8/23/19 Report - Atlantic Heating Up. Mint Error. Problems With Air Tests and Tests Gardens.

Written by the TreasureGuide for the exclusive use of treasurebeachesreport.blogspot.com.

Source: nhc.noaa.gov

An area of low pressure just east of the upper Florida Keys has a 70 percent chance of developing into a tropical cyclone over the next five days, but models disagree on what it means for South Florida this weekend.

The system, which would be named Dorian if it gains tropical storm status, has a 40 percent chance of developing over the next 48 hours.

While heavy rain is expected from the would-be Dorian, National Weather Service meteorologists in Miami said Friday morning that “global weather models are all over the place and not in good agreement with how they handle this disturbance.”

Looks like the Atlantic is becoming more active.  We might actually get improved beach detecting conditions some day.

We're getting a small bump in the surf now. In the next couple of days we might get up to three feet - which still isn't that much.

---

If you check your clad finds sometimes you'll find some interesting things.  Here is a 2016 clad quarter.

2016 P Quarter Showing Strike Through.

Here is a closer view of the strike-through.

Strike-Through on 2016 Quarter.

This has been identified as a strike-through, which is when debris is on the planchet when the die hits it to impress the image.

---

Conducting an air test or using a test garden is very different from metal detecting in the field.  When you conduct an air test, you start with a known target and do whatever is needed to get the best signal from the metal detector.  That is the opposite of what happens in the field.  In the field, instead of bringing a target to the detector and presenting it in the best way possible, you cover large areas of ground not knowing if there is a target or where in that acreage a target might be hiding.  In that situation, your behavior is very different.  You scan large areas - probably very quickly.  Your sweep pattern, including speed and height and other factors come into play, as well as various sources of noise, ranging from wind, surf, other people, tinnitus, electrical and radio interference, and ground mineralization to junk.  An air test has very little in common with actual metal detecting.  It is, however, a good starting place for learning about your metal detector.

A test garden is in a specific location.  The detector doesn't have to adjust to changing salt mineralization or any kind of changing ground mineralization, not to mention the fact that and you know where the targets are and what they are.  

I can't stress enough the huge effect of having a known target in a specific location, as compared to not knowing if there are any good targets, or where it might be in an expansive area, and not knowing what kind of target it might be if there is one.  To make that even more complex throw in an unknown quantity of randomly scattered junk targets of various types.

One of the early goals of psychologists was to measure the sensitivity of our sensory systems. They found that factors other than the sensitivity of sense receptors influence whether a stimulus is detected or not.  There is no single fixed level below which a person never detects a stimulus and above which a person will always detect it. Other factors are involved.

This approach [signal detection theory] abandons the idea of a threshold. Instead, the theory involves treating detection of the stimulus as a decision-making process, part of which is determined by the nature of the stimulus, by how sensitive a person is to the stimulus, AND by cognitive factors...  when a person is quite uncertain as to whether the stimulus was present, the individual will decide based on what kind of mistake in judgment is worse: to say that no stimulus was present when there actually was one or to say that there was a stimulus when, in reality, there was none.

To sum that up, detection of a signal is not only determined by the sensory system but also affected by decision strategies (cognitive/thought processes).  Sensory thresholds vary depending upon decision strategies and the value of targets and risk of mistakes.  Thresholds are also affected by expectations.  What weight do you put on the possibility of missing a good target versus digging junk?  Are you excited and expecting to find something big or getting worn out and tired of digging junk.  Those kinds of things can affect your focus, attention and perceptions as well as other behaviors.

An example from everyday life illustrates this point. Suppose a person is expecting an important visitor, someone that it would be unfortunate to miss. As time goes on, the person begins to "hear" the visitor and may open the door, only to find that nobody is there. This person is "detecting" a stimulus, or signal, that is not there because it would be worse to miss the person than to check to see if the individual is there, only to find that the visitor has not yet arrived. 

(See https://psychology.jrank.org/pages/585/Signal-Detection-Theory.html for more about that.)

Signal detection theory was developed during World War II when radar was invented.  They wanted to study how operators could detect planes on the radar scope also showing other return (noise).

The effect of knowing where a target is and working backward to see if you can detect it is very different and results in very different results than you would get not knowing if there is any target at all.  In a test bed, that can be somewhat minimized by closing your eyes and truing to detect as if you had no idea where the targets were.

Unfortunately there is no perfect way to compare metal detectors.  They have so many different settings and there are so many variables in how they are used.  A large part of success is determined by how you use the detector rather than its capabilities.    Air tests and test beds definitely have theie place, but the limitations should be recognized too.

---

Happy hunting,
TreasureGuide@comcast.net

6/2/14 Report - UPDATED. Metal Detecting in Black Sand, Salt Sand, and Noisy Environments, Gold Rings From Fresh Water Lake, and Increasing Surf

Written by the treasureGuide for the exclusive use of treasurebeachesreport.blogspot.com.

Gold Ring Found by Robert H.
Photo submitted by Robert H.

On the Treasure Coast the wind has increased and the surf has increased as well.  We'll have to see what that does.  I don't like the angle right now.  I expect the waves to be too much from the East.

------------------------------

UPDATE:  I went to the beach this afternoon after high tide.  I looked at about 8 different spots along a stretch of just over twenty miles.
I didn't see any erosion except for some little six inch cuts at the best of all the spots (not counting Fort Pierce South Jetty Park where the new sand has washed away to create a six plus foot cut already). 

Below are pictures of two beaches that I saw. 

Jensen beach had deteriorated since I last showed it.  Notice the sea weed.  That is a bad indicator.

And also shown below is the best of the natural beaches.  Still nothing but six inch cuts.

Jensen Beach Just After High Tide Today.

The Only Cuts I Found on South Hutchinson Island Other Than At South Jetty Park.

It seems I was right about the angle of the wind and waves.  The waves were a good four to six feet but the angles were wrong and the beach detecting conditions remain poor.

-----------------------------------------------------------

Robert H. detected a fresh water lake close to his home and found three small gold rings and a pendant. 

Above is shown one of the gold rings.  It is a very common type.  If you've been detecting very long you've probably found more than one of these.

----------------------

The signal you get from your metal detector even if it is a good signal, always occurs in a background of noise.  Noise can keep you from hearing a signal, and therefore cuts down the effective depth that you can detect targets.  Generally speaking, the more noise there is, the more good signals you will miss.

Signal detection theory was developed during World War II when they were developing radar systems and trying to identify blips on a screen indicating the presence of planes.

We all know that you don't have to talk so loud when you are in a quiet room with one other person, and you have to talk much louder to be heard and understood in a noisy room.  That is a simple illustration of the signal in noise problem.

There are a variety of sources of noise when you are detecting.  Some are external, such as wind and the noise of waves breaking.  Some internal, such as tinnitus (that ringing sound you might hear in your ears, and even distracted thoughts.  And some noise come from your detector and the ear phones, such as the signals caused by black sand or minerals, or static in the ear phones caused by various things such as lightening or power lines or nearby metal detectors.

When you do an air test some sources of noise are eliminated or minimized and the noise level can be relatively low.  That results in unnatural results, sometimes better than what you would expect in the field.  In an air test, however, the results can also be worse than what you would get in the field.

Usually there is little difficulty in detecting large shallow targets that create a loud distinct signal, however, when you are trying to detect smaller or deeper targets that give a more faint signal, many of those signals can easily get lost in the noise.

Some detectors give very steady or stable threshold sounds.  That is the sound you hear when the detector is not detecting a target.  Others have a rough or unstable threshold.  An unstable threshold is a source of noise that can cause you to miss perfectly good signals and targets.

If you can adjust your threshold so that it is more steady, you might increase the probability of hearing good signals.  I say "might" because there are other factors that must be taken into account.

If you just increase the volume you will be increasing the loudness of the good signals, but would also be increasing the noise level.  That will not necessarily help you hear the more subtle signals, which can still get lost in the noise.

Here is a key point.  Lowering the threshold level too far to either eliminate the threshold or even to create a very stable threshold is not always a good thing to do.  The threshold level that is best for you will be determined by both your detector and your own operating characteristics.

When you lower the threshold too much, besides eliminating a lot of the noise, you can also lose a lot of the good signals. 

I personally run my detector very sensitive and fairly loud.  I hear the salt mineralization and other noise.   That doesn't bother me much, because I can usually identify those sources and distinguish those sounds from the good signals. 

Since we always operate in a more or less noisy environment, you should be aware that you are always attempting to discriminate between good signals and noise (bad signals.)    Sometimes that is relatively easy and sometimes more difficult.  One good thing to do is make any adjustments you can that will help  reduce the noise to signal ratio, without losing much good information.  That includes changing detector settings, headphone adjustments, and even your mental state.

If you hunt in all-metals or pin-point mode, you will hear a lot of things, many of which are not good targets.  You might, for example, hear concentrations of black sand or salt mineralization.  I'm talking about VLF detectors here.  Some people have a lot of trouble with that.  They think they can't hunt in black sand or salt areas without decreasing sensitivity.  They complain about their detector "falsing."  I don't have much trouble with that.  I generally run my detector the same over black sand as over non-magnetic sand, and over salt mineralized sand as over dry sand.  I hear those effects, but am not bothered by them because I know what they are and can distinguish between those effects and signals produced by targets.   I almost never decrease my sensitivity settings.   I really can't remember having done that.

If you are working over layers of black sand for example, your detector will respond to the black sand.  I say it sounds like a twang.  Smooth undisturbed layers will create a gradual sound, while a footprint or distinct edge in the black sand will sound more like a target.

Watch as you detect these things and you will see what it is that your detector is responding to.

If there is a coin in the black sand you will have a lot of noise but you will still be able to identify good signals.  Coins in black sand will cause signals that are more distinct than the twang of smooth black sand. 

Don't try to avoid all noise.  I've heard very experienced detectorists using very high-end detectors complain that they could not detect in black sand.  I used the same type of detector and detected in black sand every time I saw it and didn't make any adjustments to my settings at all to adjust for the black sand.  I simply listen to the sounds made by the black sand, but can distinguish other sounds created by targets in the black sand too.

The same thing goes for wet salt sand.  Where the salt water has just come up and stopped and then receded, at that edge, you might get a false signal.   Many times you will be able to see the edge that you are detecting. (Anther reason to keep your eyes open while detecting.)

That doesn't bother me.  I know what is creating the signal (noise in this case), and it doesn't bother me at all.  That is part of getting to know your detector.

If you learn to understand your detector and what it is telling you, you won't be bothered by noises like this.  In fact when you understand what it is, the noise becomes information. 

You might be surprised by the types of environments you will be able to detect when you learn how.

Don't try to avoid all noise.  Some noise is actually information when you learn what it is.

Don't be deterred by some falsing.   Try to identify the cause the falsing, which might not be falsing at all.


I'll be watching to see how the beach develops.


Happy hunting,
TreasureGuide@comcast.net