If you just discover the GRACE Plotter series, start with this article first : Da Vinci, Saint-Exupéry and the old Irish distillery.
Lies, damned lies and statistics
You know the quote by the British Prime Minister Benjamin Disraeli. “There are three kinds of lies: lies, damned lies, and statistics”. The quote is actually from Mark Twain who attributed the sentence to Disraeli. Benjamin Disraeli was known as an exquisitely clever and subtle man. It is said that he was amongst the most intelligent men in the world, but that every time you left his office, you felt like you were the most intelligent man in the world. We suppose that as a politician, he was very aware of the power of statistics. He might even have had a very in-depth knowledge of it, hence his exclamation. What better than statistics to demonstrate that your opinion is trustworthy, especially if your intention is to convince the public? Can we make numbers say what we want them to say? Who knows. Can statistics lie? That might be a far-fetched idea. Can we bundle a pile of selected numbers into a well-presented package, and use it to support a public opinion with scientific evidence (the so-called statistics)? Your guess is as good as mine. Have statistics ever been used to mislead the public? What an outlandish suggestion!
The purpose behind the title
Of course we always try to entertain you, to make you think, and to captivate your mind. Be relieved, the purpose of this article is not nefarious… Our statistics have a very restricted reach, and they matter only to a small circle of crazy lunatic experts who find bliss by studying the gravity field of the Earth. How romantic! In our world, “statistics” are merely measurement residuals in the process of orbit restitution of geodetic satellites. A measurement residual is the difference between a quantity that was measured in flight by the satellite’s instruments (the “real measurements”) and the same quantity calculated by the software, using models and the laws of physics (the “theoretical measurements”). We study the sum of the squares of the residuals, and that number gives us a quantitive value representing the quality of the orbit restitution. If the theoretical measurements are close to the real measurements (i.e. the number is small), then we made a good job! The life of a space geodesist is to minimize the residuals. He ought to think of it by day and dream of it by night… (the well versed amongst you may have recognized Henry Ford’s quote about business). So you see, our statistics are as straightforward as it gets. There is no post-processing on them. No embellishment. Well, wait… Didn’t we weight the measurements according to the cosinus of the latitude? Well, yes, but that’s the story for another article.
New features and available data
So, let’s get back to our visualization software. The purpose of this article was to introduce you to the brand new features in our tool for gravity field, the GRACE Plotter. There are a lot of them. Any kind of quantity that comes in our out of the orbit restitution can now be visualized with only a few clicks. Here are some of them:
- Measurements (K-Band Ranging and accelerometer data),
- Orbits (intersatellite distance, altitude, semi-major axis, inclination, eccentricity, right ascension of ascending node, argument of perigee, anomaly),
- Measurement residuals,
- Arc failures, routines involved, percentage of arc successes,
- Statistics on normal equations (number of truncated eigenvalues),
- Statistics on gravity solutions (temporal coverage, monthly intertrack distance at the equator, RMS over basins, noise over deserts)
There is even a section with satellite events, where you can see what happened to the satellite while it was flying (when the instruments were down, when they rebooted the processing unit, when there is a center of mass calibration manoeuver). All of this is now at the reach of a click. Just for you eyes, courtesy of yours truly. No more digging into disk archives, no more “grep”, “cat” and “awk” in obscure g-zipped files. No more scratching your head around. We made it as easy as it could possibly be. If you want one for yourself or your kids for Christmas, contact us, we’d be happy to make one for you. Read the original articles too: Fish, tools and investment and Da Vinci, Saint-Exupéry and the old Irish distillery, where we boil down our philosophy and our design methods.Legacy version Modern version
Let’s show you a few images of what you can do, and give you the link below.
The GRACE and GRACE-FO intersatellite distance
The altitude of GRACE-C
Obviously something went wrong with the accelerometer
Other brutal events happened at 12:00 and at 16:00
A graph to compare the spectrae of solutions
A comparison between GRACE and altimetry