Reciprocity in the sense of “when the Sun and detector change position

the observed reflectance should remain the same”

its validity is tested using ADEOS POLDER level 2 data. Geometrically reciprocal （GR） pairs of data are selected from nearly a months observation of the sample region. It is found that some of these GR pairs have considerable non reciprocity

and ignoring this non reciprocity can cause up to 0.2’s uncertainty in the calculation of NDVI. Besides in ratio to wavelength

the magnitute of non reciprocity also shows a sign of correlation with NDVI and altitude. It seems that with IR bands and low NDVI

visible bands and high NDVI

IR bands and high altitude

the data show more non reciprocity.