the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Aug 2022
Monitoring snowpack SWE and temperature using RFID tags as wireless sensors
Abstract. This work shows that passive radio-frequency identification (RFID) tags can be used as low-cost contactless sensors, to measure the variations in snow water equivalent (SWE) of a snowpack. RFID tags are produced massively to remotely identify industrial goods, hence are available commercially off-the-shelf at very low-cost. The introduced measurement system consists of a vertical profile of RFID tags installed before the first snowfall, interrogated continuously by a 865–868 MHz reader that remains above the snowpack. The system deduces the SWE variations from the increase of phase delay induced by the new layers of fresh snow which slows the propagation of the waves. The method is tested both in a controlled laboratory environment, and outdoors on the French national reference center of Col de Porte, to cross-check the results against a solid reference dataset (cosmic rays, precipitation weighting, temperature monitoring, and snow pit surveys). The technical challenges solved concern multipathing interferences, snowmelt acceleration during reheats, measurement discontinuity, and wet snow influence. This non-contact and non-destructive RFID technique can estimate the SWE of dry snow, with the accuracy of ±3−30 kg/m2 depending on the number of tags and antennas. In addition, the system can monitor the snow temperature with 1 °C accuracy and spatialization, using dedicated sensors embedded in the tags.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Status: closed
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RC1: 'Comment on egusphere-2022-761', Christian Mätzler, 08 Sep 2022
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AC1: 'Reply on RC1', Mathieu Le Breton, 19 Oct 2022
Dear Christian Mätzler,
First, thank you very much for your in-depth comments. We have adressed or are adressing them. I would like to try the interactive possibilities of this open review to adress one question/clarification. It concerns these comments :
5) No information is given on the scattering and absorption cross sections of the tags used, nor of the supporting structures.
6) No information is given on the method used to discriminate the responses and the backscattered signals from different tags, and how this discrimination may be linked with the phase determination.Mainly, I do not see the motivation behind your suggestion to characterize the Radar Cross Section of the tags and supporting structure (comment 5). I think comes from a misunderstanding of the difference between a radar target and an RFID tag (comment 6), that we have clarified in the text. The answer to comment 6 is straightforward: one tag at a time is requested by the interrogator (using standard the communication & anti-collision protocol EPC Gen2) to modulate the signal it backscatters, while all the other tags and the environment backscatter a non-modulated wave (as it would do with a standard radar). The phase difference of arrival is measured between the two modulation states of the received signal, therefore linked only to the singulated tag.
Indeed in RFID, an important parameter is the DeltaRCS of the tags, which is the difference of the tag's radar cross-section between these two modulation state. We have characterized the DeltaRCS for the model of tag used (depending on frequency and input power). I can add this characterization in the 'instrumentation' section if you find it useful.
In the end,knowing how the response of each tag is discriminated, we do not see the reason for characterizing the cross-section of the tags and supporting structure (which would make sense however with a radar). Can you confirm me, or otherwise explain the motivation behind the comment 5 ?
Sincerely yours,
Mathieu Le Breton, on behalf of all the coauthors.Citation: https://doi.org/10.5194/egusphere-2022-761-AC1 -
RC2: 'Reply on AC1', Christian Mätzler, 19 Oct 2022
Dear Mathieu Le Breton,
Thank you for the comment and explanation with respect to my Comments 5 and 6. It is certainly useful for Comment 6. But my concern was not related to the radar cross section, but to the scattering properties of the inserted materials that cause multipath effects, and thus speckel noise that you see in your data. What is your explanation for the large data spread?
Best regards, Christian Mätzler
Citation: https://doi.org/10.5194/egusphere-2022-761-RC2 -
AC4: 'Reply on RC2', Mathieu Le Breton, 09 Jan 2023
Dear Christian Matzer,
First, thank you for your comments. We have just received the second referee's comment so I am answering both. We have processed your (see the answer in the attached document), they will help to improve the manuscript.
Regarding the multipathing, however, we propose an alternative approach.
We agree that there is a need to better understand the multipathing effect on RFID systems in snow contexts. However, this is far beyond the scope of the present study: multipathing is a general issue in RFID (very present for localization indoors for example). All the reflective elements should be a source of multipathing: The environment (snow surface, layers of snow, soil), and the installation itself (tags, light plastic supporting structure that holds the tag, large metallic structure that holds the reader). Any modification of geometry (snow depth) or dielectric constant (i.e., snow density, moisture content of the snow and soil) should modify the influence of multipathing on phase measurements. In practice, multipathing in RFID is more often mitigated than predicted.
It is mitigated in the study by using multiple antennas and tags (=spatial diversity). To further mitigate it in a future installation, we suggest (as you did) to use an array of tags placed very close to the ground (also necessary to reduce the thermal influence of the system). It should help average the spread due to spatial diversity, and reduce the reflection on the tags and on the supporting material.
We have a work in progress that explores more in depth the role of multipathing when using an RFID system is snow context, for which we will dedicate a communication in itself. The document attached presents (still unpublished) results of two experiments and one model: the amplitude of the phase variation induce by multipathing (from 1.4 to 3 rad) is coherent with the spread in our study (1.2 rad).
I also suggest to improve the link of our study, to existing studies related to multipathing in the snow or with RFID systems:
—The model used and preliminary results are also in:
Le Breton, M., 2019. Suivi temporel d’un glissement de terrain à l’aide d’étiquettes RFID passives, couplé à l’observation de pluviométrie et de bruit sismique ambiant (PhD Thesis). Université Grenoble Alpes, ISTerre, Grenoble, France. https://www.theses.fr/2019GREAU013 (page 144 to 156).
—Some methods exploit multipathing for snow, such as
Espín-López, P. F., Pasian, M., 2021. Determination of Snow Water Equivalent for Dry Snowpacks Using the Multipath Propagation of Ground-Based Radars. IEEE Geoscience and Remote Sensing Letters 18, 276–280. https://doi.org/10.1109/LGRS.2020.2974546;
Kulsoom, F., Dell’Acqua, F., Pasian, M., Espín-López, P. F., 2021. Snow Layer Detection by Pattern Matching in a Multipath Radar Interference Scenario. International Journal of Remote Sensing 42, 3193–3218. https://doi.org/10.1080/01431161.2020.1854890).
—Mitigating multipathing in RFID is a topic in itself. Some studies are dedicated to propose mitigation methods, such as
DiGiampaolo, E., Martinelli, F., 2020. A Multiple Baseline Approach to Face Multipath. IEEE Journal of Radio Frequency Identification 4, 314–321. https://doi.org/10.1109/JRFID.2020.3022576
In short, we encountered the multipathing issue and demonstrated a simple way to mitigate it. However, describing in detail the multipathing issue and how to further mitigate it, is a topic in itself which, in our opinion, should not be in the present paper. Instead we suggest to (a) propose a future installation that further reduce the multipathing issue, (b) to detail more about the causes of multipathing in the text, and (c) to link our observations with other studies that deal specifically about multipathing with snow or rfid.
Is this approach suitable to you ?
Best regards,
-
AC4: 'Reply on RC2', Mathieu Le Breton, 09 Jan 2023
-
RC2: 'Reply on AC1', Christian Mätzler, 19 Oct 2022
-
AC1: 'Reply on RC1', Mathieu Le Breton, 19 Oct 2022
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RC3: 'Comment on egusphere-2022-761', Anonymous Referee #2, 07 Jan 2023
This work proposes the use of RFID for monitoring the snowpack SWE and temperature. The topic and the application is interesting and the authors provided experimental results which seem to provide good results. However there are some criticism that should be clarified.
1) the authors claim to use standard RFID, that this is not really true a standard RFID do not be equipped with sensors, you must design a customised tag. The same for the battery you can't connect a battery to a standard tag. You should provide more information related to the Considered RFID schema.
2) you perform a measure of phase difference but it is not clear how. If you used inductive coupling rfid it is quite difficult. I suppose that you used a RF tag, and you claim that the reader is able to detect the phase difference. Can you please better explain how? You have to analyse the signals at the demodulator in order to detect the phase difference of did you use another technique? Please explain.
3) did you take into account the attenuation introduced in the RF signal by the snow?4) I suppose that you modified the reader, don't you? If yes please report the introduced customisations.
in this form the manuscript is not acceptable for publicatIon in this form. I suggest major revisions.
Citation: https://doi.org/10.5194/egusphere-2022-761-RC3 -
AC2: 'Reply on RC3', Mathieu Le Breton, 08 Jan 2023
Dear referee, first, thank you very much for your review, we appreciate your work.
Please find below some answers, and a question (your original text is in bold)
In short, your comments showed that we need to clarify our text, to avoid any misunderstanding (in particular, the fact that we used only commercial off-the-shelf readers and tags, without customisation), which we will do.1) the authors claim to use standard RFID, that this is not really true a standard RFID do not be equipped with sensors, you must design a customised tag. The same for the battery you can't connect a battery to a standard tag. You should provide more information related to the Considered RFID schema.
We will clarify this point. In particular, what is 'standard' is the communication protocol (EPC-Gen2) and the RF channel (ETSI-302-201). Then we used 'commercial off-the-shelf' devices, both tags and reader. We have modified the tag (UHF tag, model Survivor B, from Confidex, that embeds an EM4325 chip from EM electronic, an a small battery) ony superficially: first, we configured its memory bank wirelessely, in order to make temperature measurements, and to increase its power sensitivity. Second, we painted the tag in white to reduce the radiative heat transfer.
So we bought an industrial tag, but we have not designed a customised tag.
2) you perform a measure of phase difference but it is not clear how. If you used inductive coupling rfid it is quite difficult. I suppose that you used a RF tag, and you claim that the reader is able to detect the phase difference. Can you please better explain how? You have to analyse the signals at the demodulator in order to detect the phase difference of did you use another technique? Please explain.
We used an UHF RFID (working around 868 MHz). The reader (Impinj R700) has the capacity to read phase difference of arrival when reading a tag, out-of-the-box. Several other readers have this capacity, such as the ImpinjSR420 or the ThingMagic M6. Measurements of phase difference of arrival is largely used for RFID localization, see for example the introduction of this review :
Le Breton M, Liébault F, Baillet L, Charléty A, Larose É, Tedjini S. Dense and long-term monitoring of earth surface processes with passive RFID — a review. Earth-Science Reviews. 2022 Nov 1;234:104225.
We do not know, nor need to know, how the Impinj R700's electronic is designed in order to read the phase. For clarification, we will add a reference to research papers describing techniques to read the phase from a reader.
3) did you take into account the attenuation introduced in the RF signal by the snow?Could you please clarify ? For which aim should we take the attenuation into account ?
There are several sources of signal loss, such as, indeed, attenuation in the snow, but also detuning of the tag, reflexion at the surface, or destructive multipathing interferences. We have measured the signal strength data for each tag, but the data is messy: using signal strength is often a difficult method to exploit for RFID sensing outdoors because of its many influence factors (see again the review Le Breton et al. 2022). Indirectly, the signal strenght received by the tag can slightly influence the phase (and therefore our SWE measurement), when the tag enters non-linear behavior (for example when it receives very powerful signal). The non-linear behavior depends strongly on model of chip. With our tag, non-linearity occurs only at high power that are not reached in the study. And in any case, that would be a small source of noise.
In short: The present study exploits only the phase difference of arrival (related to wave slowness), not the signal strength (related to attenuation).
4) I suppose that you modified the reader, don't you? If yes please report the introduced customisations.
No, we have used a commercial off-the-shelf reader, not customised. The method works with any reader that is able to read the phase difference of arrival.
Citation: https://doi.org/10.5194/egusphere-2022-761-AC2
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AC2: 'Reply on RC3', Mathieu Le Breton, 08 Jan 2023
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AC3: 'Comment on egusphere-2022-761', Mathieu Le Breton, 09 Jan 2023
Dear Christian Matzer,
First, thank you for your comments. We have just received the second referee's comment so I am answering both. We have processed your (see the answer in the attached document), they will help to improve the manuscript.
Regarding the multipathing, however, we propose an alternative approach.
We agree that there is a need to better understand the multipathing effect on RFID systems in snow contexts. However, this is far beyond the scope of the present study: multipathing is a general issue in RFID (very present for localization indoors for example). All the reflective elements should be a source of multipathing: The environment (snow surface, layers of snow, soil), and the installation itself (tags, light plastic supporting structure that holds the tag, large metallic structure that holds the reader). Any modification of geometry (snow depth) or dielectric constant (i.e., snow density, moisture content of the snow and soil) should modify the influence of multipathing on phase measurements. In practice, multipathing in RFID is more often mitigated than predicted.
It is mitigated in the study by using multiple antennas and tags (=spatial diversity). To further mitigate it in a future installation, we suggest (as you did) to use an array of tags placed very close to the ground (also necessary to reduce the thermal influence of the system). It should help average the spread due to spatial diversity, and reduce the reflection on the tags and on the supporting material.
We have a work in progress that explores more in depth the role of multipathing when using an RFID system is snow context, for which we will dedicate a communication in itself. The document attached presents (still unpublished) results of two experiments and one model: the amplitude of the phase variation induce by multipathing (from 1.4 to 3 rad) is coherent with the spread in our study (1.2 rad).
I also suggest to improve the link of our study, to existing studies related to multipathing in the snow or with RFID systems:
—The model used and preliminary results are also in:
Le Breton, M., 2019. Suivi temporel d’un glissement de terrain à l’aide d’étiquettes RFID passives, couplé à l’observation de pluviométrie et de bruit sismique ambiant (PhD Thesis). Université Grenoble Alpes, ISTerre, Grenoble, France. https://www.theses.fr/2019GREAU013 (page 144 to 156).
—Some methods exploit multipathing for snow, such as
Espín-López, P. F., Pasian, M., 2021. Determination of Snow Water Equivalent for Dry Snowpacks Using the Multipath Propagation of Ground-Based Radars. IEEE Geoscience and Remote Sensing Letters 18, 276–280. https://doi.org/10.1109/LGRS.2020.2974546;
Kulsoom, F., Dell’Acqua, F., Pasian, M., Espín-López, P. F., 2021. Snow Layer Detection by Pattern Matching in a Multipath Radar Interference Scenario. International Journal of Remote Sensing 42, 3193–3218. https://doi.org/10.1080/01431161.2020.1854890).
—Mitigating multipathing in RFID is a topic in itself. Some studies are dedicated to propose mitigation methods, such as
DiGiampaolo, E., Martinelli, F., 2020. A Multiple Baseline Approach to Face Multipath. IEEE Journal of Radio Frequency Identification 4, 314–321. https://doi.org/10.1109/JRFID.2020.3022576
In short, we encountered the multipathing issue and demonstrated a simple way to mitigate it. However, describing in detail the multipathing issue and how to further mitigate it, is a topic in itself which, in our opinion, should not be in the present paper. Instead we suggest to (a) propose a future installation that further reduce the multipathing issue, (b) to detail more about the causes of multipathing in the text, and (c) to link our observations with other studies that deal specifically about multipathing with snow or rfid.
Is this approach suitable to you ?
Best regards,
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2022-761', Christian Mätzler, 08 Sep 2022
-
AC1: 'Reply on RC1', Mathieu Le Breton, 19 Oct 2022
Dear Christian Mätzler,
First, thank you very much for your in-depth comments. We have adressed or are adressing them. I would like to try the interactive possibilities of this open review to adress one question/clarification. It concerns these comments :
5) No information is given on the scattering and absorption cross sections of the tags used, nor of the supporting structures.
6) No information is given on the method used to discriminate the responses and the backscattered signals from different tags, and how this discrimination may be linked with the phase determination.Mainly, I do not see the motivation behind your suggestion to characterize the Radar Cross Section of the tags and supporting structure (comment 5). I think comes from a misunderstanding of the difference between a radar target and an RFID tag (comment 6), that we have clarified in the text. The answer to comment 6 is straightforward: one tag at a time is requested by the interrogator (using standard the communication & anti-collision protocol EPC Gen2) to modulate the signal it backscatters, while all the other tags and the environment backscatter a non-modulated wave (as it would do with a standard radar). The phase difference of arrival is measured between the two modulation states of the received signal, therefore linked only to the singulated tag.
Indeed in RFID, an important parameter is the DeltaRCS of the tags, which is the difference of the tag's radar cross-section between these two modulation state. We have characterized the DeltaRCS for the model of tag used (depending on frequency and input power). I can add this characterization in the 'instrumentation' section if you find it useful.
In the end,knowing how the response of each tag is discriminated, we do not see the reason for characterizing the cross-section of the tags and supporting structure (which would make sense however with a radar). Can you confirm me, or otherwise explain the motivation behind the comment 5 ?
Sincerely yours,
Mathieu Le Breton, on behalf of all the coauthors.Citation: https://doi.org/10.5194/egusphere-2022-761-AC1 -
RC2: 'Reply on AC1', Christian Mätzler, 19 Oct 2022
Dear Mathieu Le Breton,
Thank you for the comment and explanation with respect to my Comments 5 and 6. It is certainly useful for Comment 6. But my concern was not related to the radar cross section, but to the scattering properties of the inserted materials that cause multipath effects, and thus speckel noise that you see in your data. What is your explanation for the large data spread?
Best regards, Christian Mätzler
Citation: https://doi.org/10.5194/egusphere-2022-761-RC2 -
AC4: 'Reply on RC2', Mathieu Le Breton, 09 Jan 2023
Dear Christian Matzer,
First, thank you for your comments. We have just received the second referee's comment so I am answering both. We have processed your (see the answer in the attached document), they will help to improve the manuscript.
Regarding the multipathing, however, we propose an alternative approach.
We agree that there is a need to better understand the multipathing effect on RFID systems in snow contexts. However, this is far beyond the scope of the present study: multipathing is a general issue in RFID (very present for localization indoors for example). All the reflective elements should be a source of multipathing: The environment (snow surface, layers of snow, soil), and the installation itself (tags, light plastic supporting structure that holds the tag, large metallic structure that holds the reader). Any modification of geometry (snow depth) or dielectric constant (i.e., snow density, moisture content of the snow and soil) should modify the influence of multipathing on phase measurements. In practice, multipathing in RFID is more often mitigated than predicted.
It is mitigated in the study by using multiple antennas and tags (=spatial diversity). To further mitigate it in a future installation, we suggest (as you did) to use an array of tags placed very close to the ground (also necessary to reduce the thermal influence of the system). It should help average the spread due to spatial diversity, and reduce the reflection on the tags and on the supporting material.
We have a work in progress that explores more in depth the role of multipathing when using an RFID system is snow context, for which we will dedicate a communication in itself. The document attached presents (still unpublished) results of two experiments and one model: the amplitude of the phase variation induce by multipathing (from 1.4 to 3 rad) is coherent with the spread in our study (1.2 rad).
I also suggest to improve the link of our study, to existing studies related to multipathing in the snow or with RFID systems:
—The model used and preliminary results are also in:
Le Breton, M., 2019. Suivi temporel d’un glissement de terrain à l’aide d’étiquettes RFID passives, couplé à l’observation de pluviométrie et de bruit sismique ambiant (PhD Thesis). Université Grenoble Alpes, ISTerre, Grenoble, France. https://www.theses.fr/2019GREAU013 (page 144 to 156).
—Some methods exploit multipathing for snow, such as
Espín-López, P. F., Pasian, M., 2021. Determination of Snow Water Equivalent for Dry Snowpacks Using the Multipath Propagation of Ground-Based Radars. IEEE Geoscience and Remote Sensing Letters 18, 276–280. https://doi.org/10.1109/LGRS.2020.2974546;
Kulsoom, F., Dell’Acqua, F., Pasian, M., Espín-López, P. F., 2021. Snow Layer Detection by Pattern Matching in a Multipath Radar Interference Scenario. International Journal of Remote Sensing 42, 3193–3218. https://doi.org/10.1080/01431161.2020.1854890).
—Mitigating multipathing in RFID is a topic in itself. Some studies are dedicated to propose mitigation methods, such as
DiGiampaolo, E., Martinelli, F., 2020. A Multiple Baseline Approach to Face Multipath. IEEE Journal of Radio Frequency Identification 4, 314–321. https://doi.org/10.1109/JRFID.2020.3022576
In short, we encountered the multipathing issue and demonstrated a simple way to mitigate it. However, describing in detail the multipathing issue and how to further mitigate it, is a topic in itself which, in our opinion, should not be in the present paper. Instead we suggest to (a) propose a future installation that further reduce the multipathing issue, (b) to detail more about the causes of multipathing in the text, and (c) to link our observations with other studies that deal specifically about multipathing with snow or rfid.
Is this approach suitable to you ?
Best regards,
-
AC4: 'Reply on RC2', Mathieu Le Breton, 09 Jan 2023
-
RC2: 'Reply on AC1', Christian Mätzler, 19 Oct 2022
-
AC1: 'Reply on RC1', Mathieu Le Breton, 19 Oct 2022
-
RC3: 'Comment on egusphere-2022-761', Anonymous Referee #2, 07 Jan 2023
This work proposes the use of RFID for monitoring the snowpack SWE and temperature. The topic and the application is interesting and the authors provided experimental results which seem to provide good results. However there are some criticism that should be clarified.
1) the authors claim to use standard RFID, that this is not really true a standard RFID do not be equipped with sensors, you must design a customised tag. The same for the battery you can't connect a battery to a standard tag. You should provide more information related to the Considered RFID schema.
2) you perform a measure of phase difference but it is not clear how. If you used inductive coupling rfid it is quite difficult. I suppose that you used a RF tag, and you claim that the reader is able to detect the phase difference. Can you please better explain how? You have to analyse the signals at the demodulator in order to detect the phase difference of did you use another technique? Please explain.
3) did you take into account the attenuation introduced in the RF signal by the snow?4) I suppose that you modified the reader, don't you? If yes please report the introduced customisations.
in this form the manuscript is not acceptable for publicatIon in this form. I suggest major revisions.
Citation: https://doi.org/10.5194/egusphere-2022-761-RC3 -
AC2: 'Reply on RC3', Mathieu Le Breton, 08 Jan 2023
Dear referee, first, thank you very much for your review, we appreciate your work.
Please find below some answers, and a question (your original text is in bold)
In short, your comments showed that we need to clarify our text, to avoid any misunderstanding (in particular, the fact that we used only commercial off-the-shelf readers and tags, without customisation), which we will do.1) the authors claim to use standard RFID, that this is not really true a standard RFID do not be equipped with sensors, you must design a customised tag. The same for the battery you can't connect a battery to a standard tag. You should provide more information related to the Considered RFID schema.
We will clarify this point. In particular, what is 'standard' is the communication protocol (EPC-Gen2) and the RF channel (ETSI-302-201). Then we used 'commercial off-the-shelf' devices, both tags and reader. We have modified the tag (UHF tag, model Survivor B, from Confidex, that embeds an EM4325 chip from EM electronic, an a small battery) ony superficially: first, we configured its memory bank wirelessely, in order to make temperature measurements, and to increase its power sensitivity. Second, we painted the tag in white to reduce the radiative heat transfer.
So we bought an industrial tag, but we have not designed a customised tag.
2) you perform a measure of phase difference but it is not clear how. If you used inductive coupling rfid it is quite difficult. I suppose that you used a RF tag, and you claim that the reader is able to detect the phase difference. Can you please better explain how? You have to analyse the signals at the demodulator in order to detect the phase difference of did you use another technique? Please explain.
We used an UHF RFID (working around 868 MHz). The reader (Impinj R700) has the capacity to read phase difference of arrival when reading a tag, out-of-the-box. Several other readers have this capacity, such as the ImpinjSR420 or the ThingMagic M6. Measurements of phase difference of arrival is largely used for RFID localization, see for example the introduction of this review :
Le Breton M, Liébault F, Baillet L, Charléty A, Larose É, Tedjini S. Dense and long-term monitoring of earth surface processes with passive RFID — a review. Earth-Science Reviews. 2022 Nov 1;234:104225.
We do not know, nor need to know, how the Impinj R700's electronic is designed in order to read the phase. For clarification, we will add a reference to research papers describing techniques to read the phase from a reader.
3) did you take into account the attenuation introduced in the RF signal by the snow?Could you please clarify ? For which aim should we take the attenuation into account ?
There are several sources of signal loss, such as, indeed, attenuation in the snow, but also detuning of the tag, reflexion at the surface, or destructive multipathing interferences. We have measured the signal strength data for each tag, but the data is messy: using signal strength is often a difficult method to exploit for RFID sensing outdoors because of its many influence factors (see again the review Le Breton et al. 2022). Indirectly, the signal strenght received by the tag can slightly influence the phase (and therefore our SWE measurement), when the tag enters non-linear behavior (for example when it receives very powerful signal). The non-linear behavior depends strongly on model of chip. With our tag, non-linearity occurs only at high power that are not reached in the study. And in any case, that would be a small source of noise.
In short: The present study exploits only the phase difference of arrival (related to wave slowness), not the signal strength (related to attenuation).
4) I suppose that you modified the reader, don't you? If yes please report the introduced customisations.
No, we have used a commercial off-the-shelf reader, not customised. The method works with any reader that is able to read the phase difference of arrival.
Citation: https://doi.org/10.5194/egusphere-2022-761-AC2
-
AC2: 'Reply on RC3', Mathieu Le Breton, 08 Jan 2023
-
AC3: 'Comment on egusphere-2022-761', Mathieu Le Breton, 09 Jan 2023
Dear Christian Matzer,
First, thank you for your comments. We have just received the second referee's comment so I am answering both. We have processed your (see the answer in the attached document), they will help to improve the manuscript.
Regarding the multipathing, however, we propose an alternative approach.
We agree that there is a need to better understand the multipathing effect on RFID systems in snow contexts. However, this is far beyond the scope of the present study: multipathing is a general issue in RFID (very present for localization indoors for example). All the reflective elements should be a source of multipathing: The environment (snow surface, layers of snow, soil), and the installation itself (tags, light plastic supporting structure that holds the tag, large metallic structure that holds the reader). Any modification of geometry (snow depth) or dielectric constant (i.e., snow density, moisture content of the snow and soil) should modify the influence of multipathing on phase measurements. In practice, multipathing in RFID is more often mitigated than predicted.
It is mitigated in the study by using multiple antennas and tags (=spatial diversity). To further mitigate it in a future installation, we suggest (as you did) to use an array of tags placed very close to the ground (also necessary to reduce the thermal influence of the system). It should help average the spread due to spatial diversity, and reduce the reflection on the tags and on the supporting material.
We have a work in progress that explores more in depth the role of multipathing when using an RFID system is snow context, for which we will dedicate a communication in itself. The document attached presents (still unpublished) results of two experiments and one model: the amplitude of the phase variation induce by multipathing (from 1.4 to 3 rad) is coherent with the spread in our study (1.2 rad).
I also suggest to improve the link of our study, to existing studies related to multipathing in the snow or with RFID systems:
—The model used and preliminary results are also in:
Le Breton, M., 2019. Suivi temporel d’un glissement de terrain à l’aide d’étiquettes RFID passives, couplé à l’observation de pluviométrie et de bruit sismique ambiant (PhD Thesis). Université Grenoble Alpes, ISTerre, Grenoble, France. https://www.theses.fr/2019GREAU013 (page 144 to 156).
—Some methods exploit multipathing for snow, such as
Espín-López, P. F., Pasian, M., 2021. Determination of Snow Water Equivalent for Dry Snowpacks Using the Multipath Propagation of Ground-Based Radars. IEEE Geoscience and Remote Sensing Letters 18, 276–280. https://doi.org/10.1109/LGRS.2020.2974546;
Kulsoom, F., Dell’Acqua, F., Pasian, M., Espín-López, P. F., 2021. Snow Layer Detection by Pattern Matching in a Multipath Radar Interference Scenario. International Journal of Remote Sensing 42, 3193–3218. https://doi.org/10.1080/01431161.2020.1854890).
—Mitigating multipathing in RFID is a topic in itself. Some studies are dedicated to propose mitigation methods, such as
DiGiampaolo, E., Martinelli, F., 2020. A Multiple Baseline Approach to Face Multipath. IEEE Journal of Radio Frequency Identification 4, 314–321. https://doi.org/10.1109/JRFID.2020.3022576
In short, we encountered the multipathing issue and demonstrated a simple way to mitigate it. However, describing in detail the multipathing issue and how to further mitigate it, is a topic in itself which, in our opinion, should not be in the present paper. Instead we suggest to (a) propose a future installation that further reduce the multipathing issue, (b) to detail more about the causes of multipathing in the text, and (c) to link our observations with other studies that deal specifically about multipathing with snow or rfid.
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Best regards,
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Mathieu Le Breton
Éric Larose
Laurent Baillet
Yves Lejeune
Alec van Herwijnen
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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