The key to extracting heavy metal from water through remote sensing is to accurately obtain the absorption coefficient spectrum of the dissolved heavy metal. The first step is to calculate the absorption coefficient per unit concentration of each dissolved heavy metal. The absorption coefficient is an important parameter in our remote sensing inversion model of heavy metals in water. We measure copper ions

which are common heavy metals in water that display evident characteristics in the absorption spectrum. Therefore

extracting copper ions by using remote sensing is a breakthrough. We designed equipment

which can adjust the path length of passing light and provide accurate results at the visible and near-infrared wavelength range. Then

we use an Analytical Spectral Devices（ ASD） spectrometer to measure the radiance of direct light passing through copper ion solutions with different concentrations on the standard board. Using the ratio method to eliminate environmental errors and the effect of suspended solids in water

we calculate the extinction coefficient and the absorption coefficient per g / L of copper ion solutions. Finally

we obtain the absorption spectrum per g / L of copper ions from 400 nm to 900 nm. The absorption coefficient in the blue and green solutions is very low but rapidly increases from the red to near-infrared region

which coincides with the color of copper ions. Maximum absorption is observed at 810 nm

and the absorption coefficient is larger in red than in blue and green. This observation is caused by the d-d transition in the outermost electrons of copper ions

which mostly absorb the energy of red color. We perform numerous independent experiments and find that the standard deviations of the results are minimal

indicating the stability of our measurement results. Our results are consistent and more reasonable and accurate than those of Jancsò’s in some wavelength ranges. This conclusion is based on observations of the different light colors on the standard board between pure water and high concentration copper ion solutions. We use the absorption coefficient at 722 nm to calculate the concentration of some copper ion solutions and compare them with the real concentrations. The relative errors are less than 5%

which verifies the accuracy of our results at 722 nm. We conclude that the obtained absorption spectrum is reasonable and accurate. The results can be used as the base parameter in the remote sensing inversion model of copper ions in water. Our results suggest that the maximum absorption is at810 nm

indicating that this wavelength is the most sensitive to copper ion concentration changes in water.