slide1
Download
Skip this Video
Download Presentation
Institut für Erdmessung (IfE), Leibniz Universität Hannover, Germany

Loading in 2 Seconds...

play fullscreen
1 / 21

Institut für Erdmessung (IfE), Leibniz Universität Hannover, Germany - PowerPoint PPT Presentation


  • 115 Views
  • Uploaded on

Quality Assessment of GOCE Gradients Phillip Brieden , Jürgen Müller living planet symposium 28 June – 2 July 2010 | Bergen | Norway. Institut für Erdmessung (IfE), Leibniz Universität Hannover, Germany. Introduction. Power Spectral Density (PSD ) of GOCE GG. Correct Data?. Contents.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Institut für Erdmessung (IfE), Leibniz Universität Hannover, Germany' - thomas-kirby


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Quality Assessment of GOCE GradientsPhillip Brieden, Jürgen Müllerliving planet symposium28 June – 2 July 2010 | Bergen | Norway

Institut für Erdmessung (IfE), Leibniz Universität Hannover, Germany

introduction
Introduction

Power Spectral Density (PSD)of GOCE GG

CorrectData?

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

contents
Contents
  • Filtering of GGT L1b data
    • Why ?
    • The Method
    • Results
  • Two Validation Methods
    • Reference Gradient approach
    • Cross-Over (XO) approach
    • Basic ideas
    • Results based in real GOCE data
  • Conclusions
  • Hanover is part of the official Cal/Val team of ESA.
  • data access
  • preliminary results!

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

comparison in gradiometer reference frame measured gg gpm e g egm 08
Comparison in Gradiometer Reference Frame: Measured GG – GPM (e.g. EGM 08)

> 0.5 E

GOCE Gravity Gradients

validation within MBW filtering is necessary!

long-wavelength errors(caused by accelerometer-drift)

1 E=10-9 1/s²

MBW: between 0.005 and 0.1 Hz

0 E

 Quality Assessment at the level of some mE

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

filtering ggt components the idea
Filtering GGT Components - The Idea

GOCE

high-pass

+

GPM

low-pass

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

filtering used filter
Filtering - Used Filter
  • Finite Impulse Response filter (FIR)
  • Butterworth-filter
    • high-pass (GOCE)
    • low-pass (GPM)
    • cut-off frequency: 5 mHz

 filtering and combination in time domain!

  • Additional filtering of the combined information
    • Butterworth-filter again
    • cut-off frequency: 50 mHz spherical harmonic degree l ≈ 270
    • GOCE-only gravity field solutions up to degree ~250

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

filtering result 1
Filtering – Result (1)

GOCE

measurements

high-pass filtered GOCE

low-passfiltered EGM08

MBW

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

filtering result 2
Filtering – Result (2)

GOCE

measurements

filtering result

time series used for analyses

difference:

GOCE – filter result

  • Selection of best cut-off frequency?

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

reference gradients from gravity anomalies reference gradient approach
Reference Gradients from Gravity Anomalies (Reference Gradient Approach)

terrestrial data (incl. airborne gravimetry and satellite altimetry) of well-surveyed regional areas combined with global geopotential model (GPM)

Δg´ = ΔgG – ΔgM – ΔgRTM

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

reference gradient approach the evaluation area
Reference Gradient ApproachThe Evaluation Area
  • regional area: reference values (3D grid) available
    • residual values related to a GPM + terrestrial data
    • altitude interval: 5 km
    • resolution: 6 min

latitude φ: 40.05° - 54.95°

longitude λ: 00.05° - 19.95°

altitude:

230.0 km - 280.0 km

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

reference gradient approach calculation of the differences
Reference Gradient ApproachCalculation of the Differences
  • regional area: reference values (3D grid) available
    • residual values related to a GPM + terrestrial data
    • altitude interval: 5 km
    • resolution: 6 min
  • select GOCE data across the regional area
  • 3D-spline interpolation of reference gradients (Tij) in gradiometer position
  • restore-part of the reference gradients into the interpolation point & restore-step Tij Vij
  • analysis of the differences:
  • analysis for each track

ΔVijRG= VijGOCE – VijRefGrad

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

reference gradient approach differences v ij rg
Reference Gradient ApproachDifferences ΔVijRG
  • differences ΔVijRG [E]
    • color-coded (different scales!)
    • mean value reduced (each track)

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

reference gradient approach psd of gg differences for all track pieces

spherical harmonic degree l ≈ 270

Reference Gradient ApproachPSD of GG-differences for all track pieces

average of PSDs

GOCE requirements

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

the cross over xo approach
The Cross-Over (XO) Approach

Basic idea

Identical measurement position

  • identical gravity gradient: Vij,1 = Vij,2

Attention!

No repeated measurement positions!

  • differences in attitude and altitude that have to be reduced
  • GPM used for reduction

gravity gradient differences in XO  to be analyzed

ij = {xx, xy, xz, yy, yz, zz}

ΔVijXO = Vij1 – Vij2 – redijGPM

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

y

x

z

x

y

z

cross over xo approach results 1
Cross-Over (XO) ApproachResults (1)
  • Statistical results
    • Set up a threshold of maximum difference in all XOs
    • Percentage of differences that exceed the threshold
    • Distinction for each GGT component main diagonal components

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

cross over xo approach results 2
Cross-Over (XO) ApproachResults (2)

GGT component: XXthreshold: 11 mE

‘outliers’: 0.66 %

[mE]

  • Almost all ‘outliers’ have differences near the threshold
    • XO-approach is very suitable for GOCE data validation
    • Good data quality of GOCE gravity gradients

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

conclusions
Conclusions
  • Longer-wavelength errors require a filtering of GG measurements
    • replacement of long wavelength by GPM information
    • selection ‘the best’ cut-off frequency
  • Reference Gradient Approach
    • results perfectly meet the requirements
  • Cross-Over (XO) Approach
    • only scattered unevenly distributed outliers 

Both approaches…

  • confirm the somewhat higher noise level of Vzz compared to the other main diagonal components Vxx and Vyy
  • suitable for the validation of GOCE GG
  • confirm the very good quality of GOCE GG

good data quality

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

additional slides
Additional Slides

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

differences along one track crossing the evaluation area
Differences Along One Track Crossing the Evaluation Area

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

different gpms xo results

Cut-off frequencies: 5 mHz - lower line50 mHz - upper line

Different GPMs XO-Results

different max-degree  no significant differences

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

different cut off frequencies
Different Cut-Off Frequencies

living planet symposium 28 June – 2 July 2010 | Bergen | Norway

ad