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Sensors 2017, 17(3), 566; doi:10.3390/s17030566

Terrestrial Water Storage in African Hydrological Regimes Derived from GRACE Mission Data: Intercomparison of Spherical Harmonics, Mass Concentration, and Scalar Slepian Methods

1
Department of Geomatics, National Cheng Kung University, No. 1, University Road, Tainan City 701, Taiwan
2
National Authority for Remote Sensing and Space Sciences, Cairo, 1564 Alf Maskan, Egypt
3
Center for Space and Remote Sensing Research, National Central University, Taoyuan 32001, Taiwan
4
Cooperative Research Centre for Spatial Information, Australia, Level 5, 204 Lygon St, Carlton VIC 3053, Australia
5
Geoscience Australia, Australia, Cnr Jerrabomberra Ave and Hindmarsh Drive, Symonston ACT 2609, Australia
*
Author to whom correspondence should be addressed.
Academic Editors: Mehrez Zribi and Nicolas Baghdadi
Received: 18 December 2016 / Revised: 6 March 2017 / Accepted: 8 March 2017 / Published: 10 March 2017
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Abstract

Spherical harmonics (SH) and mascon solutions are the two most common types of solutions for Gravity Recovery and Climate Experiment (GRACE) mass flux observations. However, SH signals are degraded by measurement and leakage errors. Mascon solutions (the Jet Propulsion Laboratory (JPL) release, herein) exhibit weakened signals at submascon resolutions. Both solutions require a scale factor examined by the CLM4.0 model to obtain the actual water storage signal. The Slepian localization method can avoid the SH leakage errors when applied to the basin scale. In this study, we estimate SH errors and scale factors for African hydrological regimes. Then, terrestrial water storage (TWS) in Africa is determined based on Slepian localization and compared with JPL-mascon and SH solutions. The three TWS estimates show good agreement for the TWS of large-sized and humid regimes but present discrepancies for the TWS of medium and small-sized regimes. Slepian localization is an effective method for deriving the TWS of arid zones. The TWS behavior in African regimes and its spatiotemporal variations are then examined. The negative TWS trends in the lower Nile and Sahara at −1.08 and −6.92 Gt/year, respectively, are higher than those previously reported. View Full-Text
Keywords: terrestrial water storage; GRACE; spherical harmonics; global mascon; Slepian basis; Africa basins terrestrial water storage; GRACE; spherical harmonics; global mascon; Slepian basis; Africa basins
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Rateb, A.; Kuo, C.-Y.; Imani, M.; Tseng, K.-H.; Lan, W.-H.; Ching, K.-E.; Tseng, T.-P. Terrestrial Water Storage in African Hydrological Regimes Derived from GRACE Mission Data: Intercomparison of Spherical Harmonics, Mass Concentration, and Scalar Slepian Methods. Sensors 2017, 17, 566.

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