Measuring Our Restless Planet Earth Shin-Chan Han Civil, Surveying, - - PowerPoint PPT Presentation

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

His radius of a spherical Earth 6267 km => only 2% error from a modern determination (6371 km) The first measurement of the Earth’s figure in 200 B.C. Eratosthenes (276 – 195 B.C) of Alexandria 5000 stadia (Alexandria-Syene) 1 stadium=157.5 m

Measurements of the Earth’s flattening in 1600’s Snellius, Picard, Cassini => Measured the arc measurement and 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 => Arc measurements along the meridian

• f Barcelona – Paris – Dunkirk

carried in 1792-1798, f = 1/334 (10% error, f=1/298.257223563 ~ 0.003)

• blong
• blate

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 19th 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 shape of the Earth

Quran 79:30 (Sahih International) “And after that He spread the earth.”

~6371 km ~10 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 Vanguard-1 (launched in 1958) The load stress is supported by the mechanical strength and mantle convection.

Chicago Tribune 29th January, 1959 The Earth is pear- shaped, but not like the one Columbus thought (in 15th 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.

These complex processes change the figure, gravitational field, and rotation (polar motion and length of day) of the Earth “Three Pillars of Geodesy” The Earth’s (physical) figure is changing… Concerning change in the figure sub-mm to cm

Image by European Space Agency The constituents of ‘g’ Sensitivity of the present technologies ~ <10 nanoGal (ground) – 10 digits after the decimal point ~ 1 microGal (space) – 8 digits Surface gravity, g = 9.8072467…. m/s2

Gravity Recovery And Climate Experiment (GRACE) in 2002 Tapley [2014]

CHAMP 2000 GRACE 2002 GOCE 2009 GRAIL 2011 GRACE-FO 2017

Sensitive to mass “movement”: Land water storage Ice mass change Ocean mass change Earthquakes Land deformation Sensitive to track a few cm of water in 3002 - 4002 km2 “Any sufficiently advanced technology is indistinguishable from magic.” Arthur C. Clarke, Profiles of The Future, 1961 (Clarke's third law)

Another technique, Satellite Altimetry Measure sea, ice, lake, river, surface height Radial orbit is 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)

Measure changing Earth’s surface from a ‘fixed’ trajectory

Greenland (& neighboring islands)’s ice sheet has been thinning at a rate of 345 km3/yr

Emerging trends in global mass change (2002 – 2014)

N.B. 1 km3 of water = 1 gigatonne of water = Total water available in the Lake Macquarie (surface area = 110 km2; average depth = 8 m)

Patagonia glacier melt at a rate of 16 km3/yr The Antarctic ice sheet melt at a rate

• f 63 km3/yr

Alaska glacier melts a rate of 40 km3/yr Groundwater depletion (pumping for irrigation) across northern India at a rate of 54 km3/yr High mountain glacier melts a rate

• f 15 km3/yr

Recent droughts in southeastern US and Texas 2010 Chile earthquake and drought in southern Argentina Floods in Queensland in 2011-2012 Return to normal after wet years in early 2000s (Great Sandy Desert) Return to normal after droughts ended in 2007 (Okavango Delta) Depletion of water resources in Middle East exacerbated by droughts Overexploitation of freshwater resources in the North China Plain Post-glacial rebound after the historic ice sheet melts

Rodell [2014], Velicogna [2014], Han [2014]

Caused by natural variability, climate change, and anthropogenic activities

Post glacial rebound

Mantle viscosity 1020 - 1021 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

2004 Mw9.2 Sumatra-Andaman + 2005 Mw8.5 Nias 2004 Mw9.2 Sumatra-Andaman 2012 Mw8.6 Wharton Basin 2007 Mw8.5 Bengkulu 2011 Mw9.0 Tohoku-Oki 2006 Mw8.3 + 2007 Mw8.1 Kuril islands 2009 Mw8.1 Samoa-Tonga 2010 Mw8.8 Maule 2004, 2005, 2007, 2012 2011 2006, 2007 2009 2010

Ice mass loss of the Gulf of Alaska + present-day postseismic gravity change of 1964 Mw Prince William Sound earthquake Ice mass loss of the Patagonian ice field + present-day postseismic gravity change of 1960 Mw9.5 Valdivia earthquake

1964 1960

Emerging trends in global mass change (cont’d)

Large earthquakes also have changed the the figure

• f the Earth, episodically and gradually.

[Luthcke et al. 2011] Global Ice Mass Balance Trend (GSFC ‘mascon’ solution)

10 daily time-series of mass change in Giga Ton (GT)

• Max. amount of ice in 2007 winter is

similar with the min. in 2005 summer Loss of ice 220 GT/yr (water equivalent)

Ice Mass Balance Trend - Greenland

ICESAT elevation changes from Oct 2003 to March 2008

[Sorensen et al., 2011]

<= Measure of geometric height (volume), not mass Challenges to get mass changes:

• Firn compaction and

its changes

• Surface density (firn
• r 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

Derived mass change (ice equivalent)

Loss of ice 160 GT/yr (water equivalent)

Ice Mass Balance Trend - Antarctica

Loss of ice 40 GT/yr (water equivalent)

Ice Mass Balance Trend - Gulf of Alaska

Contribution to sea level (derived from GRACE)

Velicogna [2014] 500 Gt of the ice melts to the ocean every year

Over the last decade 2002 – 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 change) = 1.8 mm/yr

• ver 1993-2003, Ishii et
• al. [2005]

Nerem et al. [2015]

[Leuliette and Smith, 2011] Mean Sea Level change: 3.2 mm/yr (1992-present) Blue: direct observation Red: complementary

• bservation

Sea level: altimeter (TOPEX, Jason, ENVISAT) Ocean mass: GRACE Steric sea level: Argo (array of temperature/salinity profiling floats)

Sea level = GRACE + Steric Steric = GRACE - Sea level GRACE = Sea level - Steric

The Australia changing the sea level rise! The Australia – the smallest continent, but the biggest role in the global sea level and climate Fasullo et al. [2013], GRL Credit: Nerem, Willis, Boening

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

equivalent water height [cm]

Alsdorf, Han, et al. [2010]

30 cm/s for upstream cells + faster for downstream cells This mimics backwater effect on the upstream 30 cm/s uniformly applied in the entire basins Spatial pattern is consistent for

• ther uniform velocities

Dynamics of surface water

Han et al. [2011]

Contemporary research in geodesy for Earth observation

Sciences (geodetic application)

• Solid Earth deformation (earthquake, tsunami, volcanoes,

postglacial, loading, subsidence, tectonics)

• Hydrological cycles (floods, droughts, ground water)
• Atmosphere (troposphere, ionosphere, scintillation)
• Ocean (Ocean circulation, Tides, Bathymetry, Sea Level Rise)
• Cryosphere (Ice mass change, Glacier dynamics)
• Global terrestrial and celestial reference frame, precision orbit

determination

Technologies (geodetic instrument)

• GPS, INS, Radar and laser altimeter, Radar interferometer

(SAR), Gravimetry/Gradiometry, OBP, seafloor surveying, VLBI, SLR

Satellite Remote Sensing (geodetic mission)

• LAGEOS, CHAMP, GRACE, GOCE,

TOPEX/JASON/OSTM, ICESAT, CRYOSAT, SRTM

• GRACE-FO, SWOT, GRACE-II, DESDYNI, ICESAT-II,

LIST

Davis et al. [2012], A Foundation for Innovation: Grand Challenges in Geodesy Hooray for Geodesy! for your horizon being expanded.

Mars Reconnaissance Orbiter

GRAIL for the Moon MESSENGER for Mercury

Image Credit: UNAVCO