Yesterday we had a look at the orbits of imaging satellite’s from the perspective of a stationary earth. Today we are having a look at the same orbits but showing how the orbit is actually a circle with the earth rotating inside it.
We found a model of Landsat 7 on the sketchup 3D warehouse and have created a tour showing what Landsat 7’s orbit looks like. The satellite is not shown to scale but the orbit should be approximately correct. Landsat 7 crosses the equator from north to south at about 10:00 am every 98.83 minutes (yes, it’s confusing). Its orbit covers the entire earth every 16 days and then repeats.
One problem we have encountered is animating a model across the antimeridian does not work correctly in Google Earth. We have not yet found a work-around. You will notice the model appears to jump occasionally when crossing the antimeridian. Another bug is that the background of stars shakes around when playing the tour. The stars should be stationary relative to the view, as the satellite’s orbit is nearly stable with respect to the stars, drifting approximately 1 degree per day (360 degrees per year).
Here we see Landsat 7’s orbit over the course of 24 hours:
You can view it in Google Earth with this KML file
. For best results turn on sunlight (the icon with a rising sun on the toolbar). We also include in the KML the orbit for 24 hours or for the full 16 days.
Note that Landsat 8 shares the same orbit but with an 8 day offset.
This is what its 16 day orbit looks like relative to the earth:
We couldn’t record the full 16 day orbit as a tour as Google Earth couldn’t handle it. We believe it is possible to use a KML feature called a Track to improve performance, but we have not yet figured out how to do that.
For comparison, here is the layout of imagery tiles that are captured by Landsat 7 as provided by the USGS:
