Van Allen Probes - foot-points
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This is pretty, but what am I looking at?

These data are from the Van Allen Probes spacecrafts (

The time-series panel shows the L-shell position of the Van Allen Probes (in units of Earths radii). The map shows the satellites foot-points within the selected time range (no more than 24 hours at once). Move the selection arrount in the top panel and see the foot-points change. Hover over foot-points to see their UT time. And use the arrows in the top-left corner to load data for a different the period.

The 2 probes A and B were launched in August 2012 to study the Earth's radiation belts. As for most space science topics, studies will rely on measurements from the spacecrafts combined with a variety of other instruments, both space and ground based. For this reason, it is important to be able to connect measurements made by the probes (in-situ) with far-away instruments such as ground-based radars (e.g., SuperDARN radars).

The L-shell parameter provides an estimate of both the altitude and magnetic latitude of the spacecrafts, a very useful measurement in space science. It allows to place the measurement in the context of the Sun-Earth system (different L-shells are typically characterized by different physical phenomena, specifically, different type of coupling between the sun and the Earth).

The foot-point indicates where the probes are located in the frame of the Earth's magnetic field. Field lines extend into space, and due to their excellent conductivity they act as a mapping interface between the near-Earth space environement (out to several Earth radii) and the Earth' upper atmosphere (a.k.a, the ionosphere, above 80 km altitude).

Knowing both L-shell and foot-points allows to relate satellite observations to perturabations of the ionosphere, and vice-versa.

Where are these data coming from?

Once a week, a cronjob on my computer runs a Python script: this script accesses and downloads ephemeris data for the Van Allen Probes in GEO coordinates.

These ephemeris are stored in a MongoDB database.

Then, the ionospheric foot-points are calculated by following magnetic field lines from the spacecraft orbit (near the equatorial plane), down to 300 km altitude in each hemisphere. Tsyganenko's T96 model is used to perform this calculation (code here).

The data is accessed and displayed using a combination of node.js, express.js, mongodb and d3.js.

Check out the code on Github: sdelarquier/rbspd3

This app works best in Google Chrome.