (periodic) and intra-seasonal surface loads using surface displacements from GNSS and mass anomalies from GRACE. They obtained many important results, for example, changes in the Earth’s dynamic oblateness, high-resolution global time-variable gravity fields, extreme drought in the southwestern United States, and water loads from heavy rains in Japan.
In this study, researchers present long-term and seasonal changes in the displacements of GNSS stations and mass anomalies from GRACE in northern South America. They found subsidence and increase in regions of positive and negative mass anomalies, respectively. On the other hand, the GNSS stations moved in the direction from negative to positive mass anomalies. Geodetic observations in space reasonably monitor seasonal changes in hydrological loads on the earth characterized by the alternation of monsoons and monsoons near the equator.
As for the map showing mass anomalies and displacements over Hokkaido Island in northern Japan, the interannual changes in mass anomalies and amplitudes of seasonal crustal movements show well the interannual differences in the amount of snow.
Displacements and mass anomalies from GNSS and GRACE provide complementary information on seasonal changes in surface loads, such as terrestrial hydrological loads. “Due to the different spatial resolutions of the two techniques, the displacements and mass anomalies often do not agree with each other when the surface loads are composed of complex small anomalies. This will be a key direction in future geodetic investigations of surface loads,” said Prof. Kosuke Heki, visiting professor at SHAO.
In addition, continuous GNSS observations can be used to reverse the time-varying gravity field and monitor changing water loads together with GRACE measurements. “We have obtained tools to study monthly global gravity fields and high temporal-spatial resolution geophysical loads signals and such geodetic techniques in space will be important for monitoring destructive floods and droughts,” said Prof. Jin.
More information:
Kosuke Heki et al, Geodetic survey of land surface loading GNSS and GRACE, Satellite Navigation (2023). DOI: 10.1186/s43020-023-00113-6
Awarded by the Chinese Academy of Sciences
Citation: Space geodetic observations help reveal variations in Earth’s surface loads (2023, July 24) retrieved on July 24, 2023 from https://phys.org/news/2023-07-space-geodetic-reveal-variations-earth.html
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