Transcript Slide 1
The Specification and use of GPS Systems in
Agricultural Aviation
Rob Murray, Ian Yule
Centre for Precision Agriculture, Massey University.
Background
• As part of the code of practice for aerial application, NZCPA was
contracted by SFF to deal with issues related to GPS and GIS in aerial
fertiliser application
• Small survey of NZAAA members - gathering info about GPS and GIS
capability of operators.
• Current GPS equipment and functionality
• How is it integrated into operational structure
• Where can operators source the GIS information
• How do they define sensitive areas
Role of Navigation Systems
• Essentially a navigation aid, that helps to keep us on course.
• What is GNSS ?? Global Navigation Satellite System
• In agricultural aviation the role of GNSS is:
• Prevent deviations in parallel tracks (easier said than done at
200km/hr)
• Guide pilots to the next job or location
• Provides traceability and quality assurance, it may not be too far
away when councils request evidence of fertiliser application
Seasonality
•
Application from 1st June 2003 to 1st March 2004 was 392,000T
180000
160000
140000
Quantity of fertiliser applied (kg)
120000
100000
80000
60000
40000
20000
0
Summer
4
Autumn
Winter
Spring
Figure 1. Seasonality of fertiliser applied by aerial application
Application
• Current spreading methods are focussed on economics of application
rather than quality of application
– Operators reluctant to change, as it will impact on the charge out rate
– Bout widths vary between operators and products
Fixed Wing
Helicopter
Product
Urea
Superphosphate
Lime
Bout width
21-33m
12-24m
40m
Urea
30-40m
Table 1. Common bout widths used in Aerial Spreadmark survey 2004
– Operators concerned with product quality and flow characteristics
Application Methods
• Spreading around environmentally sensitive areas
–Rely on experience and good hand eye co-ordination
–Use navigation unit and rely on light bar for guidance
–Buffer distances varied from 10-40m
–Fertiliser flow and particle characteristics
–These need to be quantified and buffer distances solved for
a number of application scenarios
GNSS status
• Specification of GPS units
– NZAAA members surveyed all had and regularly used appropriate
high specification navigation and tracking equipment
Type
Channels
Satloc Lightstar II
Satloc M3
Trimble AgGPS
Trimflight II
Trimble AgGPS
Trimflight 3
AgNav 2
UTS
N/A
12
12
12
12
12
Output
Rate
N/A
5Hz
10Hz
5-10Hz
option
10Hz
5Hz
DPGS
Moving
Map
N
Y
Y
Light-bar
Y
Y
Y
NMEA
0183
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Table 2. Current DGPS used by NZAAA members
– Most fitted with, DGPS, moving map, 5hz output and lightbar
GNSS status
• Guidance and Navigation
– Around 20% of jobs are completed without satellite navigation, about
70,000 tonnes of untraceable nutrients
• Recommended Specification of GNSS units
– 5Hz receiver, outputs a geo-referenced position every 0.2 seconds, or
11m when travelling at 200kmhr-1
– Require 12 channel receivers, tracking a minimum of 10 satellites
simultaneously on the L1 Coarse Acquisition (C/A) code, 2 set aside
for satellite based augmentation systems. (SBAS)
– NMEA 0183 messages: GGA and VTG at a rate of 5Hz or greater.
GNSS status
• Future Specification of GNSS units
– GPS modernisation underway, introduce L2CS and L5 signals which
are much more robust than the current C/A code.
– Current systems are unlikely to be compatible with other global
navigation satellite systems (GNSS).
– Must stop thing about GPS and start to prepare for GNSS’s such as
GLONASS, Galileo
– Strategic co-operation between Russia and India in developing
GLONASS, expected to be operational 2007
– GALILEO is Europe’s answer to the American and Russian systems
and is set to launch its first satellite in 2005. Operational 2008
– Designed and operated under civilian control. Dual frequencies as
standard, potential for greater positioning accuracy.
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GIS status
• Operators expressed interest in using GIS techniques to pre-program
AB lines, track spacing, block boundaries and avoidance zones
– Save on time and fuel
– Further traceability
– Blocks are located by GIS/GPS further reducing downtime
• Next step could be Variable Rate Control (VRC)
– Provide value added service, make more efficient use of GIS developments
– Target fertiliser at productive land only
– Avoid sensitive areas or mitigate application around those areas
GIS & GPS Datum's
• Need to settle on a standard datum.
–Two most common datum's used in NZ are WGS84 and
NZGD49
–Some GPS units allow you to collect data using the
NZGD49, Stick with WGS84 unless you plan on further
GIS work
–Little benefit in converting between them unless you are
going to apply a projection to New Zealand map grid
(NZMG)
GD49
WGS84
110km
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Data coordinate system
• Both LINZ and Terralink have adopted the New Zealand Transverse
Mercator projection (NZTM). It replaces NZMG and NZGD49 datum. Any
new imagery is likely to be in NZTM unless otherwise stated
– It will start to have an impact as we will have to convert entire datasets back
and forth
• NZTM projection uses a datum which can be assumed as identical to
GPS’s WGS84, this makes projecting from WGS84 to NZTM much
simpler as there is no datum shift.
– Simplifies the issue around which datum to use, i.e. leave the data in WGS84
Data Sources
• Free data available from LINZ
–2.5m resolution TIFF, ~50Mb for black and white or
~145Mb Colour
–Rivers, structures, vegetation, 20m contours
available from NZTopoOnline in shapefile format
• Data from Terralink at a cost
–1m resolution imagery, for a portion of the country
–Auckland, Waikato, Gisborne, Wellington, Picton,
Christchurch have resolution of 0.125m or 12.5cm
–Vector data available in shapefile format
Conclusion
• Current spreading policy is on economics of application and not quality
assurance, this is driven by the farmers wanting to get the fertiliser on at
the cheapest cost. Until such time as this is changed, additional benefits
of GNSS and GIS will go untapped
• The operators surveyed already have the equipment
• Exiting technological developments on the horizon, which should make
signals more robust and easier to use.
• NZ starting to develop a good database of imagery, however we need to
settle on a co-ordinate system, which looks like WGS84 for GNSS and
NZTM for GIS.
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