The nature of sound propagation underwater.

So, I missed my target of one post a week. I’ve been busy learning about acoustic propagation deep ocean environments, the Soar cognitive architecture, and about other projects going on at SoarTech. Last week  my first SoarTech proposal was submitted for review. This was a Navy SBIR for Oceanography Tactics Training. Doing research on acoustic propagation reminded me of the optics class I took as an undergrad. I found it very interesting that the speed of sound changes so drastically with temperature and depth. This introduces issues when looking at propagation over large distances (many kilometers). Sound no longer propagates in a uniform manner from a point source, but curves up and down as the sound speed profile / index of refraction changes. Additionally you get interesting interference and reflection patterns near continental slopes.

I found a good book on the topic, Computational Ocean Acoustics (2nd Edition), which describes the math and theory of propagation and various simulation models such as ray tracing. The book is nice because it defines all the mathematical symbols in the text. This is something that is lacking in many of the academic papers I read. I also found the Acoustics Toolbox, a simulator package for acoustics research and associated pages with links to algorithm descriptions and other acoustics research sites.

My proposal for N182-119 described a simulation-based training system I called ShadowZone, because why not? It combines some of SoarTech’s existing web-based training products with a new Unity-based simulation and assessment environment for demonstrating acoustic propagation under various ocean conditions. It was a great two week crash course for me in acoustics and got me back into my Scientist™️ hat (you know, reading, planning, proposal writing), which was super fun and refreshing!

Craighead’s back, back again…

Once upon a time, about when I made my last post, was getting hammered with WordPress login attempts. As a result, they disabled the login page for WordPress sites. As a result of that I ignored this site for several years because every time I thought about posting something I ran into the disabled login page. While the fix was a simple permission change, I got tired of having to SSH in every time and change the permissions on wp-login.php.

Fast forward 3 years: I moved all my sites to a droplet on Digital Ocean. I’ve been running all of Silent Partner Technologies’ servers on Digital Ocean for almost six years and the service has been fantastic. Since moving this site over I’ve seen a huge speed increase when loading pages. I’m using one of the $5 droplets to host several sites and now the servers are completely under my control. On NFS the sites ran on a shared Apache instance and cost almost as much since I was paying for each site and a MySQL instance. Now all of that is on the one droplet.

I’m going to try and write at least one post a week. I’ve put my Scientist Hat back on and have taken a Research Scientist position at Soar Technology’s Orlando office. So far (it’s been 3 days) Soar has been great! I’m working on serious games, UI for training content generation, and NPC AI in the Intelligent Training group. It took 9 years, but I’m finally in a job doing research directly related to my dissertation! Weekly blog posts should help me get my writing back into shape.

I am still a partner and architect at SPT, but we’ve hired some additional programmers to take over the day to day work I was doing. Some of my posts will probably refer to SPT products and RFID because We made quite a few improvements and I learned a lot about RF since post, 3 years ago. I’m sure discussing some of it will be useful to someone on the internet. I’ve found many useful solution on blogs and maybe my writing will help someone out in the future.

CentOS6 weird file permisisons behavior.

I don’t usually write much here, but I wanted to post something about this since it took me hours to find a solution. A few weeks ago I was working on upgrading a clients server with our new web application and after copying everything over PHP kept giving me a Permission Denied error for the CakePHP database.php file. What was weird was the permissions looked fine and hadn’t changed from the previous version. After a while of messing with the permissions I ended up with the entire webroot folder at 777. Same error. After even more Googling I found a single entry on StackOverflow (unfortunately I don’t have the link any longer) that mentioned deleting and recreating the file. BINGO! Delete and recreate the file to solve a permissions issue! Weird! What I ended up doing was moving the file and using `cat` to copy it. The contents of the file were identical, the permissions were identical, but no more permission denied error.