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Measuirng crosswind velocity

 
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  #1  
Old 08-02-2009, 12:32 PM
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Location: Patagonia Mountains, Arizona
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Measuirng crosswind velocity

The article by Bryan Litz "Fullbore Bullet Update" in the latest (Aug,1009) Precision Shooting magazine was very interesting. In Fullbore and Palma the rules regarding the bullet and cartridge have forced the bullet designs to become very similar for most manufacturers. That also indicates to me that little future improvment is to be expected in the way of new bullets.

In looking at the computer simulations of hypothetical matches one thing stood out clearly. Each simulation showed the errors were dominated by horizontal stringing which I assume was the result of the simulation programs using a typical statistcallly weighted amount of error in wind deflection estimation for each shot. Is that a correct assumption?

If that's the case then it would seem to me that the area that needs most attention in long range shooting is to improve the ability to determine the crosswind velocity over the range, or at least the overall effect of whatever crosswinds exist over the trajectory. No other error source is close!

The only device to measure downrange croswinds for shooting purposes I've seen was published in the Very High Power publicatioin of the FCSA about 15 years ago. It was an article by Israeli researches using a PC, a laser, and a couple of photodetectors. They claimed a demonstrated abilty to measure and supress croswind deflection by about 90% (stilll a 10% error in detmining the effect of the crosswind relative to making no correction) and stated that to be about equal to an expert shooter esitmating defelction from watching mirage. flags, or similar indicators. I've not found anyting on that work since from web searches.

There are some references to the aiming system used on the Abrams tank which uses some form of laser crosswind measurements but few details. There was a DOD "request for proposals" for a riflescope which woiuld have both drop and crosswind compensation a few years ago. That was on both some websites and a military laser trade journal. The result of that either came to nothing or became classified. I presume the latter.

There are companies selling commerical "scintillation anemometers" which measure crosswind velocity vs distance at ranges of a few kilometers. Most list applications such as predicting the movement of atmospheric contaminants for envronmental studies.

I'm seems to me that portable device capable of measuring crosswind speed (and it's corresponding bullet defelection) without the need for donnrange equpement is pracical which could work to at ranges to at least a mile. It should not have to be large or unreasonably expensive. I would expect it would have a higher wind speed capability and a lower air temperature limit than visual estimation does when mirage vanishes becaue of the movement of thermal air cells being to rapid or too weak for the human eye to follow. PC's, fast cameras, and lasers have improved a lot in price and speed since the Israeli article. The hardware in the article was crude.

This seems to me to be an area where a considerable imprvement in long range accuracy for hunters as well as the military could be made with modest effort. The range esitmation and drop cacluation in shooting has been mastered with the laser rangefinder. Crosswind measuement seems to me to be the only major problem still to addressed. A scintillantion anemometer can measure the crossswind's vertical component too. That's just a second axis to callculate in the software. The vertical component is rarely of concern except when shooting in mountainous terrain. The scintillation anemometer cannot measure head and tail winds. There are doppler LIDAR's which can, but they are much more complex and costly. Head and tail wind have a much smaller effect on bullet trajectories, and in most cases can be ignored.

questions to this group.
1. Would a a device wich works as binoculars, a rangefinder, and calulates wind deflection be of use? At what price? Assume it weighs 3 lbs and is the size of large binoculars. It could also measure lead for moving target. Later models might be contained entirely in the riflecope. I'm not trying to market one, but I'd like to stimulate some manuacturer to do so. Leica or Leupold have the technology. Perhaps Bushnell or NcStar...

2. Would it be legal for competiton. Palma, F Class, 1000 Yd Benchrest, etc?
3. Would it be "sporting" to use for hunting? ( assuming it works reliably).
4, Any arguments against why it shoudn't work? The concept is essentaily to measure the movement of air cells the way a human measures mirage, but use an infrared laser to produce a dot at the target wihch will backscatter to the receiver. The receive then analizes the returning light not unlike the way an optical mouse watches the movement of the light patterns reflecting off desktop.. The unit could emphasize the the movement near the receiver and at intermediate distances based on the objective lens focus. It could do that for multiple distances simultainously and apply the proper weighting. It woudn't be perfect, but It should be better than a human wth a spotting scope can possible do. The human eye and brain simply don't have the speed or brightness resoluiton of a ccd camera and microprocessor, nor does a human have the abllity to reduce the moving light patterns mathematically to bullet deflections in real time.

5. Does anyone konw of unclassified articles in the area of optical downrange wind measurement ? Perhaps references on the web or available books.

And to Byran Litz. I just received your new book is great! It gives a lot of practical expanations to Robert McCoys book "Modern Exterior Ballistics". The sections on how error sources combine should be very useful to any long range shooter.
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Old 08-02-2009, 01:55 PM
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Join Date: Jan 2004
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Re: Measuirng crosswind velocity

Lou,

My response:

questions to this group.
1. Would a a device which works as binoculars, a rangefinder, and calculates wind deflection be of use? YES. At what price? Add $1000 to a good BRF or $1500 stand alone (pretty wild guesses) Assume it weighs 3 lbs and is the size of large binoculars. It could also measure lead for moving target. (Don't think moving target feature is necessary for LRH or most competitions) Later models might be contained entirely in the rifle scope. I'm not trying to market one, but I'd like to stimulate some manufacturer to do so. Leica or Leupold have the technology. Perhaps Bushnell or NcStar... You may wish to research one of the old Soviet contry's capabilities. They are more friendly and have a better listening ear for these kinds of things.

Additionally, how large of a market is there. In this living room one could count the number of 338 Edge, Snipe-tac and Allen Mags and get a reasonable guess at the market size.


2. Would it be legal for competition. Palma, F Class, 1000 Yd Benchrest, etc? Should be legal anywhere a wind flag is legal.
3. Would it be "sporting" to use for hunting? Why wouldn't it be? The whole idea is to make one shot on target with a quick humane kill. ( assuming it works reliably).
4, Any arguments against why it shouldn't work? Your concept is good. R&D may be a spot of bother. As in, how to get a return on investment. I talked to the folks at Los Alamos National Lab regarding development of a very simple electro-mechanical device. Up front $ were right at $500,000.00 (whew) then more to come later. Thus I chose the more simple route. With some parts from Radio Shack, some parts from an RC Controlled Monster Truck and some parts from the internet my son and I will have the thing up an running by the end of the month.......

5. Does anyone konw of unclassified articles in the area of optical downrange wind measurement ? Perhaps references on the web or available books. I'll do some snooping around LANL. They do all kinds of strange stuff here but, not with out a bunch of funding.
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  #3  
Old 08-02-2009, 03:30 PM
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Join Date: Mar 2007
Posts: 543
Re: Measuirng crosswind velocity

Lou,

So PS finally published that one...

They've had it for about 4 or 5 months. I'd better update my address with them so I get to see it.

Here's an interesting paper about the effectiveness of a wind measuring device like you describe:
http://stinet.dtic.mil/cgi-bin/GetTR...c=GetTRDoc.pdf

Thanks for getting my book, glad you're enjoying it!

-Bryan
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Bryan Litz
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Author of: Applied Ballistics for Long Range Shooting
And: Accuracy and Precision for Long Range Shooting

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  #4  
Old 08-02-2009, 05:04 PM
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Join Date: Oct 2007
Location: Patagonia Mountains, Arizona
Posts: 758
Re: Measuring crosswind velocity

Thanks for the reference Bryan. It will take me some time to digest the article but the scintillation method using a single laser is similar to what I was suggesting. The article also mentions the dopper method though I don't beiieve the additional information it provides is very useful or practical to implement in a portable battery powered unit. Considering that article is ten years old I would hope that the hardware and software has improved considerably.

There is another mehod which simply uses one or two lasers for illumination and two CCD cameras to monitor plant or dust partcles along the path. The angular velocity of each particle is monitered as they move though the beams and distance is determined by simple triangulation, giving the crosswind component along the path. It's fairly accurate but slow, expecially if the air is clear with few particles. The scintillation method does not require any particles in the air, only thermal anomolies which are present at all times. Even if they are weak they still move at the same speed as the wind.

Maybe our President will delare peace in the middle east and these devices will show up on the surplus maket the way night vision equpment was available after the Gulf war.
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