CFOSAT Mission's objectives

Starting in 2018, the CFOSAT satellite’s mission will be to study the characteristics of ocean surface winds and waves.

Developed jointly by CNES and the China National Space Administration (CNSA), CFOSAT will carry two radar instruments: SWIM (Surface Waves Investigation and Monitoring), a wave scatterometer supplied by CNES; and SCAT (wind SCATterometer), a wind-field scatterometer supplied by CNSA. SWIM’s 6 rotating beams will enable it to measure wave properties (direction, wavelength, etc.), while SCAT will measure wind intensity and direction. The data will be downlinked to French and Chinese receiving stations.

These data will allow scientists to achieve more accurate ocean forecasts and give earlier warning of severe weather events like storms and cyclones. CFOSAT will also help climatologists to learn more about exchanges between the oceans and atmosphere, which play a key role in climate. Conceived by the LATMOS atmospheres, environments and space observations laboratory in Paris and Guyancourt, the SWIM instrument is being built by Thales Alenia Space with oversight and funding from CNES. Other mission partners include the French institute of marine research and exploration IFREMER, the French national weather service Meteo-France, and SHOM, the French naval hydrographic and oceanographic office.

Summary of CFOSAT mission capabilities

CFOSAT is a world premiere mission : simultaneous measurements of wind (SCAT) and directional spectra of ocean waves (SWIM)
Access for the first time in space to 2D wave spectrum over the whole energetic spectrum (~70-500 m) at global scale, potential for complex sea situations (multi-wave systems)
SCAT: implementation of a new type of Scat (Rotating Fan-Beam)
SWIM is a new spaceborne instrument with technological innovations (Rotating antenna, n-board advanced digital processing)
CFOSAT, as a new component contributing to spatial oceanography systems, will:
- Serve the operational community (wind/wave forecast, ocean surface analysis for ocean model forcing)
- Serve the scientific meteo-oceanographic community (new data for studying wind/wave/flux/boundary layers teractions)
- Reinforce international multi-mission observation strategy for a better survey of the ocean surface.

CFOSAT Mission's objectives and requirements

CFOSAT is a pre-operational mission of joint measurements of winds and waves which aims is to supply wind/waves observations in near-real time to the meteorological agencies to improve their forecast and sea state models. These measurements will also be supplied to the scientific community for the oceanographic and climate research to improve the sea models as well as the understanding of the influence of sea state in surface fluxes.

Mission duration: 3 years at least,
Data availability: Near-real time (less than three hours after acquisition) for the meteorological agencies (to be confirmed),
Data distribution:
- on request through a server and an authentication for the scientists,
- systematically through meteorological servers for the meteorological agencies (to be confirmed).
Coverage: global at a 13 days scale for SWIM and at a 3 days scale for SCAT,
Altitude: ~500 km

Main Objectives regarding the ocean surface

CFOSAT is designed to provide at the global scale, observations of wind at the ocean surface and spectral properties of surface ocean waves. The objective is multifold. It will serve both operational needs for the surface wind and wave forecast (marine meteorology and climatology), and research needs by improving our knowledge on the hydrodynamics of the waves, on the interactions between waves and the atmospheric or oceanic layers close to the surface, and on the interactions between electromagnetic signals and the ocean surface.
These main objectives can be detailed as:

Modeling and prediction of ocean surface wind and waves
Physical processes of wind and wave
Interactions between surface waves, atmosphere and ocean
Interactions between electromagnetic signals and the ocean surface
Wave evolution in coastal region

Opportunity studies of polar ice sheet and land surface processes

The objectives listed below are secondary objectives to the CFOSAT mission, and specifications specific to these goals are to be met on a best effort basis.

Polar ice sheet
Land surfaces

Scientific requirements to fulfill the objectives of CFOSat

The payload is composed of two instruments: a wind-scatterometer (SCAT) and a wave-scatterometer spectrometer (SWIM: Surface Waves Investigation and Monitoring instrument). The requirements are:

to estimate directional spectra of ocean waves along the satellite track at scales ranging from 50 x 50 km² to 70 x 70 km²
to transmit data in near real-time within 3 hours after acquisition
to estimate wind speed and significant wave height from nadir-looking beam, in a way similar to altimeter missions
to estimate the wind vector over a swath of about 900 km with a nominal resolution of 50 x 50 km² (goal 25 x 25 km²)
to sample spectral wave properties with a global coverage at a temporal scale of 10 to 15 days
to sample wind with a global coverage at a temporal scale of 1 to 2 day
accuracy for wave estimates: minimum detectable wavelength of about 70 m, maximum detectable wavelength about 500m, accuracy in wave propagation direction of about 15°, accuracy in wavelength of 10 to 20%, accuracy in significant wave height of 10% or better than 40-50 cm (TBC)
accuracy on wind speed estimates of ±2m/s or 10% (whichever is larger) and on wind direction of ±20° in the range 4-24 m/s
to estimate the radar cross-section dependence with incidence (from 0 to 10° and from 18 to 50° for SWIM and SCAT, respectively) and azimut, in order to derive from these profiles:
- Properties on the statistics of the sea surface slope (mean square slope, shape of the slope probability density function)
- Estimate of wind direction and wind speed
- In the polar ice sheet, the contribution of volume scattering with respect to surface scattering, and ice surface and snow pack characteristics
- Humidity and roughness of bare soils over land surface