b'Education matters SMOS provides global high spatial andGeocenter motion is the motion of the temporal resolution (i.e. 40 km 2, 3-day)centre of mass of the Earth system with near-surface (05 cm) soil moisturerespect to the geometric centre of figure estimates from microwave brightnessof the solid Earth surface because of the temperature observations. In contrast,continual deformation of the Earth by the GRACE mission provides accurategeo-physical processes. This motion is measurements of the entire verticallyimportant both in theory and in practice integrated terrestrial water storageto understand and interpret various column, but it is characterised by lowmass transport phenomena and their spatial and temporal resolutions (i.e.consequences, such as sea-level rise, 300km 2, monthly). An ensemble Kalmanpost-seismic relaxation, polar ice melting, smoother based global data assimilationand glacial isostatic adjustment. The system was developed to resolveInternational Terrestrial Reference Frame the discrepancy between model and(ITRF) is realised using measurements of observations in space and time. the relative motion between satellites orbiting around the centre of mass on The use of data assimilation integratesone hand and stations placed on the these two measurements to effectivelyEarth surface on the other. Therefore, Drought poses the greatest threat toconstrain model simulations and toreliable modelling of the geocenter freshwater availability and food security,accurately characterise the verticalmotion is vital for the stability and affecting larger areas for longer periodsdistribution of water storage. Comparedthe accuracy of the ITRF. In turn, the than any other natural hazards. In manywith model estimates without theinterpretation of many geo-dynamic regions, droughts increase in frequencyassimilation or single-variant assimilation,quantities of current interest, such as and severity due to climate change.joint assimilation typically led to morethe mean sea-level, depends heavily As a slow developing natural disaster,accurate soil moisture profile andon the quality of the adopted reference better estimates of water availability cangroundwater estimates with improvedframe. Space geodetic measurement of be valuable for forecasting droughtsconsistency with in situ measurements.the true geocenter motion, however, is and their impacts on ecosystem,The improved water storage estimatesdifficult due to the discrete and therefore agriculture and food security. Withintegrated at different depths were usedincomplete sampling of the Earth surface accurate knowledge of root-zone soilto determine the vegetation accessibleby geodetic stations. In other words, water and groundwater dynamics,storage in association with vegetationthere is a discrepancy between the effective planning of water resourcesgrowth and surface greenness. Accessiblecentre of figure of the Earth surface and and agriculture can be made months instorage reflects a combination of verticalthe centre of network of the stations, advance. However, the simulated root- root distribution and soil properties,called the network effect, arising from zone soil moisture and groundwaterand its spatial distribution correlatesthe sampling bias of the geodetic are often highly uncertain due to thewith aridity and vegetation type. Skilfulnetwork.unpredictable nature of soil water andforecasts of vegetation conditions are groundwater dynamics caused by humanachievable several months in advanceIn this work, we develop a method to activities such as water extraction andfor most of the worlds drylands, whichestimate the magnitude of the network irrigation. Ground-based and remotelyoffers exciting new prospects for theeffect for a network of a given size N. sensed measurements of water contentimprovement of drought early warningFor a given crustal deformation model, are often limited in both spatial coveragesystems to help reduce human sufferingwe consider the Helmert parameters and temporal resolution. Therefore,and economical and environmentalof transformation between the centre quantifying the change of waterdamage. of figure frames before and after the availability and its impacts on vegetationdeformation event. Our proposed conditions at large scales remains largelyUmma Jamilla Zannat, Australianestimate for the network effect, which we unexplored. National University: Network effect incall the expected bias, is the standard geocenter motion. deviations of the changes in these For the first time, contrasting satelliteparameters by the event as measured observations of water presence overby a random network of the size N. We different vertical domains have beenshow that, in accordance with probability assimilated into a global water balancetheory, the expected bias scales as 1/ p model, provided unprecedentedN, and we provide an explicit formula accuracy of soil moisture pro le andfor this estimate in terms of the vector groundwater storage estimates. Thespherical harmonics expansion of water availability at different depthsthe displacement field. We assess the observed from soil moisture (SMOS)effectiveness of the expected bias as and space gravity (GRACE) missionsan estimate of the network effect by provides an opportunity to separatesimulating the displacement fields for total water storage vertically intotwo illustrative geo-dynamical processes: different layers through data assimilation.(instantaneous) co-seismic deformation However, combining these two datadue to great earthquakes, and (time-sets is challenging due to the disparitydependent) elastic deformation in temporal and spatial resolution atdue to surface water movements. both vertical and horizontal scales.We accordingly concentrate on the 37 PREVIEW DECEMBER 2019'