Time-variable Gravity Measurements from the GRACE Mission and Applications Pavel Ditmar Department of Geoscience and Remote Sensing Delft University of Technology Challenge the future 1 GRACE Mission Overview Challenge the future 3 “X-raying” of the Earth: how to look inside the Earth from space? Challenge the future 4 Measurement principle of satellite gravimetry M Newton's law of universal gravitation: F Newton's 2nd law: a Equation of motion: x Challenge the future 5 GRACE Satellite Mission • Agencies: NASA, DLR • Launch date: March 17, 2002 • Initial altitude: ≈ 500 km (C) http://www.csr.utexas.edu • Satellite-to-satellite distance: ≈ 200 km • Primary sensor: K-Band Ranging (KBR) system • Inter-satellite ranging accuracy: ≈ 10-6 m Challenge the future 6 Major strong points and limitations of the GRACE mission Strong points: Limitations: • Directly senses mass variations themselves • Temporal resolution is about 1 month • Senses mass re-distribution at any depth • Horizontal spatial resolution is 200 – 500 km (depending, among other, on temporal scale) • Sensitivity to meteorological conditions is limited • No vertical resolution Challenge the future 7 Observation of mass re-distribution of various origins with GRACE Challenge the future 8 Hydrological applications Challenge the future 9 GRACE and hydrology: water balance ∆S (Storage change) = P (Precipitation) – ET (Evapotranspiration) – R (Runoff) http://www.hinchingbrookeschool.co.uk/geography/images/hydrologic-cycle-big.jpg Challenge the future 10 Comparison of total water stock variations in Amazon river basin GRACE-based estimate vs. hydrological model PCR-GLOBWB Challenge the future 11 Assimilation of GRACE data into a hydrological model: case study in the Rhine River basin • Hydrological model: Openstreams HBV-96 • Two variants of hydrological modelling: • Local forcing data (E-OBS) • Global forcing data (Princeton global meteorological dataset) A319C* • GRACE product: CSR-RL05 (postprocessed with empirically defined filters) • Results are validated against in-situ well measurements at 18 locations * Station full name: 02348X0009/319C Challenge the future 12 Assimilation of GRACE data into a hydrological model: groundwater time-series at A319C station Local forcing data Global forcing data Challenge the future 13 Assimilation of GRACE data into a hydrological model: statistics over 18 locations Average correlation coefficients Local forcing data Global forcing data Average RMS differences Local forcing data Global forcing data Challenge the future 14 Usage of GRACE data to detect longterm anthropogenic mass trends Irrigated area in SE Turkey (GAP project) Irrigated area NE of Buraydah (SA) Irrigated area in the Tigris river basis (Iraq) Disappearing Bakhtegan and Tashk Lakes (Iran) Challenge the future 15 Ice sheet studies Challenge the future 16 Shrinking of Arctic glaciers in 2003–2008 observed with GRACE (DMT-2 model) Alaskan Glaciers Glaciers in the Canadian Arctic Archipelago Novaya Zemlya Svalbard (Spitsbergen) Jakobshavn Glacier Iceland Kangerdlugssuaq Glacier Equivalent water heights (cm/yr) Challenge the future 17 Shrinking of Greenland Ice Sheet: long-term mass trend (2003-2013) 2003 CSR RL05 ~ 270 Gt/yr m/yr (EWH) Challenge the future 18 Shrinking of Greenland Ice Sheet: time series (2003-2013) Mass loss acceleration: -13 Gt/yr2 (CSR) -14 Gt/yr2 (GFZ) Challenge the future 19 Mass and volume trends in Antarctic in 2002 – 2009 Mass trend (GRACE, CSR RL05) Volume trend (ICESat) (EWH) Challenge the future 20 Gunter et al. (2013, TCD) Mass trends in Antarctic: Ice vs. solid Earth snow snow iceice iceice snow snow GIA GIA M V V M V V observed snow GIA iceice snow pre-defined V V V V V V Ice mass trend (-146 Gt/yr in 2003 – 2013) GIA mass trend (64 Gt/yr) Challenge the future 21 Gunter et al. (2013, TCD) Shrinking of Antarctic Ice Sheet in 2002-2013 Mass loss acceleration: -5.3 Gt/yr2 (CSR) Challenge the future 22 Mass change trends in 2003-2010: an overview (Jacob et al, 2012) Region Rate (Gt/yr) Iceland -11 ± 2 Svalbard -3 ± 2 Novaya Zemlya -4 ± 2 Alaska -46 ± 7 Buffin Island (Canada) -33 ± 5 Other glaciers in the Canadian Arctic Archipelago -34 ± 6 Greenland -222 ± 9 Antarctica -165 ± 72 ... Total -536 ± 93 Total in terms of global sea level rise 1.5 ± 0.3 mm/yr Challenge the future 23 Global sea level rise in the 21st century: IPCC AR5 projections Challenge the future 24 GRACE mission: current status and outlook Challenge the future 25 Gaps in GRACE data during long-eclipse periods due to battery degradation Year 2011 2012 2013 2014 Data gaps Jan-01 to Feb-06 Jun-01 to Jul-06 Nov-17 to Dec-12 Apr-20 to May-31 Sep-26 to Nov-05 Duration (days) 37 36 26 42 41 Feb-27 to April-10 Aug-05 to Sep-24 Jan-18 to Feb-22 43 51 36 Challenge the future 26 GRACE mission: orbit decay Semi-Major Axis (prediction as of 30.09.2011) Semi-Major Axis (actual) Challenge the future 27 http://www.csr.utexas.edu/grace/ GRACE Follow-On (GFO) Mission • Agency: NASA • Expected launch date: Aug. 2017 • Mission set-up: similar to that of GRACE • Primary sensor: K-Band Ranging (KBR) system (≈ 10-6 m precision) • Experimental sensor: laser interferometer of nanometre-level ranging precision Challenge the future 28 Conclusions • Satellite gravimetry mission GRACE is an important instrument to monitor mass re-distribution in the Earth system. GRACE delivers unique information that cannot be acquired by other remote sensing techniques • GRACE data are particularly valuable at large spatial scales and temporal scales • Value of satellite gravimetry will increase, as new missions are launched and their accuracy improves Challenge the future 29 Acknowledgements The author thanks colleagues from the TU Delft for providing a contribution to the presentation: • • • • • • • • • • Hassan Hashemi Farahani Olga Didova Sun Yu Roland Klees Natthachet Tangdamrongsub Susan Steele-Dunne Brian Gunter Reinier Oost Riccardo Riva Jiangjun Ran Challenge the future 30
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