What was the purpose of the WIVERNex-UK Campaign?

The goal of the WIVERNex-UK campaign was to validate algorithms which may be used for the WIVERN (Wind Velocity Radar Nephoscope) mission. WIVERN is one of the candidates for the 11th Earth Explorer mission, and if the mission is approved, it will carry a 94 GHz scanning Doppler cloud radar in a 500 km orbit to provide global profiles of in-cloud winds with 20 km horizontal resolution and daily visits at mid-latitudes.

These observations would complement the clear air winds from the Aeolus-2 Doppler lidar that may be launched by the end of the decade. Assimilation of the clear-air winds from the first Aeolus Doppler lidar (2018-2023) led to the biggest reduction of weather forecasts errors of any single satellite instrument. A similar improvement in forecasts is predicted for the in-cloud wind observations from WIVERN.

Outcome of the campaign

14 wet days of 94 GHz data at vertical incidence were gathered during February-April 2023 and 6 days at the WIVERN incidence angle of 42 degrees during May-July 2023. The standard Doppler technique is to measure the phase shift from two successive pulses, but from space the campaign team must use 94 GHz (to have a small footprint) and so the pulse separation must be just 20 µs (3 km).

The campaign team have developed a new technique whereby the two pulses are labelled by having one polarised H and the other V. Potential problems arise due to cross talk between H and V returns if the hydrometeor targets are oblate leading to “ghost echoes” that are displaced from the real target by 3 km with the following conclusions.

1. Ghost echoes can be identified by a fall in the correlation between the H and V returns and an increased noisiness of the Doppler
2. Ghost echoes do not bias the velocity estimates so are acceptable for data assimilation
3. Ghost echoes affect trailing pulses, so reflectivity can be derived from leading pulses
4. Statistics of LDR (linear depolarisation ratio) of hydrometeors has been obtained
5. Using CloudSat observed climatology the campaign team can predict ghosts will be rare for WIVERN
6. Observations of polarimetric variables from the H and V returns show that for WIVERN the differential phase shift between the H and V returns is too noisy and cannot be used to infer values of ice water content

Download the WIVERNex-UK Final Report

Digital Object Identifier: European Space Agency, 2023, WIVERNex_UK, Version Final, https://doi.org/10.57780/esa-6eb57e5

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