Most remote-sensing satellites inhabit a polar orbit, and it is the descending side of this orbit that is the most important to an operator because the descending side is the interval when the ground is in sunlight and imaging is possible. This article provides an efficient way to visualize and report on the start times of each descending pass of a satellite in a polar orbit.
You need to use Analysis Workbench (AWB) to create the intervals.
- In AWB, create a new scalar calculation on your satellite. Set the type to Data Element and set the data element to LLA State -> Fixed -> Lat. This enables you to access the current detic latitude of the satellite in AWB. Name it "Latitude" or something similar.
- Create another scalar calculation of type Derivative. Name it "LatitudeRate" or something similar. Set the target scalar to the new Latitude scalar that you created in step 1 and click OK. A negative latitude derivative indicates that the satellite is on the descending side of its orbit.
- Create a scalar condition of type Scalar Bounds. Set the scalar to your LatitudeRate scalar, the Operation to Below Maximum, and the Maximum value to 0 deg/sec. This condition, satisfied on the descending side of the orbit, it what you will use as a constraint for an interval list in the next step.
- Select the Time tab of AWB and create a new interval list of type Satisfaction. Give it a unique name and set the condition to your scalar condition. Click OK.
After completing these steps, you can report the descending time intervals by right-clicking your interval list in AWB and clicking Report, or by creating a custom report using the Report & Graph Manager.
