ESA conducts airborne and ground-based campaigns to support the development of new instruments, and calibration and validation of existing instruments. These campaigns simulate satellite-based instruments and are conducted all over the world in support of a wide range of applications.

The WIVERNex-UK campaign supported the validation of algorithms for the WIVERN (Wind Velocity Radar Nephoscope) mission, which is one of the candidates for the 11th Earth Explorer. If WIVERN is selected, the satellite will carry a 94 GHz scanning Doppler cloud radar in a 500 km orbit, which will provide global profiles of in-clod winds with 20 km horizontal resolution and daily visits at mid-latitudes. Data from WIVERN would complement the clear air wind data acquired by the upcoming Aeolus-2 mission, and it is expected that WIVERN would offer a similar improvement in weather forecasts as Aeolus did during its lifetime. 

To support WIVERN, the campaign used a ground-based radar at the Chilbolton Observatory in the United Kingdom.

Normally, the Doppler technique measures the phase shift from two successive pulses, but space-based radar must use 94 GHz to reduce the footprint, so the pulse separation is only 20 µs (3 km). The WIVERNex-UK campaign team developed a new technique, which labels the two pulses by H or V polarisation. However, this technique can cause issues if the hydrometeor targets are oblate, and there is cross-talk between the H and V values. When this occurs, it results in “ghost echoes” where a target may be displaced by 3 km from its actual location.
 

The WIVERNex-UK campaign consisted of two phases: 

• The first phase acquired 14 days of 94 GHz data at vertical incidence between February and April 2023. This gathered many observations of ghost echoes, to enable testing of new algorithms to remove the ghosts. 
• The second phase acquired 6 days of 94 GHz data, with an incidence angle of 42 degrees, which is the expected configuration for the WIVERN satellite. Observations were gathered between May and July 2023.

The campaign team analysed these observations and drew the following conclusions: 

• Ghost echoes can be identified by a fall in the correlation between the H and V returns and an increased noisiness of the Doppler
• Ghost echoes do not bias the velocity estimates, so are acceptable for data assimilation
• Statistics of Linear Depolarisation Ratio (LDR) of hydrometeors were obtained
• Ghost echoes were observed frequently in ground-based observations, but are expected to be rare for the space-based WIVERN. This was validated using CloudSat data.
• Observations of polarimetric variables from the H and V returns show that WIVERN’s differential phase shift between the H and V returns will be too noisy and will not be suitable to infer values of ice water content

WIVERNex-UK performed useful measurements and conclusions that will help refine the configuration of the candidate WIVERN satellite instrument. The dataset produced for the campaign also provides a preview of what the WIVERN mission could provide.

Data acquired during both phases of the campaign were produced in NetCDF format and are openly available for download following submission of a data access request.
 

Learn more about the WIVERNex-UK campaign and how to request the data