Airborne Hyperspectral Data Acquisition and Processing in the Arctic: A Pilot Study Using the Hyspex Imaging Spectrometer for Wetland Mapping

Jordi Cristóbal,Anupma Prakash,Marcel Buchhorn,Rudi Gens,Nikki Guldager,Mark Bertram,Patrick Graham

doi:10.3390/rs13061178

Abstract

A pilot study for mapping the Arctic wetlands was conducted in the Yukon Flats National Wildlife Refuge (Refuge), Alaska. It included commissioning the HySpex VNIR-1800 and the HySpex SWIR-384 imaging spectrometers in a single-engine Found Bush Hawk aircraft, planning the flight times, direction, and speed to minimize the strong bidirectional reflectance distribution function (BRDF) effects present at high latitudes and establishing improved data processing workflows for the high-latitude environments. Hyperspectral images were acquired on two clear-sky days in early September, 2018, over three pilot study areas that together represented a wide variety of vegetation and wetland environments. Steps to further minimize BRDF effects and achieve a higher geometric accuracy were added to adapt and improve the Hyspex data processing workflow, developed by the German Aerospace Center (DLR), for high-latitude environments. One-meter spatial resolution hyperspectral images, that included a subset of only 120 selected spectral bands, were used for wetland mapping. A six-category legend was established based on previous U.S. Geological Survey (USGS) and U.S. Fish and Wildlife Service (USFWS) information and maps, and three different classification methods—hybrid classification, spectral angle mapper, and maximum likelihood—were used at two selected sites. The best classification performance occurred when using the maximum likelihood classifier with an averaged Kappa index of 0.95; followed by the spectral angle mapper (SAM) classifier with a Kappa index of 0.62; and, lastly, by the hybrid classifier showing lower performance with a Kappa index of 0.51. Recommendations for improvements of future work include the concurrent acquisition of LiDAR or RGB photo-derived digital surface models as well as detailed spectra collection for Alaska wetland cover to improve classification efforts.

Highlights

In Alaska, wetlands cover twenty-two percent of the state’s area, according to the most recent survey carried out by [1]
The goal of this study was to demonstrate the capability of airborne hyperspectral imaging for wetland mapping using the Yukon Flats as a test case by means of (a) commissioning a hyperspectral imaging system, HySpex, in a small aircraft for airborne data acquisition in high-latitude environments; (b) correcting for geometric and radiometric distortions that are uniquely inherent in a high-latitude environment; (c) developing image processing protocols to generate prototypes of seamless mosaics, hypercubes, and thematically classified image products; and (d) mapping major wetland types in selected sites in the Yukon Flats
0.5 m in geometric correction obtained for the whole dataset collected in this study shows configuration robustness for both the platform and geometric correction choice that yielded the configuration robustness for both the platform and

Summary

Introduction

In Alaska, wetlands cover twenty-two percent of the state’s area, according to the most recent survey carried out by [1]. The degradation or loss of wetlands may result in significant changes in weather systems and alter precipitation patterns themselves [7]. Wetlands in Alaska represent an important habitat that provide essential ecosystem functions and many benefits to humans, plants, and animals from local to continental scales. These benefits include food and habitat for vegetation, wildlife, fish and shellfish species, food and habitat for human subsistence gathering, flood storage and stormflow modification, ground-water recharge and discharge, and the maintenance of water quality [7,8]

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Results

Conclusion