DOI: 10.6096/msec.laos.9
title: Electrical resistivity tomography survey data, Houay Pano, Laos

description: The database has 2 sections:<br>
<b>1- Data from Electrical Resistivity Tomography (ERT) surveys</b> that have been carried out to address the spatial variability of electrical resistivity (i) along hillslopes to study soil and saprolite layering from crest to stream (2003, 8 profiles); (ii) with a focus on river banks to study the pathways linking groundwater and surface water (2005, 19 profiles ; 2006, 3 profiles); (iii) across a swamp to study sediment accumulations (2007, pseudo 3D survey 15 profiles); (iv) across landslides to study soil and saprolite layering associated to these exceptional phenomenons (2012, 12 profiles); (v) with a focus across a gully to study the pathways linking groundwater and surface water (2015, 6 profiles); (vi) along hillslopes, associated with rain fall simulation or over land flow monitoring (2014-2015, 3 profiles).<br>
The ERT measurement were done using (i) a SYSCAL R2 with multinode system or a SYSCAL Pro equipment manufactured by Iris Instruments Company (Orléans, France) and (ii) 64 or 72 electrodes with electrode spacing of 0.4, 0.5, 1.0, 1.2, 1.5, or 4.0 m depending on the target of the survey.<br>
The measurements were done using quadrupoles including a pair of electrodes C1 and C2 to inject an electrical current of known intensity in the soil and a pair of electrodes P1 and P2 to measure the resulting difference of electrical potential at soil surface. Most of the measurements were done using reciprocal Wenner-Schlumberger array (P1C1C2P2 with C1C2=a and P1C1=C2P2=na, noted WS) or Wenner Alpha array (C1P1P2C2 with C1P1= P1P2=P2C2= a, noted WA). In 2003 other electrode arrays were also used: Wenner Beta (C1C2P1P2 with C1C2= C2P1=P1P2= a, noted WB), forward and backward pole-dipole (C1P1P2 with C1P1= na and P1P2= a and C2 in a remote location much larger than n*a, noted ANM and MNB), Pole-Pole (C1P1 with C1P1= a, P2 and C2 in remoted locations much larger than a, noted PP).<br>
Each resistivity measurement was repeated at least 3 times and up to 6 times, when the experimental dispersion was larger than 1%. Measurements that were still less reproducible than 1% were not kept. In the most unfavorable cases, the rejected measurement points represent about 5 % of the total set of measurements along the traverse.<br>
All the ERT files have the extension *.dat. They are written according to the general format of RES2DINV inversion software that is described in « RES2DINVx64 User manual » (May 2019, p.14)<br>
<b>2- Topographical data</b> (XYZ coordinates) that have been measured for each electrode along the traverses and sometimes more extensively over the surveyed area (swamp in 2007, landslides in 2012, Gerlach experimental site in 2014).<br>
The geographical coordinates have been measured with a hand GPS (GARMIN XL12 or GARMIN GPSMAP65) and the topography with a laser theodolite (NIKON DTM 332). The DEM of the whole catchment was calculated with a co-registration approach using (i) a DGPS survey (TRIMBLE 5700) carried out in 2006 and (ii) a Digital Surface Models (DSM) generated from Pleiades satellite stereo pairs.<br>
The coordinates system used is WGS84 UTM zone 48N. The accurate relative X, Y coordinates measured with the theodolite were rotated and translated in order to be fitted with the absolute but inaccurate Easting, Northing coordinates from hand GPS measurements. The accurate relative Z coordinates measured with the theodolite were shifted to be fitted with the absolute but of lower resolution AMSL elevations of the DEM.<br>
All the topographic files are in *.xlsx format (MS-Excel 2013).