EVALUATING ATMOSPHERIC CORRECTION METHODS USING ASTER IMAGE

This research presents an evaluation of two atmospheric correction (AC) methods applied to ASTER image. The aim of this study was to determine the most suitable atmospheric correction method for ASTER satellite images by evaluating different methods of AC. The ASTER images used in this research were acquired in October 2004, over Kangankunde, an area with rare earth elements deposit found in Balaka district of Malawi. The study also used laboratory USGS ASTER resampled spectral reflectance library data.
In this research, FLAASH and Log residual AC methods were applied to ASTER image. The results of the AC methods were compared separately with each other. Then the comparisons were done with laboratory USGS ASTER resampled spectral reflectance library data. Lastly, band ratio technique was used to map different mineral groups at the study area.
From the results, FLAASH AC method was found to be a better AC method for mineral exploration and mapping. The log residual method, appeared to miss some specific absorption features as it could generalize much in terms of reflectance. Each of the AC methods did show some unknown features at different wavelengths which are recommended for further investigation. Mineral maps produced by band ratio techniques showed some small differences in mineral abundances as well as, spatial distributions. The comparisons were affected by unavailability of some datasets such as field data to show correlation between the image corrected data and field data through scatterplots. We expect this research to contribute its value to the understanding of potential issues and sources of errors in processes of AC and image analysis techniques and the selection of suitable AC method for aster image. Overall, we found that the FLAASH method is a better AC method than the log residual method.

The aim of this study was to determine the most suitable atmospheric correction method for ASTER satellite images by evaluating different methods of AC. The ASTER images used in this research were acquired in October 2004, over Kangankunde, an area with rare earth elements deposit found in Balaka district of Malawi. The comparisons were affected by unavailability of some datasets such as field data to show correlation between the image corrected data and field data through scatterplots. We expect this research to contribute its value to the understanding of potential issues and sources of errors in processes of AC and image analysis techniques and the selection of suitable AC method for aster image.

Kangankunde is located 100km North of Blantyre and 25km from the Nacala rail corridor. The place is chosen as a study area based on several reasons:
1. the area hosts hydrothermal mineral groups consisting of VNIR and SWIR active minerals;
2. data availability which can be easily downloaded from USGS website;
3. the area has scarce vegetation hence appropriate for geological remote sensing studies.
The Kangankunde Carbonatite Complex is one of the largest REE deposits in the Chilwa Alkaline. The complex has been a target for mineral exploration due to its amenable REE Minerals concentrations hence a detailed description of the complex is given in previous studies (Chikanda et. Al., 2019). The Lower Cretaceous Kangankunde complex is aligned N–S parallel to rift valley faults a few kilometers to the west of the East African Rift System. The complex consists of the main complex and a northern and southern knoll. There is a distinct zonation with regards to the lithologies of the main complex. The central core lithology which consists of carbonatite agglomerate is cut by carbonatite dykes and surrounded by a ring of feldspathic breccia and agglomerate. The first intrusion stage comprises apatite–dolomite characteristics and followed by the intrusion of dolomitic to ferroan–dolomitic carbonatite. The Kangankunde Carbonatite Complex is similar to other carbonatites in that it comprises a carbonatite body surrounded by a fenite aureole.

Traditional authority: TA Nsamala

District: Balaka

Coordinates: -15.08565, 35.0101