Cartografía de calizas con datos hiperespectrales AISA Eagle II en una zona montañosa con vegetación densa: cómo orientar geológicamente la corrección atmosférica

Abstract

Carbonated rocks are crucial targets for oil exploration, outcropping often in large areas with minimum spectral differences among geological units. The typical carbonate spectral absorptions in 2200 nm and 2300 nm, are excluded from the wavelength range of AISA Eagle II. AISA Eagle II hyperspectral data are processed in flight lines of 1024 swath pixels in the visible to near-infrared wavelength range (400 to 970 nm). The flight has a spatial resolution of 1 m and records a total of 128 channels with a spectral resolution of 4,8 nm. The area of study is a carbonate rocky mountain densely vegetated, covered by variably dense trees and bushes. Masking vegetation cover and shade effects is prior to any geological analysis using hyperspectral image processing. Carbonate units occur in mountain slopes, with small areas of ridges of rock outcrops and wide fans of loose material. The background soil of different geological units differ spectrally only by overall reflectance. Instead, limestone rocky outcrops display spectral responses with smooth typical iron oxide absorptions that distinguish them apart from loose boulders of limestone. Trying to enhance spectral differences in the visible wavelength range among carbonate geological units, an atmospheric correction using field spectra from geologically selected targets in a limestone quarry was performed. This way, it was possible to map apart lithologically similar detrital units dominated by carbonate in a river plain. The limy river bottom displays spectra with a straight line in the visible wavelength range due to abundant organic matter and small grain size. The spectra of the upper terraces record spectral absorption features related to iron oxide contents similar to the rock outcrops in ridges of mountains. The use of field spectra from geologically selected targets improves the mapping capability of hyperspectral imagery in areas with geological units with a homogeneous spectral response.