If you want to take your own photos,? here's an article I wrote about aerial near infrared photography that appeared in Treasure Magazine in 1992...
IR Photography - An Affordable Technology
By Marc Austin
For decades now, professional treasure hunters have been reaping the benefits from advances in technology such as satellite imagery, submersibles, and computers.? ?Discoveries like the Atocha, and the USS Central America, remind us that technology has spawned a new era in the quest for treasure.
As treasure recoveries increase, the chances of an "average TH'er" making a really large find becomes less and less likely. There just aren't that many "big ones" to go around. While there will still be some lucky TH'ers that will make sizable recoveries, the majority of treasure recoveries in the future will be made by professional TH'ers with the latest technologies at their fingertips.
Fortunately for the rest of us, there are a few affordable technologies that may still give us an edge over our high tech competition. One of them is infrared photography. A technique used by archaeologists since the 1950's to locate and map archaeological sites is proving that you don't have to spend millions of dollars to find millions of dollars.
The Basics of IR Film--Kodak IE135
Kodak IE135 is the only near infrared, false color slide film that is affordable and easy to use. It has three main advantages over standard color film. (1) It has a higher color contrast. (2) It has an ability to distinguish between growing and dormant vegetation, and (3) it has an ability to distinguish between differences in soil moisture. These advantages make IE135 the film of choice when taking aerial or ground photos of a suspected treasure location.
Fine Tuning For TH'ing
Since it is the near infrared reflectance? which will? reveal differences in soil moisture, it is necessary to enhance the films sensitivity to it by employing light blocking filters. These filters, a Wratten #15 gelatin filter, and a screw-on polarizing (PL) filter, attach to the lens of the camera and are available at most larger photographic supply stores.
The Wratten filter looks like a thin, cheap piece of yellow plastic, but it is actually a very precisely colored gelatin. It? blocks out some of the UV, all of the blue, and little of the green light. It comes in two sizes, 75mm x 75mm, and 100mm x 100mm. The smaller, 75mm size is for 35mm applications. A special holder is available for gelatin filters, but the following technique works just as well, and will save money... Cut the gelatin sheet into a perfect circle so that it fits snugly between the lens of the camera and the screw-on PL filter. The PL filter becomes the gelatin filter holder. Be careful not to scratch, bend, or leave fingerprints on the gelatin.
Other combinations of filters may be used as you become more familiar with their light absorbing? characteristics. For most outdoor applications though, the #15, and PL combination works best.
To Fly or Not to Fly
Most IR photography is done from light planes or helicopters. While ground shots can be helpful, it is aerial IR photography that has the greatest potential for locating lost or buried treasures. Aerial IR photos can reveal foundations, trails, even towns that are no longer visible from the air or the ground.
The only reason for not photographing from the air would be if the site is heavily wooded...IR film can't "see" through thick foliage. If the site is very heavily wooded, IR photography, from the air or the ground, probably isn't worth the effort.
Aerial photography is not much more difficult than standard ground photography. The biggest difference is in the planning. Scheduling a flight, with the proper plane, at the proper time, under the proper weather conditions can be a little tricky.? Communication with the pilot is essential. It's best to tell him exactly what you intend to do. (Leave the T word out of course!)? Make sure he knows exactly where you want to go, and how high you want to fly ahead of time . This will save you a lot of hassles once your airborne.
Best Plane, Best Price
The most cost effective, and commonly chartered aircraft for aerial photography is a Cessna 172, but any high wing, slow flying plane should be OK. The Cessna 172 is a high wing, 4 seat airplane with an ability to fly as slow as 90 mph. This ability to fly slow will allow you to fly as low as 500 ft. above the ground without any problems. (500 feet is as low as the FAA will allow you to fly in rural areas) . Check around, some planes are even equipped with camera mounts located on the floor. This arrangement is highly recommended
Cameras
Any quality,? 35mm camera that has a manual shutter speed control will work with IE135 film. The lens should be no larger than 50mm.
Handling IR film
Load and unload film in subdued light. Keep the film frozen until 1 1/2 hours prior to shooting, then freeze it again until your ready to have it developed. Since there are only a couple of labs in the country that develop IE135,? it will probably be necessary to ship the film to a lab. This is best done by shipping the film in a thermos filled with ice, (make sure the film is very well wrapped to avoid getting it wet) or by packing the film in a well insulated box, along with one or two of those gel-type ice packs.? I prefer this method. Be sure to mark on the box, "IR film keep frozen" . Then ship the film overnight to the lab. The lab I use? is;
? ?
Rocky Mountain Film Lab
145 Madison St.
Denver, CO 80206
303-399-6444
Exposure
IE135 is rated at 100 asa.? Because ordinary light meters are not calibrated for infrared radiation, you'll need to bracket your exposures in order to apply the correct stop factor.? First, set your shutter speed at 1/250th of a second, then set your F-stop at 4. As you begin shooting, increase your F-stops by 1/2 increments. In other words, begin at 4, then increase your F-stop to between 4 and 5.6, then 5.6 and 8,? then 8, and so on.. Take careful notes of all your exposures for future reference. By the time of your flight you'll know approximately what exposure settings to use.
Focusing
Since you'll be flying at least 500 feet,? the only focusing necessary is to set your focusing ring on the infinity mark. If you are shooting from the ground, you'll have to focus at a slightly? shorter distance than your subject. Many cameras have infrared focusing marks. Check your owners manual.
What and when to shoot
Aerial IR can reveal many things about a site. Long gone buildings, trails, garbage dumps, burial sites, and other human remains which are no longer visible, may still reveal themselves to IR film.
These "cultural remains" are always revealed by the surface anomalies associated with them. Contrary to some claims, IR film can not detect underground objects by themselves. For example, burial sites are revealed because the soil has been disturbed, creating a difference in moisture retention and surface reflection characteristics. It is not the buried object that creates this anomaly. Roads that are no longer visible to the eye, or standard film, may be located because the soil? has become compacted, and therefore holds less moisture.
These anomalies can be divided into two categories, soil marks, those images caused by disturbed soil, and shadow marks. Soil marks show up most readily under dry conditions, and shadow marks when the sun is low on the horizon.
The best time to shoot aerial IR film is when the skies are clear and the foliage dormant. Late winter , or early spring is ideal. Mid-day, full sun is recommended, partly cloudy skies are acceptable, rain is not . It's best to call the airport a couple of hours prior to your flight in order to check weather conditions.
More on developing
IE135 requires what is called E-4 processing. This process was at one time a standard process, but today, only a few labs develop it. They are; Rocky Mountain Film Lab, John Hopkins University, and with the? PK20 mailer, Kodak.
IE135 is a false color reversal film. This film is developed into slides. For enlargements, transparencies, or duplicates, an internegative must first be made of the slide. The "interneg"? is the same thing as a standard negative.
Total darkness is required to develop IR film. For this reason, only the most experienced developers should attempt it
.
Interpretation
The most time consuming and difficult part of aerial IR photography is interpretation. For the treasure hunter though, it may also be the most rewarding. Some people find that they just don't have a knack for reading IR prints. If this is your case, you can check with any universities archaeology department. Most professors of archaeology have experience reading IR photos.
The only way to learn how to interpret IR photos is by doing it.? Whether you have prints made, or you just interpret your slides, there is one thing you must remember...it's best to enlarge your photos as much as possible.? Small prints may be OK for reference, but they won't work for interpretation. 20" x 30" prints are the most commonly used, they cost around $20.
Once you have your enlargements or slides, carefully begin a methodical search for anomalies. Anomalies can be anything that looks man made, or out of place.? Anomalies can be anything from an old cart trail, which will show up as a straight, double line, to a burial site which can show up as either a lighter or darker area. Foundations will show up as a rectangular image.. Whether these images are darker or lighter than the surrounding terrain, doesn't matter.
Once you have found some anomalies, the next step is to verify these images on the ground....
Here's a tip........8 1/2" x 11"color copies of your prints can be helpful when your out in the field. Enlargements are too bulky and expensive...As you begin searching you may notice that some of these anomalies are just shadows, and have no importance. Other anomalies may prove to be very significant and should be investigated further.
Summary
Aerial IR photography is a simple, effective technique that is well within the abilities of most treasure hunters. With a quality 35mm camera, the proper light absorbing filters, and Kodak IE135 infrared film,? remote sensing becomes an affordable technology.
Other Sources of IR Photos
U.S.? Geological Survey Dept. of Interior
EROS Data Center
Sioux Falls, SD? 57198
The National Air Photo Library
Surveys and Mapping Building
615 Booth St.
Ottawa, Ontario KIA OE9
Canada
Note; The scale of the photos available from either EROS or NAPL are generally considered to be to small for the purpose of locating cultural anomalies
Recommended reading
Kodak publication M-28, Applied Infrared Photography
Kodak Publication M-5, Photography From Lightplanes And Helicopters
