Wednesday, June 2, 2010

A paper!

It's been a while since I've posted. The main reason is that I've been busy. One of the things that I've been doing is writing a scientific paper describing the prototype hardware, and the results of our season.

The paper is finally done, and submitted to "Nuclear Instruments and Methods," a journal that publishes papers on instrumentation for nuclear, particle and astro-physics. There it will be peer reviewed by anonymous referees (most likely 2 reviewers), who will recommend whether it should be published or not. Most likely, they will recommend acceptance, but they will also most likely suggest some ways to improve the paper. At the same time, the preprint version was posted to the Cornell preprint server, as number 1005.5193; click on 'PDF' on the upper right to get the paper text.

It may not be obvious, but writing any scientific paper is a lot of work, even a relatively 'simple' paper like this one. Besides the text, there are figures (graphs, plots, etc) which can take a lot of work to make. There are also many numbers to be checked. When you actually sit down to write a paper, you are forcibly confronted with all of the pesky details that you've successfully avoided over the past few months.

This was true even though we made some specific decisions to speed things up. For example, we do not discuss our on-going data analyses. These are interesting, but there is a lot to do before we're ready to publish these analyses.

The major 'result' in this paper is a measurement of the ice thickness at our site: 572 +/- 6 m. In principle, this is a simple calculation - take the round-trip travel time for the radio waves we bounced off the ice-water interface, and divide by twice (for travel in both directions) the speed of light. Unfortunately, nothing is that simple. In any material, the radio waves travel slower than Einstein's famous unchanging speed of light - that invariance only holds in a vacuum. The reason is that the radio waves interact with the medium. One way to think about this is to imagine the radio waves scattering off the atoms in the ice, so they don't travel in a direct, straight line. The speed of the waves depends on the snow/ice density throughout the trip. The top 75 meters of snow/ice (the 'firn') changes gradually from snow (density 40% of that of ice) at the top, to pure ice about 75 m down. After trying to model this myself, I consulted with colleagues and poked around in the library (now mostly on the internet), and finally found a review written by two real professionals who bounce radio waves through Antarctic ice sheets for a living. Suddenly, it was simple. Their article even included different density profiles for different places in Antarctica, along with estimates of the consequent uncertainty.

Another thing that took some time was getting comments from the other authors, and responding to them. Our paper has 7 authors from 3 institutions; everyone who contributed to the experiment and wanted to be an author. We also got some comments from non-authors, mostly people who were involved less directly.

Most of the comments were good, and strengthened the paper. Of course, a good suggestion (e.g. improve this figure by...) takes longer to implement than a bad idea that can be rejected. And, there is always discussion about expanding the scope of the paper.

With larger groups,dealing with comments can get sticky, especially if people disagree on what should or should not go into the paper (that wasn't the case for us). Large collaborations, like IceCube have formal policies and procedures for internally reviewing papers, collecting and mediating over comments from collaborators, etc.

In the end, I think that the paper came out pretty well. But I may be biased.