Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Characterizing Rain Cells as Measured by a Ka-band Nadir Radar Altimeter: First Results and Impact on Future Altimetry Missions

Version 1 : Received: 27 September 2021 / Approved: 28 September 2021 / Online: 28 September 2021 (21:32:59 CEST)

How to cite: Picard, B.; Picot, N.; Dibarboure, G.; Steunou, N. Characterizing Rain Cells as Measured by a Ka-band Nadir Radar Altimeter: First Results and Impact on Future Altimetry Missions. Preprints 2021, 2021090477 (doi: 10.20944/preprints202109.0477.v1). Picard, B.; Picot, N.; Dibarboure, G.; Steunou, N. Characterizing Rain Cells as Measured by a Ka-band Nadir Radar Altimeter: First Results and Impact on Future Altimetry Missions. Preprints 2021, 2021090477 (doi: 10.20944/preprints202109.0477.v1).

Abstract

The impact of large atmospheric attenuation events on data quality and availability is a critical aspect for future altimetry missions based on Ka-band altimetry. The SARAL/AltiKa mission and its Ka-band nadir altimeter offer a unique opportunity to assess this impact. Previous publications (Tournadre et al. 2009, 2015) already analyzed the impact of rain on the waveforms at Ka-band and proposed a definition of an elaborate rain flag. This notion tends to give a simpler black and white view of the atmospheric attenuation when the effect on the altimeter measurement is intense. But in practice, there is continuum of measurements that may be partially distorted or corrupted by rain events. The present study proposes a wider point of view , the ACECAL approach providing statistics on rain cells occurrences as well as their amplitude and their size, as guidelines for future Ka-band missions concerning the impact of the atmosphere. At global scale, 1 % of the measurements are affected by an attenuation larger than 23 dB and 10 % of the atmospheric attenuation events have a size larger than 40 km. This study demonstrates that the data quality and availability over some regions of particular interest for oceanography as Gulf Stream, North Pacific and Brazil currents could be affected compared to global statistics. It also opens some perspectives on the benefits that the community could be drawn from the systematic distribution of the rain cells parameters as secondary products of altimetry missions.

Keywords

rain cells; atmospheric attenuation; microwave radar; Ka-band; altimetry

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