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Abstract. The launch and operation of the first spaceborne Doppler windlidar (DWL), Aeolus, is of great significance for observing the global windfield. Aeolus operates on a sun-synchronous dawn–dusk orbit to minimize thenegative impact of solar background radiation (SBR) on wind observationaccuracy. Future spaceborne DWLs may not operate on sun-synchronousdawn–dusk orbits due to their observational purposes. The impact of the localtime of ascending node (LTAN) crossing of sun-synchronous orbits on the windobservation accuracy was studied in this paper by proposing two givenAeolus-type spaceborne DWLs operating on the sun-synchronous orbits withLTANs of 15:00 and 12:00 LT. On these two new orbits, the increments of theaveraged SBR received by the new spaceborne DWLs range from 39 to 56 mW m−2 sr−1 nm−1 under cloud-free skiesnear the summer and winter solstices, which will lead to uncertainties of0.19 and 0.27 m s−1 in the increment of the averaged Rayleigh channel windobservations for 15:00 and 12:00 LT orbits using the instrument parameters ofAeolus with 30 measurements per observation and 20 laser pulses permeasurement. This demonstrates that Aeolus operating on the sun-synchronousdawn–dusk orbit is the optimal observation scenario, and the random errorcaused by the SBR will be larger on other sun-synchronous orbits. Increasingthe laser pulse energy of the new spaceborne DWLs is used to lower the windobservation uncertainties, and a method to quantitatively design the laserpulse energy according to the specific accuracy requirements is proposed inthis study based on the relationship between the signal-to-noise ratio andthe uncertainty of the response function of the Rayleigh channel. The laserpulse energies of the two new spaceborne DWLs should be set to 70 mJ basedon the statistical results obtained using the method. The other instrumentparameters should be the same as those of Aeolus. Based on the proposedparameters, the accuracies of about 77.19 % and 74.71 % of the bins ofthe two new spaceborne DWLs would meet the accuracy requirements of theEuropean Space Agency (ESA) for Aeolus. These values are very close to the76.46 % accuracy of an Aeolus-type spaceborne DWL when it is free of theimpact of the SBR. Moreover, the averaged uncertainties of the two newspaceborne DWLs are 2.62 and 2.69 m s−1, which perform better than that ofAeolus (2.77 m s−1).

Relationship between wind observation accuracy and the ascending node of the sun-synchronous orbit for the Aeolus-type spaceborne Doppler wind lidar