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