Browsing by Author "Tangdamrongsub, Natthachet"

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Along-Track Geopotential Difference and Deflection of the Vertical from GRACE Range Rate: Use of GEOGRACE
(2016-02)
Tangdamrongsub, Natthachet
;
Hwang, Cheinway
;
土木工程學系
;
Department of Civil Engineering
We present a theory and numerical algorithm to directly determine the time-varying along-track geopotential difference and deflection of the vertical at the Gravity Recovery and Climate Experiment (GRACE) satellite altitude. The determination was implemented using the GEOGRACE computer program using the K-band range rate (KBRR) of GRACE from the Level-1B (L1B) product. The method treated KBRR, GPS-derived orbit of GRACE and an initial geopotential difference as measurements used in the least-squares estimation of the geopotential difference and its formal error constrained by the energy conservation principle. The computational procedure consisted of three steps: data reading and interpolation, data calibration and estimations of the geopotential difference and its error. The formal error allowed removal of KBRR outliers that contaminated the gravity solutions. We used the most recent models to account for the gravity changes from multiple sources. A case study was carried out over India to estimate surface mass anomalies from GEOGRACE-derived geopotential differences. The 10-day mass changes were consistent with those from the MASCON solutions of NASA (correlation coefficient up to 0.88). Using the geopotential difference at satellite altitude avoids the errors caused by downward continuation, enabling the detection of small-scale mass changes.
Intensified water storage loss by biomass burning in Kalimantan: Detection by GRACE
(2017-03-01)
Han, Jiancheng
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Tangdamrongsub, Natthachet
;
Hwang, Cheinway
;
Abidin, Hasanuddin Z.
;
土木工程學系
Biomass burning is the principal tool for land clearing and a primary driver of land use change in Kalimantan (the Indonesian part of Borneo island). Biomass burning here has consumed millions of hectares of peatland and swamp forests. It also degrades air quality in Southeast Asia, perturbs the global carbon cycle, threatens ecosystem health and biodiversity, and potentially affects the global water cycle. Here we present the optimal estimate of water storage changes over Kalimantan from NASA's Gravity Recovery and Climate Experiment (GRACE). Over August 2002 to December 2014, our result shows a north-south dipole pattern in the long-term changes in terrestrial water storage (TWS) and groundwater storage (GWS). Both TWS and GWS increase in the northern part of Kalimantan, while they decrease in the southern part where fire events are the most severe. The loss rates in TWS and GWS in the southern part are 0.560.11cmyr(-1) and 0.550.10cm yr(-1), respectively. We use GRACE estimates, burned area, carbon emissions, and hydroclimatic data to study the relationship between biomass burning and water storage losses. The analysis shows that extensive biomass burning results in excessive evapotranspiration, which then increases long-term water storage losses in the fire-prone region of Kalimantan. Our results show the potentials of GRACE and its follow-on missions in assisting water storage and fire managements in a region with extensive biomass burning such as Kalimantan.
Preliminary Analysis of Lake Level and Water Storage Changes over Lakes Baikal and Balkhash from Satellite Altimetry and Gravimetry
(2011-04-01)
Hwang, Cheinway
;
Kao, Yu-Chi
;
Tangdamrongsub, Natthachet
;
土木工程學系
;
Department of Civil Engineering
Lakes Baikal and Balkhash are two of the world's major lakes affecting fresh water supplies in their catchments. Measurements from satellite altimetry (TOPEX/Poseidon, Jason-1 and -2), satellite gravimetry (GRACE) and a hydrological model (LDAS) are used to see the relationship between lake level change (LLC) and water storage change in these two lakes. At Lake Baikal, the average rate of LLC is negative for 1992 - 1998 and positive for 1998 - 2007, and the reversal of the LLC trend concurs with that of the temperature trend during the 1997 - 1998 El Nino. The rate of gravity change ranges from -0.5 to 0.5 mu gal yr(-1) with a low over the Tian Shan and a high over western Lake Baikal. Due to the climates over the two lakes, the phases of the annual gravity changes differ by up to 100 days. Using the rates of LLC and gravity changes, the ratios between the mass changes of the lake and its catchment over Lakes Baikal and Balkhash are estimated to 0.6 and 0.3, respectively. The result may help to establish water balance models over these two lakes.
Regional surface mass anomalies from GRACE KBR measurements: Application of L-curve regularization and a priori hydrological knowledge
(2012-11-08)
Tangdamrongsub, Natthachet
;
Hwang, Cheinway
;
Shum, C. K.
;
Wang, Lei
;
土木工程學系
We present a method of directly estimating surface mass anomalies at regional scales using satellite-to-satellite K-band Ranging (KBR) data from the Gravity Recovery and Climate Experiment (GRACE) twin-satellite mission. Geopotential differences based primarily on KBR measurement are derived using a modified energy integral method with an improved method to calibrate accelerometer measurements. Surface mass anomalies are computed based on a downward continuation process, with optimal regularization parameters estimated using the L-curve criterion method. We derive the covariance functions in both space-and space-time domains and use them as light constraints in the regional gravity estimation process in the Amazon basin study region. The space-time covariance function has a time-correlation distance of 1.27 months, which is evident that observations between neighboring months are correlated and the correlation should be taken into account. However, most of the current GRACE solutions did not consider such temporal correlations. In our study, the artifact in the regional gravity solution is mitigated by using the covariance functions. The averaged commission errors are estimated to be only 6.86% and 5.85% for the solutions based on the space-covariance function (SCF) and the space-time covariance function (STCF), respectively. Our regional gravity solution in the Amazon basin study region, which requires no further post-processing, shows enhanced regional gravity signatures, reduced gravity artifacts, and the gravity solution agrees with NASA/GSFC's GRACE MASCON solution to about 1 cm RMS in terms of water thickness change over the Amazon basin study region. The regional gravity solution also retains the maximum signal energy while suppressing the short wavelength errors.
Sediment-Mass Accumulation Rate and Variability in the East China Sea Detected by GRACE
(2016-09-01)
Liu, Ya-Chi
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Hwang, Cheinway
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Han, Jiancheng
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Kao, Ricky
;
Wu, Chau-Ron
The East China Sea (ECS) is a region with shallow continental shelves and a mixed oceanic circulation system allowing sediments to deposit on its inner shelf, particularly near the estuary of the Yangtze River. The seasonal northward-flowing Taiwan Warm Current and southward-flowing China Coastal Current trap sediments from the Yangtze River, which are accumulated over time at rates of up to a few mm/year in equivalent water height. Here, we use the Gravity Recovery and Climate Experiment (GRACE) gravity products from three data centres to determine sediment mass accumulation rates (MARs) and variability on the ECS inner shelf. We restore the atmospheric and oceanic effects to avoid model contaminations on gravity signals associated with sediment masses. We apply destriping and spatial filters to improve the gravity signals from GRACE and use the Global Land Data Assimilation System to reduce land leakage. The GRACE-derived MARs over April 2002-March 2015 on the ECS inner shelf are about 6 mm/year and have magnitudes and spatial patterns consistent with those from sediment-core measurements. The GRACE-derived monthly sediment depositions show variations at time scales ranging from six months to more than two years. Typically, a positive mass balance of sediment deposition occurs in late fall to early winter when the southward coastal currents prevail. A negative mass balance happens in summer when the coastal currents are northward. We identify quasi-biennial sediment variations, which are likely to be caused by quasi-biennial variations in rain and erosion in the Yangtze River basin. We briefly explain the mechanisms of such frequency-dependent variations in the GRACE-derived ECS sediment deposition. There is no clear perturbation on sediment deposition over the ECS inner shelf induced by the Three Gorges Dam. The limitations of GRACE in resolving sediment deposition are its low spatial resolution (about 250 km) and possible contaminations by land hydrological and oceanic signals. Potential GRACE-derived sediment depositions in six major estuaries are presented.
Water storage loss in central and south Asia from GRACE satellite gravity: correlations with climate data
(2011-11-01)
Tangdamrongsub, Natthachet
;
Hwang, Cheinway
;
Kao, Yu-Chi
;
土木工程學系
;
Department of Civil Engineering
Recent decrease of water supply in central Asia and south Asia affects billions of people here. By filtering the errors at higher frequency components and correcting for the contaminated components, we enhance the monthly GRACE gravity fields to improve the determination of change in equivalent water height (EWH). The water storage changes from GRACE and the GLDAS hydrology model all show decreasing trends in this region. At the annual and inter-annual time scales, significant correlations between the variations in EWH and the variations in temperature, precipitation and snow equivalent height are found, especially at high altitude stations, suggesting that climate change is the driving factor for the water depletion in central Asia and south Asia.