Fig. 3From: Using geophysical logs to identify Milankovitch cycles and to calculate net primary productivity (NPP) of the Late Permian coals, western Guizhou, ChinaSpectral analysis of the Late Permian coal seams from the Songhe mining area, western Guizhou. a, b, c show spectral analysis results of the 17 + 18#, 17# and 18# coal seams respectively. DLW, DEN (Density) and GR represent apparent resistivity, gamma-gamma and natural-gamma logs respectively. MEM and MTM represent the maximum entropy method and multitaper method respectivelyBack to article page