Monitoring North American Geoid Change

Progress in Geoid Modelingfrom Satellite Missions

2009 Workshop on Monitoring North American Geoid ChangeBoulder, Colorado

21-23 October 2009

John RiesCenter for Space Research

The University of Texas at Austin

Monitoring North American Geoid Change

• Mission Highlights

– Geoid models

• Mean fields: GGM03C, EIGEN-GL05C, ITG-GRACE03SEGM2008

• Time variable fields (86 monthly solutions through August 2009)

– Nearly 100 % of scientific measurements for over seven years have been collected and analyzed

• NASA 2009 Senior Review successful

– Extension to 2011 approved by NASA

– DLR approved mission funding through 2009• Last steps being taken to assure funding past 2009

• Flight Segment Generally Robust

– All systems in nominal operation

– Certain sub-systems are single-string on both s/c

– New thermal regimes to conserve battery life

– Instrument performance continues to meet mission requirements

GRACE Mission StatusOrbitLaunched: March 17, 2002 Over 7 years in orbit

Initial Altitude: 500 km Current Altitude: ~460 km (-10 m/day)Inclination: 89º Eccentricity: ~0.001Separation Distance: ~220 kmNon-Repeat Ground Track, Earth Pointed, 3-Axis Stable

Predicted Lifetime: 2013+

Monitoring North American Geoid Change

Progress from EGM96

GFZ05C=EIGEN-GL05C

more power

improvement

Monitoring North American Geoid Change

Improvement in GRACE-only Models

mgal

GGM01S-EGM96(deg/order 120)

GGM03S-EGM96(deg/order 120)

GGM02S-EGM96(deg/order 120)

Scale is +/- 10 mgal

Monitoring North American Geoid Change

Progress in Gravity Determination from Space

GGM01S(111 days of GRACE data)

GGM03S(4 years of GRACE data)

Monitoring North American Geoid Change

Estimated Total Geoid Error

GFZ05C=EIGEN-GL05C

Monitoring North American Geoid Change

Degree-banded GPS Leveling TestLimiting the test to a selected degree range using a degree-banded approach

(Huang et al., 2002), 1149 GPS/leveling points over Canada were compared to the GGM02C, EIGEN-GL04C, and EGM2008 geoids

12

13

14

15

16

17

18

19

80 120 160 200 240 280 320 360

Canada

GGM02C

GFZ04C

EGM08

RM

S (

cm)

Degree

11.5

12

12.5

13

13.5

14

14.5

15

15.5

80 120 160 200 240 280 320 360

US

GGM02C

GFZ04C

EGM08

RM

S (

cm)

Degree

With EGM08, test now appears to be limited by GPS/leveling data errors, not geoid

Monitoring North American Geoid Change

Short Wavelength Marine Geoid ResidualsEIGEN-GL04C

The residuals are the difference between a ‘high-frequency DOT’ defined as (GSFCMSS00 – geoid) and the same DOT smoothed to ~900 km

Scale is +/- 25 cm

‘Blending’ space-based and terrestrial gravity information smoothly and without ‘artifacts’ has been one of the most significant challenges

(to degree/order 360)

Monitoring North American Geoid Change

Short Wavelength Marine Geoid ResidualsEIGEN-GL05C

The residuals are the difference between a ‘high-frequency DOT’ defined as (GSFCMSS00 – geoid) and the same DOT smoothed to ~900 km

Scale is +/- 25 cm.

As GRACE component becomes more accurate and skill in blending the two pieces of information improves, ‘artifacts’ are greatly reduced

(to degree/order 360)

Monitoring North American Geoid Change

Short Wavelength Marine Geoid ResidualsEGM2008

The residuals are the difference between a ‘high-frequency DOT’ defined as (GSFCMSS00 – geoid) and the same DOT smoothed to ~900 km

Scale is +/- 25 cm.

EGM2008 is relatively free of ‘artifacts’ while also providing the most accurate and highest resolution marine geoid model (degree/order 2159+)

(to degree/order 360)

Monitoring North American Geoid Change

microgal

Difference between two 2-year means (2003-2004 and 2005-2006)

Secular Gravity Changes (1)

Arctic and North America Antarctic

Monitoring North American Geoid Change

Difference between two 2-year means (2003-2004 and 2005-2006)

Secular Gravity Changes (2)

Europe Asia

microgal

Monitoring North American Geoid Change

Secular Gravity Changes (3)

Long-term geoid change dueto ∆J2 ~ 0.2 mm/yr

Monitoring North American Geoid Change

Seasonal Geoid Variations

Mass variations are observed in Amazon basin with ~400 km resolution

A clear separation can be observed between the large Amazon watershed and the smaller watersheds to the north (e.g., the Orinoco

watershed), indicating that basin-scale variability is resolved.

1 mm geoid ≈ 2 cm water

Monitoring North American Geoid Change

Gravity field and steady-state OceanCirculation Explorer (GOCE)

• Launched March 2009

• Drag-free mode May 2009– Allows operation at ~270 km

• Measurement mode September 2009

• Mission lifetime ~18 months

Monitoring North American Geoid Change

Impact of GOCE on Geoid Accuracy

Combining GOCE with GRACE is expected to extend geoid resolution from space by a factor of 2 or more

Note that the long wavelength geoid information (including temporal variability) must be provided by

GRACE-type missions

Monitoring North American Geoid Change

In The Near Future

• Continue routine operations and delivery of good quality data and products

– RL05, Quick-Look fields, and other exciting developments…

– Extension of Memorandum of Understanding between NASA and DLR on extended GRACE mission operations

– Closely monitor data and products for any signs of aging or environmentally related degradation in quality

• GRACE Science Team Meeting: Nov 5-6, in Austin, TX (USA)

– http://www.csr.utexas.edu/grace/GSTM

– Registration is now open

• Looking forward to the contribution of GOCE to geoid accuracy