Aerospace and Electronic Systems - October 2018 - 14

Feature Article:

DOI. No. 10.1109/MAES.2018.170125

Performance Analysis of GNSS Units in Manned
Helicopter Operations
Roberto Rodriguez III, Daniel M. Jenkins, Department of Molecular Bioscience and
Biological Engineering, University of Hawaii at Manoa
James J.K. Leary, Department of Natural Resources and Environmental Management,
University of Hawaii at Manoa
Karyn M. Nolan, Pacific GPS, LLC, Honolulu, HI
Brooke V. Mahnken, Maui Invasive Species Committee, Makawao, HI

INTRODUCTION
Global Navigation Satellite System (GNSS) receivers make use
of the United States' Global Positioning System (GPS), Russia's
Global Navigation Satellite System (GLONASS), Europe's Galileo, China's Beidou, and Japan's Quasi-Zenith Satellite System
constellations to determine the geolocation of the receiver based
on the location of satellites and measurements of the distance and
travel time of the GNSS signals. GNSS signals are dependent on
line of sight to satellites with reflections or obstructions resulting
in errors in the estimated position [1]. GNSS systems, while having their origin in military applications [2], have been adopted for
many civilian uses from recreational navigation [3] to automated
vehicle location systems [4]. While the GPS Standard Positioning
Service without any correction sources establishes a 30 m range
error limit for civilian use, GPS receivers typically perform better
than this standard with errors primarily from atmospheric interference [5]. This is further improved in mobile devices by assisted
GPS, WiFi, and cellular positioning when available [6].
GNSS is commonly used for transmitting the location of an
aircraft to other aircraft or air traffic control, providing collision
avoidance and optimized routing [7]. While GNSS provides valuable information to pilots, crew, and air traffic control, the GNSS
Research was supported by U.S. Department of Agriculture
(USDA) Forest Service, Special Technology Development
Program Award R5-2012-01 through collaboration with the
Hawaii Department of Land and Natural Resources Forest
Health Program, The Hawaii Invasive Species Council award
# POC 40466, the USDA Hatch Act Formula Grant project
112H, and USDA Renewable Resources Extension Act.
Authors' current addresses: R. Rodriguez III, D. M. Jenkins,
Department of Molecular Bioscience and Biological Engineering, University of Hawaii at Manoa, Honolulu, HI 96822, USA,
Email: roberto6@hawaii.edu. (continued on page 20.)
Manuscript received June 26, 2017, revised October 29, 2017,
and ready for publication January 8, 2018.
Review handled by M. Braasch.
0885/8985/18/$26.00 © 2018 IEEE
14

signals are subject to a number of errors. Tropospheric and ionospheric refraction, GPS ephemerides, and orbit error are spatially
correlated errors due to atmospheric and constellation variation,
but can be mitigated using differential correction sources [8]-[9].
Leptich et al. [10] further found that GPS accuracy of hand-held
devices was impacted by obstruction of the antenna by aircraft
surfaces. GNSS signals are also strongly influenced by materials
frequently found in aircraft construction, including aluminum and
plastic, due to multipath errors [11].
GNSS, combined with Geographic Information Systems (GIS),
is used extensively in natural resource and wildlife management including the monitoring of geological [12], animal [13], and plant
[14] resources and associated control activities [15], [16]. The forested watersheds of the volcanic Hawaiian Archipelago have extreme
topography, with deep gulches, steep surfaces, and complex vegetation layers, making natural resource managers reliant on aircraft for
a multitude of activities, e.g., surveillance and management of invasive species. In previous work, Rodriguez et al. [17] demonstrated
the utility of a custom Android application using a consumer-grade
GNSS receiver in a Nexus 7 tablet (ASUS®, Taipei, Taiwan) recording surveys of Hawaiian watersheds from a Hughes 500 helicopter.
Despite the expanded computing capabilities of a mobile device, the
GNSS receivers installed are typically inferior to those in dedicated
GNSS receivers in part due to the interactions between antenna(s)
and other hardware assembled within the device [18]-[19]. Moreover, Gantz et al. [20] found substantial deviations in GNSS position
in areas of extreme topography due to obstructions by the terrain.
Thus, it can be expected that the application referred to above by
Rodriguez et al. may have substantial errors in spite of the valuable
performance metrics generated in resource management.
Aerial monitoring and management of natural resources from a
helicopter is an inherently dynamic process [21]. Dynamic testing
of GNSS receivers has been conducted under various controlled
conditions including rotating fixtures [22], straight-line fixtures
[23], or as comparisons to real-time kinematic GNSS systems
[24]-[25], which have all demonstrated that deviation from a static
position will negatively impact GNSS receiver accuracy. The aim
of this study was to test the accuracy of consumer-grade, handheld,

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