1. The problem statement, all variables and given/known data You have a geostationary satellite (location 0◦N 0◦E, 36000 km above geoid). Assume the Earth to be spherical with a radius of REarth = 6372km When observing a region centered at 60◦N 0◦E: What is the incidence angle of the satellite’s line of sight (at pixel center; surface parallel≡ 0 ◦ , nadir≡ 90◦ )? 2. Relevant equations φ = 60◦ r = 6370 km 3. The attempt at a solution http://s716.photobucket.com/user/Pitoraq/media/Rs_zpstcj5qby5.png.html?sort=3&o=0 Im not sure how to calculate the angle of incidence by that figure. This is from an exam and the solution is: b = r × sin φ = 5517 km a = r − r × cos φ = 3185 km scan-angle (off nadir) β: tan β = b/(h+a) = 5517/(36000+3185) = 0.1408, β = 8.014◦ parallel surface: 90◦ − φ = 30◦ incidence-angle: γin = 90◦ − (φ + β) = 21.99◦ where do they get the relation 90◦ − φ = 30◦ from ? and where is β in my figure ?