GPS aircraft navigation test plan

38 Pages·1994·2.3 MB·English

by  Thistle, Harold

Historic, Archive Document
Do not assume content reflects current
scientific knowledge, policies, or practices.

DGPS Navigation
systems for
Agricultural Aircraft
3400 FPM
October 1994
9534-2807-MTDC in Forestry: Test Plan
Reserve
aSB953
. 154
1994
Ulalitsyemel Ci
Department of
Agriculture
INPW HLOINENE
AGRICULTURAL
LIBRARY
Advancing Access to
Global Information for
PNetaraulieelte
GPS Aircraft Navigation Test Plan
Prepared by:
Harold Thistle, Ph.D.
Anthony Jasumback
William Kilroy
Missoula Technology and Development Center
USDA-Forest Service, Bldg. 1, Ft. Missoula
Missoula, MT 59801
August 2, 1994
Final Draft
2
1a.tneo Minbetoes,
BP se : “~y t
has Lntroductiion
The field of Global Positioning System (GPS) based navigation
is rapidly growing with technology currently available which can
positively impact the effectiveness of USDA-Forest Service Forest
Pest Management (FPM) operations. This technology is based on the
receipt of signals from a constellation of satellites. These
satellites were originally intended for military use but as time
goes on, the capabilities of civilian technology based on GPS are
increasing rapidly.
Currently, instrumentation using the signals from this
satellite constellation can yield positions on the surface of the
Earth with less than 2m absolute error under optimal conditions.
The applications of this type of accurate positioning are numerous.
Of great interest to FPM (investigation and implementation of this
technology has been noted as a priority by the National Spray Model
Advisory Steering Committee, the Steering Committee for Gypsy Moth
and Eastern Defoliators, and many other groups within the USDA-
Forest Service) is the ability to accurately know and log to a
stored file the exact position of an aerial or ground spray system
during an application event. This ability can eliminate the
problem of treating the wrong area making flagmen and block marking
unnecessary in most cases. Questions raised in litigation can be
directly addressed with detailed records. Lost pilot time due to
finding home can be reduced, costs associated with returning to
base for reloading and then returning to the exact position
application ceased can be reduced and misses or gaps can be spotted
immediately by the applicator or operational manager allowing
corrective action to be taken. In general, costs can be lowered,
safety improved and efficiency increased if GPS navigation systems
were integrated into FPM pesticide application operations.
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Pie eroblem Statement
There are two distinct sets of problems from the standpoint of
FPM regarding GPS navigation technology. The first problems are
technical concerns. The primary one is whether the signal can be
reliably received by aircraft operating in mountainous or complex
terrain. GPS navigation equipment is gaining wide acceptance among
agricultural aviators, however, they typically work in relatively
flat terrain. Much of the FPM application work is carried out
under conditions where ground based transmitters which are used to
increase the accuracy of the system, would be obscured. Also, in
extreme terrain, the aircraft would not ‘view’ enough satellites to
resolve position. Another technical issue is that aerial
applicators in complex terrain often fly ‘contours’ instead of
straight swaths. The shape of the contours is determined by the
local terrain. This type of application requires a higher level of
sophistication in the associated GPS software and control systems.
Further technical concerns are associated with operator safety and
workload. If the systems are properly designed, safety should be
improved and workloads reduced compared to current operational
methods.
The second set of problems involves the acceptance and
integration of this technology into the current modus operandi.
Various field trials have demonstrated that this technology can
provide the positional accuracy claimed for it (Mierzejewski 1993,
Sampson 1993, Falkenberg et al. 1994, among others). Beyond the
specific technical questions listed above, most of the basic
technical concerns have been addressed. However, a critical part
of this program is to provide a demonstration of this technology in
order to provide a clear rationale and justification (assuming the
remaining technical issues can be adequately resolved) for FPM to
move forward and implement GPS based aircraft navigation.
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