Preprints
https://doi.org/10.5194/amt-2021-219
https://doi.org/10.5194/amt-2021-219

  16 Aug 2021

16 Aug 2021

Review status: this preprint is currently under review for the journal AMT.

Impact of second trip echoes for space-borne high PRF nadir-looking W-band cloud radars

Alessandro Battaglia1,2,3 Alessandro Battaglia
  • 1Politecnico of Torino, Turin, Italy
  • 2University of Leicester, Leicester, UK
  • 3National Centre for Earth Observation, Leicester, UK

Abstract. The appearance of second trip echoes generated by mirror images over the ocean and by multiple scattering tails in correspondence of deep convective cores has been investigated for space-borne nadir-looking W-band cloud radar observations. Examples extracted from the CloudSat radar are used to demonstrate the mechanisms of formation and to validate the modeling of such returns. A statistical analysis shows that, for CloudSat observations, second trip echoes are rare and appear only above 20 km (thus easy to remove). CloudSat climatology is then used to estimate the occurrence of second trip echoes in the different configurations envisaged for the operations of the EarthCARE radar, which will adopt pulse repetition frequencies much higher than the one used by the CloudSat radar in order to improve its Doppler capabilities. Our findings predict that the presence of such echoes in EarthCARE observations cannot be neglected: in particular, over the ocean, mirror images will tend to populate the EarthCARE sampling window with a maximum frequency at its upper boundary. This will create an additional fake cloud cover in the upper troposphere (of the order of 3 % at the top of the sampling window and steadily decreasing moving downwards) and, in much less frequent instances, it will cause an amplification of signals in areas where clouds are already present. Multiple scattering tails will produce also second trip echoes but with much lower frequencies: less than one profile out of 1000 in the Tropics and practically no effects at high latitudes. At the moment Level-2 algorithms of the EarthCARE radar do not account for such occurrences. We recommend to properly remove these second trip echoes and to correct for reflectivity enhancements, where needed. More generally this work is relevant for the design of future space-borne Doppler W-band radar missions.

Alessandro Battaglia

Status: open (until 07 Oct 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-219', Anonymous Referee #1, 07 Sep 2021 reply
    • AC1: 'Reply on RC1', Alessandro Battaglia, 07 Sep 2021 reply

Alessandro Battaglia

Alessandro Battaglia

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Short summary
Space-borne radar returns can be contaminated by artifacts caused by radiation that undergoes multiple scattering events and appear to originate from ranges well below the surface range. While such artifacts have been rarely observed from the currently deployed systems they may become a concern in future cloud radar systems potentially enhancing cloud cover high up in the troposhere via ghost returns.