A New Integrated High-Latitude Thermal Laboratory for the Characterization of Land Surface Processes in Alaska’s Arctic and Boreal Regions

Abstract

Alaska's Arctic and boreal regions, largely dominated by tundra and boreal forest, are witnessing unprecedented changes in response to climate warming. However, the intensity of feedbacks between the hydrosphere and vegetation changes are not yet well quantified in Arctic regions. This lends considerable uncertainty to the prediction of how much, how fast, and where Arctic and boreal hydrology and ecology will change. With a very sparse network of observations (meteorological, flux towers, etc.) in the Alaskan Arctic and boreal regions, remote sensing is the only technology capable of providing the necessary quantitative measurements of land-atmosphere exchanges of water and energy at regional scales in an economically feasible way. Over the last decades, the University of Alaska Fairbanks (UAF) has become the research hub for high-latitude research. UAF's newly-established Hyperspectral Imaging Laboratory (HyLab) currently provides multiplatform data acquisition, processing, and analysis capabilities spanning microscale laboratory measurements to macroscale analysis of satellite imagery. The specific emphasis is on acquiring and processing satellite and airborne thermal imagery, one of the most important sources of input data in models for the derivation of surface energy fluxes. In this work, we present a synergistic modeling framework that combines multiplatform remote sensing data and calibration/validation (CAL/VAL) activities for the retrieval of land surface temperature (LST). The LST Arctic Dataset will contribute to ecological modeling efforts to help unravel seasonal and spatio-temporal variability in land surface processes and vegetation biophysical properties in Alaska's Arctic and boreal regions. This dataset will be expanded to other Alaskan Arctic regions, and is expected to have more than 500 images spanning from 1984 to 2012.

An Improved Single-Channel Method to Retrieve Land Surface Temperature from the Landsat-8 Thermal Band

“…In situ surface temperature measurements at the flux towers were derived from pyrgeometer data following [29] methodology that was successfully applied for Landsat-5 TM and Landsat-7 ETM+ thermal data evaluation [30]. Before converting pyrgeometer data into surface temperature, data was averaged over 5 min intervals for data stability.…”

Surface Energy Flux Estimation in Two Boreal Settings in Alaska Using a Thermal-Based Remote Sensing Model

“…In this case, the understory is covered by shrubs (Betula nana, Ledum palustre) and mosses (Sphagnum spp. ).Both field sites were equipped with a sonic anemometer, a gas analyzer operating at 20 Hz sampling rate, four-component net radiometer sensor and air temperature sensors at different heights (for further details on tower instrumentation see [58]). Ground heat was monitored at both sites by temperature and soil moisture probes and heat flux plates installed in the subsurface soil layers.…”

“…For both modes, vegetation properties such as f G and LAI were derived using remote sensing estimates. As a local source of surface temperature, T RAD , upwelling longwave data from the four component net radiation sensor were converted to T RAD [58]. For model runs using satellite-based T RAD , Terra/Aqua MODIS T RAD from Terra/Aqua MODIS LST product (MOD11) was used.…”

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

“…Prior to 2015, there was no direct access to a research-grade hyperspectral imaging system in Alaska that could be deployed for airborne hyperspectral remote sensing [18]. It was only in 2017-2018 that National Aeronautics and Space Administration (NASA) acquired Airborne Visible Infrared Imaging Spectrometer Next Generation (AVIRIS NG) data over Alaska's boreal forests [19].…”

“…In particular, hyperspectral imaging, also called imaging spectroscopy, has the advantage of capturing the distinct spectral signatures of land covers associated with wetlands within the 400 to 2500 nm spectral region [23]. However, hyperspectral imaging in high latitudes does come with challenges from low sun angles that introduce pronounced anisotropic effects to images [18]. 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.…”