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					Observation and analysis of gravity data
for earth science application: from static
           to moving platform
                      Cheinway Hwang
    Department of Civil Engineering, National Chiao Tung
    University, 1001 Ta Hsueh Road, Hsinchu 300,Taiwan

             International Geomatics Forum
             May 28-30, 2009, Qingdao, China
         Applications of gravity in natural and
                 engineering sciences
• Geodesy: geoid modeling, vertical datum, orbit determination, GPS
  leveling etc
• Geophysics: density distribution, isostasy, crustal-mantle structure,
  seafloor topography
• Metrology: pressure, work and power are gravity-dependent
• Gravitational constant, G
• Terrestrial navigation
• Deposit exploration
• Geodynamics: tectonics, earthquake etc
• Climate change
• Hydrology
• Oceanography
• New applications are yet to be exploited
Gravity measurements: sensors and platforms

• Space-borne gravimetry: GRACE (K-band ranging),
  GOCE (gradiometer), CHAMP and COSMIC (GPS),
  LAGEOS (SLR), satellite altimetry (sea only)
• Airborne gravimetry
• Shipborne gravimetry
• Relative gravimetry
• Superconducting gravimetry
• Absolute gravimetry
Laboratory of Geodesy and Geodynamics,
                Hsinchu




                                 L&R Air-Sea
 FG5-231 and T48   Graviton-EG   Gravity System
                                 II
    Satellite gravimetry:
    GRACE and COSMIC




• The joint Taiwan-US mission FORMOSAT-3/COSMIC (FM/COSMIC)
  was launched on April 17, 2006, deploying six micro-satellites at altitudes
  ranging from 750 to 800 km and at an inclination of 72 degree in the final
  mission phase. The expected lifetime is 5 years.
• Two single-patch antennas, mounted on the upper part of the main body,
  are for precise orbit determination (POD)
• Combining COCMIC GPS and GRACE KBR for gravity determination
    Kinematic orbits as 3-D tracking data

• In the kinematic POD based on zero-
  differenced phase measurements, satellite
  coordinates are estimated together with one
  GPS receiver clock parameter every epoch
• In the NCTU kinematic orbit determination for
  the COSMIC mission, we first produce a 30-h
  orbit arc (from -3 h of a GPS day to +3 h),
  which is then truncated to a 24-h arc (0 to 24 h
  of a GPS day) for further applications,
  especially for gravity recovery.
                               Assessment of orbit accuracy


Kinematic orbit (a) 5 s sampling interval                                      Dynamic orbit     (a) 5 s sampling interval
            Radial           Along-track       Cross-track                      Radial          Along-track     Cross-track (cm)
          5h       6h        5h       6h       5h        6h                 5-h       6-h      5-h       6-h      5-h       6-h
FM1      2.49    2.70       2.86     2.99     2.69      3.13         FM1    2.68      2.86     2.70      3.07    2.81      3.19
FM2      2.62    2.69       2.50     2.56     2.70      3.17         FM2    2.37      2.42     2.29      2.40    2.05      2.10
                                                                     FM3    2.67      2.72     2.85      2.88    3.05      3.17
FM3      2.96    3.22       3.73     3.76     4.18      4.33
                                                                     FM4    2.92      3.00     3.27      3.32    3.23      3.29
FM4      3.33    3.35       3.23     3.25     4.20      4.34
                                                                     FM5    2.35      2.58     2.40      2.43    3.14      3.16
FM5      2.49    2.58       2.62     2.77     3.50      3.86
                                                                     FM6    2.65      2.66     2.51      2.57    3.35      3.44
FM6      3.40    3.43       3.19     3.58     4.71      4.79

Kinematic orbit     (b) 30 s sampling interval (5 h)                       Dynamic orbit (b) 30 s sampling interval (5 h)
                                                    Cross-
              Radial            Along-track                                  Radial            Along-track           Cross-track
                                                     track
 FM1              2.51              1.85           2.28        FM1            2.62                2.23                2.74
 FM2              2.06              1.89           2.04        FM2            1.83                1.63                1.50
 FM3              2.38              3.08           3.52        FM3            2.45                2.45                2.62
 FM4              2.59              2.65           3.51        FM4            2.25                2.77                2.79
 FM5              1.87              2.10           2.87        FM5            1.98                2.21                2.99
 FM6              2.64              3.08           4.17        FM6            2.10                2.06                2.86
Standards for the orbit dynamics of COSMIC satellites

           Model/parameter                                        Standard



  Conventional inertial reference frame                            J2000

                N-body                                          JPL DE-403
          Earth gravity model                                  GGM02S [17]
              Polar motion                                  IERS standard 2000
          Reference ellipsoid                                ae = , f =1/298.257
                  GM                                                3s-2


              Ocean tides                                      GOT00.2 [18]
            Solid Earth tides                               IERS standard 2000
                                          Mass Spectrometer Incoherent Scatter (MSIS) Empirical Drag
          Atmosphere density
                                              Model [19]

        Earth radiation pressure             Second-degree zonal spherical harmonic model [20]

        Solar radiation pressure                       one coefficient every 1.5 hours
           Atmosphere drag                             one coefficient every 1.5 hours
         General accelerations                          9 parameters every 1.5 hours
Percentages of accepted 5-second kinematic
orbits in August 2006




  Percentages of acceptance of kinematic orbits for normal point computations
Statistics of standard errors of normal
point kinematic orbits
             MAX. (mm)   MEAN (mm)   MIN. (mm)


    FM1        7.38         7.13       6.77


    FM2        7.38         7.06       6.68


    FM3        7.30         6.98       6.68


    FM4        7.23         6.93       6.57


    FM5        6.87         6.49       6.20


    FM6        7.72         7.24       6.75
Combined COSMIC-GRACE gravity solution




Geoid variation to spherical harmonic degree 25 from the combined COSMIC
                             and GRACE solution
Airborne and shipborne gravimetry
Airborne and shipborne
gravimeter: L&R Air-Sea Gravity
System II

 resolution   0.01 mGal

 accuracy     <1.00 mGal

    size      71 x 56 x 84 cm

  weight      116 kg

  power       240 watts (avg), 450
                 watts (max)
 frequency 1 Hz
   Taiwan airborne gravity
   survey
• Numbers of survey lines:
  North-south : 64
  East-west : 22
  Northeast-southwest : 10
  Northwest-southeas : 6
• The cross-line spacing is 4.5 km, except
  the east-west lines, which are spaced
  at 20 km.
• A LaCoste and Romberg (LCR) System II
  air-sea gravimeter on a King-Air
  Beechcraft-200 aircraft was used to
  collect the airborne gravity data.
     Error sources in mobile gravity mapping
 • The differential change of gravity value:

                              2v h
dg z  da z  (2we cos  sin    )dv h  2we v h cos  cos d  2we v h sin  sin d
                             Rz
 Required accuracy for a one-mgal accuracy in airborne gravity value
 for an average latitude 23.5 degree and velocity of 85 m/s
 Term                Required accuracy
 Vertical
                                                  5
 acceleration           1 mgal, equivalent  10
                                         5 to          ms-1 in vertical velocity
 Horizontal                          
                        37.5 cms-1 for  0,180
 velocity                           
                        6.2 cms-1 for  90
                                    
                        9.3 cms-1 for  270

 Azimuth                3 for   0,180 , equivalent to 7.5 cms-1 in horizontal
                                          velocity
 Latitude               657 for   90,270 , equivalent to 12898 m in horizontal
                                                position
Kinematic GPS positioning of aircraft and
ship: the standard pratice
• Precise aircraft position, velocity and acceleration are
  critical to the success of an airborne gravity survey
• Two kinematic solutions: (1) GPSurvey solution, using the
  broadcast ephemeris, and (2) Bernese 5.0 solution, using
  the IGS precise ephemeris of GPS.
• GPSurvey solution was used to assess the quality of
  airborne gravity data along a survey line and to decide
  whether a re-flight is necessary. Bernese solution
  provided the final positioning result and was carried out
  after several weeks of data collection.
Gravity anomalies at 5156m
Accuracy assessment of airborne gravity anomaly
       : impact of crossover adjustment

     Case           Max       Min       Mean     RMS

     Before         13.97     -13.33    -0.24    4.92
     adjustment
     After          10.07     -9.17     0.00     2.98
     adjustment


             Statistics of crossover difference of
             airborne gravity anomaly (mgal)
      Geoid models from airborne gravity and
               other gravity data
•   The geoid models were evaluated
    using the “observed” geoidal heights
    along four first-order leveling routes
•   An “observed” geoidal height is the
    difference between the GPS-derived
    ellipsoidal height (from 24-hour
    observation and at cm-level accuracy)
    and the precision leveling-derived
    orthometric height (at mm-level
    accuracy).


                     North route     Center route   South route   East route
     Geoid model

     KMS             0.059           0.187          0.080         0.022
     NCTU            0.002           0.116          0.190         0.055
     Hwang           0.080           0.258          0.222         0.140
     (1997)
   Bouguer anomaly : numerical integration
The perturbing potential due to the mass between the sea level and the surface is
                    h                   dxdydz
V  G         
         x y z 0
                        ( x  x p ) 2  ( y  y p ) 2  ( z  s) 2

                        
 G: gravitational constant;: the density of terrain.

At point P of the flight altitude, the gravity effect due to terrain is
                V
 AT  (           ) |s  h p  G   f ( x, y)dxdy
                s                 x y

  where
                                        1                                                        1
  f ( x, y)                                                      1
                                                                          
                                                                                                                 2 12
                [( x  x P ) 2  ( y  y P ) 2  (h  h p ) 2 ]       2
                                                                              [( x  x P ) 2  ( y  y P ) 2  h p ]

 Thus, the Bouguer anomaly at the flight altitude is
  Ba  g  AT

  g : free-air gravity anomaly at the flight altitude
The density of terrain is set to 2.67 g cm-3 at land and 1.64 g cm-3 at sea.
The elevation h is positive at land and negative at sea.
                   Bouguer anomaly




BA at flight altitude (5156m)        BA at sea level
Satellite Altimeter as an Ocean Current Meter: Contribution
          of Marine Geoid and Airborne Gravimetry
           Altimeter current meter at a crossover
Geostrophic current:
                                   ζ: dynamic height , difference
             g    g              between ellipsoidal height and
East:    u                    geoidal height
             f y   f
             g   g
North:    v       
             f x  f
Along-track gradients of dynamic
height:

   a cos  a  d cos  a

      sin  a   d 
    a sin  d  d sin  a

       sin  a   d 
             Crossover A: T/P –
             Jason1




•Persistent north-going flows, consistent
with the pattern of Kuroshio
•Mean velocity = 133 cm/s, azimuth =
30.57 degree
•Seasonal variation
•Flows seem to be weaker after 2004
Shipborne gravimetry
Shipborne gravimetry on
a small vessel




           L&R Air/Sea Gravity System II
                    gravimeter
Bernese relative positioning procedure and accuracy
         analysis for shipborne gravimetry
                           PRETAB
       BXOBV3        將GPS精密星曆轉成表列格式
      資料格式轉換
                       並輸出GPS衛星時錶差
                                                   4 hrs
                                                            1     4 hrs
                                                            hr
       CODSPP                 ORBGEN
單點定位、 接收儀時鐘與GPS時同步   建立Bernese自訂的標準軌道格式




       SNGDIF                                              基隆        小琉球
     組成一次差觀測量

                                           Standard        9.62           8.67
                                          deviation of
      MAUPRP
    週波脫落偵測與補償                              ellip. Ht
                                              (cm)

             GPSEST
     以相位二次差觀測量進行各相關參數之解算




                                                                            27
Crossover analysis of gravity
Crossover analysis of shipborne
      gravity (unit: mgal)
    Keelung     Max       Min      Mean     Std     RMS
     Before
                7.552    -11.762   -1.169   4.511   4.599
   adjustment
      After
                2.358    -6.121    0.000    1.873   1.895
   adjustment



    Lioucioui   Max       Min      Mean      Std    RMS
     Before
                14.539   -9.446    -0.419   4.997   4.954
   adjustment
      After
                4.745    -4.281    0.000    1.968   1.944
   adjustment
Gravity from satellite altimetry
Satellite altimetry in gravity field modeling
• High frequency information of the marine gravity field is
  mainly based on satellite altimetry
• Currently , satellite altimetry is able to map the mean sea
  surface and marine gravity anomaly with a spatial
  resolution of 2’ X 2’ or higher
• Over coastal zones, altimetry-gravity can improve/degrade
  geoid accuracy, depending on how altimeter data quality
• With more data and improved processing methods,
  improved accuracy and spatial density of altimeter data
  are expected
Altimetry-gravity conversion: the inverse
  Vening Meinesz formula

        
g p 
       4                                    
              H   q cos  qp   q sin  qp d q

       
    
      4    
              H  qp d q


 kernel functionH               pq cos  pq  3  2 sin  pq 
                                                              
                           cos              2            2 
                    H          2                           
                                  pq        pq          pq 
                           2 sin      2 sin      1  sin
                                                              
                                  2          2            2  
      Selected altimeter missions and data
 Mission     Repeat      Data          Orbit      Inclination    mean track
             period     duration    height (km)    angle (˚)      separation
              (day)                                             at the equator
                                                                     (km)
  Seasat      no      78/8-78/11       780           108             165
Geosat/GM     no      85/03-86/09      788           108                4
Geosat/ERM    17      86/11-90/01      788           108              165


ERS1-/35d     35      92/04-93/12      781           98.5             80
                      95/03-96/06

ERS-1/GM      no      94/04-95/03      781           98.5              8
ERS-2/35d     35      95/04-98/10      785           98.5             80

   T/P        10      92/12-00/06      1336           66              280
      Global assessment of altimetry-gravity


                                                      (4)
                                        (1)
(6)                (9)   (10)
                                                    (3)
             (7)
                                (11)
                                                            (5)
                                              (2)


       (8)

                                 (12)
RMS differences (in mgal) between predicted and shipborne gravity anomalies
in 12 areas in the world
                          This work       Hwang et al.      Improvement
   Comparison area                          (1998)
(1) Alaska Abyssal          4.887            5.168             0.281
(2) East Pacific Rise       3.057            6.786             3.729
(3) Caribbean Sea           9.840           11.399             1.559
(4) Reykjanes Ridge         5.122            5.202             0.080
(5) Sierra Leone Basin      3.678            3.688             0.010
(6) Mediterranean Sea       13.026          13.480             0.454

(7) Carlsberg Ridge         7.347            7.397             0.023
(8) Kerguelen Plateau       6.017            6.931             0.914

(9) South China Sea         8.004            8.229             0.225
(10) Mariana Trench         11.561          11.814             0.253
(11) Fiji Plateau           13.365          14.148             0.783
(12) Ross Sea               7.634            8.477             0.843
           Absolute gravimetry



Micro-g FG5 Absolute Gravimeter
                               Relative gravimetry

Graviton-                                                              CG-5
EG




             Parameter            Graviton EG        Scintrex CG-5
            Sensor type           Zero length spring Fused quartz with
                                                     electrostatic nulling
            Resolution            1 μgal             1μgal
            Repeatability         1 μgal             3 μgal
            Nominal drift         <0.03 mgal/day     <0.02 mgal/day
            Data acquisition      Automatic leveling Automatic leveling
                                  and reading        and reading
            Operating range       Worldwide          8000 mgal
 Monitoring surface deformation over Central
Taiwan using absolute and relative gravimetry




                                           38
                   Relative Gravity Network

                       ¹ ü Ƥ
                         ¤ ¿                                                ¤ ¿
                                                                          ¹ ü Ƥ
                                                                                       HS01

                                       WTES
                                                                                               WTES
         G041
                 TAES    I025                                      TAES
                                                          G041                                HS02
                                        HS02                                 I025
              TAESAG                                              TAESAG
            DGES                                                                    HS03
                        HS03
                  DKES                                           DKES               HSBM
JYES                  HS04 HSBM                  JYES
                                                                                  HS04

           ª ¿
         ¶ ³ L¤                 HS05                         ª ¿
                                                           ¶ ³ L¤             HS05
G049                    PKBD                   G049
                                                                           PKBD
         G051
                                                        G051
                                                                             ¸ ¿
                                                                           ¹ Åq ¤
                         ¸ ¿
                       ¹ Åq ¤
  X202          X217
                                                                   X217

  2004/12 Gravity Network with LCR Graviton EG          2005/4 Gravity Network with LCR Graviton
     EG
2005/12, 2006/7 and 2006/11 Gravity Networks with Scintrex CG-5,
   2007/4 with LCR Graviton EG

                            ¤ ¿
                          ¹ ü Ƥ

                                                         LNES
                          ª ¿
                        ¶ ³ L¤           WTES

          G041     TAES    I025
             TAESAG
                                     TKHS
                 DKES
 JYES
                                  KTES



  G049                    PKBD

                            ¸ ¿
                          ¹ Åq ¤
               Adjustment of gravity network

• Datum-free constraints in GMM
    ST X  0         AS  0


• Solution

ˆ
X   ( AT PA  SS T )1 AT PL  ( N  SS T )1U


• Error covariance matrix
        2                                                2
 X    0 ( AT PA  SS T ) 1 AT PA( AT PA  SS T ) 1   0 ( AT PA) 

     V T PV
  
  ˆ 2
             ,r 1
     nu  r
    0
Rate of gravity change and rate of subsidence
      from absolute gravimetry (FG5)
                                                                                                                     Time Series of Absolute Gravity at TAES

                      978867810
                                                                                                                                                                                                                                                                                  978867805.628
                      978867800


                      978867790
Gravity (micro-Gal)




                      978867780


                                                                                                                                                                            978867771.669
                      978867770
                                                                                                  978867764.720
                      978867760


                      978867750
                                           978867746.947

                      978867740
                                  Oct-04

                                            Nov-04

                                                     Dec-04

                                                              Jan-05

                                                                       Feb-05

                                                                                Mar-05

                                                                                         Apr-05

                                                                                                   May-05

                                                                                                            Jun-05

                                                                                                                      Jul-05

                                                                                                                               Aug-05

                                                                                                                                        Sep-05

                                                                                                                                                 Oct-05

                                                                                                                                                          Nov-05

                                                                                                                                                                   Dec-05

                                                                                                                                                                             Jan-06

                                                                                                                                                                                      Feb-06

                                                                                                                                                                                               Mar-06

                                                                                                                                                                                                        Apr-06

                                                                                                                                                                                                                 May-06

                                                                                                                                                                                                                          Jun-06

                                                                                                                                                                                                                                   Jul-06

                                                                                                                                                                                                                                            Aug-06

                                                                                                                                                                                                                                                     Sep-06

                                                                                                                                                                                                                                                              Oct-06

                                                                                                                                                                                                                                                                       Nov-06

                                                                                                                                                                                                                                                                                Dec-06

                                                                                                                                                                                                                                                                                         Jan-07

                                                                                                                                                                                                                                                                                                  Feb-07

                                                                                                                                                                                                                                                                                                           Mar-07

                                                                                                                                                                                                                                                                                                                    Apr-07
                                                                                                                                                                            TIME




                                  Rate of gravity: 22.72±2.78μ-Gal/year
                                  Equivalent rate of subsidence: 7.6
                                  cm/year
                                                                                                                                                                                      Apr-07                                                                                                                              Apr-07
                                                                                                                                                                                                                                                      190.35
                                                                                               184.51




                                                                                                                                                                                      Mar-07                                                                                                                              Mar-07
                                                                                                                                                                                      Feb-07                                                                                                                              Feb-07
                                                                                                                                                                                      Jan-07                                                                                                                              Jan-07
                                                                                                                                                                                                                                                    179.88
                                                                                                                                82.50




                                                                                                                                                                                      Dec-06                                                                                                                              Dec-06
                                                                                                                                                                                      Nov-06                                                                                                                              Nov-06
                                                                                                                                                                                      Oct-06                                                                                                                              Oct-06
                                                                                                                                                                                      Sep-06                                                                                                                              Sep-06
                                                                                                                 129.35




                                                                                                                                                                                                                                                                 141.45




                                                                                                                                                                                      Aug-06                                                                                                                              Aug-06
                                                                                                                                                                                      Jul-06                                                                                                                              Jul-06
                                                                                                                                                                                      Jun-06                                                                                                                              Jun-06
                                                 Adjusted Gravity Change at WTES




                                                                                                                                                                                                      Adjusted Gravity Change at PKBD
Gravity values Changes along Taiwan High Speed




                                                                                                                                                                                      May-06                                                                                                                              May-06
                                                                                                                                                                                      Apr-06                                                                                                                              Apr-06
                                                                                                                                                                                      Mar-06                                                                                                                              Mar-06
                                                                                                                                                                                               TIME




                                                                                                                                                                                                                                                                                                                                   TIME




                                                                                                                                                                                      Feb-06                                                                                                                              Feb-06
                                                                                          193.82




                                                                                                                                                                                                                                                                144.45




                                                                                                                                                                                      Jan-06                                                                                                                              Jan-06
Railway (micro-Gal) using relative gravimetry




                                                                                                                                                                                      Dec-05                                                                                                                              Dec-05
                                                                                                                                                                                      Nov-05                                                                                                                              Nov-05
                                                                                                                                                                                      Oct-05                                                                                                                              Oct-05
                                                                                                                                                                                      Sep-05                                                                                                                              Sep-05
                                                                                                                                                                                      Aug-05                                                                                                                              Aug-05
                                                                                                                                                                                      Jul-05                                                                                                                              Jul-05
                                                                                                                                                                                      Jun-05                                                                                                                              Jun-05
                                                                                                                                                                -27.99




                                                                                                                                                                                                                                                                                                    -24.10




                                                                                                                                                                                      May-05                                                                                                                              May-05
                                                                                                                                                                                      Apr-05                                                                                                                              Apr-05
                                                                                                                                                                                      Mar-05                                                                                                                              Mar-05
                                                                                                                                                                                      Feb-05                                                                                                                              Feb-05
                                                                                                                                                                                      Jan-05                                                                                                                              Jan-05
                                                                                                                                                    0.00




                                                                                                                                                                                                                                                                                             0.00




                                                                                                                                                                                      Dec-04                                                                                                                              Dec-04
                                                                                   250


                                                                                         200


                                                                                                           150


                                                                                                                          100


                                                                                                                                        50


                                                                                                                                                    0


                                                                                                                                                                         -50


                                                                                                                                                                               -100




                                                                                                                                                                                                                                        250


                                                                                                                                                                                                                                              200


                                                                                                                                                                                                                                                               150


                                                                                                                                                                                                                                                                          100


                                                                                                                                                                                                                                                                                  50


                                                                                                                                                                                                                                                                                             0


                                                                                                                                                                                                                                                                                                             -50


                                                                                                                                                                                                                                                                                                                   -100
                                                                                                                 Variation (micro-Gal)                                                                                                                               Variation (micro-Gal)
                                                                                                        49.94




                                                                                                                                                                                      Apr-07
                                                                                                                                                                                      Mar-07
                                                                                                                                                                                      Feb-07
                                                                                                                                                                                      Jan-07
                                                                                                                                                                                      Dec-06




                                                                                                                                                      -9.10
                                                                                                                                                                                      Nov-06
                                                                                                                                                                                      Oct-06
                                                                                                                                                                                      Sep-06




                                                                                                                                                           -11.08
                                                                                                                                                                                      Aug-06
                                                                                                                                                                                      Jul-06
                                                                                                                                                                                      Jun-06
                                                 Adjusted Gravity Change at KTES
                                                                                                                                                                                      May-06
                                                                                                                                                                                      Apr-06
                                                                                                                                                                                      Mar-06




                                                                                                                                                                                               TIME
                                                                                                                                                                                      Feb-06
                                                                                                                                                                                      Jan-06




                                                                                                                                             0.00
                                                                                                                                                                                      Dec-05
                                                                                                                                                                                      Nov-05
                                                                                                                                                                                      Oct-05
                                                                                                                                                                                      Sep-05
                                                                                                                                                                                      Aug-05
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                                                                                                                                                                                      May-05
                                                                                                                                                                                      Apr-05
                                                                                                                                                                                      Mar-05
                                                                                                                                                                                      Feb-05
                                                                                                                                                                                      Jan-05
                                                                                                                                                                                      Dec-04




                                                                                   80


                                                                                          60


                                                                                                                 40


                                                                                                                                  20


                                                                                                                                             0


                                                                                                                                                                     -20


                                                                                                                                                                               -40
                                                                                                                 Variation (micro-Gal)
                    Gravity change over Mt Yangming: sign of
                     volcano eruption or hydrological effect?
                               Gravity change and equivalent vertical motion
           50
                             10.607 ug/year
                dg/dt=39.589 ±
                                dU/dt=-23.274 ±
                                6.236 cm/year                                  rise of magma causes gravity increase
dg(ugal)




           0




      -50
       2006          2006.25     2006.5   2006.75   2007    2007.25   2007.5
   Gravity change due to Pingtung earthquake

• Model: viscoelastic-gravitational dislocation theory (Wang,2006)
• Result
               Predicted     Observed
Vertical motion: -1.2 cm        -2.1 cm
Gravity change: 2.4 micro-gal 5 micro-gal
  Superconducting gravimetry




SG048                   SG049
Superconducting gravity stations in GGP
Tidal spectrum from two years of raw
        gravity records of T48

                          Two clusters are present at
                          the semi-diurnal and
                          diurnal wave bands.
Gravity changes: observations by SG T48
              and models

                          Without the body tide
                          and ocean tide gravity
                          effects) and modeled
                          gravity changes at HS.
                          The time starts from
                          March 2006.
Amplitudes and phases of the annual gravity change at HS
                from different sources
          Source                   Amplitude   Phase
                                   (μgal)       (˚)
          Observation (T48)        6.24        -26.07
          Ground water             5.48        -88.95
          Atmosphere               2.98        -135.34
          Soil moisture            1.41        -14.04
          Polar motion             1.58        -13.98

Modeled and FG5-observed rates of gravity change (in
μgal /year) at HS
         Source                                   Rate
         Atmosphere                              -1.289
         Ground water                             3.778
         Soil moisture                            0.491
         Polar motion                             0.435
         Free-air motion of site                 -0.700
         Total                                    2.715
         FG5 observations                         2.206
Gravity shifts due to earthquakes around
              Taiwan at HS
         Date          Distance Depth (km) Magnitude of   Gravity shift
    (month/day/year)    (km)                earthquake       (μgal)
       04/01/06          214         9          6.2           1.19
       04/15/06          223        17          6.0          -0.17
       04/28/06          109         8          5.2          -0.61
       07/28/06          170        49          6.0           1.01
       08/27/06          197       145          6.0           0.00
       10/12/06          181        44          5.8          -0.13
       12/14/06          120         7          4.8          -1.10
       12/23/06          138        10          5.4            0.48
       12/26/06          296        44          7.0           -0.41
       01/16/07          191        21          5.4            0.10
       01/25/07          226        26          6.2           -0.31
       05/12/07          101        44          4.9           -0.41
       07/23/07          155        31          6.0           -0.41
       08/09/07          201         4          5.9           -1.41
       09/06/07          155        54          6.6            0.60
       10/11/07           92        80          5.2            0.27
       10/17/07          176        42          5.7            0.01
       11/28/07           91        69          5.4           -0.94
Co-seismic gravity change, given as a jump (step
function) in the SG gravity records at HS, due to
      the earthquake on September 6, 2007
                   Conclusions

• Space-based and terrestrial based gravimetry has
  gained tremendous progress in the past few decades,
  both in spatial-temporal resolutions and noise
  reduction
• Applications of gravity measurements are to be
  exploited, locally and world-wide, in geodesy,
  geophysics and oceanography
  International Workshop on Gravity, GPS and
    Satellite Altimetry Observations of Tibet,
            Xinjiang and Siberia (TibXS)
• Date: August 20-22, 2009
• Venue: Urumqi, Xinjiang, China
• Objective: Bring together scientists to present
  their research results and thoughts in the
  fields of, but not limited to, geodynamics,
  climate change, hydrology, over Tibet, Xinjiang
  and Siberia using the tools of gravimetry, GPS
  and satellite altimetry
          Organizer and committee
• Organizer and sponsor
School of Geodesy and Geomatics/Key Laboratory of Geospace Environment
    and Geodesy, Wuhan University, Wuhan 430079, China
Department of Civil Engineering, National Chiao Tung University, Hsinchu 300,
    Taiwan
Bureau Seismology Xinjiang, (Beijing South Road 42), Urumqi 830011, China
Bureau Survey Xinjiang, (Zhongshan Road 45), Urumqi 830002, China
International Association of Geodesy, Commission SC2.5 (satellite altimetry)
• Scientific committee:
C Hwang, B Chao, CK Shum, H Hsu, W Sun, Q Wang, K Heki and more

				
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