1. Coastal Altimetry Challenges
CIOSS Science Review Meeting
Dynamics Working Group
Oregon State University
September 8-9, 2005
John Lillibridge
NOAA Laboratory for Satellite Altimetry

2. Altimetry Issues in the Coastal Regime
Coverage & space/time sampling
Proximity to the coast
Contamination of radiometer by land
Small-scale tidal variations
Sept. 8-9, 2005
CIOSS Science Review - Dynamics WG

3. Multi-Mission Altimetric Coverage
Four concurrent altimeters
Topex (black) : 10 day repeat
Jason-1 (red) : 10 day repeat
GFO (green) : 17 day repeat
Envisat (blue) : 35 day repeat
Radar Altimeter Database System
All data & corrections within RADS
Normally data provided at 1 Hz (7 km)
Capable of handling 10 Hz high-rate data
Does NOT account for radial orbit errors
Coarse sampling near shore
Assimilation into coastal models
Will only get worse as we lose Topex, GFO…
Sept. 8-9, 2005
CIOSS Science Review - Dynamics WG

4. Proximity to the Coastline
1 Hz averaged data (red)
7 km spacing too coarse
Data gaps due to editing or radiometer contamination
10 Hz high-rate data (black)
700 m spacing - sufficient?
Careful near shore editing
Agility of altimeter acquiring sea surface after land/sea transition
Waveform retracking
Sept. 8-9, 2005
CIOSS Science Review - Dynamics WG

5. CIOSS Science Review - Dynamics WG
Waveform Retracking
10 Hz altimeter waveforms from Geosat Geodetic Mission
Ascending ground track (black) leaves coast near Crescent City, CA
Color illustrates return power of radar return ‘echo’:
Lo-power pre-arrival noise (purple)
Track point in leading edge (blue)
Hi-power trailing plateau (yellow/green)
Correct height data when track point not centered in middle of waveform
Track crosses Pt. St. George and reacquires sea surface to the North
Crescent City
Sept. 8-9, 2005
CIOSS Science Review - Dynamics WG

6. Radiometer Wet Troposphere Correction
Radiometer footprint of ~50 km > radar’s
Land contamination increases radiometer wet correction
Workarounds:
Use model wet
Extrapolate to coast with Dwet constant
Coastal met. model?
Sept. 8-9, 2005
CIOSS Science Review - Dynamics WG

7. CIOSS Science Review - Dynamics WG
Coastal Tides
courtesy C. K. Shum
Largest errors in global models on shelf
Small scale variability
Non-linear tides: M4 and other species
Need regional tide models embedded in open-ocean model
Sept. 8-9, 2005
CIOSS Science Review - Dynamics WG

8. CIOSS Science Review - Dynamics WG
Future Work
Hi-Rate 10 or 20 Hz RADS database for coastal altimetry
Waveform retracking tailored to land/sea transition
Refined radiometer wet tropo. correction & flagging
Regional/Coastal tide models melded with global model
Orbit error estimation prior to multi-satellite assimilation
Sept. 8-9, 2005
CIOSS Science Review - Dynamics WG