the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 30 May 2024
Calibration of Optical Particle Spectrometers Using Mounted Fibres
Abstract. Calibrations of OPSs are non-trivial, and conventionally involve aerosolisation techniques which are challenging for larger particles. In this paper, we present a new technique for OPS calibration, which involves mounting a static fibre within the instrument sample area, measuring the scattering cross section, then comparing it with a calculated value. In addition, we present a case for the use of GLMT simulations to account for deviations in both minor and major axis beam intensity, which has a significant effect on particles which are large compared to the beam waist, in addition to reducing the need for a ‘top-hat’ spacial intensity profile. The described technique is OPS independent and could be applied to a field calibration tool, which could be used to verify the calibration of instruments before they are deployed. In addition to this, the proposed calibration technique would be suited for applications involving mass production of low-cost OPSs.
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Status: closed
-
RC1: 'Comment on amt-2024-55', Anonymous Referee #2, 08 Jul 2024
This manuscript introduces a novel calibration method for optical particle spectrometers (OPS) using statically mounted fibres, which simplifies the calibration process and reduces dependency on traditional aerosol-based techniques.
The method leverages Generalized Lorenz-Mie Theory (GLMT) to accurately calculate the scattering cross section of fibres, ensuring that the OPS provides reliable measurements across different conditions and settings.
Highlighted as both practical and versatile, this new technique offers significant improvements in OPS calibration, making it ideal for field applications and mass production of low-cost instruments.The paper is well-written and describes the new calibration method systematically, making it comprehensible for readers with knowledge of particle measurement using scattering technique. Indeed, the manuscript may not be easily understood by readers not familiar with the topic. If the author wishes to reach a broader audience, it would be beneficial to elaborate more on the fundamentals of measurement techniques and calibration.
The paper would greatly benefit if the author applied the new fibre calibration not only to the UCASS instrument but also demonstrates its effectiveness on another device, such as the OPC-N3 from Alphasense which uses a similar technique and is widely used in field application.
There is nothing to criticize about the writing style of the manuscript. However, the author should consider whether Figure 2 could be more effectively presented in colour, as the lines in the black and white plot are very close together, making it difficult for the reader to distinguish them.
A potential typographical error may be found in line 330. "However, The addition" should be replaced with "However, the addition".
Citation: https://doi.org/10.5194/amt-2024-55-RC1 -
AC2: 'Reply on RC1', Jessica Girdwood, 22 Sep 2024
# Author Response to RC1
## Jessica Girdwood -- jessica.girdwood@ncas.ac.uk
---
We thank the reviewer for their comments. Our response is as follows:
- In order to reach a more broad audience, we have added a paragraph in the
introduction highlighting where optical scattering measurements fit into
general aerosol measurement.
- While we agree that the OPC-N3 would be a good device to apply this
calibration technique to, we were unable to get data with this instrument
since the lab where I performed the original experiments was shut down while
moving to a new building, and a new fibre mount would have had to have been
developed. In addition, I am no longer at this institution, which adds
another layer of complexity to this. However, the OPC-N3 uses exactly the
same optical layout as the UCASS, since they were both branches off the same
device (Kaye and Hirst 2015). This means that the calibration technique would
implicitly be applicable to the OPC-N3, and I have stated this in the
Conclusions section.
- The dash-dot line in figure 2 was changed to blue.
- The typographical error was corrected.Citation: https://doi.org/10.5194/amt-2024-55-AC2
-
AC2: 'Reply on RC1', Jessica Girdwood, 22 Sep 2024
-
RC2: 'Comment on amt-2024-55', Anonymous Referee #1, 02 Aug 2024
The manuscript “Calibration of Optical Particle Spectrometers Using Mounted Fibres” by Girdwood et al describes a new technique to calibrate OPSs – instead of the commonly used glass spheres the authors design a fibre mount and calibrate with that instead. This will be useful for calibration since it is much easier to use also in the field. The authors then compare the new technique to commonly used methods and show there is good agreement, using a UCASS instrument. The method with a static fibre could be also used on other instruments. Therefore, I think this manuscript is ideal for AMT and will be a useful addition after some minor changes.
My comments:
- Abbreviations in the abstract are not explained. In line 205 “ABS” is also not explained.
- Line 100 and 114: What exactly is “sufficiently” small?
- Line 135 delete “which”
- Line 180: The laser was modified to pulse with a gaussian profile. How easy/hard is that to do for an operator in the field? Would the instrument have to be removed from operation or not? How long would this procedure take?
- Fig 3 is mentioned after fig 4
- Line 207: “fixed distance” – what is it? Is it the same every time?
- Line 225: delete comma
- Line 236: Swap figure order such that 6 and 7 are mentioned in order.
- Figures 6/7: How exactly was the fit done, were only two/three data points used? Because the fit with two data points is not following these two points.
- Line 339: “mothodolody” (typo)
Citation: https://doi.org/10.5194/amt-2024-55-RC2 -
AC1: 'Reply on RC2', Jessica Girdwood, 22 Sep 2024
# Author Response to RC2
## Jessica Girdwood - jessica.girdwood@ncas.ac.uk
---
We thank the reviewer for their comments, and respond as follows:
- Line 205 -- abbreviation of ABS clarified as acrylonitrile butadiene styrene.
- Abbreviations in the abstract are now defined.
- Line 100 -- the stated assumptions describe an optical system where the
proportion of light from a single diffraction fringe measured is independent
of change in y-direction, which is true for the UCASS as determined
experimentally. I have re-stated the assumptions to describe this directly.
- Line 114 -- the definition of sufficiently large might vary depending on the
beam width of the instrument, and the definition of this is effectively the
topic of this section. The manuscript was amended to state this.
- Line 134 -- This sentence makes more sense if the parenthetical information is
within commas. Thank you for pointing this out.
- Line 135 -- "which" was removed.
- Line 180-189 -- The LPD was used in this case because we possess the knowledge
to modify the chosen instruments, we would actually recommend to instrument
manufacturers that they build this capability into their instruments if they
wish to calibrate them this way. For a field calibration, a mechanism by
which the laser is flashed using mechanical means would be far more
attainable. A sentence at the end of this paragraph was inserted to clarify
this.
- Swapped figures 3 and 4 around.
- Line 207 -- the fixed distance refers to a distance between the two parts of
the fibre holder which was sufficient to cause no interference to neither the
direct nor scattered light within the OPS. The manuscript has been amended to
reflect this.
- Line 225 -- comma deleted.
- Figs 6 and 7 swapped.
- Since figure 6 is now 7 and vice versa, I will refer to these as the LG and
HG figures respectively (after reorder). Both HG and LG fits were done with 3
data-points, thus mimicking a realistic factory calibration for a low-cost
instrument. For the HG fits, an aerosol datum was incorporated into the fibre
data, because a fibre with a small enough diameter could not be sourced. This
is the datum which is labelled fa0. This was explained at the beginning of
the method section (3), but I have re-stated this in the discussion section
to avoid further confusion.
- Line 339 -- corrected to "methodology"Citation: https://doi.org/10.5194/amt-2024-55-AC1
Status: closed
-
RC1: 'Comment on amt-2024-55', Anonymous Referee #2, 08 Jul 2024
This manuscript introduces a novel calibration method for optical particle spectrometers (OPS) using statically mounted fibres, which simplifies the calibration process and reduces dependency on traditional aerosol-based techniques.
The method leverages Generalized Lorenz-Mie Theory (GLMT) to accurately calculate the scattering cross section of fibres, ensuring that the OPS provides reliable measurements across different conditions and settings.
Highlighted as both practical and versatile, this new technique offers significant improvements in OPS calibration, making it ideal for field applications and mass production of low-cost instruments.The paper is well-written and describes the new calibration method systematically, making it comprehensible for readers with knowledge of particle measurement using scattering technique. Indeed, the manuscript may not be easily understood by readers not familiar with the topic. If the author wishes to reach a broader audience, it would be beneficial to elaborate more on the fundamentals of measurement techniques and calibration.
The paper would greatly benefit if the author applied the new fibre calibration not only to the UCASS instrument but also demonstrates its effectiveness on another device, such as the OPC-N3 from Alphasense which uses a similar technique and is widely used in field application.
There is nothing to criticize about the writing style of the manuscript. However, the author should consider whether Figure 2 could be more effectively presented in colour, as the lines in the black and white plot are very close together, making it difficult for the reader to distinguish them.
A potential typographical error may be found in line 330. "However, The addition" should be replaced with "However, the addition".
Citation: https://doi.org/10.5194/amt-2024-55-RC1 -
AC2: 'Reply on RC1', Jessica Girdwood, 22 Sep 2024
# Author Response to RC1
## Jessica Girdwood -- jessica.girdwood@ncas.ac.uk
---
We thank the reviewer for their comments. Our response is as follows:
- In order to reach a more broad audience, we have added a paragraph in the
introduction highlighting where optical scattering measurements fit into
general aerosol measurement.
- While we agree that the OPC-N3 would be a good device to apply this
calibration technique to, we were unable to get data with this instrument
since the lab where I performed the original experiments was shut down while
moving to a new building, and a new fibre mount would have had to have been
developed. In addition, I am no longer at this institution, which adds
another layer of complexity to this. However, the OPC-N3 uses exactly the
same optical layout as the UCASS, since they were both branches off the same
device (Kaye and Hirst 2015). This means that the calibration technique would
implicitly be applicable to the OPC-N3, and I have stated this in the
Conclusions section.
- The dash-dot line in figure 2 was changed to blue.
- The typographical error was corrected.Citation: https://doi.org/10.5194/amt-2024-55-AC2
-
AC2: 'Reply on RC1', Jessica Girdwood, 22 Sep 2024
-
RC2: 'Comment on amt-2024-55', Anonymous Referee #1, 02 Aug 2024
The manuscript “Calibration of Optical Particle Spectrometers Using Mounted Fibres” by Girdwood et al describes a new technique to calibrate OPSs – instead of the commonly used glass spheres the authors design a fibre mount and calibrate with that instead. This will be useful for calibration since it is much easier to use also in the field. The authors then compare the new technique to commonly used methods and show there is good agreement, using a UCASS instrument. The method with a static fibre could be also used on other instruments. Therefore, I think this manuscript is ideal for AMT and will be a useful addition after some minor changes.
My comments:
- Abbreviations in the abstract are not explained. In line 205 “ABS” is also not explained.
- Line 100 and 114: What exactly is “sufficiently” small?
- Line 135 delete “which”
- Line 180: The laser was modified to pulse with a gaussian profile. How easy/hard is that to do for an operator in the field? Would the instrument have to be removed from operation or not? How long would this procedure take?
- Fig 3 is mentioned after fig 4
- Line 207: “fixed distance” – what is it? Is it the same every time?
- Line 225: delete comma
- Line 236: Swap figure order such that 6 and 7 are mentioned in order.
- Figures 6/7: How exactly was the fit done, were only two/three data points used? Because the fit with two data points is not following these two points.
- Line 339: “mothodolody” (typo)
Citation: https://doi.org/10.5194/amt-2024-55-RC2 -
AC1: 'Reply on RC2', Jessica Girdwood, 22 Sep 2024
# Author Response to RC2
## Jessica Girdwood - jessica.girdwood@ncas.ac.uk
---
We thank the reviewer for their comments, and respond as follows:
- Line 205 -- abbreviation of ABS clarified as acrylonitrile butadiene styrene.
- Abbreviations in the abstract are now defined.
- Line 100 -- the stated assumptions describe an optical system where the
proportion of light from a single diffraction fringe measured is independent
of change in y-direction, which is true for the UCASS as determined
experimentally. I have re-stated the assumptions to describe this directly.
- Line 114 -- the definition of sufficiently large might vary depending on the
beam width of the instrument, and the definition of this is effectively the
topic of this section. The manuscript was amended to state this.
- Line 134 -- This sentence makes more sense if the parenthetical information is
within commas. Thank you for pointing this out.
- Line 135 -- "which" was removed.
- Line 180-189 -- The LPD was used in this case because we possess the knowledge
to modify the chosen instruments, we would actually recommend to instrument
manufacturers that they build this capability into their instruments if they
wish to calibrate them this way. For a field calibration, a mechanism by
which the laser is flashed using mechanical means would be far more
attainable. A sentence at the end of this paragraph was inserted to clarify
this.
- Swapped figures 3 and 4 around.
- Line 207 -- the fixed distance refers to a distance between the two parts of
the fibre holder which was sufficient to cause no interference to neither the
direct nor scattered light within the OPS. The manuscript has been amended to
reflect this.
- Line 225 -- comma deleted.
- Figs 6 and 7 swapped.
- Since figure 6 is now 7 and vice versa, I will refer to these as the LG and
HG figures respectively (after reorder). Both HG and LG fits were done with 3
data-points, thus mimicking a realistic factory calibration for a low-cost
instrument. For the HG fits, an aerosol datum was incorporated into the fibre
data, because a fibre with a small enough diameter could not be sourced. This
is the datum which is labelled fa0. This was explained at the beginning of
the method section (3), but I have re-stated this in the discussion section
to avoid further confusion.
- Line 339 -- corrected to "methodology"Citation: https://doi.org/10.5194/amt-2024-55-AC1
Data sets
Fibre Calibration Repository Jessica Girdwood https://github.com/wolkchen-cirrus/FibCalRepo
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