Wide-Swath Altimeter Science Goals. Wide Swath Altimetry targeted at measurements of: Oceanic mesoscale eddies, fronts, and boundary currents, which are the most energetic elements of the oceanic general circulation.
F = 2p D r/l = 2pB sin Q/l
h = H - r sin Q
Topex Orbit, 2 Altimeters:
150km equatorial spacing, 10 day repeat
Topex Orbit, 1 satellite, fixed yaw coverage
Wide-Swath altimeter, 10 day repeat
High resolution ocean topography measurements requires several coordinated nadir altimeters. A better coverage from a single platform can be obtained using an instrument which can image a swath instantaneously.
• The WSOA down-linked data resolution is ~12km in the along-track direction and < 500m in the cross-track direction.
• The data are are sampled every ~650m in the along-track direction
Best case land contamination: only the range cells over land are affected, but range cells over the ocean are unaffected.
Worst case land contamination: every resolution cell is affected by its fraction over the land.
GPSP antennas & front-end electronics (not shown)
bus electronics include portions of GPSP and WSOA, and all of SIES
WSOA deployable antenna and feed structure
AMR antenna & electronics
WSOA two-sided deployable mast
WSOA tip-mounted electronics
LRA mounted on nadir side of spacecraft
Single Observation Error Budget
Long wavelength (>100km)
not relevant for geodesy
Error budget based on 15 km height postings. Interferometric precision degrades by the area ratio for higher postings.
Assuming all observations can be used
Assuming 1/4 of all observations can be used
The number of observations in a 10 day period for WSOA on OSTM in fixed yaw mode is shown below.
Fixed yaw coverage occurs for about ~22 day periods every ~60 days
Along track direction
Along track direction
30 Degree Yaw
(Figures not to scale in the range direction. Number of along-track looks also underrepresented)
Although the along-track resolution is ~12 km, significant measurement overlap exists (~10 measurements/footprint)
It is possible to attempt improving the resolution through inverse or deconvolution methods
Wide-Swath Altimetry can be improved by using synthetic aperture techniques ( a la K. Raney, delayed Doppler altimeter).
SAR WSOA scenario based on sea ice instrument proposed to NASA IIP in ‘02