The Odin orbit is circular and sunsynchronous at an altitude near 600km with a period of 96 minutes. The orbital inclination of 98 degrees from the equator provides near-global coverage as the corresponding sampled latitude range for nominal on-track instrument pointing is from 82 degrees S to 82 degrees N . The local time of the ascending node, i.e. the northward equatorial crossing, is 1800h. The satellite remains very close to local dusk on the entire ascending track and close to local dawn on the descending track, sweeping quickly through noon at high northern latitudes and through midnight at high southern latitudes. This figure shows a plot of the satellite latitude as a function of local time.
A consequence of the Odin dusk/dawn orbit is that the winter hemisphere is not illuminated by the sun. The following is a plot of contours of the solar zenith angle at the OSIRIS tangent point as a function of latitude during 2002. In the gray shaded regions the sun is below the horizon at the tangent point and trace gas and aerosol inversion are not possible. During these orbital segments, measurements of the nighttime airglow are made. For two time periods in each year, in approximately February and October, the Odin orbit track is closely aligned with the solar terminator and so provides a solar zenith angle at the tangent point of the line of sight that is very close to 90 degrees at all latitudes.
A second consequence of the dusk/dawn orbit is that the variation in solar zenith angle is somewhat limited. A dusk or dawn local time implies that the sun is very close to the horizon. The following figure shows that the range of solar zenith angles over a year is between approximately 60 and 120 degrees, with most of the variation occurring at the poles where the local time quickly sweeps from dusk to dawn or vice versa. The near polar inclination of the orbit also limits the variation in solar scattering angle. It also ranges from approximately 60 to 120 degrees and is most often near 90 degrees. All OSIRIS measurements fall within the gray area on the plot. It can be seen from the figure that when the solar zenith angle is near 90, the full range of solar scattering angles are possible; however, as the sun rises higher in the sky, the solar scattering angle becomes closer to 90 degrees.