Figure 3
Data for atomic mercury monitoring at the Emperor Qin mausoleum. Panels (a–d) correspond to measurement location #1, (e–h) to location #2, and (i–l) to location #3. Curves (a,e,i) are recorded lidar backscattering signals, (b,f,j) are magnified sections of the curves, where recordings for on- and off-absorption wavelengths close to 254 nm are shown individually in red and blue, respectively. DIAL curves, obtained by dividing on- by off-resonance recordings are finally shown in (c,g,k). These curves would have a constant value of 1.00 (apart from noise) for all ranges in the absence of atmospheric atomic mercury, but are in fact sloping, where a larger slope corresponds to a higher gas concentration. Mercury concentration maps over the mound are shown in panels (d,h,l), as obtained from locations #1, #2, and #3, with the concentrations given in ng/m3 and color-coded, to be evaluated against the color scales to the right of the maps. Here also the measurement directions corresponding to the individual data shown to the right of each map are indicated by yellow dashed lines. Since the maps are generated by averaging over several DIAL curves of the type shown in (c,g,k), the colored map data along the yellow lines are not fully matching the individual raw data curves shown.
