The Specification and use of GPS Systems in The Specification and use of GPS Systems in Agricultural AviationAgricultural Aviation

Rob Murray, Ian Yule

Centre for Precision Agriculture, Massey University.

• 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

BackgroundBackground

• 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

Role of Navigation SystemsRole of Navigation Systems

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

Figure 1. Seasonality of fertiliser applied by aerial application

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

Summer Autumn Winter Spring

Qu

an

tity

of

fert

ilis

er

ap

plie

d (

kg

)

ApplicationApplication

• 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

Table 1. Common bout widths used in Aerial Spreadmark survey 2004

Product Bout width Fixed Wing Urea 21-33m Superphosphate 12-24m Lime 40m Helicopter Urea 30-40m

Application MethodsApplication 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 statusGNSS 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

Table 2. Current DGPS used by NZAAA members

Type Channels Output Rate

DPGS NMEA 0183

Moving Map

Light-bar

Satloc Lightstar II N/A N/A Y Y N Y Satloc M3 12 5Hz Y Y Y Y Trimble AgGPS Trimflight II

12 10Hz Y Y Y Y

Trimble AgGPS Trimflight 3

12 5-10Hz option

Y Y Y Y

AgNav 2 12 10Hz Y Y Y Y UTS 12 5Hz Y Y Y Y

GNSS statusGNSS 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 statusGNSS 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.

GIS statusGIS 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'sGIS & 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)

WGS84GD49

110km

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• 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 coordinate systemData coordinate system

• 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

Data SourcesData Sources

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• 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.

ConclusionConclusion