[IEEE 2005 IEEE International Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. - Seoul, Korea (25-29 July 2005)] Proceedings. 2005 IEEE International Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. - Different approximations to the computation of reflected and refracted angles thanks to snell-descartes laws and fresnel coefficients