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.