Title of Paper: The Wide-Swath Ocean Altimeter: Interferometry
for Global Ocean Mapping
Principal Author: Dr. Brian Pollard
Abstract: The recent Shuttle Radar Topography Mission
(SRTM) has demonstrated the capability for global interferometric topographic
mapping with meter level accuracy and 30 meter spatial resolution. The next
challenge in radar interferometry is the measurement of ocean topography: the
global characterization of ocean mesoscale eddies requires global coverage
every 10 days, with centimetric height accuracy, and a spatial resolution of 15
km.
Over the past three years, under the NASA Instrument Incubator Program
(IIP), we have developed an instrument concept that combines a conventional
nadir altimeter suite with an interferometer to meet the above requirements.
The centimetric accuracy levies very stringent requirements on the knowledge
and stability of the interferometric
baseline and antennas. We show that these requirements can be met using a
very stable, stiff mast and novel, lightweight reflectarray antenna designs,
combined with a post-collection calibration scheme that uses the ocean surface
itself as a calibration reference. We present the predicted stability
performance of the mast and antenna, and discuss the results of detailed
studies that demonstrate our ability to meet the above height accuracy
requirements.
The desire to fly this instrument in conjunction with a nadir-looking
altimeter/radiometer suite on a small spacecraft bus poses further challenges
for our design in terms of mass, power, and data rate. We discuss our
lightweight, low power solutions to those problems, including the ultra-light,
deployable reflectarray antennas for the interferometer; a novel five frequency
feed horn for the radiometer and altimeter; an ultra-low mass and power MMIC
three frequency radiometer; and an onboard data processor. Finally, we present
the integrated measurement concept, and show how it could fit within the
constraints of the upcoming Jason instrument and bus.