This is a generally very well written and very solid documentation of the setup and calibration procedure for flux measurments from a unique low flying aircraft. A necessary basis for any follow-on studies using observations from this particular system, but as such there is little novelty in concepts or methods or data

In highlights + associated comments in the attached document I suggest a number of mere technical/editorial improvements.

In addition a few issues require a bit more attention, some preferably in the form of an explicit discussion.

The integration of the Picarro trace gas analyser is poorly documented. E.g. there must a significantly long inlet tube between instrument in cabin and inlet (I assume) in wing pod. What flow rate/pump was used? How were unavoidable significant time delays dealt with (documented a bit late in the text)? Why are lag times of H2O treated differently from CO2 and CH4 if all 3 signals come from the same instrument/setup?

A bit more discussion discussion and/or analysis of the differences/pros/cons of wavelet vs reynolds flux calculation would be welcome. Same for use of 2km integration windows with only 200m stepsize, which artificially reduces random errors and increases (sometime unrealisticly) autocorrelations between data points. Sharp transitions in surface fluxes (e.g. lake) might be unnecessary convoluted.

Since your turbulence probe is mounted in a wingpod, ie off the symmetry-axis of the fuselage, may be you can discuss a bit the implications this has (implicitly or explicitly) for the calibration procedures/parameterisations for the true wind vector.

Unlike your near-perfect wind spectra, for the other signals they are (much) less perfect. Can you show that this does not affect calculated fluxes as you claim, eg using cospectra? How might that change if you fly lower? Somewhat related, do you do any high/low freq corrections?

The paper describes a new airborne system intended to measure fluxes via eddy covariance and wavelet methods. The paper describes the calibration of the system in detail and presents an example of data taken over Germany. Overall this is an excellently written paper. I think it does an good job of explaining all the different possible errors that go into making turbulent wind measurements from an aircraft. It does not spend much time on the uncertainties in the gas measurements themselves or on additional errors when these instruments are put on an aircraft. I’ve made some comments about this. The gas measurements are clearly not the focus of this paper and that is fine, but it might be worth pointing that out. At least that uncertainties in the gas measurements have not been evaluated.

I have some minors comments listed below

Line 96: insert ‘and’ before (2)

Lines 120:135: It would be good to include some detail on the placement of the gas sensors and their inlets distance from the wind probe in this section. Estimated time of flight between inlet and sensor.

Table 2: Have you evaluated the accuracy of the gas sensors? Short and long term drifts which particularly could effect your flux measurements. Depending on cell flush time, have you checked that the 10 Hz data are truly independent? Are the numbers here based on your own measurements using the sensors or just copied from the spec sheet from the company?

Line 169: data ‘were’ merged (not was)

Lines 224:226 You might want to add something about the lag between the Picarro sensors here or at least mention that it’ll be discussed later as this seems a natural section to the reader.

Line 406: Could you provide some rational to using 200 m and 2000m for the distances. Did you use Ogive analysis or some other method to determine the length needed to sum over relevant frequencies. 200 m seems especially short.

Line 620:621: Did you try doing a null experiment to check that the gas measurements are uncorrelated with the wind. In general I didn’t see any description of how you calibrated the gas sensors. While in theory the noise should be uncorrelated, there may be changes in alignment, valves (leading to pressure changes), etc. that may correlate with vertical turbulence but may appear to be noise. Running calibration gas through the system and seeing that you get something close to zero flux would show that there really was not correlation between the gas measurement ‘noise’ and atmospheric turbulence.

Line 680: Do you really mean uncertainty here or variability. You are listing uncertainty with an uncertainty. And given the range of uncertainty, it may be more than 100% of the flux?

Line 681: You have clearly used twice in a row.