反射率基法是目前最常用、最有效的可见光近红外通道在轨辐射定标方法。在该方法中，准确的场地反射率测量是得到高精度定标结果的重要前提之一。利用双光谱仪法进行了野外地物反射率时间序列测量，避免了用传统测量方法可能出现的辐射条件不一致问题。用中心区和高反区场地反射率测量值对VIIRS传感器的表观反射率进行了模拟，并将VIIRS可见光近红外9个通道(I1、I2、M1～M7)的卫星观测表观反射率值与6S辐射传输模型模拟值进行了对比。除M6通道外(水汽吸收)，相对偏差均在3%以内，验证了场地反射率测量的准确性。

The reflectance-based calibration is the most common and effective in-orbit radiometric calibration method for visible and near infrared channels at present. In the method, accurate field reflectivity measurement is one of the important prerequisites for obtaining high precision calibration results. The time series measurement of field surface reflectance is performed by using a two-spectrometer method. The inconsistency of radiation conditions which may occur in traditional measurement methods is avoided. The reflectivity measurement values both in the central area and in the high reflectivity area are used to simulate the apparent reflectance of the VIIRS sensor. The apparent reflectance values observed by nine visible and near infrared channels (I1, I2, M1 to M7) of the VIIRS sensor are compared with the simulation values of a 6S radiation transmission model. The relative deviation of all channels except M6 (water vapor absorption) is less than 3%, which verifies the accuracy of the proposed surface reflectance measurement method.