Based on the near infrared radiative transfer theory

the retrieval method of precipitable water vapor （PWV） with MODIS near infrared band data is analyzed under the simulation of radiative transfer model

MODTRAN. The effect of surface nonlinear reflective spectrum on PWV estimation is emphasized on. Both two bands ratio method and three bands ratio method are taken into account. The study indicates that the error due to the surface nonlinear reflective spectrum is very large if the reflectance ratio of water vapor band to atmospheric windows band is not equal to 1.The error is proportional to the ratio of transmittance ratio between these two bands. The ratio of band reflectance is calculated for hundreds kinds of surface material such as rocks

minerals

soils

vegetation and water in Johns Hopkins University spectral library. Most of the reflectance ratios have a considerable difference with 1.And the difference from 1 of two bands ratio method is smaller than three bands method. That indicates three bands method is predominant over two bands method. The coefficients used in three bands method is recalculated based on the spectral library. The result shows that their coefficients should be gained from the regression of whole spectral library and the sum of coefficients should be equal to 1.