They flew two cameras over the barrier island earlier this year. The first one was probably a visible/infrared camera which is capable of picking up heat signatures as well as high definition pictures. These cameras are very advanced. While commercial cameras are only up to a maximum of 25 megapixels, these advanced reconnaissance cameras can go up to 81 megapixels and probably even higher these days. So the pictures are very clear. Much clearer that you would see on Google Earth or Bing Maps. And you can keep zooming in and zooming in without losing much clarity.
The second camera that they flew was probably a hyperspectral camera. This camera takes a "chemical signature" of the landscape. It works very much the same way that you would analyze chemicals in a liquid sample or a blood sample. It uses the wavelengths of light to determine which chemicals are present. And the decomposition process of a human body puts out a chemical (I am not sure which specific chemical) which this hyperspectral camera can detect and quantify.
And it really doesn't matter if the body is buried. because the chemicals will still be released from the body and migrate through the soil and escape into the air. Certain soil types, such as clay, may impede the release of the vapors. However, on the south shore of Long Island, the soil is primarily a sandy loam and vapors would pass through that relatively easily.
When they searched Captree Island this past June, it was likely because of the hits they received from the second camera. But they probably turned out to be decaying fowl or other animals such as fox, racoons, possum, etc.
Here's a good article on the technology:
http://www.chem.info/News/Feeds/201...-detectives-know-where-the-bodies-are-buried/