Browsing by Author "Ghobadi-Far, Khosro"
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- Along-Orbit Analysis of GRACE Follow-On Inter-Satellite Laser Ranging Measurements for Sub-Monthly Surface Mass VariationsGhobadi-Far, Khosro; Han, Shin-Chan; McCullough, Christopher M.; Wiese, David N.; Ray, Richard D.; Sauber, Jeanne; Shihora, Linus; Dobslaw, Henryk (American Geophysical Union, 2022-02)We examined the sensitivity of GRACE Follow-On (GRACE-FO) laser ranging interferometer (LRI) measurements to sub-monthly time-variable gravity (TVG) signals caused by transient, high-frequency mass changes in the Earth system. GRACE-FO LRI provides complementary inter-satellite ranging measurements with higher precision over a wider range of frequencies than the baseline K-band microwave ranging system. The common approach for studying mass variation relies on the inverted TVG or mascon solutions over a period of, for example, one month or 10 days which are adversely affected by temporal aliasing and/or smoothing. In this article, we present the alternative along-orbit analysis methodology in terms of line-of-sight gravity difference (LGD) to fully exploit the higher precision LRI measurements for examination of sub-monthly mass changes. The discrepancy between "instantaneous" LGD LRI observations and monthly-mean LGD (from Level-2 data) at satellite altitude indicates the sub-monthly gravitational variability not captured by monthly-mean solutions. In conjunction with the satellite ocean altimetry observations, high-frequency non-tidal atmosphere and ocean models, and hydrology models, we show that the LGD LRI observations detect the high-frequency oceanic mass variability in the Argentine Basin and the Gulf of Carpentaria, and sub-monthly variations in surface (river) water in the Amazon Basin. We demonstrate the benefits gained from repeat ground track analysis of GRACE-FO LRI data in the case of the Amazon surface water flow. The along-orbit analysis methodology based on LGD LRI time series presented here is especially suitable for quantifying temporal and spatial evolution of extreme, rapidly changing mass variations.
- Barystatic and steric sea level variations in the Baltic Sea and implications of water exchange with the North Sea in the satellite eraKarimi, Armin Agha; Ghobadi-Far, Khosro; Passaro, Marcello (Frontiers, 2022-08)Satellite altimetry, satellite gravimetry, and in-situ subsurface salinity and temperature profiles are used to investigate the total, barystatic, and steric sea level variations in the Baltic Sea, respectively. To estimate the steric sea level, the density variations are weighted in deeper layers to prevent overestimation of their contribution. We show that the sum of barystatic and steric components exhibits excellent cross correlation (0.9) with satellite altimetry sea level variations and also explains up to 84% of total signal variability from 2002 to 2019. Considering the dominance of barystatic sea level variations in the basin and the limitation of satellite gravimetry in resolving the mass change in water-land transition zones (known as the leakage problem), the mismatch is likely attributed to the inadequate accuracy of the barystatic datasets. The total sea level and its contributors are further decomposed into seasonal, interannual, and decadal temporal components. It is shown that despite its insignificant contributions to seasonal and interannual changes, the steric sea level plays an important role in decadal variations. Additionally, we show that the interannual variations of the barystatic sea level are governed by the North Atlantic Oscillation in the basin. The sea level variation in the North Sea is also examined to deduce the water exchange patterns on different time scales. A drop in the North Sea level can be seen from 2005 to 2011 which is followed by the Baltic Sea level with a similar to 3-year lag, implying the outflow from the Baltic Sea to the North Sea.
- Groundwater Volume Loss in Mexico City Constrained by InSAR and GRACE Observations and Mechanical ModelsKhorrami, Mohammad; Shirzaei, Manoochehr; Ghobadi-Far, Khosro; Werth, Susanna; Carlson, Grace; Zhai, Guang (American Geophysical Union, 2023-03)Groundwater withdrawal can cause localized and rapid poroelastic subsidence, spatially broad elastic uplift of low amplitude, and changes in the gravity field. Constraining groundwater loss in Mexico City, we analyze data from the Gravity Recovery and Climate Experiment and its follow-on mission (GRACE/FO) and Synthetic Aperture Radar (SAR) Sentinel-1A/B images between 2014 and 2021. GRACE/FO observations yield a groundwater loss of 0.85-3.87 km(3)/yr for a region of similar to 300 x 600 km surrounding Mexico City. Using the high-resolution interferometric SAR data set, we measure >35 cm/yr subsidence within the city and up to 2 cm/yr of uplift in nearby areas. Attributing the long-term subsidence to poroelastic aquifer compaction and the long-term uplift to elastic unloading, we apply respective models informed by local geology, yielding groundwater loss of 0.86-12.57 km(3)/yr. Our results suggest Mexico City aquifers have been depleting at faster rates since 2015, exacerbating the socioeconomic and health impacts of long-term groundwater overdrafts.
- Spatiotemporal Groundwater Storage Dynamics and Aquifer Mechanical Properties in the Santa Clara Valley Inferred From InSAR Deformation Over 2017-2022Ghobadi-Far, Khosro; Werth, Susanna; Shirzaei, Manoochehr; Burgmann, Roland (American Geophysical Union, 2023-11-22)We used Interferometric Synthetic Aperture Radar (InSAR)-derived vertical land motion (VLM) timeseries during 2017–2022 to examine the compounding impacts of natural and anthropogenic processes on groundwater dynamics in the Santa Clara Valley (SCV). VLM strongly correlates (>0.75) with groundwater level in both unconfined and confined aquifers. We show that VLM in SCV is mainly driven by groundwater dynamics in deep aquifer layers below 120 m. Our results show that during the most recent drought from March 2019 to November 2021, Santa Clara County subsided up to 30 mm due to groundwater depletion, three times as large as average seasonal amplitude of VLM. Owing to the managed aquifer recharge, the region has been able to avoid unrecoverable land subsidence. We utilize InSAR data to calibrate storage coefficient and lag time related to delayed response of clay interbeds to groundwater level changes, which further serves to estimate groundwater volume loss in confined aquifer units during drought.