Measuring Our Restless Planet Earth Shin-Chan Han Civil, Surveying, and Environmental Engineering University of Newcastle “Potential uses of GPS Geodetic measurement are limited only by our imaginations.” from B. Parkinson (1980) Presented at Newcastle Museum, 29 July 2015
The first measurement of the Earth’s figure in 200 B.C. Eratosthenes (276 – 195 B.C) of Alexandria His radius of a spherical Earth 6267 km => only 2% error from a modern 5000 stadia determination (Alexandria-Syene) (6371 km) 1 stadium=157.5 m
Measurements of the Earth’s flattening in 1600’s Snellius, Picard, Cassini => Measured the arc measurement and oblong astronomic latitude and found that the meridian arc in the northern part is shorter than the one o the southern part. f = –1/95 (oblong) Newton, Huygens => Computed through gravity theory, the flattening, f =1/230, 1/576 (oblate) Delambre, Mechain oblate => Arc measurements along the meridian of Barcelona – Paris – Dunkirk carried in 1792-1798, f = 1/334 (10% error, f=1/298.257223563 ~ 0.003 )
Measurements of the Earth-Sun distance (A.U.) in 1769 Capt. James Cook (1728 - 1779) A explorer and cartographer who obtained Venus transit measurements for the A.U. 1 A.U. = 149,597,870,700 m
From the ellipsoid to the ‘physical’ shape (geoid) in 1800’s In the 19 th century, Laplace, Gauss, Bessel, and others already noticed the systematic deviations in their measurements and found the ellipsoidal model is no longer tenable. Carl Friedrich Gauss (1777–1855) One of those who had an idea of physical Quran 79:30 (Sahih shape of the Earth International) “ And after that He spread the earth .”
~10 km ~6371 km ~10 m
The first measurement of the pear-shaped Earth in 1959 John O’Keefe (NASA) The pear-shape of the Earth, measured by tracking The load stress is supported by Vanguard-1 the mechanical strength and (launched in 1958) mantle convection.
Chicago Tribune 29 th January, 1959 The Earth is pear- shaped, but not like the one Columbus thought (in 15 th century)!
The plumb line follows the direction of the gravity field. The satellite trajectory is determined by the gravity field.
The father of space geodesy William M. Kaula (1926-2000) - Born in Sydney, Australia - Educated in The Ohio State University - Worked Space Geodesy at NASA Goddard - Became a Professor in UCLA - Most notable in using early earth satellites to produce gravity maps of Earth (and in very good knowledge of good restaurants from Gerry Schubert)
The first measurement of the general shape in 1960’s One of the early determinations of the Earth’s figure (geoid undulation wrt the ellipsoid) by Bill Kaula (1964), and many others.
The geoid determined in 2010’s Results from extensive ground, marine, and airbone survey, from three decades of satellite altimetry, and from decades of tracking multiple spacecraft, from numerous government agencies (incld. Military, NASA, ESA) from various countries. Accuracy ~5 cm at a 9 km scale; 2 cm at 100 km Implications toward Earth interior, tectonics, oceanography, hydrography, surveying, defense, and aerospace, and many more. => This is by no means the end of the game, but only a well-started one.
The Earth’s (physical) figure is changing… Concerning change in the figure sub-mm to cm These complex processes change the figure, gravitational field, and rotation (polar motion and length of day) of the Earth “ Three Pillars of Geodesy ”
The constituents of ‘ g ’ Surface gravity, g = 9.8072467 …. m/s 2 Image by European Space Agency Sensitivity of the present technologies ~ <10 nanoGal (ground) – 10 digits after the decimal point ~ 1 microGal (space) – 8 digits
Gravity Recovery And Climate Experiment (GRACE) in 2002 “ Any sufficiently advanced technology is indistinguishable from magic. ” Arthur C. Clarke, Profiles of The Future, 1961 (Clarke's third law) Sensitive to mass “movement”: Land water storage Ice mass change Tapley [2014] Ocean mass change Earthquakes Land deformation Sensitive to track a few cm of water in 300 2 - 400 2 km 2 GRAIL GRACE-FO GRACE GOCE CHAMP 2011 2017 2002 2009 2000
Another technique, Satellite Altimetry Measure sea, Measure ice, lake, river, changing surface height Earth’s surface from a ‘fixed’ Radial orbit is trajectory as good as 2-3 cm Mature techniques, tested since 1973, developed until now, to be developed. (~19 s/c, NASA, ESA, CNES, NOAA, US Navy, CNSA)
Emerging trends in global mass change (2002 – 2014) Caused by natural variability, climate change, and anthropogenic activities Groundwater Greenland (& depletion (pumping Alaska glacier melts High mountain neighboring islands)’s Overexploitation of for irrigation) across a rate of 40 km 3 /yr glacier melts a rate ice sheet has been freshwater resources in northern India at a of 15 km 3 /yr thinning at a rate of 345 the North China Plain rate of 54 km 3 /yr km 3 /yr Depletion of water resources in Middle East exacerbated by droughts Recent droughts in southeastern US Return to normal after and Texas droughts ended in 2007 (Okavango Delta) 2010 Chile Return to normal after earthquake and wet years in early drought in southern 2000s (Great Sandy Argentina Desert) Patagonia glacier Floods in Queensland melt at a rate of 16 in 2011-2012 km 3 /yr The Antarctic ice sheet melt at a rate of 63 km 3 /yr Post-glacial rebound N.B. 1 km 3 of water = 1 gigatonne of water after the historic ice sheet melts = Total water available in the Lake Macquarie (surface area = 110 km 2 ; average depth = 8 m) Rodell [2014], Velicogna [2014], Han [2014]
Post glacial rebound Mantle viscosity 10 20 - 10 21 Pa s determined the rate of rebound. Surface deformation and gravity change maps and time-series are being exploited to infer the structure of the Earth interior and its rheology GPS records several mm/yr uplift
Emerging trends in global mass change (cont’d) Ice mass loss of the Gulf of Alaska + 2006 Mw8.3 2011 Mw9.0 present-day postseismic gravity + Tohoku-Oki change of 1964 Mw Prince William Sound earthquake 2007 Mw8.1 Kuril islands Ice mass loss of the Patagonian ice field + present-day postseismic 2004 Mw9.2 gravity change of 1960 M w 9.5 Sumatra-Andaman Valdivia earthquake + 2005 Mw8.5 Nias 2009 Mw8.1 Samoa-Tonga 2012 Mw8.6 Wharton Basin 1964 2006, 2007 2011 2004 Mw9.2 Sumatra-Andaman 2004, 2010 2009 2005, 2007, 2010 Mw8.8 2007 Mw8.5 1960 2012 Maule Bengkulu Large earthquakes also have changed the the figure of the Earth, episodically and gradually.
Global Ice Mass Balance Trend (GSFC ‘ mascon ’ solution) 10 daily time-series of mass [Luthcke et al. 2011] change in Giga Ton (GT)
Ice Mass Balance Trend - Greenland Max. amount of ice in 2007 winter is similar with the min. in 2005 summer Loss of ice 220 GT/yr (water equivalent)
Derived mass change (ice ICESAT elevation changes equivalent) from Oct 2003 to March 2008 <= Measure of geometric height (volume), not mass Challenges to get mass changes: - Firn compaction and its changes - Surface density (firn or ice); how one implements this can cause 30% difference in total mass change 191 ± 23 Gt yr−1 to 240 ± 28 Gt yr−1 for the period October 2003 to March 2008, depending on how one processes the data, very similar in numbers with GRACE results [Sorensen et al., 2011]
Ice Mass Balance Trend - Antarctica Loss of ice 160 GT/yr (water equivalent)
Ice Mass Balance Trend - Gulf of Alaska Loss of ice 40 GT/yr (water equivalent)
Contribution to sea level (derived from GRACE) Over the last decade 2002 – 2014 500 Gt of the ice melts to the ocean every year Velicogna [2014]
The global sea-level rise (derived from Altimeters) => 3.3 mm/yr sea level change 10-25 cm rise by 2100 [Meier et al., 2007] The steric (thermal expansion and salinity Nerem et al. [2015] change) = 1.8 mm/yr over 1993-2003, Ishii et al. [2005]
Mean Sea Level change: 3.2 mm/yr (1992-present) Blue: direct observation Red: complementary Sea level = GRACE + Steric observation Sea level: altimeter (TOPEX, Jason, ENVISAT) Steric = GRACE - Sea level Ocean mass: GRACE Steric sea level: Argo (array of temperature/salinity GRACE = Sea level - Steric profiling floats) [Leuliette and Smith, 2011]
The Australia changing the sea level rise! The Australia – the smallest continent, but the biggest role in the global sea level and climate Credit: Nerem, Willis, Boening Fasullo et al. [2013], GRL
Hydrodynamic assimilation of GRACE ocean tide solutions GRACE solutions and corrections to TPXO7.1 from assimilation Han et al. [2007] and Egbert et al. [2009]
Hydrological Cycle (Mass Balance) Land Surface Model P – ET = Q + dS/dt River Routing Model Q along the channel Example: Amazon Basin Year 2003, bi-weekly Alsdorf, Han, et al. [2010] equivalent water height [cm]
Dynamics of surface water 30 cm/s for upstream cells + faster 30 cm/s uniformly applied in for downstream cells the entire basins This mimics backwater effect on the Spatial pattern is consistent for upstream Han et al. [2011] other uniform velocities
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