Future Gravity Missions Research Articles

Laboratory demonstration of an off-axis optical bench design for future gravity missions.

The inter-satellite laser ranging interferometer is one of the core components of future gravity missions to achieve high ranging precision. This work builds a preliminary breadboard of the off-axis optical bench design, which integrates the merits of the off-axis optical bench design of GRACE Follow-On mission and other on-axis designs. The study finds that the displacement noise between two optical benches has been reduced to 20nm/Hz at a frequency of 10 mHz, and the differential wavefront sensing noise has been suppressed to 10-5rad/Hz at 1kHz as well. In addition, the tilt-to-length coupling noise related to the piston effect is restricted within 30μm/rad, and the relative parallelism error of the transmitting beam and receiving beam is less than 4.5%. The results show that this off-axis optical bench design is an important candidate for China's future gravity missions.

Research on Inter-Satellite Laser Ranging Scale Factor Estimation Methods for Next-Generation Gravity Satellites

The scale factor serves as a ruler for converting raw phase measurements into physical displacements and significantly impacts the preprocessing of data from the Laser Ranging Interferometer (LRI) in laser ranging systems. In the current GRACE Follow-On (GRACE-FO) mission for low–low tracking gravity satellites, most of the existing LRI scale factor estimation algorithms heavily rely on cross-calibration between instantaneous/biased ranges from the Ka-Band Ranging Interferometer (KBR) and the LRI. However, due to the nonlinearity of the objective function (which includes terms involving the product of scale and time shifts), the scale factor estimation may absorb errors from timing noise. Moreover, future gravity missions or gravity detection tasks may no longer incorporate KBR ranging instruments. To address these challenges, this paper proposes an energy-based method for scale factor estimation using inter-satellite baseline solutions. Comparative analysis indicates that the proposed method effectively disentangles two parameters in the objective function and can be applied in scenarios where KBR data are unavailable, demonstrating promising prospects for practical application. The experimental results show that when the KBR validation residuals are lower than 0.8 mm, the SYSU LRI1B V01 products exhibit residuals below the payload design accuracy thresholds in the frequency band of 2 mHz to 0.1 Hz. Additionally, the stability of the scale factors obtained from the baseline can reach 10−7. Although this is still below the required precision of better than 10−8 for the laser frequency stability in next-generation gravity satellites, advancements in orbit determination technology and the enhanced stability of GPS receivers offer potential for future precision improvements. Currently, this method appears suitable for roughly extracting the scale factor as a stochastic mean over several months or serving as a backup validation strategy for future missions, but it is not well suited to measure day-to-day variations.

A Regionally Refined and Mass‐Consistent Atmospheric and Hydrological De‐Aliasing Product for GRACE, GRACE‐FO and Future Gravity Missions

AbstractDe‐aliasing products are used in the estimation process of satellite‐based gravity field computation to reduce errors from high‐frequency mass variations that alias into monthly gravity fields. The latest official product is AOD1B RL07 and describes non‐tidal atmosphere and oceanic mass variations at 3‐hourly resolution. However, the model‐based de‐aliasing products are inevitably incomplete and prone to temporally and spatially correlated errors that substantially contribute to errors in the estimated gravity fields. Here, we investigate possible enhancement of current de‐aliasing products by nesting a regional high‐resolution atmospheric reanalysis over Europe into a global reanalysis. As further novelty we include almost mass consistent terrestrial water storage variability from a regional hydrological model nested into a global model as additional component of the de‐aliasing product. While we find in agreement with earlier studies only minor contributions from increasing the temporal resolution beyond 3‐hourly data, our investigations suggest that contributions from continental hydrology and from regional non‐hydrostatic atmospheric modeling to sub‐monthly mass variations could be relevant already for gravity fields estimated from current gravity missions. Moreover, in the context of extreme events, we find regionally contributions from additional moisture fields, such as cloud liquid water, in the order of a few mm over Europe. We suggest this needs to be taken into account when preparing data analysis schemes for future space gravimetric missions.

Alternative Approach to Tilt-to-Length Coupling Estimation for Laser Ranging Interferometers in Future Gravity Missions

Tilt-to-length coupling, a non-constant systematic error source caused by satellite attitude variations, has been observed in the laser ranging signals of the GRACE Follow-On mission. This error can be corrected by certain calibration maneuvers performed regularly in orbit. In this paper, we introduce an alternative approach to tilt-to-length coupling estimation for a laser ranging interferometer in future gravity missions, using the ranging signals without any specific calibration maneuvers, which allows daily estimation. An analytical model of laser ranging signals is derived. The tilt-to-length estimation is performed under different conditions using the least squares method as well as the simulated data. The pointing angle noise is found to be the most significant limiting factor. When the pointing angle noise is below 0.3μrad/Hz1/2, the RMS of the estimation error is below 4 nm, much better than the tilt-to-length error of GRACE Follow-On. In the case of low pointing angle noise, the estimation error of an under 1.5 m offset between the center of mass and the interferometer reference point is not obviously different from the case with only a 0.5 mm offset, which provides installation flexibility for the laser ranging interferometer.

Studying an off-axis optical bench for future gravity missions from the perspective of carrier-to-noise ratio.

The inter-satellite laser ranging heterodyne interferometer is vital for future gravity missions to achieve high ranging accuracy. This paper proposes a novel off-axis optical bench design which integrates merits of the off-axis optical bench design of GRACE Follow-On mission and other on-axis designs. This design makes use of lens systems subtly to restrict the tilt-to-length coupling noise and takes advantage of the DWS feedback loop to maintain the transmitting beam and receiving beam anti-parallel. The critical parameters of the optical components are determined and the carrier-to-noise ratio for a single channel of the photoreceiver is calculated to be more than 100 dB-Hz for the high case. The off-axis optical bench design is a potential candidate for China's future gravity missions.

Assessment of changing satellite gravity mission architectures using terrestrial gravity and GNSS-leveling data in the Kingdom of Saudi Arabia

This research investigates the effect of the ‘future’ gravity mission (FGM) architectures i.e. Bender, Helix, Pendulum, and Cartwheel up to spherical harmonics (SH) degree/order (d/o) 120/120 to improve the estimation of the gravitational field in the Saudi Arabia. For this purpose, we evaluate ground-truth gravity anomalies and GNSS/Leveling data with the satellite-based gravity models of each aforementioned FGMs. The comparison with gravity anomalies given by the FGM provides refinements of about 57 – 61 μGal with respect to (w.r.t.) those of GRACE- and GOCE-based GGMs. The comparison with GNSS/Leveling indicates that the least differences in terms of standard deviations (STD) of geoid heights are provided by the Bender-type FGM that provides the overall least STD differences of about 62.58 cm w.r.t. the GRACE- and GOCE-based GGMs, that provide STD differences of about 62.88 cm and 62.62 cm, respectively. The outcome of this study shows that implementing additional gravity information in different flight directions of the proposed FGMs (i.e along-track, cross-track, and radial) showed slight improvement (sub of a millimeter).

Sensitivity to Mass Changes of Lakes, Subsurface Hydrology and Glaciers of the Quantum Technology Gravity Gradients and Time Observations of Satellite MOCAST+

The quantum technology absolute gravimeters, gradiometers, and clocks are at the forefront of the instrumentation to be exploited in a future gravity mission (the QSG mission concept). Apart from the quantum payload, the mission design defines the choice of the number of satellites and the satellite orbit constellation, with the goal of optimizing the observation of the earth’s gravity field and reducing aliasing phenomena. Our goal is to define the realistic gravity field changes generated by glaciers and lakes and define the sensitivity of the quantum gravity mission for the detection of hydrologic and cryospheric mass changes. The analysis focuses on mass changes in the high mountains of Asia and the South American continent. The mass changes are based on terrestrial and satellite observations and are of a climatic origin. We show that compared to the existing GRACE-FO mission, a quantum gravity mission significantly improves the detection of the climatic mass gain of lakes and mass loss of glaciers, allowing for smaller mass features to be distinguished, and smaller mass losses to be detected. The greater signal is the seasonal signal with a yearly period, which would be detected at the 10 Gt level for areas > 8000 km2. The yearly mass loss of the Patagonian glaciers can be detected at the 5 Gt/yr level, an improvement from the 10 Gt/yr detectable by GRACE-FO. Spatial resolution would also be improved, with an increase of about 50% in spatial frequency for the detection of the mass change rate of lakes and glaciers in Tibet. The improved spatial resolution enables an improved localization of the lakes and glaciers affected by climatic mass change. The results will contribute to defining the user requirements of the future QSG missions.

On-Axis Optical Bench for Laser Ranging Instruments in Future Gravity Missions.

The laser ranging interferometer onboard the Gravity Recovery and Climate Experiment Follow-On mission proved the feasibility of an interferometric sensor for inter-satellite length tracking with sub-nanometer precision, establishing an important milestone for space laser interferometry and the general expectation that future gravity missions will employ heterodyne laser interferometry for satellite-to-satellite ranging. In this paper, we present the design of an on-axis optical bench for next-generation laser ranging which enhances the received optical power and the transmit beam divergence, enabling longer interferometer arms and relaxing the optical power requirement of the laser assembly. All design functionalities and requirements are verified by means of computer simulations. A thermal analysis is carried out to investigate the robustness of the proposed optical bench to the temperature fluctuations found in orbit.

A New 1‐Hourly ERA5‐Based Atmosphere De‐Aliasing Product for GRACE, GRACE‐FO, and Future Gravity Missions

AbstractThe current state‐of‐the‐art of satellite gravity data processing makes use of de‐aliasing products to reduce high‐frequency mass anomalies. For example, the most recent official Atmosphere and Ocean De‐aliasing products (AOD1B‐RL06) are applied for the Gravity Recovery and Climate Experiment (GRACE) and GRACE‐Follow On (GRACE‐FO) missions. The temporal resolution of AOD1B‐RL06 is 3 h, and spectrally, they are computed up to degree and order 180. In this study, we explore a refined, e.g., geometrically, physically, and numerically improved, mass integration approach that is important for computing the atmosphere part of these products. Besides, the newly available ERA5 climate data are used to produce a new set of non‐tidal atmosphere de‐aliasing product (HUST‐ERA5) that is computed hourly up to degree and order 100, covering 2002 onwards. Despite an overall agreement with AOD1B‐RL06 (correlation0.99), considerable discrepancies still exist between HUST‐ERA5 and AOD1B‐RL06. The possible reasons are therefore analyzed, and we find the input climate data, sampling rate and integration method may result in a product difference of ∼0.3, ∼0.15 and ∼0.05 millimeter geoid height, respectively. The total differences between HUST‐ERA5 and AOD1B‐RL06 can lead to a mean variation of ∼7.34 on the laser ranging interferometry (LRI) range‐rate residuals, for example, during January 2019, which is already close to the LRI precision. This impact is invisible for the GRACE (‐FO) gravity inversion because of the less accurate on‐board KBR (K‐band ranging) instrument, however, it will be non‐negligible and should be considered when the LRI completely replaces the KBR in the future gravity missions.

Combined observables in different inter-satellite line-of-sight directions from simulated satellite gravity mission architectures for retrieving total water storage – regional case study: the Nile River Basin

Numerous studies for improving gravity field determination from future gravity missions beyond the GRACE/GRACE-FO missions have been proposed during the last decade. In this contribution, full-scale simulated observations of four satellite missions, namely Bender-, Cartwheel-, Helix- and Pendulum-type, in addition to GRACE-FO as a reference mission will be used to retrieve the total water storage over the Nile River Basin (NRB). The findings show a superiority of investigated configurations in retrieving the total water storage (TWS) w.r.t. the GRACE-FO mission. Moreover, the Bender-type provides improved global TWS recovery showing the least standard deviations (STD) of about 3.43cm in terms of equivalent water heights (EWH) (up to d/o 80). The Pendulum, Cartwheel and Helix missions provide STD of about 6.34cm, 8.35cm and 5.78cm in terms of EWH, respectively. In addition, the Bender-type provides improved local TWS recovery over the NRB without any distortion w.r.t. both the “simulated” and “real” GRACE-FO solutions.

Potential and scientific requirements of optical clock networks for validating satellite-derived time-variable gravity data

SUMMARY The Gravity Recovery and Climate Experiment (GRACE) and GRACE-FO missions have provided an unprecedented quantification of large-scale changes in the water cycle. However, it is still an open problem of how these missions’ data can be referenced to a ground truth. Meanwhile, stationary optical clocks show fractional instabilities below 10−18 when averaged over an hour, and continue to be improved in terms of stability and accuracy, uptime and transportability. The frequency of a clock is affected by the gravitational redshift, and thus depends on the local geopotential; a relative frequency change of 10−18 corresponds to a geoid height change of about 1 cm. Here we suggest that this effect could be exploited for sensing large-scale temporal geopotential changes via a network of clocks distributed at the Earth’s surface. In fact, several projects have already proposed to create an ensemble of optical clocks connected across Europe via optical fibre links. Our hypothesis is that a clock network with collocated GNSS receivers spread over Europe—for which the physical infrastructure is already partly in place—would enable us to determine temporal variations of the Earth’s gravity field at timescales of days and beyond, and thus provide a new means for validating satellite missions such as GRACE-FO or a future gravity mission. Here, we show through simulations how glacial, hydrological and atmospheric variations over Europe could be observed with clock comparisons in a future network that follows current design concepts in the metrology community. We assume different scenarios for clock and GNSS uncertainties and find that even under conservative assumptions—a clock error of 10−18 and vertical height control error of 1.4 mm for daily measurements—hydrological signals at the annual timescale and atmospheric signals down to the weekly timescale could be observed.

Combination Analysis of Future Polar-Type Gravity Mission and GRACE Follow-On

Thanks to the unprecedented success of Gravity Recovery and Climate Experiment (GRACE), its successive mission GRACE Follow-On (GFO) has been in orbit since May 2018 to continue measuring the Earth’s mass transport. In order to possibly enhance GFO in terms of mass transport estimates, four orbit configurations of future polar-type gravity mission (FPG) (with the same payload accuracy and orbit parameters as GRACE, but differing in orbit inclination) are investigated by full-scale simulations in both standalone and jointly with GFO. The results demonstrate that the retrograde orbit modes used in FPG are generally superior to prograde in terms of gravity field estimation in the case of a joint GFO configuration. Considering the FPG’s independent capability, the orbit configurations with 89- and 91-degree inclinations (namely FPG-89 and FPG-91) are further analyzed by joint GFO monthly gravity field models over the period of one-year. Our analyses show that the FPG-91 basically outperforms the FPG-89 in mass change estimates, especially at the medium- and low-latitude regions. Compared to GFO & FPG-89, about 22% noise reduction over the ocean area and 17% over land areas are achieved by the GFO & FPG-91 combined model. Therefore, the FPG-91 is worthy to be recommended for the further orbit design of FPGs.

Spatio-Temporal Polar-Inclined Space Mission Architecture for a Refined Retrieve of the Earth’s Gravity Field

Future satellite gravity missions (FGMs) have been intensively studied during the last recent years for the era beyond the successful previous GRACE and current GRACE Follow-on satellite missions. Previous studies have investigated the gravity field recovery derived from combined two satellite-pairs (referred here as PI-FGM, a single polar satellite-pair like the GRACE mission combined with another inclined satellite-pair) with different orbital heights of few kilometers and different repeat orbital periods. In this contribution, new innovative idea is introduced by designing the inclined satellite-pair of the FGM at the same orbital height of the polar-type with shifted spatio-temporal (ST-FGM) orbital parameters to avoid any possible collision risk between the two satellite-pairs, polar and inclined, of the FGM architecture. The repeat orbits issue will be taken into consideration through the manuscript and will be set as identical as possible for a fair comparison. The findings through a full-scale simulation analysis show that the new design of shifted spatio-temporal polar-inclined (ST-FGM) mission architecture basically outperforms the two satellite-pairs having different orbital heights (i.e. the PI-FGM mission configuration). Regarding the gravity field recovery, the ST-FGM architecture retrieves the geoid heights with standard deviations of about 17.0 mm providing more isotropic error distribution. An overall improvement by a factor of about 80 and 60 is provided by the ST-FGM and PI-FGM mission architectures, respectively, with respect to the GRACE-like formation and a factor of about 2.4 and 1.8, respectively, with respect to the smoothed gravity solution using the Gaussian filter at radius 400 km. Therefore, the shifted spatio-temporal polar-inclined (ST-FGM) is worthy recommended as stable mission architecture and would be considered as one of the future gravity missions.

Applicability of NGGM near-real time simulations in flood detection

Abstract The GRACE mission has demonstrated a tremendous potential for observing mass changes in the Earth system from space for climate research and the observation of climate change. Future mission should on the one hand extend the already existing time series and also provide higher spatial and temporal resolution that is required to fulfil all needs placed on a future mission. To analyse the applicability of such a Next Generation Gravity Mission (NGGM) concept regarding hydrological applications, two GRACE-FO-type pairs in Bender formation are analysed. The numerical closed loop simulations with a realistic noise assumption are based on the short arc approach and make use of the Wiese approach, enabling a self-de-aliasing of high-frequency atmospheric and oceanic signals, and a NRT approach for a short latency. Numerical simulations for future gravity mission concepts are based on geophysical models, representing the time-variable gravity field. First tests regarding the usability of the hydrology component contained in the Earth System Model (ESM) by the European Space Agency (ESA) for the analysis regarding a possible flood monitoring and detection showed a clear signal in a third of the analysed flood cases. Our analysis of selected cases found that detection of floods was clearly possible with the reconstructed AOHIS/HIS signal in 20% of the tested examples, while in 40% of the cases a peak was visible but not clearly recognisable.

Earth's surface mass transport derived from GRACE, evaluated by GPS, ICESat, hydrological modeling and altimetry satellite orbits

Abstract. The Gravity Recovery and Climate Experiment (GRACE) delivered the most accurate quantification of global mass variations with monthly temporal resolution on large spatial scales. Future gravity missions will take advantage of improved measurement technologies, such as enhanced orbit configurations and tracking systems, as well as reduced temporal aliasing errors. In order to achieve the latter, sub-monthly to daily innovative models are computed. In addition, non-conventional methods based on radial basis functions (RBFs) and mascons will give the ability to compute models in regional and global representations as well. We show that the RBF modeling technique can be used for processing GRACE data yielding global gravity field models which fit independent reference values at the same level as commonly accepted global geopotential models based on spherical harmonics. The present study compares for the first time a complete global series of solutions in order to quantify recent ice mass changes. We further compare the ice-induced crustal deformations due to the dynamic loading of the crustal layer with the Global Positioning System (GPS) uplift measurements along Greenland's coastline. Available mass change estimates based on Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry measurements both in Greenland and Antarctica are used to assess the GRACE results. A comparison of GRACE time series with hydrological modeling for various basin extensions reveals overall high correlation to surface and groundwater storage compartments. The forward computation of satellite orbits for altimetry satellites such as Envisat, Jason-1 and Jason-2 compares the performance of GRACE time-variable gravity fields with models including time variability, such as EIGEN-6S4.

Treatment of ocean tide aliasing in the context of a next generation gravity field mission

Current temporal gravity field solutions from Gravity Recovery and Climate Experiment (GRACE) suffer from temporal aliasing errors due to undersampling of signal to be recovered (e.g. hydrology), uncertainties in the de-aliasing models (usually atmosphere and ocean) and imperfect ocean tide models. Especially the latter will be one of the most limiting factors in determining high-resolution temporal gravity fields from future gravity missions such as GRACE Follow-On and Next-Generation Gravity Missions (NGGM). In this paper a method to co-parametrize ocean tide parameters of the eight main tidal constituents over time spans of several years is analysed and assessed. Numerical closed-loop simulations of low-low satellite-to-satellite-tracking missions for a single polar pair and a double pair Bender-type formation are performed, using time variable geophysical background models and noise assumptions for new generation instrument technology. Compared to the single pair mission, results show a reduction of tide model errors up to 70 per cent for dedicated tidal constituents due to an enhanced spatial and temporal sampling and error isotropy for the double pair constellation. Extending the observation period from 1 to 3 yr leads to a further reduction of tidal errors up to 60 per cent for certain constituents, and considering non-tidal mass changes during the estimation process leads to reductions of tidal errors between 20 and 80 per cent. As part of a two-step approach, the estimated tide model is used for de-aliasing during gravity field retrieval in a second iteration, resulting in more than 50 per cent reduction of ocean tide aliasing errors for a NGGM Bender-type formation.

From GOCE to NGGM: Automatic Control Breakthroughs for European future Gravity Missions

After the successful European gravity mission GOCE (Gravity field and steady-state Ocean Circulation Explorer), which provided an unprecedented high resolution static global map of the Earth’s gravity field, the European Space Agency has proposed several preparatory studies for a Next Generation Gravity Mission (NGGM). The NGGM mission objective aims at measuring the temporal variations of the Earth gravity field over a long time span with an unprecedented level of accuracy, both in spatial and temporal resolution. The GOCE technological heritage is leveraged as starting point while defining the NGGM future mission concept. Nonetheless, to accomplish its challenging scientific objective, the NGGM mission concept envisages a wide range of innovations, with respect to the past or flying missions, both on technological and automatic control side. Thus, this paper focuses on the guidance, navigation and control design evolution for the European gravity missions, from GOCE to NGGM. After recalling the GOCE GNC main design concepts, the paper will describe the most important innovation required by NGGM. Indeed, such a future concept will consist of a two-satellite long-distance loose formation, where each satellite is controlled independently to be drag-free, GOCE-like. The satellite-to-satellite distance variations, encoding gravity anomalies, will be then measured by laser heterodyne interferometry for inter-satellite ranging at 20 nm resolution, or better. Hence, an orbit and formation control is now required to counteract bias and drift of the residual drag-free accelerations, in order to reach a bounded orbit/formation long-term stability. Finally, GOCE control flight results as well as NGGM simulated results, via a high-fidelity simulator, will be provided. These results highlight the GOCE GNC in-flight achievements as well as the NGGM concept validity, showing that the expected control performances are in agreement with the consolidated mission requirements, all over the 10-year mission.

High precision dynamic orbit integration for spaceborne gravimetry in view of GRACE Follow-on

Future gravity missions like GRACE Follow-on and beyond will deliver low-low satellite-to-satellite ranging measurements of a much increased precision on the order of nanometers. This necessitates a re-evaluation of the processes used in gravity field determination with an eye to numerical stability and computational precision. This study investigates the computation of dynamic orbits, which are used for multiple purposes in gravity recovery. They are, for example, used in computing linearized observations for the low-low satellite-to-satellite tracking instruments. The precision at which the dynamic orbits are determined thus must surpass the precision of the ranging observations.Dynamic orbits for GRACE were computed both in a simple simulation, where the force model was reduced to a static potential of degree and order 60, and for real observational data. Encke’s method was employed while using a novel reference trajectory determined through rigorous optimization. This reference trajectory was parametrized with equinoctial elements to minimize errors resulting from imprecision in the reference motion.The differences in coordinates between successive iterations of orbit determination were used as a benchmark for the quality of the orbit solution. Using Encke’s method with equinoctial elements, the coordinate difference between iterations was reduced from on the order of tens of micrometers to some nanometers in the spectral range relevant to GRACE satellite-to-satellite tracking observations. The resulting dynamic orbits are self-consistent to below the expected precision of the GRACE Follow-on ranging instruments.

On the observability of epeirogenic movement in current and future gravity missions

Next generation gravity missions are expected to improve the accuracy of temporal gravity models significantly. The periodic signals and trends retrieved by these missions are induced by mass redistribution in the Earth system, carrying essential information on dynamic processes in the atmosphere, cryosphere, continental hydrosphere, the oceans and the solid Earth. While temporal gravity signals induced by deep Earth's processes are commonly thought to lie below the observational threshold of satellite gravity missions, as one assumes them to be small in amplitude and restricted to the longest spatial and temporal scales, there exists evidence from the geologic record for rapid uplift and subsidence events at regional scales, especially along passive continental margins, related to flow in the underlying mantle. Here we explore novel mantle flow retrodictions for geodynamically plausible, compressible, high resolution Earth models with ≈670 million finite elements. These time-dependent Earth models link to geologic observables in the late Paleogene that can be tested independently, while at the same time indicating mantle flow induced geoid rates on the order of 5μm/year, at spatial scales of 1000km. We assess the signal retrievability of the modeled rates in closed-loop numerical simulations, with different satellite gravity retrieval mission assumptions, including GRACE, GRACE-FO and a next generation gravity mission. We find the modeled deep Earth signal to be on the edge of detectability, but coming into the range of detectability in future temporal gravity field solutions, suggesting the use of satellite gravity data to validate geodynamic Earth models. Importantly, the application of forward modeled dynamic mantle signals seems to be essential for improved de-aliasing and signal separation in future gravity missions.

Metamorphic CO2 production in calc-silicate rocks from the eastern Himalaya

The Tibetan Plateau is one of the most geologically dynamic systems and the highest plateau in the world with ongoing three-dimensional crustal deformation. The Plateau is uplifting and deforming horizontally as observed by present-day global navigation satellite system (GNSS) and repeated leveling measurements. Crustal mass is conservative and less dense than the mantle, thus the horizontal shortening must be accompanied by crustal thickening and horizontal extrusion. According to the level of isostatic compensation, the thickening is partitioned into topographic uplift and Moho deepening. Here, we investigate the mass change induced gravity signal observed at or near the crust, and discuss whether this signal could be detected using terrestrial or satellite gravity observations. We set up a model for the Tibetan Plateau crustal thickening and calculate the expected gravity signal. The predictions are then compared with the present-day gravity changes observed by GRACE and with published in situ absolute gravity rates. We conclude that the crustal thickening signal cannot be neglected and that it contributes significantly to the observed signal. Those studies with focus on the mountain glacier and hydrologic mass fluxes should be aware that, if neglected, the crustal signal could introduce a significant bias. The observations give a positive gravity rate over central Tibetan Plateau, unexplained by the hydrologic or cryospheric signals, and a negative rate over the Himalayas and at its foothill, which is attributable to terrestrial hydrologic signals including human depletion of groundwater. Our model shows that the positive gravity rate could be explained by elevation uplift, and a stable or upwelling Moho. The negative gravity change signal is due primarily to the strong elevation-gradient at the foothill of the Himalayas, and to an uplift accompanied by crustal thickening and Moho lowering. The estimated gravity rates can be used when defining the requirements on future gravity missions, as the tectonic signal should be resolved in order to improve its separation from hydrologic and/or cryospheric processes generating a gravity change.