Improving the reliability of soil EC-mapping: Robust apparent electrical conductivity (rECa) estimation in ground-based frequency domain electromagnetics

Hanssens, Daan; Delefortrie, Samuël; Bobe, Christin; Hermans, Thomas; Smedt, Philippe De

doi:10.1016/j.geoderma.2018.11.030

Cited by 21 publications

(21 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…limitations imposed by high conductive environments can be overcome through more robust interpretation of collected QP data (e.g. Hanssens et al, 2019). This further extends the potential of FDEM to characterize SGD and SI in littoral zones.…”

Section: Discussionmentioning

confidence: 70%

“…Different from most studies, we convert the LIN ECa data to robust ECa (rECa), making a qualitative interpretation of the FDEM data, acquired in highly conductive environment, possible. We follow the non-linear approach of Hanssens et al (2019), in which rECa (mS m -1 ) data are calculated from the QP data to accurately estimate ECa at higher induction numbers (Figure 3). Ultimately, the data were interpolated to a 2 by 2 m grid, via natural neighbour interpolation.…”

Section: Processingmentioning

confidence: 99%

“…Ground conductivity instruments designed to operate under low induction number conditions (LIN) (e.g. CMD-MiniExplorer, DUALEM-421S, Geonics EM34, and EM31) provide apparent electrical conductivities (ECa) which are not valid in highly conductive environments (McNeill, 1980 ;Hanssens et al, 2019), which is probably why the technique has rarely been applied in the intertidal zone. Only the ECa values were used in the interpretation of all following cited FDEM studies.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Combining resistivity and frequency domain electromagnetic methods to investigate submarine groundwater discharge (SGD) in the littoral zone

Paepen¹,

Hanssens²,

Smedt³

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

Abstract. Submarine groundwater discharge (SGD) is an important gateway for nutrients and pollutants from land to sea. The study of SGD is thus important for nearshore ecosystems and the management of coastal freshwater reserves. The discharge occurs at the limit between land and sea, a dynamic environment, making the assessment difficult. And more important, SGD is characterized by a significant spatial and temporal variability. Therefore, a variety of techniques and measurements in multiple periods is needed to capture the magnitude of SGD in one particular site. To detect zones of discharge, we combine several geophysical methods in the intertidal zone, as well as on the upper beach, in the dunes, and shallow coastal area. Electrical resistivity tomography (ERT) – on land, roll-along ERT and on sea, marine continuous resistivity profiling (CRP) – is used from the shallow continental shelf up to the dunes, combined to frequency domain electromagnetics (FDEM) mapping in the intertidal zone. The highly saline environment we work in causes FDEM instruments operated under low induction number (LIN) to underestimate the apparent electrical conductivity (ECa). Here, we apply a quadrature-phase algorithm to obtain a robust ECa (rECa), valid at low and high induction numbers. De Westhoek (Belgium) was chosen as a test site, which is bordered by the North Sea. It is a strong dynamic environment, with semi-diurnal tides between 3 and 5 m. Providing approximately 6 hours between low and high tide, this leaves little time to work close to the low water line. CRP is usually applied in calmer conditions, but we prove that a survey is possible on the North Sea, providing additional information to the ERT survey which is mainly restricted to the land. The 2D inversion models created from ERT and CRP data clearly indicate the presence of SGD on the lower beach (in the East) or below the low water line (in the West of the study area). The discharge originates from a potable freshwater lens underneath the dunes, which delimit the sandy beach. The fresh groundwater flows underneath a thick saltwater lens, present from the dunes to the lower beach, which is fully observed with ERT. FDEM mapping reveals discharge at the same locations and clearly displays the lateral variation of the zone of discharge. ERT, CRP, and FDEM are complementary tools in the investigation of SGD. They provide a high-resolution 3D image of the salt and freshwater distribution in phreatic coastal aquifer over a relatively large area, both off- and onshore.

show abstract

Section: Discussionmentioning

confidence: 70%

Section: Processingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Combining resistivity and frequency domain electromagnetic methods to investigate submarine groundwater discharge (SGD) in the littoral zone

Paepen¹,

Hanssens²,

Smedt³

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…Note that the conductivity of the water layer is introduced as a soft constraint and is not fixed during the inversion. This option was used to prevent the creation of artefacts of inversion, as these can occur when (potentially erroneous) strong constraints are introduced (Henderson et al, 2010;Caterina et al, 2014).…”

Section: Processingmentioning

confidence: 99%

“…Resistivity surveying can be extended to water bodies by burying cables or resting them on top of the sediments (marine electrical resistivity -MER; e.g. Swarzenski et al, 2006;Taniguchi et al, 2007;Swarzenski and Izbicki;Henderson et al, 2010). In the case of saline water, MER provides a better resolution, since the conductive water layer on top has less effect on the signal compared to continuous resistivity profiling (CRP), where the current has to pass the water layer before entering the sediment.…”

Section: Introductionmentioning

confidence: 99%

Combining resistivity and frequency domain electromagnetic methods to investigate submarine groundwater discharge in the littoral zone

Paepen

Hanssens

Smedt

et al. 2020

Hydrol. Earth Syst. Sci.

Self Cite

View full text Add to dashboard Cite

Abstract. Submarine groundwater discharge (SGD) is an important gateway for nutrients and pollutants from land to sea. While understanding SGD is crucial for managing nearshore ecosystems and coastal freshwater reserves, studying this discharge is complicated by its occurrence at the limit between land and sea, a dynamic environment. This practical difficulty is exacerbated by the significant spatial and temporal variability. Therefore, to capture the magnitude of SGD, a variety of techniques and measurements, applied over multiple periods, is needed. Here, we combine several geophysical methods to detect zones of fresh submarine groundwater discharge (FSGD) in the intertidal zone, upper beach, dunes, and shallow coastal area. Both terrestrial electrical-resistivity tomography (ERT; roll-along) and marine continuous resistivity profiling (CRP) are used from the shallow continental shelf up to the dunes and combined with frequency domain electromagnetic (FDEM) mapping in the intertidal zone. In particular, we apply an estimation of robust apparent electrical conductivity (rECa) from FDEM data to provide reliable lateral and vertical discrimination of FSGD zones. The study area is a very dynamic environment along the North Sea, characterized by semi-diurnal tides between 3 and 5 m. CRP is usually applied in calmer conditions, but we prove that such surveys are possible and provide additional information to primarily land-bound ERT surveying. The 2D inversion models created from ERT and CRP data clearly indicate the presence of FSGD on the lower beach or below the low-water line. This discharge originates from a potable freshwater lens below the dunes and flows underneath a thick saltwater lens, present from the dunes to the lower sandy beach, which is fully observed with ERT. Freshwater outflow intensity has increased since 1980, due to a decrease of groundwater pumping in the dunes. FDEM mapping at two different times reveals discharge at the same locations, clearly displays the lateral variation of the zone of discharge, and suggests that FSGD is stronger at the end of winter compared to the beginning of autumn. ERT, CRP, and FDEM are complementary tools in the investigation of SGD. They provide a high-resolution 3D image of the saltwater and freshwater distribution in the phreatic coastal aquifer over a relatively large area, both off- and onshore.

show abstract

Toward high‐resolution agronomic soil information and management zones delineated by ground‐based electromagnetic induction and aerial drone data

Hebel

Reynaert²,

Pauly

et al. 2021

Vadose Zone Journal

View full text Add to dashboard Cite

Detailed knowledge of the intra-field variability of soil properties and crop characteristics is indispensable for the establishment of sustainable precision agriculture.We present an approach that combines ground-based agrogeophysical soil and aerial crop data to delineate field-specific management zones that we interpret with soil attribute measurements of texture, bulk density, and soil moisture, as well as yield and nitrate residue in the soil after potato (Solanum tuberosum L.) cultivation. To delineate the management zones, we use aerial drone-based normalized difference vegetation index (NDVI), spatial electromagnetic induction (EMI) soil scanning, and the EMI-NDVI data combination as input in a machine learning clustering technique. We tested this approach in three successive years on six agricultural fields (two per year). The field-scale EMI data included spatial soil information of the upper 0-50 cm, to approximately match the soil depth sampled for attribute measurements. The NDVI measurements over the growing season provide information on crop development. The management zones delineated from EMI data outperformed the management zones derived from NDVI in terms of spatial coherence and showed differences in properties relevant for agricultural management: texture, soil moisture deficit, yield, and nitrate residue. The combined EMI-NDVI analysis provided no extra benefit. This underpins the importance of including spatially distributed soil information in crop data interpretation, while emphasizing that high-resolution soil information is essential for variable rate applications and agronomic modeling.

show abstract

Improving the reliability of soil EC-mapping: Robust apparent electrical conductivity (rECa) estimation in ground-based frequency domain electromagnetics

Cited by 21 publications

References 30 publications

Combining resistivity and frequency domain electromagnetic methods to investigate submarine groundwater discharge (SGD) in the littoral zone

Combining resistivity and frequency domain electromagnetic methods to investigate submarine groundwater discharge (SGD) in the littoral zone

Combining resistivity and frequency domain electromagnetic methods to investigate submarine groundwater discharge in the littoral zone

Toward high‐resolution agronomic soil information and management zones delineated by ground‐based electromagnetic induction and aerial drone data

Contact Info

Product

Resources

About