1. The problem statement, all variables and given/known data A duck is walking in a flat desert (yes, the proff. is creative...). According to atmospheric conditions the Refractive index is n(y)=1.0006-0.0003y. y in KM. An observer is on the ground, 26.2 KM far. Where will he see the duck? Show the gragh of the ray path. 2. Relevant equations d(ne)/ds= grad n e- the ray path direction 3. The attempt at a solution I used the eikonal equation, and some matematical manipulations to get the following equation: dy/dx= sqrt((a-by)^2/c^2-1) (a=1.0006, b=0.0003, c=1.0006*cos(theta_0)) In order to try and find y as a function of x, I tried to solve the latter eq. by seperating it, and using the variable replacment: m=a-by I got: ln(m+sqrt(m^2-c^2))=exp(-bx/c) now I dont know wheather my way till now is correct, and how to display y as y(x). Thanks for your help!