Abstract
Ocean surface winds and currents are tightly coupled, essential climate variables, synoptic measurements of which require a remote sensing approach. Global measurements of ocean vector winds have been provided by scatterometers for decades, but a synoptic approach to measuring total vector surface currents has remained elusive. Doppler scatterometry is a coherent burst-scatterometry technique that builds on the long heritage of spinning pencil beam scatterometers to enable the wide-swath, simultaneous measurement of ocean surface vector winds and currents. To prove the measurement concept, NASA funded the DopplerScatt airborne Doppler scatterometer through the Instrument Incubator Program (IIP) and Airborne Instrument Technology Transition (AITT) program. DopplerScatt has successfully shown that pencil beam Doppler scatterometry can be used to form wide swath measurements of ocean winds and currents, and has increased the technology readiness level of key instrument components, including: Ka-band pulsed radar hardware, optimized scatterometer burst-mode operation, calibration techniques, geophysical model functions, and processing algorithms. With the promise and progress shown by DopplerScatt, and the importance of air-sea interactions in mind, the National Academy’s Decadal Survey has targeted simultaneous measurements of winds and currents from a Doppler scatterometer for an Earth Explorer class spaceborne mission. Besides DopplerScatt’s place as a technology stepping stone towards a satellite mission, DopplerScatt provides scientifically important measurements of ocean currents and winds (400 m resolution) and their derivatives (1 km resolution) over a 25 km swath. These measurements are enabling studies of the submesoscales and air-sea interactions that were previously impossible, and are central to the upcoming NASA Earth Ventures Suborbital-3 Submesoscale Ocean Dynamics Experiment (S-MODE). This paper summarizes the development of DopplerScatt hardware, systems, calibration, and operations, and how advances in each relate to progress towards a spaceborne Doppler scatterometer mission.
Highlights
At large scales, ocean currents play an important role in governing global climate balance and weather, including the dynamics of El Niño and the Pacific Decadal Oscillation
DopplerScatt’s first engineering flights were over the Rosamond dry lakebed in Southern California, where radar corner reflectors exist for calibration
Analysis on the Shelf (SPLASH) experiment were flown with some coordination with the deployment of Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) drifters [16], the majority of drifters were deployed farther out in the Gulf of Mexico and/or carried by prevailing currents away from the DopplerScatt flight area
Summary
Ocean currents play an important role in governing global climate balance and weather, including the dynamics of El Niño and the Pacific Decadal Oscillation. Ocean surface currents play a significant role in the dissipation of energy and heat in the upper ocean [1], pollution dispersion (e.g., oil spills), ocean biology (via nutrient and phytoplankton advection and up/downwelling) [2], and coastal shipping. Despite their scientific and operational importance, global total ocean currents are not presently measured, besides their geostrophic approximation from satellite altimetry, which is restricted to scales of about 100 km and time scales of weeks [3]. Drastic improvements in our understanding of wind-driven upwelling, boundary layer dynamics, equatorial circulation, flux transport, and nutrient and pollutant advection [8] are enabled by the simultaneous measurement of submesoscale winds and total currents
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