Data for Manuscript Submitted to Near Surface Geophysics Entitled “Diurnal observation and correction for spontaneous potential gradient measurement”

In both study areas, the geoelectric diurnal data were processed with the following steps: (1) contrast correction, (2) background value correction, and (3) the calculation of diurnal norm and phase angle. At 45 degrees north, the geomagnetic diurnal data were processed with (1) background value correction only.

The geomagnetic diurnal data were plotted together with simultaneously observed geoelectric diurnal data for analysis. Spontaneous potential gradient data were processed with the following steps: (1) contrast correction, (2) conversion to spontaneous potential, and (3) diurnal correction using the equations derived in the paper. After processing with the above methods, spontaneous potential contour maps for the entire study area can be obtained by interpolating the spontaneous potential data (before and after diurnal corrections) along all measuring lines on regularly spaced grids.