slide 66

If the orbit of a star satellite is inaccurate, it affects the baseline between two satellites, leading to imperfect removal of the flat-earth and topography phases. The residuals of these phases have a similar pattern to the flat-earth phase but with less dense fringes. The flat-earth phase is a long wavelength phase across the whole interferon, and the residuals are also long wavelength. This is called orbital error, which is more obvious in older satellites but generally small in modern ones with precise orbit determination. If the orbit of the star satellite is not accurate, it causes the wrong baseline between two star satellites. The calculation of the flat-earth phase and topography phase requires the baseline. So inaccurate baseline leads to the imperfect removal of the flat-earth phase and topography phase. The residuals of the two phases represent the similar pattern to the flat-earth phase, but with less dense fringes. You can see two formulas. For the topography phase, there is a large number of r in the denominator. So the magnitude of the flat-earth phase is larger than the topography phase. So the residuals are more like to the flat-earth phase. Looking back to the left slide, the flat-earth phase is a spatial long wavelength phase across the whole interferon. The residual is also a spatial long wavelength phase. We call it orbital rate. The orbital error is obvious in the older star satellites. However, modern star satellites usually have precise orbit determination. It means the given orbit of those is accurate. Orbital error is generally small letters, not matter.