Jeffrey K. Gillan

Jeffrey K. Gillan

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Jeffrey K. Gillan

University of Arizona School of Natural Resources and the Environment, Arizona Remote Sensing Center, The University of Arizona, 1064 E. Lowell Street, Tucson, AZ 85721, USA

Research Focus & Metrics

Academic Career Length

11Years (2016-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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6 April 2020 in Environmental Monitoring and Assessment
Verified
Journal Article
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JGJeffrey K. Gillan
Jeffrey K. Gillan
JKJason Karl
Jason Karl
Willem van LeeuwenWillem van Leeuwen
Willem van Leeuwen

1 July 2019 in Rangeland Ecology & Management
Verified
Journal Article
Closed access
JGJeffrey K. Gillan
Jeffrey K. Gillan
MMMitchel P. McClaran
Mitchel P. McClaran
TSTyson Swetnam
Tyson Swetnam
PHPhilip Heilman
Philip Heilman

1 March 2016 in Rangeland Ecology & Management
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Journal Article
Closed access
JGJeffrey K. Gillan
Jeffrey K. Gillan
JKJason Karl
Jason Karl
NBNichole N. Barger
Nichole N. Barger
AEAhmed Elaksher
Ahmed Elaksher
MDMichael C. Duniway
Michael C. Duniway

5 July 2021 in Ecosphere
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Journal Article
Open access
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JGJeffrey K. Gillan
Jeffrey K. Gillan
GPGuillermo E. Ponce‐Campos
Guillermo E. Ponce‐Campos
TSTyson L. Swetnam
Tyson L. Swetnam
AGAlessandra Gorlier
Alessandra Gorlier
PHPhilip Heilman
Philip Heilman
MMMitchel P. McClaran
Mitchel P. McClaran
In adaptive management of rangelands, monitoring is the vital link that connects management actions with on‐the‐ground changes. Traditional field monitoring methods can provide detailed information for assessing the health of rangelands, but cost often limits monitoring locations to a few key areas or random plots. Remotely sensed imagery, and drone‐based imagery in particular, can observe larger areas than field methods while retaining high enough spatial resolution to estimate many rangeland indicators of interest. However, the geographic extent of drone imagery products is often limited to a few hectares (for resolution ≤1 cm) due to image collection and processing constraints. Overcoming these limitations would allow for more extensive observations and more frequent monitoring. We developed a workflow to increase the extent and speed of acquiring, processing, and analyzing drone imagery for repeated monitoring of two common indicators of interest to rangeland managers: vegetation cover and vegetation heights. By incorporating a suite of existing technologies in drones (real‐time kinematic GPS), data processing (automation with Python scripts, high performance computing), and cloud‐based analysis (Google Earth Engine), we greatly increased the efficiency of collecting, analyzing, and interpreting high volumes of drone imagery for rangeland monitoring. End‐to‐end, our workflow took 30 d, while a workflow without these innovations was estimated to require 141 d to complete. The technology around drones and image analysis is rapidly advancing which is making high volume workflows easier to implement. Larger quantities of monitoring data will significantly improve our understanding of the impact management actions have on land processes and ecosystem traits.

19 May 2024 in Remote Sensing
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Journal Article
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KLKangsan Lee
Kangsan Lee
Willem van LeeuwenWillem van Leeuwen
Willem van Leeuwen
JGJeffrey K. Gillan
Jeffrey K. Gillan
DFDonald A Falk
Donald A Falk
Pre-fire environmental conditions play a critical role in wildfire severity. This study investigated the impact of pre-fire forest conditions on burn severity as a result of the 2020 Bighorn Fire in the Santa Catalina Mountains in Arizona. Using a stepwise regression model and remotely sensed data from Landsat 8 and LiDAR, we analyzed the effects of structural and functional vegetation traits and environmental factors on burn severity. This analysis revealed that the difference normalized burn ratio (dNBR) was a more reliable indicator of burn severity compared to the relative dNBR (RdNBR). Stepwise regression identified pre-fire normalized difference vegetation index (NDVI), canopy cover, and tree density as significant variables across all land cover types that explained burn severity, suggesting that denser areas with higher vegetation greenness experienced more severe burns. Interestingly, residuals between the actual and estimated dNBR were lower in herbaceous zones compared to denser forested areas at similar elevations, suggesting potentially more predictable burn severity in open areas. Spatial analysis using Geary’s C statistics further revealed a strong negative autocorrelation: areas with high burn severity tended to be clustered, with lower severity areas interspersed. Overall, this study demonstrates the potential of readily available remote sensing data to predict potential burn severity values before a fire event, providing valuable information for forest managers to develop strategies for mitigating future wildfire damage.

26 May 2022 in Land
Verified
Journal Article
Open access
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Kyle HartfieldKyle Hartfield
Kyle Hartfield
JGJeffrey K. Gillan
Jeffrey K. Gillan
Cynthia NortonCynthia Norton
Cynthia Norton
CCCharles Conley
Charles Conley
Willem van LeeuwenWillem van Leeuwen
Willem van Leeuwen
Accurate identification of cacti, whether seen as an indicator of ecosystem health or an invasive menace, is important. Technological improvements in hyperspectral remote sensing systems with high spatial resolutions make it possible to now monitor cacti around the world. Cacti produce a unique spectral signature because of their morphological and anatomical characteristics. We demonstrate in this paper that we can leverage a reflectance dip around 972 nm, due to cacti’s morphological structure, to distinguish cacti vegetation from non-cacti vegetation in a desert landscape. We also show the ability to calculate two normalized vegetation indices that highlight cacti. Furthermore, we explore the impacts of spatial resolution by presenting spectral signatures from cacti samples taken with a handheld field spectroradiometer, drone-based hyperspectral sensor, and aerial hyperspectral sensor. These cacti indices will help measure baseline levels of cacti around the world and examine changes due to climate, disturbance, and management influences.