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heave_correction.md

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LIMRAD94 - Eurec4a Heave Correction

Problem:
A Doppler cloud radar measures vertical fall velocities of hydrometeors. Due to the up and down movement of the RV-Meteor (the so called heave), those fall velocities have a systematic error corresponding to the heave rate.
The heave rate or heave velocity is heave per second and thus has a unit of m/s. Another component is the roll and pitch induced heave. Since the radar was placed off center of the ship, the roll and pitch movements of the ship also induce a heave motion on the radar.

Solution:
Correct the mean Doppler velocity of each chirp by the heave rate, calculated from measurements of the heave by the RV-Meteor. To do this a python function called heave_correction is written. Because the correction is applied to each chirp, the function is called in LIMRAD94_to_Cloudnet_v2.py which calculates the radar moments from the measured Doppler spectra.

Step by Step

1. Calculate heave rate for corresponding day

Three components:

  • heave rate
  • pitch induced heave
  • roll induced heave

TODO: Adjust calculation based on date -> higher resolution of Seapath measurements after 27.01.20

2.