First Software Engineering Run for Advanced LIGO

Most of the visible work on Advanced LIGO has been revolving around the installation of new instruments that are needed to increase the sensitivity of LIGO about 10 fold.  While this is exciting, it can feel a little like being on the outside looking in for data analysts like myself.  But there is still much to prepare for!

The first step in that preparation starts in a few days with the first Software Engineering Run (which we abbreviate ER1 - there's longish, boring story on why it isn't being called SE1).  The goal of this is to start testing our computing infrastructure and data analysis methods with simulated data (remember, Advanced LIGO is still not complete).  For this first run, we will be simulating the channels of data that would contain information about a gravitational wave.

But what is a channel?  Just like channels on a TV, LIGO has many different data streams called channels that report on basically everything involving the instrument.  Besides the channel that will carry information about gravitational waves, we also have channels of data from seismometers that tell us how the ground is moving beneath us, channels from microphones placed around the detector that tell us about loud noises like thunder that can cause vibrations in the detector, and channels that tell us how different places on a mirror inside of LIGO is moving (and we can combine channels like this to tell if the mirror is moving up, down, sideways, front to back, rolling, etc.).  This is just the beginning of the channels we record at LIGO (there are hundreds per detector)!  We use these to cancel out unwanted movement and to double check if a potential gravitation wave is real or caused by vibrations in our environment (we would be less likely to claim a detection around the time that our seismometers indicate a train moving on the tracks a few miles away from the detector here in Louisiana).

So, we are starting out small with ER1 and focusing on just the gravitational wave channels (with simulated gravitational waves included to give the detection software a workout).  In the future, more of the Advanced LIGO channels will be simulated and included in the run.  We plan on having about 5 or 6 of these runs until Advanced LIGO is ready to give us all of the channels for real.  But, the transition from Software Engineering Run to Engineering Run should be seamless.  Engineering Runs precede Science Runs to allow us to work out any bugs in the real detector before we start using the data for science purposes - but data from engineering runs is handled like it would be if it were science data.  As more subsystems in LIGO are installed and producing data, the simulated data for those channels will be replaced with real data.  The only difference between the last Software Engineering Run and an Engineering Run will be that none of the data is simulated anymore.

It is anticipated that, by having these ER runs, that the computational infrastructure for Advanced LIGO will be ready to handle the new demands of the more sensitive detector.  We are entering a new era in LIGO where detections will be expected on a fairly regular basis (once the detector has been tuned into its design sensitivity).  We need to be able to respond quickly to potential detections to alert others in the astronomical community and for us to vet the detection in a time efficient way.  We want to be able to clear detections off of the table, so to speak, before others become backlogged.  Honestly, I am excited at the prospect of this since I have worked with LIGO since it took its first science data and I remember collaboration meetings being focused on how to make the data clean enough that we could see more than just instrumental artifacts or environmental contaminants.  Now I'm thinking about backlogged detections!

LIGO has several supercomputer clusters and one of them is located right here at the LIGO Livingston Observatory.  So, I went downstairs (from my office) and took a few pictures of our cluster today:

Above is a picture of the computers facing the front of the room.  Since these computers produce a large amount of heat and noise, they are isolated in their own room which also allows for the efficient use of extra air conditioning (and noise containment).  This is an odd room to be in because of the noise but also because of strong air currents moving the heat around.  The wind is noticeable and it can change quickly between a warm breeze to a cold one as you walk.

This is a close look at the computers in the racks (as we call the large rectangular container).  Each one of the horizontal shelves is a computer.  Many computers are used simultaneously to search LIGO data for gravitational waves.

This is the back of the rack shown in the previous picture.  If you are ever chilly, this is the place to stand since the heat pushed through the fans from the computers is dumped here.

About Time...

I know that I haven't been posting as much as I usually do (I like to post once a week) but life gets in my way.  For example, I had a tooth break that needed fixed and both my husband and I have come down with the cold that has been making its way around the observatory.  Basically, between life and getting work done, I haven't had a lot of time.

But today is an important day since we will reach GPS time 1,000,000,000.  This time is measured in seconds from Sunday January 6, 1980 at midnight UTC (this is the official time of the planet measured at the Prime Meridian passing through Greenwich, England) without any leap second corrections to match the rotation of the Earth (astronomers use a similar time keeping method called Julian Date which is the number of days since January 1, 4713 BC without any corrections for outright changes to the calendar [like to the Gregorian calendar - which is the calendar we use today]).  Here at LIGO, this is important to us since this is how we measure the official time for everything and this time needs to be very accurate since we will never believe a potential gravitational wave detection unless it is measured at different observatories within the time it would take a it to travel between the sites - for the two LIGO observatories, the maximum time is 10 milliseconds.

Other than it being cool to watch the time roll over to one billion (like watching your car odometer roll over to 100,000 miles) this event can cause issues with the data analysis programs that we write to search for gravitational waves.  For example, I wrote a software package while I was in grad school that we still use to produce simulations to test the efficiency of data analysis software.  My baby is called GravEn (for GRAVitational-wave ENgine) and uses the GPS time to determine where the simulations will be added to the real data (this data with fake signals is never saved together so that we don't trick ourselves into thinking we saw something real).  GravEn has specifications in its programing to return the time of the simulation in whole GPS seconds in one column of the log file and the nanoseconds after that time in another column.  I have made it so that the whole-second time is returned with 9 digits and this is now an issue since the time will be 10 digits.  It is easy enough to fix, but it must be fixed!

This new 1,000,000,000 time is not going to be of any serious concern like people feared the Y2K bug to be.  Instead, all of us code monkeys (as computer programers are lovingly referred to) need to go back and make sure that we allow enough (10) digits in the parts of our programs that use GPS time.

So, GPS 1,000,000,000 will happen today (September 14) at 1:46:25 UTC (or September 13 at 9:46:25 PM in Eastern Daylight Time).



***

My next blog post will be on Thursday and will answer the reader question on exactly what kind of gravitational waves Einstein@home seeks and how it looks for them.

Conference Calls and a Poster

Conference Calls

When you work with scientists from around the world, you end up on a lot of phone meetings.  Today (and every Wednesday) I had two. 

The first one was the "Burst" data analysis call and I drew the short straw and got to take the minutes of the meeting.  I am not someone who is good with names (I once had a class of 4 students and I messed their names up all that time - I knew each person well, I just forgot their label); now imagine that you only have a voice to go on.  This is not my strong point but it wasn't too bad today.  We discussed what needs to be done now that our latest science data run is over to complete our analysis looking for gravitational waves.

The second call was with people I collaborate with at Penn State to keep the MATLAB library of software that has been written for various LIGO purposes available and up to date.  That doesn't mean that we write it all (I have only written some of it), but we work with the program authors to make sure that their work makes gets into the hands of the other scientists to use.  Right now we are working on taking some of the programs that have been written to perform utility functions (like checking to see if a time is in daylight savings or doing calculations on where a star was at any given time) and pulling them together into a general toolbox.  Creating a toolbox like this will help keep duplication of effort to a minimum (that is, to keep people from repeatedly reinventing the wheel) and help insure that users are getting the correct values from these basic utilities.  We are right in the middle of going through this pool of computer programs to make sure that they are documented well and up to date.

Poster

Last year, I had the honor and privilege of working with the APS to create a poster on gravitational waves.  It was a wonderful experience getting to be someone who communicated the science of LIGO to the public and I learned much from the APS editors on how to express concepts in more understandable ways.  I wrote way too much content for the poster with the idea that it is better to have too much and cut it down, than to not have enough and have to create more content later.  The side benefit to this is the full version of the text that I wrote was then adapted for the science pages on the ligo.org site!

The poster as premiered by the APS at the joint APS/AAPT Meeting in Washington, DC this past February.  LIGO also arranged to have the posters included with the November issue of the AAPT magazine "The Physics Teacher" and to have the posters mailed to every physics department in the US.  I was thrilled!  So, now I am starting to spot the poster in the wild.

A few days ago, a friends of mine who is now at the Coastal Carolina University sent me a picture of it hanging outside his office:

I also just got my November issue of "The Physics Teacher" and it was so cool to get a copy of the poster in my mail box!

If you would like to get a FREE copy, you can request it (or another great poster on the top 10 reasons to study physics) from the APS here.

Sorry for getting so giddy about this!  This is just one of those things that make your day and remind you why you get out of bed in the morning.  :)

This Past Week

This week I've done both outreach and science.  If you aren't familiar, outreach is working to bring science to people who don't do science for a living; to educate the public.  This is a particular passion for me (hence this blog) since outreach lets me share my excitement for what I do with people who are interested.  It lets me remind myself of why I do what I do everyday.  Let me give you an example: looking for gravitational waves is getting the chance to discover something that no one has ever gotten to directly detect before (not that I am the only scientist looking for gravitational waves [I will do a post on the large LIGO-Virgo collaboration later] and we do know that gravitational waves exist [the 1993 Nobel Prize in Physics was awarded for the proof]) which is very exciting, but there is a huge amount of detailed work, that can sometimes seem removed from gravitational waves, that needs to be done to reach that goal.  That means, that sometimes I sit in my office and think, "Why am I so concerned about X?  This doesn't feel like it is going to make a difference."  That's when you need to take a step back from the work and see where in the big picture your work fits in.  Then I feel my motivation return.  But when I get to do outreach, I get to share what I do with someone who may have never heard about gravitational waves before.  I get to see the awe in gravitational waves that sometimes get buried in the daily work that needs to be done.  When I do outreach, I return to my desk with a vigor that I would have not had otherwise.

Last Saturday, I came into the observatory to give a tour to about 25 first year physics students from Tulane University in New Orleans.  Since I don't get to work with college students much, this day went a little differently than when I work with middle or high school students.  The questions are sometimes a little deeper (I say sometimes because you would be surprised at the insight that a 5th grader can demonstrate) and I don't need to rephrase my responses as much (meaning that I can sometimes use the big words without explaining them).  The one thing that is always the same no matter if the group is middle/high school, college, or public is that when they get to explore the exhibit hall in the Science Education Center everyone becomes a kid again.  Everyone darts from exhibit to exhibit for the first 5-10 minutes until they find one that really catches their attention and then they start experimenting on deeper levels.  I often tell groups the best part about my job is that I have a key to the Center and I know how to turn all the exhibits on (and it is the truth).

Then on Wednesday and Thursday I got to give tours of the observatory to middle school students.  The most rewarding part of working with these groups is hearing the students talk amongst themselves about how they want to work as a scientist or engineer someday.  Hearing that reminds me of when I was their age and dreamed of being a scientist.  That really makes going back to your office and doing all of the details that need to be done easier - I get to live my dream.

So, what kind of science did I do this week?  Well, I specialize in creating computer programs that go through the enormous amounts of data we take everyday to look for gravitational waves in the sea of noise that comes out of our detector.  That means that many of my issues I need to work through involve computer programming and statistics (I hope you can see now why sometimes I lose sight of the bigger picture).  To that end, I am also a 'librarian' for the computer programs that are written in MATLAB in the LIGO-Virgo Collaboration; this library is called MatApps.  I work with others from Penn State to help keep MATLAB easy to use for the collaboration and to help keep the programs we have written in a central location.  So, this week I spent time working on a tool to make it easy for MatApps users to use the programs it contains.

I also worked on reviving a project that I started about 2 years ago that will help us evaluate if any candidate gravitational waves are real by checking that the measurements are physically possible based on the detection time difference between each detector and the strength that each detector saw the signal.  I am reviving this so that I can collaborate with a friend to tailor this to the needs of the physicists that look for gravitational waves from two stars or black holes rotating around each other and merging to become one (I specialize in looking for short duration gravitational waves from unknown or unmodeled sources call bursts).  We also hope to write of the results of this work and publish it in a scientific journal.

Outside of some doctors appointments (I've had recent troubles with a kidney stone that clogged up the works), this was pretty much my week.