Remote Sensing Project 2017

We selected AVIRIS hyperspectral data because it has high spectral resolution at approximately 10 nanometers or 0.01 micrometers in 224 bands covering a wide spectrum from 380 nm to 2500 nm.  This is useful in precisely determining the unique spectral characteristics of 6 chosen endmembers.  We selected gypsum and halite as 2 of the 6 endmembers because they are both evaporites and halite is commonly associated with gypsum in arid environments.  We chose several mixtures with sediment that was abundant in the localized vicinity since retrieving a pixel with 100% of a single endmember would pose unlikely with a spatial resolution of 15.9 m (pixel size).  For example, the ancestral Lake Otero sediment is known to contain gypsum along with several clay mineral and limestone.  For this location we selected a calcite plus kaolinite mixture.  For the other clay rich Holocene playas we used a montmorillonite plus illite mixture.

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Algorithms

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We ran 2 supervised classifications because we were only interested in 6 classes and there were several published aerial photographs, field data, and geologic maps which made this classification more useful than unsupervised.  Of the supervised classifications we selected 2 algorithms, the Spectral Angle Mapper (SAM) and Linear Spectral Unmixing (LSU).  SAM calculates the angle of reflectance of set endmember spectral profiles and classifies pixels that are spectrally similar to those references.  SAM is easy to make visual interpretations since all 6 endmembers are displayed at once, where the pixel with the most spectral similarity to a referenced endmember takes that classification.  This is also known as “winner takes all”.  9 bands (70, 71, 72, 147, 148, 149, 203, 204, & 205) were used to run the SAM algorithm since they show unique spectral characteristics.  LSU was also used to calculate the relative abundance of the 6 endmembers for each pixel.  All 226 bands were used in this calculation.

 

(Linear Spectral Unmixing Images are included in the Gallery page)

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Environment

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The White Sand Dunes in Southern New Mexico has summer storms which pool surface water in Lake Lucero, the lowest elevation point at 1,152 m.  In the winter and spring months the area is more arid and South-West spring winds cut out gypsum that was created by ground water and deposits it on the present dune field between the ancestral Lake Otero shoreline and L1 shoreline.  Our data was collected in the month of May year 2011, after the summer storms of 2010 to investigate mountain alluvium run-off for gypsum from Permian formations (Yeso & San Andres formations) to determine if they are active sources.  The data also represents a period of increased aridity in our study area when gypsum is created to better visualize the alkali flats and playa lakes as gypsum sources.