Just like the human eye, remote sensors capture the light reflected on the surface of the earth. The difference lays on the fact that the “light” measured by this technology has a wider range of “colors”, many of which are invisible to the human eye. Technically speaking, the physical property that is measured by these sensors is the electromagnetic energy, which spans a wide range of wavelengths. The wavelengths that range from 400 to 700 nanometers belong to the visible spectrum, i.e. the wavelengths that can be detected by the human eye. There are ranges, though, that cannot be seen by the human eye, and those are the ones that provide the most valuable information.
This technology is based on the electromagnetic energy emitted by the sun, which is reflected after crossing the atmosphere and interacting with the earth’s surface. This interaction generates differential absorption at different wavelengths depending on the type of material it interacted with. Besides, after a certain wavelength, the intensity of the electromagnetic energy reflected by the sun becomes insignificant compared to the electromagnetic energy emitted by the Earth. This is the Thermal Infrared from the electromagnetic spectrum.
Remote Sensing surveys are carried out in different stages, each with its own objectives, types of sensors and platforms, purposes and levels of work.
The first stage involves the detection of potential prospective targets, by selecting and acquiring the available satellite imagery, mainly multispectral images with global coverage, such as LandSat (5 TM, 7 ETM+, 8 OLI), ASTER, MODIS, and radar imagery and data (SRTM, PALSAR, etc.). This procedure allows narrowing down the exploration areas within a basin, determining possible alteration areas, etc.
On the next stage, a great amount of spectral processing techniques are applied in order to obtain different kinds of product images (mineral indexes, vegetation indexes, soil coverage and uses, structures and lineaments, and topography, among others), so as to characterize the geological properties of the previously defined target.
The final stage of a project comprises the field validation of the targets by means of HytecAltoAmericas’ state-of-the-art hyperspectral remote sensors, both airborne, which can be adapted to any platform (planes or helicopters), or portable, used on field surveys, punctual samplings and in the lab. It is possible, this way, to determine intrinsic characteristics of each target and evaluate its potential.
The integration of all the generated remote sensing data into a Geographic Information System (G.I.S.) provides an invaluable working tool for mining projects as well as for oil & gas exploration.
By combining diverse remote sensing processing and interpretation techniques, it is possible to detect hydrocarbons. This can be achieved by means of direct methods, based on the spectral identification of oil seeps, and indirect methods, through the detection chemical, physical and thermal anomalies generated by hydrocarbon migration.
Physical and chemical alterations are produced on the surface, among which it is possible to identify soil anomalies and outcroppings caused by the reduction of iron oxides, kaolinization of feldspar, which is generally associated with faults and lineaments, and vegetation anomalies produced by the change in the vegetation physiologic state. Besides, hydrocarbon reservoirs are usually associated with thermal anomalies, which can be detected by analyzing temperature brightness and apparent thermal inertia.