General Comments

                Overall I think this paper is well laid out and provides a thorough examination of the calibrations of the different measurement systems. I believe that this work fits well into the current state of knowledge on this topic. I encourage the authors to continue their work trying to find cheaper and more portable ways to measure bedload and look forward to future papers.

Specific Comments

                It is unclear to me why the authors mention and include a Power Fit in Section 2 and Table 5 but then do not mention it in any of the discussions about their results.

                Lines 284-287 talk about a variability in the kb value for the SPG and MPA systems for a certain range of masses. It is unclear what this variability is: whether it is the range of kb values for each of the Obernach experiments, or whether it is the range of kb values when considering only certain size classes, or whether it is something else entirely.

Technical Comments

Line 40 – remove the word “this”

Line 73 – change “to detect” to “the detection of” or similar

Line 74 – remove the word “indicate”

Line 148 – change “the full raw signal is” to “the full raw signal was”

Figure 6 – The legend entries are in boxes of different sizes. This can lead the reader to think that these sizes are significant. In addition, the light green colored equation is very difficult to read

Lines 268-269: I cannot make sense of this statement. Suggest re-wording for clarity.

Line 271 – remove the words “and”, “if” so the it reads “For all four sites (for the Erlenbach…”

Line 282 begins a long and complicated sentence. I suggest breaking it into two sentences “… by larger particle impacts. This is evidenced….”

Line 296 – remove the word “relatively”

Line 317 – remove one of the “that”s

Line 346 – remove the comma

Line 352 – remove the word “clearly”

Line 353 – remove the word “already”

Line 359 needs to be reworded. For example “… occurs only for maximum amplitudes that are close ….”

Line 361 needs to be reworded. For example “… range (500 g) were signal-saturating impacts observed.”

Line 379 – The last “and” should be “with” to match the rest of the sentence

Line 383 – remove the word “Thereby,”

Line 394 – remove the word “clearly”

Line 428 – remove the word “generally” and change the word “sensible” to “sensitive”

Line 434 – remove the word “the” between “all” and “four”

Line 435 – remove the phrase “to the data of the SPS system”

Line 448 – remove the phrase “at all”

Line 454 – remove the word “a” after “MPA system led to”

Line 457 – remove the phrase “at least”

Line 465 – I suggest ending the sentence instead of using a semi-colon

I very much enjoyed reading this maniscript on the calibration of various acoustic impact systems for measuring bedload transport. Given the challenges of obtaining bedlaod transport data,  I believe this is an important topic for the disciline and the authors present results that are both scientifically interesting and practical. I believe this paper should be published given that some minor comments are addressed by the authors. 

General Comments: 

I am unsure what the purpose of the IQA measurements are – the authors should elaborate more on how this was used in the analyses.

In the methods section, the authors describe fitting both linear and power relations to the data, but only show results form the linear models subsequently. Is this because the power relations were not as strong? In this case, I would consider removing from the article or mentioning their inferior performance somewhere in the results.

Section 4.5 and the results of the SPS system seem to come out of the blue and are a bit awkward in my opinion to be presented here. I wonder if the authors consider placing this as a main objective, or at minimum introducing this system earlier.

Specific Comments:

Line 40: Remove the “this”

Line 44: Missing parentheses bracket here.

In Figure 1 it appears that the acoustic measuring systems are installed within a concrete liner – could the authors elaborate more on their installation? Is this the nature of the stream in this location, or is the concrete slab place directly within the streambed?

Line 128-129: How are the authors sure that the metal frames are robust against these forces? Are the previous studies or measurements confirming this?

Lines 149-151: Can the authors elaborate more on how they chose the recording frequency for each  system?

Table 2: For units, is V = volts and g = ?  

Line 166: Check that A min is showing up correctly as a subscript.

Line 189: Can the authors explain what the centroid frequency is?

Lines 246-249: Is this change in calibration relation also attributed to the change in the cable?

Figure 5b: Is M shows here independently measured bedload mass?

In Figure 5b, it is difficult to distinguish the ‘before June 2016’ and ‘after June 2016’ points, particularly for the JPM system, for which it is important. I would consider using a different colour to make it more visible.

Line 259: This is the first mention of this fixed rough bed upstream – I would like to see more elaboration on this set up.

Line 281: I would choose either “generally” or “clearly” to simplify the sentence.

Figure 12: The authors should check to make sure the figure titles and axes labels show up without the spelling error red lines in this figure and in other figures (I believe the issue is in Figures 13 and 14 as well)

Line 346: No need for a comma after “occur”