[J_Player]

Yesterday I made a preliminary study to learn something about using an IR thermometer for treasure hunting. I took an infrared thermometer with similar specifications to the Mastech MS6530 to the beach to see if there was any promising indications that it can be used for dry sand hunting. The thermometer was an inexpensive Alltrade model #480742, with a 0.1 degree resolution, single laser pointer, and D:S ratio of 10:1. The D:S ratio of 10:1 is fairly close to the 12:1 ratio of the Mastech MS6530, but the slight difference is not important in the close range study I conducted.

The purpose of the study was to see if this thermometer would pick up any usable readings from coin-sized objects buried in the local beach sand. If I could find some consistent readings over coins and other buried objects, then It would warrant further testing to determine how to detect these objects in the sand. I brought along a collection of small objects to bury that included the following:

New US dollar coin, silver quarter, clad quarter, sterling salt shaker 1.5" tall, sterling silver ingot 1"x2"x1/2" thick, 0.8 gram sterling silver ring, 7 gram 14K men's ring, 3.5 gram 14K womans ring, new US nickel, gold plated men's watch without band, clad dime, clad penny, aluminum dog tag 1.25 inch dia on a steel ring, aliminum clip 1/2"x1.5"x1/16" thick, nugget of melted aluminum 1"x1/2", 2 brass keys on a steel key ring, toy cast zinc car 3" long, 16-penny steel nail, 2 stainless steel buttons, 1-tablespoon stainless steel measuring spoon, bent copper strap 3"x1/2"x1/32" thick, 3-oz flat lead fishing weight, 1-oz oval lead fishing weight, lead sheet 1.5"x3/4"x0.10"

These items were chosen because they have different heat transfer properties, and are items that could be expected to be found on a beach. (in fact, all of them were found on the beach except the silver ingot and the nail). I also added a steel pliers/knife tool to see if a larger object would make any difference.

The study was performed in hazy sunshine with a cool 60F degree breeze coming from the ocean. Before conducting the study, I marked a 3-foot by 6 foot area of the sand to bury these objects. This area was located about 2 feet vertically above the high tide line in dry sand. I scanned the area with a VLF metal detector and removed all the metal targets I could find within 2 feet of the test area. Then I raked through the sand to remove any pebbles over 1/2 inch size. I took preliminary readings I took temperature readings from 6 inches above the surface. I found the sand temperature varied between 78F degrees and 110 degrees depending on where the shadows were. In order to eliminate any cool readings from shadows, I dragged a board over the sand to smooth it so there were no shadows, and waited a half hour for the temperature to stabilize. at the end of this time, a survey showed that the temperature varied between 94 and 106 with as much as a 5-degree gradient over a 1-foot area of smooth flat sand. I waited another half hour and found no change in the temperatures. Further investigation showed that the sand was damp below the dry sand at depths that varied from 4 inches to 7 inches in the test area. It seemed likely that the non-uniform damp sand beneath could be influencing the surface temperature. After checking other areas of the dry sand, I discovered this entire beach has the same uneven damp sand layer beneath the dry sand.

So I used the test area and buried the objects with their top surface 1 inch deep to see if there were any noticeable changes in the areas where they were buried. After an hour had elapsed I could find no changes. I figured that maybe these objects need to be closer to the surface to be detected with an Infrared thermometer. So I dug them up an buried them at the surface, and I covered them with 1/8 inch sand over the top. 1/2 hour later I took readings, and found that there were minor variations in temperature where a few of the objects were buried that registered up to 1F degree. The problem was that some of these readings were higher at the buried object, others were lower, as in the case of several silver objects. But most of the buried objects showed no change in temperature where they were buried.

For example, none of the gold or aluminum showed any change. The Silver ingot was 1F degree cooler, the silver salt shaker was about 1/2 degree warmer, the silver quarter showed no change. The steel pliers area was about 3/4 degree cooler. Sand is used as a thermal insulator in some heat-treating methods, as it helps buried metals to maintain their temperature. If I had to guess, I would think that the bulkier objects in this test retain their heat longer than the lightweight objects. I moved these objects from 1 inch depth of cooler sand to 1/8 inch depth, so I would expect the lighter objects to heat up more rapidly from conduction of the sand surface layer. But none of these temperature variations at the buried objects seems very significant when considering the temperature gradients of the sand area before burying these objects. If I also consider the high temperature variations caused by shadows from the footprints in the sand, I can't imagine finding any buried objects anywhere on the beach this day using an infrared thermometer.

After running this preliminary study, I was left with a feeling that Infrared may not be a very good tool to detect small objects buried in the local beach sand. The biggest problem is the sand temperature varies with the shadows from footmarks in sand to enough to obscure the targets during the daylight. Second, it appears small targets need to be close to the surface in order to detect the small temperature variation at all in the daylight, and so far, I got no consistent readings on the buried objects. The cheapest metal detector can locate buried objects better than the infrared thermometer did in this study. Keep in mind this is only a simple study, not a definitive test. And my feelings are only applicable to what I experienced at this particular beach.

I think that there still may be some use for infrared possibly for larger objects closer to the surface. If an object is buried in soil that allows bulky objects to heat up during the day, then these objects may retain their heat into the twilight and dark times. This may work better in regular soil than in beach sand. If such a condition of lingering warm spots on the surface exists, then I think a thermal imaging camera is a much better tool to find the warm and cold spots rather than an infrared thermometer.

(Unrelated note: While I was waiting for the test area sand temperature to stabilize, I hunted the beach with my VLF metal detector and found a handful of coins and a 14K gold ring that I dug from 7 inch depth).