the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Mispointing correction methods for the conically scanning WIVERN Doppler radar
Filippo Emilio Scarsi
Alessandro Battaglia
Frederic Tridon
Paolo Martire
Ranvir Dhillon
Anthony Illingworth
Abstract. Global measurements of horizontal winds in cloud and precipitating systems represent a gap in the global observing system. The WIVERN mission, one of the four candidates to be the ESA's Earth Explorer 11 mission, aims at filling this gap based on a conically scanning W-band Doppler radar instrument. The determination of the antenna boresight mispointing angles and the impact of their uncertainty on the line of sight velocities is critical to achieve the mission requirements. While substantial industrial efforts are on their ways for achieving accurate determination of the pointing, alternative (external) calibration approaches are currently under scrutiny. This work discusses four methods applicable to the WIVERN radar that can be used to correct antenna mispointing both in the azimuthal and in the elevation directions at different time scales.
Results show that elevation mispointing is well corrected at very short time scales by monitoring the range at which the surface peak occurs. Azimuthal mispointing is harder but can be tackled by using the expected profiles of the non-moving surface Doppler. Biases in pointing at longer time scales can be monitored by using well established reference database (e.g. ECMWF reanalysis) or ad-hoc ground based calibrators.
Although tailored to the WIVERN mission, the proposed methodologies can be extended to other Doppler concepts featuring conically scanning or slant viewing Doppler systems.
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Filippo Emilio Scarsi et al.
Status: open (until 18 Oct 2023)
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RC1: 'Comment on amt-2023-117', Anonymous Referee #1, 31 Aug 2023
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The manuscript “Mispointing correction methods for the conically scanning WIVERN Doppler radar” analyzes different methods for the correction of azimuthal and elevation mispointing for the Earth Explorer Candidate WIVERN. The authors nicely describe the respective methods and derive the respective precisions and temporal / spatial scales.
The paper is well structured, easy to read and the analysis is profound and well described. Nevertheless, it could benefit from some minor revisions.
1 Introduction
L 16: Abbreviation ALADIN not introduced.
Please revise the citations for the Aeolus mission. E.g. Lux et al., 2021, is a paper on a very specific topic on laser frequency stability and probably not a good reference for the whole Aeolus mission. A good overview of the Aeolus mission is given e.g. by ESA (2008).
In line 24f, you motivate the WIVERN radar as a complementation of current global wind measurements in cloudy conditions. However, you do not clearly state the limitations of the other observation techniques, especially Aeolus, before. This could be added e.g. in line 21.
2 Mispointing errors
Your whole paper is based on equation (1). Could you please add a proper derivation of this very important equation?
3 Doppler correction methods
Eq (2): The variable HS/C is not introduced.
L 79: Why “therefore”? Maybe better “unfortunately”?
L 87: blue -> orange dashed
L 88: How is the noise subtracted? Does this noise subtraction method have an impact on the precision of your correction method(s)?
L 140: Why 0.4 m/s? In the introduction you state that it should be below 0.3 m/s.
L 151f: Why do you choose these box sizes?
Figure 7: What is the difference between dashed and solid lines? Description is missing.
L265: The method is in detail described by Weiler et al. 2021. So maybe this is a better reference here.
Figure 13: Is this Figure really necessary?
L 182: Why only between -65° and 65° latitude?
Figure 14: Difficult to see the difference between solid and dotted lines. Please adapt line style.
4 Summary and conclusion
L 332: And on which time scales can such models be considered unbiased? What about the wish to have model-independent measurements?
In the introduction you motivate your study with phase 0 industry studies showing mispointing errors above 0.3 m/s particularly for slow varying components. Are the time scales of your methods sufficiently fast to correct for these? So, what exactly are “slow varying components”? This should be addressed either here or in the introduction.
References
European Space Agency (ESA): “ADM-Aeolus Science Report,” ESA SP-1311, 121 pp., available at: https://earth.esa.int/documents/10174/1590943/AEOL002.pdf, 2008.
Weiler, F., Rennie, M., Kanitz, T., Isaksen, L., Checa, E., de Kloe, J., Okunde, N., and Reitebuch, O.: Correction of wind bias for the lidar on board Aeolus using telescope temperatures, Atmos. Meas. Tech., 14, 7167–7185, https://doi.org/10.5194/amt-14-7167-2021, 2021.
Citation: https://doi.org/10.5194/amt-2023-117-RC1 -
AC1: 'Reply on RC1', Filippo Emilio Scarsi, 20 Sep 2023
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Please, find our reply in the attached document.
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AC1: 'Reply on RC1', Filippo Emilio Scarsi, 20 Sep 2023
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Filippo Emilio Scarsi et al.
Filippo Emilio Scarsi et al.
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