The Specification and use of GPS Systems in Agricultural Aviation

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The Specification and use of GPS Systems in
Agricultural Aviation Rob Murray, Ian
Yule Centre for Precision Agriculture, Massey
University.
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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

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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

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Seasonality

• Application from 1st June 2003 to 1st March 2004
  was 392,000T

Figure 1. Seasonality of fertiliser applied by
aerial application
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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
• Operators concerned with product quality and flow
  characteristics

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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

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GNSS status

• Specification of GPS units
• NZAAA members surveyed all had and regularly used
  appropriate high specification navigation and
  tracking equipment
• Most fitted with, DGPS, moving map, 5hz output
  and lightbar

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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.

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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 GNSSs such as GLONASS, Galileo
• Strategic co-operation between Russia and India
  in developing GLONASS, expected to be operational
  2007
• GALILEO is Europes 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

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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 GPSs 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

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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

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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.