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Advanced Marksmanship mirage thoughts

goober

Sergeant
Full Member
Minuteman
Jun 13, 2008
195
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Auckland , New Zealand
I love this subject matter and am always wanting to pick the brains of those that know more than me -they are many I am sure !
Here is an article I found that looks quite good.

You can link to it here also and click on the images that dont work or show here
http://southtexasshooting.org/multimedia/text/mirage.html

South Texas Marksmanship Training Center
MIRAGE AND CONDITIONS THAT EFFECT TARGET IMAGE IN RIFLE SHOOTING

CLICK IMAGES TO ENLARGE DIAGRAMS CLICK HERE to download in Word format
The smallbore rifle shooter can, when conditions are difficult, fire many sighting shots to verify his judgment and
determine the correct sight settings before beginning to fire his record score. The high power rifle shooter has only two
(2) sighting shots before firing his record string at long range. It is therefore important that he develop the ability to
“read” wind conditions at long range, and before beginning a string-of-fire at long range. The shooter must take
advantage of all the indicators available – range flags, trees, grass, dust, smoke and mirage and be able to interpret
them. Since the high power rifle shooter has only two sighting shots, the ability to read mirage can make the difference
between merely a good score and a possible a high-X score.

A mirage condition is not a handicap, since it offers a very accurate method of perceiving small wind changes which, if
time permits, may be waited out. Not all wind changes can be waited out; therefore the shooter needs some
understanding of the ways in which various mirage conditions can affect the target image.

The term ”mirage” as used by the shooter does not refer to a true mirage, but to heat waves and the refraction of light
as it is bent passing through air layers of different density. Light which passes obliquely from one wind medium to
another it undergoes an abrupt change in direction, whenever its velocity in the second medium is different from the
velocity in the first wind medium; the shooter will see a “mirage”.

A familiar example is a stick projecting from water. The water surface is the plane separating the two (2) mediums, (air
and water), and the stick has the appearance of being bent at the water surface. The same phenomenon occurs as
the light from target to shooter passes obliquely downward through an atmosphere at uniform temperature. The
bending is due to this refraction; which is barely perceptible at 1000 yards and negligible at 500 and 600 yards, but
nevertheless it is present.

The density of air, and therefore its refraction, varies with its temperature. A condition of
cool air overlaying warm air next to the ground is the cause of heat waves or “mirage”.
The warm air, having a lower index of refraction, is mixed with the cooler air above by
convection, irregularly bending the light transmitting the target image to the shooter’s eye.
(Fig. 1) shows greatly exaggerated, the vertical displacement of the target image by heat
waves. An elevation correction is evidently necessary in order to center a shot on the
target.

Heat waves are easily seen with the unaided eye on a hot, bright day and can be seen with spotting scope on all but
the coldest days. To observe heat waves, the scope should be focused on a point about midway to the target. This will
cause the target to appear slightly out of focus, but since the high power rifle shooter generally does not try to spot
bullet holes, the lack in target clarity is more than compensated by clarity of the heat waves.

Classifying mirage density
The sight correction necessary to compensate for mirage, at a given range, will increase as density of the mirage
increases. Therefore the shooter should be able to distinguish different densities of mirage, which should be recorded
in the scorebook for future reference. An individual just starting competitive shooting should not attempt to classify the
mirage into more than three (3) categories, namely: light, intermediate and heavy. The light mirage is associated with a
cool or cloudy day, when the sun can not heat the ground, and is seen through the spotting scope as a series of fine,
faint lines. Target distortion is minimal. This mirage is very useful to the shooter in detecting slight wind changes which
require the merest pinch of windage adjustment; while the mirage correction, which will be shown later in this manual is
practically negligible. An intermediate mirage will be present on the perfect shooting day with 70 to 75 degree
temperature and normal relative humidity (45 to 55 percent). The mirage is barely perceptible with the unaided eye,
but is easily seen through the spotting scope as distinct lines. Target distortion begins to be apparent and each major
change in wind velocity will also require a correction for the change in mirage. Conditions are more difficult than those
brought about by a light mirage, but are not the most difficult.

A heavy mirage will occur on hot, sultry days (60 to 75 percent humidity)
when heat waves can be seen easily with the unaided eye, and appear as
very dense lines viewed through the spotting scope. Target distortion is
extreme, small bullet hole spotters are difficult to locate, and any change
in the wind velocity will require that the shooter take into consideration the
mirage corrections. (Fig 2) shows the appearance of the three (3) mirage
categories.

In addition to the three categories of mirage that the beginning shooter should learn to recognize, there are four (4)
distinct classes of mirage in each category from each side of the target, plus the vertical mirage. Hence there is a
minimum of twenty-five (25) mirage conditions that the beginner may use in detecting wind changes – or that he must
cope with, depending on his state of mind.

It may be stated here that the shooter’s mental state may be the most difficult condition that the beginning shooter
must overcome. Wind and mirage affect all shooters on the firing line more or less equally, and in many cases it is the
shooter who creates the impossible conditions. Conditions do change for successive relays of shooters. Owing to the
different wind conditions for different shooting relays: the U. S. Army in order to select the “true best shooter” will select
the 2 or 3 shooters firing the highest score on each relay to be re-squadded for a “shoot-off”. This method will
determine the true match winner. This procedure is used in the Wimbledon Cup Match and the Leech Cup Match held
at the National Matches.

Wind causes changes!
How do the four (4) different classes of mirage come about?
Wind blows the heat waves as they rise, causing them to move vertically, obliquely, or laterally across the target. The
amount that they vary from the vertical depends on the cross wind velocity, within limits from zero (0) to about twelve
(12) miles per hour (m.p.h.). As each mirage class is described, you must keep in mind that the description also
applies to each category, and to a wind from right (3 o’clock) or from the left (9 o’clock).

The first class to be considered is the boiling mirage, with heat waves rising vertically as in
(Fig 3). A boiling mirage is present when there is no measurable wind, and when the wind
blowing from the shooter directly toward the target (6 o’clock wind) or from the target toward the
shooter (12 o’clock wind). This mirage class condition requires that the rear sight be lowered, to
center the shot group within the target. The amount of correction will depend on the category
(density) of the mirage and vision of the individual shooter. An accurate scorebook record of
mirage category, mirage classification, wind, temperature, light, sling tension, etc., combined
with knowing the rifle’s no wind zero and the zero for that distance, will enable the beginning
shooter to refine the values given below to fit his particular location.

Although the boiling mirage presents little problems in itself, the near 6 o’clock wind or near 12 o’clock wind which
appears as a boiling mirage to the inexperienced shooter can present quite a problem when it is fishtailing from about
11:30 to 12:30 or 5:30 to 6:30.

Wind correction is generally rated as a fraction of the wind’s 3:00 or 9:00 o’clock effect, with the 11:00, 1:00, 5:00, and
7:00 o’clock winds being half value. The 11:30, 12:30, 5:30, and 6:30 o’clock winds could be rated as eight value
each, while the wind fishtailing from one side of 6-12 o’clock line to the other gives a combined effect of quarter (1/4)
value. With .30 cal ammunition of National Match type this will amount to a windage correction of one minute at 600
yards for a 10 m.p.h. wind and a two (2) minute correction at 1000 yards with the same wind. This small change in wind
direction is very difficult to detect by feel, but secondary heat wave lines will begin to show up in the mirage and have
the appearance of just leaning away from vertical, signaling the shooter that a change in wind direction has occurred.

A Slow Mirage
A slow mirage; the second classification, exist during a light air of one to 3 m.p.h. blowing from
3 o’clock or 9 o’clock. Heat waves will be slightly inclined as they move across the target from
7 o’clock to one o’clock of from 5 o’clock to 11 o’clock (Fig 4). Target displacement with the slow
mirage requires both an elevation and windage correction. As with the boiling mirage, the rear
sight is lowered to correct for vertical component of the apparent displacement. The horizontal
component requires a wind correction which will be into the wind, in addition to the correction for
wind drift of the bullet.

Since the heat waves are crossing from 7 o’clock to one (1) o’clock or 5 o’clock to 11 o’clock,
they are making an angle of 30 degrees with the vertical, and their vertical and horizontal
components.

can be computed in relation to the total apparent displacement:
p = total apparent displacement
v = vertical component of D
H = horizontal component of D
Then,
V = D cosine 30 degrees = 0.87 D, and
H = sine 30 degrees = 0.50 D

Experience has shown the total displacement due to heavy mirage amounts to be ≈ 1 ½ minutes. The vertical
correction due to heavy-slow mirage will be 1.31 or 1 ¼ minutes, and the horizontal correction will be 0.75 or ¾ of a
minute.

As the 3 or 9 o’clock wind rises to a light breeze of 4 to 7 miles per hour, the heat waves will
make a greater angle with the vertical and will have the appearance of crossing from 8 o’clock
to 2 o’clock or 4 o’clock to 10 o’clock. This gives the third classification, is a medium mirage
(Fig 5). The medium mirage will also require both elevation and windage corrections of different
amounts than for slow mirage. Changing the angle from 30 degrees to 60 degrees because of
the increased inclination, the corrections become:

V = D cosine 60 degrees = 0.50 D
and
H = D sine 60 degrees = 0.87 D

Going back to the total displacement of 1 ½ minutes caused by the heavy mirage, the vertical correction for a heavy-
medium mirage will be 0.75 of ¾ minute and the horizontal correction will be 1.31 or 1 ¼ minutes. Again the rear sight
is lowered and the windage correction is added to that required for wind drift.

The Effect
How examine the mirage effect with the same heavy mirage during a wind increasing from one to 3 m.p.h. (slow
mirage) to 4 to 7 m.p.h. wind is applied, the rear sight must be lowered 1 ¼ minutes and ¾ minute windage added for
horizontal component of the mirage. During the string, the mirage picture changes from heavy-slow to heavy-medium
which signals the increase in wind velocity. The necessary wind correction is made and an additional ½ minute applied
to give a total horizontal correction of 1/1/4 minutes for mirage. Adjusting for the vertical component of the mirage is
accomplished in a similar manner. The sight was originally lowered 1 ¼ minutes and the mirage picture now indicates
that only ¾ minute is needed, so the sight is raised the difference, which is ½ minute. The beginner shooter should
practice mentally so that he is able to make the necessary changes without becoming confused.

A fast mirage, the fourth classification, will be visible when the wind velocity reaches the
gentle breeze stage of 8 to 12 m.p.h. from 3 o’clock or 9 o’clock. The heat waves will move
horizontallyacross the face of the target (Fig.6) and the apparent target displacement will be
only horizontal. The fast mirage thus requires only additional windage correction. Wind
velocities over 12 m.p.h. are indicated by the heat waves having the appearance of being
stretched straight, and letups can be detected by slight waves beginning to appear on the
mirage lines.

Boiling with lateral movement
The last and most difficult mirage picture to identify is the “boiling mirage with lateral left or
right secondary heat waves” ( Fig.7), which is an indication of the wind coming in from
between 9 and 12, 9 and 6, 3 and 12, or 3 and 6 o’clock. An easy
scorebook notation is the word “boiling” with an arrow drawn through
it to indicate the direction of the secondary heat waves. The primary
and secondary heat waves are caused by the 2 components of the
wind, a 6-12 o’clock and a 3-9 o’clock component, the latter being the
more important in detecting wind shifts. The secondary heat wave lines
should be read in the same manner as the previously mentioned classes,
with the secondary lines indicating that both vertical and horizontal
corrections will be necessary to compensate accurately for the mirage
displacement. The new shooter should be on the lookout for the
appearance of these secondary waves while firing in the other mirage
classes.

Mirage can also be used to determine the true wind direction. Traverse the spotting scope until a “boil” is seen, then
the wind is parallel to the axis of the scope. Turning the scope through 90 degrees will be equivalent to observing a 3
or 9 o’clock wind. The mirage classification gives the wind velocity up to about 12 m.p.h.

The beginning shooter can possibly keep abreast of the mirage changes, during slow-fire competition, by plotting them
on the call circle in the scorebook. You can draw one or 2 wavy lines through the circle to indicate the mirage
classification. A category change can easily be shown by putting the initial L, I, or H in the circle and still have
sufficient space remaining to plot the call for the shot. However, do not spend to much valuable time at this. It should
not require more than 3 to 4 seconds to note a mirage in this manner and the target will, no doubt be in the pits during
that time. If more time is being consumed, additional practice is necessary and several trips into the country, between
matches, with the spotting scope can b beneficial.

(Fig. 8) is a tabulation of corrections in minutes, that will aid the new
shooter in learning the effect that mirage can have on the target image.
The new shooter, wishing to apply the methods of doping the mirage that
have been described, must keep in mind that intensity of the mirage
seen will very according to each person’s vision.

The tabulation of corrections was extracted, mostly, from the experience
of shooters. Values given will have to be modified somewhat by new
shooters for mirage pictures that are distinct to him, at his geographical
location.
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Fig 1
Fig 2
Fig 3
Fig 4
Fig 5
Fig 6
Fig 7
Fig 8
 
Re: mirage thoughts

One error, some EIC Service Rifle Competitions do not allow for sighters. This competition favors folks who get the wind exactly right during the 300 yard rapid fire event.
 
Re: mirage thoughts

Don't think there is no mirage in cold weather. Anyone who has done any shooting on the tundra of the Arctic or snow covered plains knows mirage is there.

Regardless of Temps, air moves and light reflects off that air (or moisture in the air).
 
Re: mirage thoughts

Temps matter,

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"><span style="text-decoration: underline">Cause</span>

Cold air is denser than warm air and has therefore a greater refractive index. As light passes from colder air across a sharp boundary to significantly warmer air, the light rays bend away from the direction of the temperature gradient. When light rays pass from hotter to cooler, they bend toward the direction of the gradient. If the air near the ground is warmer than that higher up, the light ray bends in a concave, upward trajectory.

Once the rays reach the viewer’s eye, the visual cortex interprets it as if it traces back along a perfectly straight "line of sight". This line is however at a tangent to the path the ray takes at the point it reaches the eye. The result is that an "inferior image" of the sky above appears on the ground. The viewer may incorrectly interpret this sight as water which is reflecting the sky, which is, to the brain, a more reasonable and common occurrence.

In the case where the air near the ground is cooler than that higher up, the light rays curve downward, producing a "superior image".

The "resting" state of the Earth's atmosphere has a vertical gradient of about -1° Celsius per 100 metres of altitude. (The value is negative because it gets colder as altitude increases.) For a mirage to happen, the temperature gradient has to be much greater than that. According to Minnaert,[1] the magnitude of the gradient needs to be at least 2°C per metre, and the mirage does not get strong until the magnitude reaches 4° or 5°C per metre. These conditions do occur with strong heating at ground level, for example when the sun has been shining on sand or asphalt, commonly generating an inferior image.
</div></div>

In colder temps is Fata Morgana

http://en.wikipedia.org/wiki/Mirage
 
Re: mirage thoughts

Whilst 3-9 oclock mirage is easy enough to read can some one give me how they go about handling an acute mirage from say 11 oclock wind .
 
Re: mirage thoughts

You don't, you just read it as left to right not fine angles.

The frequency of the waves will give you the full value reading, but you can't Kestrel a 10:30 wind and say the Kestrel reads 8 MPH, then look at the frequency of the mirage as it will be a bit subjective as to whether it is 5, 6, 8, etc. based on the visual of the waves.

All it really helps with is an overall direction, with a subjective velocity based on the look... the angle off center is not represented to the finite degree you are looking for. This is why it helps in light winds to determine downrange direction as it is influenced to a higher degree than say a tree leave.
 
Re: mirage thoughts

One method is to rotate the spotting scope on it's stand until the mirage is straight up, you are now pointed up or down wind, there is your angle.

Given fine control of the focus and a deft hand, you can focus in/out on waves starting at the ground and see which focus sharpens the image towards the top of the FOV, near or far, combine that with any other downrange indicators to get a good read on angle.

Wind reading is an art, not a science, unless you are building one of those laser inferometer gizmos they keep promising to deliver. As I explain it in class, I can tell you what I see, I can't tell you what YOU see. It's like seeing the differance between two Renaissance painters, some people just have an eye for it, some need a little work and some will just never get it.
 
Re: mirage thoughts

Mirage shows speed and direction but not angle. You have to figure that out for yourself. You also have to figure out if the mirage you are watching is the ONLY mirage between you and the target, and out where LL and I are, most of the time it is not at ranges beyond 300 yards.
 
Re: mirage thoughts

But the boil doesn't really tell you much, you already know the wind is coming from 10:30 so why move around that much ? That either means on a spotter and not on target or if you are on target coming off. The frequency across the target front is more important than the angle.

I would much rather look at the left - right than worry about the boil direction. I can read that at my position, then use the mirage for changes in speed / frequency. Where it is coming from to me is neither here nor there from a downrange perspective, I want the course adjustment from it, not the finite angle. Just changes in frequencies, speed.
 
Re: mirage thoughts

boil means "hold up" its gonna change and that change is gonna bite you in the butt.
 
Re: mirage thoughts

I generally find "boil" means shoot fast, or at least faster... because I hold my wind and not dial it, I have the ability to engage quickly, thus not getting bit. It's guys who dial on the wind who get hurt by a boil, because they don't have time to remove it.

But in the context of what they are saying by turning into the mirage to find the boil, that is not a shooting situation. At least not in this case, they are talking about looking for the angle from center.
 
Re: mirage thoughts

Yeah, the turning the scope thing is just a teaching aid, it helps noobs understand more about what they are looking at downrange. Other than a square range as a coach, it's not what I'd call practial for much else.

The methods sort of 'trickle down'. You start off with the best spotter on a solid tripod, then a field scope on a less than optimum position, then call it yourself in the riflescope, and eventually you call it by Mark 1 Mod 0 eyeball fairly close. It's a learned skill, but like many others, one you never truly perfect.
 
Re: mirage thoughts

Do any of you have any good clips you can post and comment on what you are seeing ?I have down loaded one but want to edit it -if possible to post as it shows some great mirage sequences .
It does blow me away that only the most experienced guys are currently answering this post -this is a great subject and one all shooters should try growing to be proficient with -where are the noobs??
 
Re: mirage thoughts

Is there a practical exercise one can do to become more proficient in a mirage condition?

I shoot small bore, read .22lr, silhouette and mirage kicks my butt more than the wind.
I have a pretty decent spotter telling me what the mirage is doing but to translate that in a solution at times escapes me!

N
 
Re: mirage thoughts

The thing I like about mirage is it is often easier to see mirage at different distances than other wind indicators such as blowing dust, leaves shaking, etc. Out in the desert there is plenty of mirage but not so much of other indicators at times.

Also, mirage gives you the correction whereas a wind meter gives you a speed and then you have to figure whether it is 1/2 value, full value, etc. Basically a full value 7 mph mirage looks similar to a half value 10 mph mirage from the shooter's perspective. If you get good at reading the mirage you can get pretty good at SWAG wind calls.
 
Re: mirage thoughts

Allen- practice is all I can suggest. Get behind the scope yourself and get familiar with what mirage looks like and how it behaves.

Develop a dialogue with your spotter so you can understand eachother. Have him look through a spotting scope and have him tell you what he sees while you are looking through a scope at the same time. Then you will understand what he is saying when you aren't on the scope.

In the end, you need to learn how to look at the mirage and know what adjustments to make based off what you see. Have someone else shoot while you spot the wind based off mirage and give your shooter calls. You will learn from experience what decisions result in a good call versus a bad call.