Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Superconducting Gravimeters: A Novel Tool for Validating Remote Sensing Evapotranspiration Products

Version 1 : Received: 29 May 2023 / Approved: 30 May 2023 / Online: 30 May 2023 (05:31:13 CEST)

A peer-reviewed article of this Preprint also exists.

Pendiuk, J.; Degano, M.F.; Guarracino, L.; Rivas, R.E. Superconducting Gravimeters: A Novel Tool for Validating Remote Sensing Evapotranspiration Products. Hydrology 2023, 10, 146. Pendiuk, J.; Degano, M.F.; Guarracino, L.; Rivas, R.E. Superconducting Gravimeters: A Novel Tool for Validating Remote Sensing Evapotranspiration Products. Hydrology 2023, 10, 146.

Abstract

The practical utility of remote sensing techniques relies on validating them with ground-truth data. Validation requires similar spatial-temporal scales for ground measurements and remote sensing resolution. Evapotranspiration (ET) estimates are commonly compared to weighing lysimeter data, which provide precise but localized measurements. To address this limitation, we propose using superconducting gravimeters (SG) to obtain ground-truth ET data at larger spatial scales. SG measure gravity acceleration with high resolution (tenths of nm/s2) within a few hundred meters. Similar to lysimeters, gravimeters provide direct estimates of water mass changes for determining ET without soil disturbance. To demonstrate the practical applicability of SG data, we conducted a case study in Buenos Aires Province, Argentina (-34.87, -58.14). We estimated cumulative ET values for 8-day and monthly intervals using gravity and precipitation data from the study site. Comparing these values with MODIS-based ET products (MOD16A2), we found a very good agreement at the monthly scale, with an RMSE of 32.6 mm/month (1.1 mm/day). This study represents progress in using SG for hydrogeological applications. The future development of lighter and smaller gravimeters is expected to further expand their use.

Keywords

remote sensing; ground-truth data; validation; superconducting gravimeters; evapotranspiration

Subject

Environmental and Earth Sciences, Remote Sensing

Comments (3)

Comment 1
Received: 31 May 2023
Commenter:
The commenter has declared there is no conflict of interests.
Comment: The study shows a very interesting new approach to estimate ET and a comparison with MOD16A2 is carried out. Maybe, results or more details about water balance data/results near the analyzed station can be added to compare with the gravimeter’s and MOD16A2’s result.
-Eq 4, maybe insert a cite supporting the value of alpha.
-In point 2.4.2 the effect of solar radiation in decreasing gravity residuals can be commented, to explain that decrease from December 2017
-Maybe a cite can be included in this sentence: “typically ranging from 10% to 30% when ET is estimated by eddy flux towers”
-Page 9: Maybe “The ET estimated by both methods shows” instead of “show”
-Page 9: ETM values tend to be higher than ETSG values instead of “ET”
-Maybe more discussion about this source of noise can be added: “a 14-day non-hydrological periodical signal in the gravity residuals”
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Response 1 to Comment 1
Received: 5 June 2023
Commenter:
The commenter has declared there is no conflict of interests.
Comment: Dear Mauro Holzman (MH)

Thank you very much for your constructive comments.

Q-MH. - The study shows a very interesting new approach to estimate ET and a comparison with MOD16A2 is carried out. Maybe, results or more details about water balance data/results near the analyzed station can be added to compare with the gravimeter’s and MOD16A2’s result.

R-Authors. - The superconducting gravimeter provides a direct estimation of water storage changes in the study area (R=1300 m), while classical hydrological sensors for resolving the water balance provide point measurements (within a few centimeters). Therefore, a direct comparison between the two techniques is not possible due to their different footprints.

Q-MH. - Eq 4, maybe insert a cite supporting the value of alpha.

R-Authors. - According to different studies (*) conducted in the province of Buenos Aires alpha in Eq. 4 is 0.05
(*) 1-Kruse E, Laurencena P (2005) Aguas Superficiales: relación con el régimen subterráneo y fenómenos de anegamiento. Geología y Recursos Minerales de la Provincia de Buenos Aires. La Plata, Argentina. 2-Auge MP, Wetten C, Baudino G, Bonorino AG, Gianni R, González N, Grizinik MM, Hernandez MA, Rodríguez J, Sisul AC, Tineo A, Torres C (2006) Hidrogeología de Argentina. Instituto Geológico y Minero de España, Boletín Geológico y Minero, 117(1): 7-23.

Q-MH. -In point 2.4.2 the effect of solar radiation in decreasing gravity residuals can be commented, to explain that decrease from December 2017.

R-Authors. - Section 2.4.2 aims to show the input of water into the system through precipitation and the response of delta g. While there is energy availability in summer (high radiation) that contributes to the decrease in delta g, it is not our intention to represent the effect of radiation.

Q-HM. - Maybe a cite can be included in this sentence: “typically ranging from 10% to 30% when ET is estimated by eddy flux towers”

R-Authors. -We will include a citation, for example, (*) Allen et al. 2011 and Pimentel et al. 2023 (**), which provide comparisons with uncertainties of this magnitude.
(*) https://doi.org/10.1016/j.agwat.2010.12.015.
(**) https://doi.org/10.1029/2022WR033447

Q-HM. -Page 9: ETM values tend to be higher than ETSG values instead of “ET”

R-Authors. Ok, is ETSG

Q-HM. -Maybe more discussion about this source of noise can be added: “a 14-day non-hydrological periodical signal in the gravity residuals”

R-Authors. -It is necessary to conduct a more extensive numerical analysis to model and remove these effects, but now, we are focused on eliminating the residuals.
Comment 2
Received: 7 June 2023
Commenter:
The commenter has declared there is no conflict of interests.
Comment: Tank you for the response
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