Geodetic Science 8873 (GS8873)
Advanced Satellite Geodesy
(http://geodesy.geology.ohio-state.edu/course/gs873)
Autumn Semester 2013
Instructor: C.K. Shum (ckshum@osu.edu)
TAs: Chunli Dai (dai.56@buckeyemail.osu.edu)
Junkun Wan* (wan.70@buckeyemail.osu.edu)
Laboratory No. 2*
Analysis of TOPEX/POSEIDON Satellite Radar Altimetry Data
Backgrounds
(1) TOPEX/POSEIDON
NASA website: http://sealevel.jpl.nasa.gov/missions/topex/
WIKI: http://en.wikipedia.org/wiki/TOPEX/Poseidon
Launched in 1992, TOPEX/POSEIDON is a joint venture between NASA and CNES that
measured ocean surface topography with an accuracy of 4.2 cm or better, enabled scientist to
forecast the 1997-1998 EL Nino, and improved understanding of ocean circulation and its effect
of global climate. While a 3-year prime mission was planned, with a 5-year store of expendables,
TOPEX/ POSEIDON delivered a much longer record of 13+ years of sea level record from space.
(2) RADS
Website: http://rads.tudelft.nl/rads/rads.shtml
Manual: http://rads.tudelft.nl/rads/radsmanual.pdf
The Radar Altimeter Database System (RADS) is Delft Technical University (DUT)/DEOS’ effort
[Remko Scharroo et al.] in establishing a harmonized, validated and cross-calibrated sea level data
from satellite altimeter data. It operates within the framework of the Netherlands Earth
Observation NET work NEONET, an internet facility, funded by the Dutch government (BCRS and
SRON), for exploitation of remote-sensing expertise and data. RADS is an open source application
which is widely used and supported previously by NOAA/Laboratory for Satellite Altimetry, and
DEOS, and presumably will now also be support by EUMETSAT, Germany.
Equation for Sea Surface Height Anomaly (SSHA) (Altika_Products_handbook_v2.1.pdf)
Sea Surface Height Anomaly (SSHA) = altitude of satellite (alt) – corrected altimeter range (range)
– ionospheric correction (iono_cor) – dry tropospheric correction (dry_tropo_corr) – wet
tropospheric correction (wet_tropo_corr) – sea state bias correction (sea_state_bias) – solid
earth tide height (solid_earth_tide) – geocentric ocean tide height solution (ocean_tide_sol) –
geocentric pole tide height (pole_tide) – inverted barometer height correction (inv_bar_corr) –
high frequency fluctuations of the sea surface topography (hf_fluctuations_corr) – mean sea
surface (mean_sea_surface)
RADS Scripts
Running script /0/share/wan.70/GS8873/tx/txa_rads2asc
For gridding script, check for the command rads2grd in the manual
Namelist for Setting Parameters /0/share/wan.70/GS8873/tx/getraw_tx.nml
Header file for TOPEX: /0/share/wan.70/GS8873/tx/txa.h
Fortran code /0/share/wan.70/GS8873/tp/
Questions
The fundamental objective is to for the class to learn RADS to be proficient in its application
for study geodesy and oceanography. Follow the instructions to process one 10-day repeat
cycle of TOPEX/POSEIDON Geophysical Data Record data using RADS, generate the data and
plots for Cycle 10 & Cycle 100 for the:
(a) averaged mean sea surface (MSS) model based on Cycles 10 and 100, by combining the
sea surface height using the two values. How is this computed model different from the
MSS or geoid models packed on the RADS data record (EGM08 geoid, DTU10 MSS, CLS11
MSS)? Choose one geoid model and one MSS model to illustrate and explain the
differences between these models and your computed model based on two cycles of data
only. Explain what would be a better approach to generate the averaged MSS model, i.e.,
as DTU10 or CLS11 MSS model was computed.
(b) sea surface height anomalies (SSHA=SSH-MSS, the result may be different based on MSS
you choose). How does one represent this quantity and interpretations? Compute the
standard deviations of the SSHA of each of the two cycles (Cycle 10 and Cycle 100) and plot
the results. Conduct a physical explanation of the results. Is Cycle 10 SSHA different from
Cycle 100, if so, why?
(c) wet troposphere corrections (from the radiometer or observed delay, or from ECMWF
model) for both cycles. What are the differences and can they be explained?
(d) ionosphere corrections (from the dual-frequency measurement, and from smoothed
dual frequency measurement or NIC09) for both cycles. What are the differences and can
they be explained?
(e) ocean tide corrections (from FES2004 model, or from GOT4.9 model) for both cycles.
Plot and explain the total tidal amplitudes from one of the models in both cycles, are there
any differences? Pick Cycle 10, what are the differences between the two tide models, and
can you explain the difference?