1. Satellite Altimetry for Gravity, geoid and marine applications (MSS + LAT)
Dr Ole B. Andersen,
DTU Space, Denmark,

2. Region

4. NGS Bathymetry holdings

5. Focus

7. Part 1: Mkdata…….. Prepare data to isolate Remove EGM Remove MDT
Cross-over adjust data
You can download the excersize bundle from
ftp.space.dtu.dk/Altimetry/Gravity Excersize_June2017

8. Before Crossover adjustment
Example:
3 latitude by 10 longitude cell were found to give best removal of long wavelength errors.

9. After Crossover adjustment

10. Data are now ready for computing gravity / geoid.
Corrected the range for as many known signals as possible.
Accuracy of geoid+gravity is directly related to accuracy of sea surface height
Retracking enhances amount and quality of data
Removed Long wavelength Geoid part – will be restored.
XOVER: Limited errors + time varying signal (Long wavelength).
Small long wavelength errors can still be seen in sea surface heights.

11. Part 2. MKfft

12. GEOGRID Δh Interpolation for FFT (Using LSC)
GEOGRID (GRAVSOFT) can perform interpolation using second order Gauss Markov Covariance function.
r is the distance, C0 is the signal variance, α is the correlation length
We will try this in the excersizes………

13. Interpolated these using LSC

14. GEOFOUR From height to gravity using 2D FFT
Remembering: N = T/γ
High Pass filter operation (time with wavenumber) -> enhances high frequencies.
Optimal filter was designed to handle white noise + power spectral decay obtained using
Frequency domain LSC with a Wiener Filter (Forsberg and Solheim, 1997)
Power spectral decay follows Kaulas rule (k-4)
Resolution is where wavenumber k yields (k) = 0.5

15. Use GRAVSOFT GeoFour to convert from geoid to Gravity using FFT

16. Restore EGM to get altimetric gravity field.