Associate Professor of Geomatics at the Space Application department of National Space Research and Development Agency (NASRDA), Dr. Lazarus Ojigi, has said that the value of remote sensing data to mineral exploration has evolved and increased with advancement in space technology.
Ojigi, who spoke at the National Space Dialogue held recently in Abuja, stated that in the early days, aerial photographs were used to evaluate topography and plan mineral prospecting and sampling surveys.
“The site analyses and survey plans for Coal and Tin mining in Enugu, Okaba, and Jos respectively were largely supported by aerial photographs,” he said. “If a particular type of mineral deposit was being mined in a district, aerial photos would be used to locate similar features elsewhere within the district , but with obvious limitation in ability to detect underground deposits.”
A number of minerals and rocks have diagnostic spectral features that allow their composition and relative abundance to be recognized and mapped from space.
Remote sensing depends upon observed spectral difference in the energy emitted from features of interest (color differentiation).
Also multispectral remote sensing is the science of observing features at varied wavelengths to derive information about these features and their distribution.
Just like the aerial photographs, optical remote sensing have huge limitations in mineral resources detecting and mapping, hence the need for other special techniques through the airborne system to be integrated.
Although hyperspectral imaging, which is the acquisition of images in hundreds of registered, contiguous spectral bands such that for each picture element of an image it is possible to derive a complete reflectance spectrum, the use of HSI for detailed materials mapping has been demonstrated for a variety of scientific disciplines .
Today, airborne HSI sensors provide high-spatial resolution (2-20m), high-spectral resolution (10-20nm), and high Signal-to-Noise Ratio (SNR) (>500:1) data for a variety of scientific disciplines.
Ojigi noted that an Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) was flown by NASA/Jet Propulsion Laboratory (JPL), and comprised of a 224-channel imaging spectrometer with approximately 10 nm spectral resolution covering the 0.4 – 2.5 micrometer spectral range interpreted June 9th 2000 AVIRIS data of northern Death Valley, Nevada.
He hinted that in Nigeria, there has not been much attempt at using remote sensing in mineral exploration. Much of the work on the Basement Complex of Nigeria that employs remote sensing has been targeted at hydro geological applications.