# Spatial and Temporal Sampling Properties of a Large GNSS-R Satellite Constellation
## 3 GNSS-R Coverage Simulations
### Effect of Orbit Planes on Constellation Coverage  
The second critical design feature of a constellation is how its satellites are distributed between orbit planes. In this series of design options, an orbit plane is defined as a group of satellites orbiting with the same ascending node longitude. With that definition in mind, we find that when a singular plane satellite constellation is divided into a constellation with multiple planes, its ZTC increases. However, when only looking at certain latitude zones on the globe, this trend may not be uniform.  
To better understand how the temporal coverage depends on the distribution of planes, two experiments were conducted where the total number of satellites and satellite inclination were held constant. These experiments first simulate the performance of a single plane of 24 evenly distributed satellites all orbiting at the same inclination. Then, the simulation is repeated for a second constellation in which the plane is split into two planes of twelve evenly distributed satellites separated by 180\({}^{\circ}\) longitude. Finally, a third constellation is considered in which the satellites are further split into three planes of eight evenly distributed satellites separated by 120\({}^{\circ}\) longitude. These results are presented in Figure 6, where the orbit inclination is set to 30\({}^{\circ}\).  
In this scenario, the ZTC in the zone near the orbit peaks grows when the original constellation is divided into more planes. There is also a ZTC increase at latitudes lower than the peaks when the constellation is redistributed from one plane to three planes. However, when observing the two-plane constellation, the ZTC measurements at latitudes near the equator can remain near stagnant.  
Using this understanding of orbit planes and inclinations, designers can better tune their constellation orientations so that both spatial and temporal coverage metrics are optimized. For this experiment, we consider a constant number of satellites all at the same inclination and in the same plane. In this case, a 24-satellite constellation at 30\({}^{\circ}\) inclination is selected. The performance of this constellation is seen in the blue curve of Figure 7. Note that coverage is lacking near 60\({}^{\circ}\). To improve it, we divide the plane into a constellation  
Figure 6: 24 h Temporal Coverage measurements at different latitudes for 24-satellite constellations at 800 km, 30\({}^{\circ}\) inclination, 16 parallel measurements per sampling, and operating with an RCG Threshold of 15. Increasing the number of constellation planes while keeping the total number of satellites constant will increase the constellation’s Zonal and Global Temporal Coverage.  
of two 12-satellite planes, one of which orbits at 30\({}^{\circ}\) and the other at 60\({}^{\circ}\), resulting in the red curves in Figure 7. As these curves demonstrate, adding this second plane at a higher inclination has the desired effect of increasing coverage above 30\({}^{\circ}\). Furthermore, if coverage at even higher latitudes was desired, the constellation could be divided into a third plane with an inclination of 90\({}^{\circ}\). This third plane will also eliminate the coverage drop near the equator present in constellations with two planes.