DOI: 10.6096/msec.laos.8
title: Electrical resistivity tomography time-lapse monitoring data, Houay Pano, Laos

description: The database has 2 sections:<br>
<b>1- Data from Electrical Resistivity Tomography (ERT) time-lapse monitoring</b> that have been carried out along 3 traverses to address the temporal variability of electrical resistivity along hillslopes (i) traverse RIB72 located at the head of the catchment on shale rock (317 data files with a=0.5m from 2006 to 2009 ; 443 data files with a=1.5m from 2006 to 2013); (ii) traverse RIB48, in a swampy area of the central part of the catchment (183 data files with a=0.5m from 2006 to 2010 ; 520 data files with a=1.5m from 2006 to 2019); (iii) traverse RIB33, further downstream on mudstone rock (133 data files with a=0.5m from 2006 to 2010 ; 283 data files with a=1.5m from 2006 to 2013).<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 unit electrode spacing of 0.5 m or 1.5 m.<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. The measurements were done using reciprocal Wenner-Schlumberger array (P1C1C2P2 with C1C2=a and P1C1=C2P2=n*a, noted WS) or Wenner Alpha array (C1P1P2C2 with C1P1= P1P2=P2C2= a, noted WA).<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)
The database also includes 3 *.xlsx files (MS-Excel 2013) with the annual agenda of the measurements along the 0.5 m and 1.5 m traverses of each site : from 2006 to 2013 for RIB33 and RIB72, and from 2006 to 2019 for RIB48.<br>
<b>2- Topographical data</b> (XYZ coordinates) that have been measured for each electrode along the traverses. These data files also include the coordinates of hydrological instruments such as limnimeters, piezometers, access tube for TDR, etc., that are located close to the resistivity measurement traverses.<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 Model (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).