On the Optimal Design of Doppler Scatterometers

Abstract

Pencil-beam Doppler scatterometers are a promising remote sensing tool for measuring ocean vector winds and currents from space. While several point designs exist in the literature, these designs have been constrained by the hardware they inherited, and the design is sub-optimal. Here, guidelines to optimize the design of these instruments starting from the basic sensitivity equations are presented. Unlike conventional scatterometers or pencil-beam imagers, appropriate sampling of the Doppler spectrum and optimizing the radial velocity error lead naturally to a design that incorporates a pulse-to-pulse separation and pulse length that vary with scan angle. Including this variation can improve radial velocity performance significantly and the optimal selection of system timing and bandwidth is derived. Following this, optimization of the performance based on frequency, incidence angle, antenna length, and spatial sampling strategy are considered. It is shown that antenna length influences the performance most strongly, while the errors depend only on the square root of the transmit power. Finally, a set of example designs and associated performance are presented.

Integrated Observations of Global Surface Winds, Currents, and Waves: Requirements and Challenges for the Next Decade

“…In particular, the high-sensitivity of the cross-polarization signal inspired future mission concepts (Fois et al, 2015), and EUMETSAT (European Organization for the Exploitation of Meteorological Satellites) together with ESA (European Space Agency) now plan to add a cross-polarized channel to the next generation of operational scatterometer missions (i.e., the next Polar System Second Generation) dedicated to the ocean surface wind measurement at medium resolution (Stoffelen et al, 2017). Other mission concepts (e.g., Ardhuin et al, 2018;Rodriguez, 2018;Gommenginger, 2019) also suggest relying on Doppler and radar backscatter measurements at multiple angles and targeting combined wind, waves, and current measurements.…”

Remotely Sensed Winds and Wind Stresses for Marine Forecasting and Ocean Modeling

“…Planned advances include the use of Doppler information to improve accuracy in future Indian instruments and upgraded antenna technology for modest improvements of resolution and polarization in the follow-on to the ASCAT series of instruments . One goal of the remote sensing community is to add Doppler capability to future scatterometers (Rodriguez, 2018;Rodriguez et al, 2019, this issue) and altimeters (Ardhuin et al this issue) in a manner that allows for measurements of surface currents. Traditionally, surface currents are poorly defined, thought of as currents at the surface or in the upper few meters, and more often as currents in the mixed layer (GCOS, 2015;Belward et al, 2016).…”

The Winds and Currents Mission Concept

“…The measurement requirements lead to a sensor that has the following characteristics: ability to measure currents and winds simultaneously; large swath (∼ 1, 800 km); high spatial resolution (< 5 km); continuous spatial coverage without significant gaps; current speed errors better than 50 cm/s. Rodriguez (2018) has proposed a design approach for WaCM that meets these requirements. Some highlights include:…”

“…The peak output power is 100 Watts (solid line), 400 Watts (circles), and 1.5 kWatts (squares). From Rodriguez (2018).…”