technical meeting on the use of gps in the agricultural surveys in africa, 27-28 november 2008 1...

TECHNICAL MEETING ON THE USE OF GPS IN THE AGRICULTURAL SURVEYS IN AFRICA, 27-28 November 2008 1

West Shoa area frame project – experiences in using of the GPS

technology for area estimation

Experiences in using of the GNSS technology in agriculture in Europe


In the presentation

• Agriculture Unit

• Area-based subsidy in Europe - numbers

• Why to test tools?

• Validation of the tools on example of Garmin GPS72

• Conclusions


France - Soft WheatYield - Area

y = 0.1409x + 4.1052R2 = 0.8819

y = -0.0033x2 + 0.2222x + 3.7532R2 = 0.8998

3.504.004.50

5.005.506.006.50

7.007.508.00

YEAR

T/ha

2100.00

2600.00

3100.00

3600.00

4100.00

4600.00

5100.00

5600.00

1000 ha

YIELDMARSyAREALinear (YIELD)Poly. (YIELD)

MARS-PAC (GeoCap) →

Direct Payments to Farmers

Agri4Cast ↓

Crop Yield Forecasting for EU

FOODSEC ↓

Crop monitoring outside EU

Who we are?


Area-based subsidy controls in 2008

• 8.6 Million applications for 155 Million ha in 27 MS• area of ~12.8 Million hectares controlled/measured• 8.1 Million hectares measured on the satellite images (CwRS)• 4.7 Million hectares measured in the field using GPS receivers, tapes

and other tools

GeoCAP (MARS PAC): Compliance and Control of Area-based subsidies in Agriculture and Regional Policies


Introduction: Area measurement validation scheme

– Purpose of the scheme• to define an approach for the validation of area

measurement methods for agricultural parcels, • mainly using (but not restricted to) GPS

equipment.

– Motivation • The availability of relatively low-priced GPS tools• However, both the EC and Member States need

assurance that the tools on offer are able to perform to acceptable standards.


Why validation?

• Assessment of precision of the tool (random error)• Assessment of accuracy of the tool (a systematic error)• Evaluation of the time effectiveness of the tool• Feeling on a general performance of the tool (practical

issues, batteries life etc.)

Decision: is the tool suitable for the needs of the project?


Assessment of precision and accuracy of Garmin 72.

Test design

West Shoa area frame project – experiences in using of the GPS technology for

area estimation.


With what we measured?

Garmin GPS 72

GeoXT -Trimble


Test site

6 fields – representation of the landscape(shape, size, obstructions of horizon (borders))

• Forest on a slope ~0.10 ha

• Steep slope, border with a forest ~0.21 ha

• Flat ~0.04 ha

• Moderate slope ~0.15 ha

• Flat ~0.31 ha

• Flat ~0.57 ha


Field A: ~0,31ha, flat


Field B: ~0,04ha, flat


Field C: ~0,15ha, moderate slope


Field D: ~0,10ha, Forest on a slope


Field E: ~0,21ha, steep slope, border with the forest


Field F: ~0,57ha, flat


Artificial borders clearly marked:


How many times?:5 runs with 4 repetitions =

20 measurements of one field with one receiver

How to measure?

When?:1 run 4 measurements in row for a field = repeatability

conditions (influence of the satellite system limited)

runs should start at different time of the day = reproducibility conditions (influence of the satellite system taken into account)


Practical issues:

• Within one run walk clockwise and anti-clockwise,

• Try to have one operator per field,

• Make the border of the field comfortable for walking,

• GPS receivers give the projected (horizontal) area,

• GPS area measurements are only comparable with

rope & compass on flat fields!!!


Statistics

• Reference area (GeoXT with data post-processing)

• Outliers detection (Grubbs’ and Cochran’s tests)

• Repeatability standard deviation

• Reproducibility standard deviation

• Bias of the measurements

• Additionally: ANOVA to analyze influence of factors like: operator, field, size, border type etc.


Assessment of precision and accuracy of Garmin GPS72

Relative standard deviation (1sigma/area*100%) and the bias of the measurements

depending on the area

-2

-1

0

1

2

3

4

5

6

7

8

9

10

11

0 1000 2000 3000 4000 5000 6000 7000

area [m2]

rela

tive

std

ev, b

ias

[%]

Rel_Std_dev Bias


Conclusions:

• The CSA have capacity to design and run validation tests of the GNSS receivers,

• Garmin GPS72 is a user-friendly tool, easy to handle even for absolute beginners,

• Garmin GPS 72 seems not to give any significant systematic error with random errors (1σ) below 3.4% for fields >0.2ha,

• Time-efficiency has been proven during the tests (up to 20 fields per hour)


• Impact of usage of the projected area instead of the sloped should be analyzed,

• Storing results of the measurements in a database could benefit and support spatial and temporal analysis of the data

• Other GNSS receivers owned by the CSA should be tested before using them for area measurements.

Conclusions:


Thank you for your attention!

technical meeting on the use of gps in the agricultural surveys in africa, 27-28 november 2008 1...

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