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Remote Sens. 2017, 9(11), 1105; https://doi.org/10.3390/rs9111105

Exploring Subpixel Learning Algorithms for Estimating Global Land Cover Fractions from Satellite Data Using High Performance Computing

1
NASA Ames Research Center, Moffett Field, CA 94035, USA
2
Universities Space Research Association (USRA), 7178 Columbia Gateway Drive, Columbia, MD 21046, USA
3
Bay Area Environmental Research Institute (BAERI), Sonoma, CA 95476, USA
4
Airbus Engineering Centre India, Whitefield Road, Bangalore 560048, India
5
VISA INC., 800 Metro Center Blvd, Foster City, CA 94404, USA
6
Division of Science & Environmental Policy, California State University Monterey Bay, Seaside, CA 93955, USA
*
Author to whom correspondence should be addressed.
Received: 15 August 2017 / Revised: 19 October 2017 / Accepted: 20 October 2017 / Published: 29 October 2017
(This article belongs to the Special Issue Machine Learning Applications in Earth Science Big Data Analysis)
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Abstract

Land cover (LC) refers to the physical and biological cover present over the Earth’s surface in terms of the natural environment such as vegetation, water, bare soil, etc. Most LC features occur at finer spatial scales compared to the resolution of primary remote sensing satellites. Therefore, observed data are a mixture of spectral signatures of two or more LC features resulting in mixed pixels. One solution to the mixed pixel problem is the use of subpixel learning algorithms to disintegrate the pixel spectrum into its constituent spectra. Despite the popularity and existing research conducted on the topic, the most appropriate approach is still under debate. As an attempt to address this question, we compared the performance of several subpixel learning algorithms based on least squares, sparse regression, signal–subspace and geometrical methods. Analysis of the results obtained through computer-simulated and Landsat data indicated that fully constrained least squares (FCLS) outperformed the other techniques. Further, FCLS was used to unmix global Web-Enabled Landsat Data to obtain abundances of substrate (S), vegetation (V) and dark object (D) classes. Due to the sheer nature of data and computational needs, we leveraged the NASA Earth Exchange (NEX) high-performance computing architecture to optimize and scale our algorithm for large-scale processing. Subsequently, the S-V-D abundance maps were characterized into four classes, namely forest, farmland, water and urban areas (in conjunction with nighttime lights data) over California, USA using a random forest classifier. Validation of these LC maps with the National Land Cover Database 2011 products and North American Forest Dynamics static forest map shows a 6% improvement in unmixing-based classification relative to per-pixel classification. As such, abundance maps continue to offer a useful alternative to high-spatial-resolution classified maps for forest inventory analysis, multi-class mapping, multi-temporal trend analysis, etc. View Full-Text
Keywords: machine learning; subpixel classification; Landsat; WELD; mixed pixel; global endmembers; land cover; high performance computing; nighttime lights machine learning; subpixel classification; Landsat; WELD; mixed pixel; global endmembers; land cover; high performance computing; nighttime lights
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Kumar, U.; Ganguly, S.; Nemani, R.R.; Raja, K.S.; Milesi, C.; Sinha, R.; Michaelis, A.; Votava, P.; Hashimoto, H.; Li, S.; Wang, W.; Kalia, S.; Gayaka, S. Exploring Subpixel Learning Algorithms for Estimating Global Land Cover Fractions from Satellite Data Using High Performance Computing. Remote Sens. 2017, 9, 1105.

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