Synthesis of the main conclusions and recomandations

Group 1

Do we have enough evidence from the various studies to validate the response?

• No• We need additional tests which can give

information concerning the slop, canopy cover and so on according to the characteristics of the different African countries

• Relationships between differential GPS and compass and tape (see nest slide)

How precise can be the measure of crop area given by GPS receiver as compared to

the true area?• What is the true area the area calculated with

compass and tape or the area given by differential GPS?

• Relationships between differential GPS and compass and tape

• How precise is the GPS result? • Different GPS devise have different precision

according to the price of the GPS and to the level of training of the enumerator

Does the type of GPS have an impact on the accuracy of measurement?

• Yes• According to study conducted on the

available data set, it seems that the Garmin 60 is the best.

• Garmin 72 and Garmin 12 are a bit worse than G60

• Magellan 400 give unstable results, very good for the second measurement and bad for the first and the third

How stable is the measurement of area with GPS?Does repetition of measurement improve the

accuracy?

• Theoretically for sure• We would suggest repetition for pilot studies • For operational project, at least two

measurements can give the possibility to detect very bad measurements

• We have to make further cost- benefit analysis on available data set for operational projects

• The Ethiopian and other data sets that will include plots in different conditions will allow a better assessment of the stability

Is there a link between accuracy of measurement of GPS and plot size?

Is there a cut-off point?

• According to the data base, there is not a clear link between the size of the plot and the accuracy of the measurement

• If we segment the plots according to the size, we have some problems particularly with extra small plots

• It is difficult to give a cut-off point valid for various countries

Extra small plots - equality of medians rejected Wilcoxon signed-rank test Variable | Obs Mean Std. Dev. Min Max Median-------------+-------------------------------------------------------- difference | 160 61.7875 196.7237 -370 1214 9 reldiff | 160 .1135625 .3330015 -.63 .95 3.8%

Very small - equality of medians not rejected

Variable | Obs Mean Std. Dev. Min Max median-------------+-------------------------------------------------------- difference | 53 70.36283 435.8523 -895 1461 -52 reldiff | 53 .0455283 .2103337 -.316 .731 -2.1%

Small - equality of medians not rejected Variable | Obs Mean Std. Dev. Min Max Median-------------+-------------------------------------------------------- difference | 33 -16.21818 260.4032 -430 1097.7 -35.5 reldiff | 33 -.0030606 .069689 -.125 .3 -0.9%

Larger plot - equality of medians not rejected Variable | Obs Mean Std. Dev. Min Max Median-------------+-------------------------------------------------------- difference | 77 -49.97234 1289.079 -3178 8265 -100.4 reldiff | 77 .004026 .1397709 -.204 .972 -1.3%

How faster is to measure crop area with GPS?

• Traditional method long• measuring an area with a GPS takes the time of

walking around the plot• possible additional manipulations Magellan 400• GPS measures more than 4 times shorter than

the traditional measures• For large plots, this ratio can go up to 17 times• No significant differences amongst the receivers

tested• Magellan 400 more complex to use according to

the field enumerators.

Do we need additional analysis of available data?

• Yes

What other uses can be made of the GPS to improve agricultural surveys?

• We have to make further cost- benefit analysis on available data set for operational projects

• The Ethiopian and other data sets that will include plots in different conditions will allow a better assessment of the stability

• Cut-off point according to the situation of different countries, particularly Ethiopian one

Do we need additional field tests?What changes should be made to the protocol

used?

• Yes

• Analysis of the agricultural environment

• Stratification

• Representativeness

• Involvement of African universities

• Involvement of the producers

What area operational issues?

• Batteries, maybe rechargeable

• Memory

• Download to laptop

• Training of trainers