The Winds and Currents Mission

The proposed Winds and Current Mission (WaCM) is designed to collect data on ocean winds and currents simultaneously through satellite observance. While QuikSCAT and ASCAT had the ability to collect wind data, they could not sufficiently sample surface currents. Current measurement requires a new system be built. Because the winds and currents in oceans affect ocean circulation, fluxes, transportation of heat, nutrients, and gases, and atmospheric forcing, WaCM will improve understanding of the following:

1. Ocean Atmosphere Interactions
• Ocean heat uptake and carbon outgassing (carbon released by the Earth)
• Upwelling mechanisms (the cycle where colder, nutrient-filled, denser water goes to the surface, pushing the nutrient-free water underneath)
2. Ocean Atmosphere Biosphere Interactions
• Ocean productivity and ecosystems
3. Ocean Atmosphere Cyrosphere Interactions
• The cycle of fresh water coming from melting ice sheets
4. Other
   • Weather forecasting
   • Marine debris and pollution tracking
   • Shipping, coastal safety, and coastal fishery assessments
   • Ice cover and iceberg tracking, which is useful for shipping and climate monitoring

WACM will be able to measure the surface wind velocities, the current velocities, the curl of the wind stress (which is error prone), and the curl of the surface currents (which is error prone). In order to do this, the satellite has the following requirements:

• global coverage
• sampling rate of 1-2 times a day
• simultaneous current and wind sampling
• current measuring precision of 60 cm/s; wind measurement accuracy of better than 1 m/s
• high spatial resolution for:
1. avoiding land/rain contamination
2. computing spatial derivatives
3. resolving finer resolution features like wind and currents
4. consistency between wind and current estimates
5. discriminating between land/ice and water

To fulfill these requirements, the satellite employs a Ka-band (vertically polarized) Doppler scatterometer with ~5 m by 0.3 m rotating pencil-beam antenna. The scatterometer pulse repetition frequency that varies with the antenna azimuth angle. The sensor measures wind and currents at the same time over a large swath (~1800 km) at a high spatial resolution (<5 km) with continuous spatial coverage. Figure 1 shows the effects of the swath and measurement noise have on the RMS error and resolution, and clearly shows that a wider swath and a lower measurement noise produces the most accurate image.

Factors included in designing the WACM mission include:

1. Scatterometers can only provide adequate data for winds of 25km or less. While higher wind speeds can be estimated, it limits the spatial resolution.
• Solution: using a Ka-band instead of a Ku-band
2. The currents are measured proportional to the line of sight, but the currents at 10m deep are more commonly used.
• Solution: Stoke's drift can be estimated using the wind (which is another reason why currents and winds need to be measured together) and that can provide the data for the 10m depth that we want.

A paper describing the WACM mission in more detail can be found here

Citation: Rodríguez E, Bourassa M, Chelton D, Farrar JT, Long D, Perkovic-Martin D and Samelson R (2019) The Winds and Currents Mission Concept. Front. Mar. Sci. 6:438. doi: 10.3389/fmars.2019.00438