My name is Claire Bunch, I'm a hydrologic technician in Tucson, Arizona with the US
Geological Survey and today I'll be talking a little bit about particle tracking.
Particle tracking is a method that's being developed to measure stream flow by using
a video camera.
We can set up a video camera at a USGS gaging station so that it will record the water surface
and then we can take that video and then we can process it with the particle tracking
software, and actually get the surface velocity with that.
And if we know the geometry then we can go ahead and use that to get a discharge.
If the video is taken at any kind of an angle other than directly down on the water surface,
four points are needed within the frame of reference to orthorectify the image, the video.
In that case it's best to have four survey points that are put in place ahead of time
before the video is taken.
Hello I'm Fletcher Brinkerhoff, I work with the US Geological Survey.
What I did is I put some flags in the river.
I'm using four flags that we'll be using for reference points.
Additionally, a cross section of the stream is needed just to determine area for the computation
of discharge.
We are now looking across from the river right at our measurement section, and you can see
where the measurement flag is and also where the most downstream left bank flag is.
Those are 15ft apart.
The utility in this is that you could very quickly go to many different sites just take
a 40 sec video and move on to your next site and have a very comprehensive estimate of
velocity without actually having to do a real discharge measurement.
And a true discharge measurement can take an hour, hour and a half depending on how
wide a stream is, and during that time you can have debris you can have changes in stage.
LSPIV, also known as particle tracking, takes video that is recorded from the stream and
breaks that video up into multiple images.
Those images can be analyzed either by looking at the waveforms in the image or looking at
the individual particles in those images.
Those particle or waveforms as they move between images allows for the software to analyze,
not only the direction of flow, but also the magnitude of that velocity.
When you shoot video it typically shoots 30fps, so if you look at 5 secs of video, that's
150 pictures that can be used in the software.
So what it does, it takes the video creates these pictures and then what the video does,
it looks for changes from picture to picture to actually evaluate the velocity from those
changes.
Particle tracking provides some advantages safety wise for discharge measurements also,
especially during high flow flood events.
Traditionally, the only way that we could get velocity measurements is to have somebody
physically measuring the water and submerging equipment and instruments into the water column.
To be able to get velocity measurements when, one nobody is there if we had a camera set
up, or two just very quickly without having to put our people or our equipment at risk
in a large flood, can be very helpful to keeping people safe and getting a really good estimate
of velocity when normally we couldn't do that.
So the USGS in Arizona is developing a stream gage that employs the methods we just talked
about.
This includes having a video camera that is on site and connected to a data logger.
The data logger senses what the stream stage is and if that stream stage exceeds a certain
elevation, a certain level, the video camera is trigger to take video without anybody being
on site.
This gives the USGS a method for evaluating stream flow during events when nobody is on
site.
So, in addition, to video captured either by a permanent installation or by a stream
gager, we can use video that is filmed by local residents, news stations, or just other
bystanders.
Even though they won't be filming it with the intention of using particle tracking,
it can be valuable data that we can use to compute a discharge from.
The future of particle tracking is what I'm really excited about.
Here in Arizona we've developed the continuous slope area method.
I believe if we go ahead and use the particle tracking along with the continuous slope area
method I believe we can really come up with a really nice way to collect a lot of different
type of data.