1. Item 5.1 of the agenda Preliminary results of LUCAS 2009 Part II
WORKING GROUP
“Land Cover/Use Statistics”
7th – 8th June 2010 Luxembourg
LUCAS TEAM

2. Content Background information: Quality assurance; Data processing;
Warnings in the interpretations of the results.

3. Quality assurance
Quality assurance guaranteed in all the phases of the survey. Different actions put in place:
Standardization and computerization of the main phases of the data management;
Continuous monitoring of the work;
Various training steps;
Different actors/level of controls including:
an internal quality check (field work companies)
an external quality check (external company)
A further check at ESTAT level

4. External quality check
Both automatic and manual controls were applied.
Main manual controls consisted of:
Checking whether data are:
compliant with LUCAS instructions and rules;
without formal errors;
without obvious content errors.
Comparing 2009 with 2006 data (where available);
Checking transect;
Checking GPS tracks to verify whether surveyors actually reached the correct location of the points;
Checking the quality of the photos.

5. External quality check: Rate by country

6. External quality check: error rate

7. External quality check: main results
Main conclusion of the external quality check:
the overall quality of the data is very good since only 4.5% had serious measurement errors;
Main sources of error:
Mistakes in classification of the transect
Mistakes in attribution of land cover and land use;
photos were not always taken in a proper way.

8. Eurostat quality check: sample
Eurostat sample:
Selection of points with highest probability of being mistaken;
both points already checked by the external company and those delivered directly by field work contractors were selected;
2,335 points out of the 234,561(1% sampling rate);
rate of rejection not meaningful.

9. Eurostat quality check: results
Main source of rejection at Eurostat level:
remote observation ( > 100 m ) and Photo Interpretation ( PI ) in the field due to questionable reasons.
Potential impact:
low for LC/LU in homogenous landscape ( ex : grass fields in Ireland, forests in Finland ), but higher in mixed landscape;
significant for transect since linear elements can be missed or misinterpreted from distance;
relevant for the landscape photos since they do not necessary provide a picture of the landscape in the point.

10. Data processing Data processing involved two main stages:
Data imputation for partial missing data;
Estimation procedure .

11. Data processing: Imputation of partial missing data
A simplified nomenclature was used for PI points with cropland coverage due to the difficulties in properly distinguishing among specific classes in orthophotos.
Simplified classification:
Arable land
Permanent crops
This issue appeared in 2130 points.

12. Data processing: imputation of partial missing data
A methodology was developed to attribute more fine classes to the points roughly classified as arable land and permanent crops. Points received the LC from a set of donors belonging to the same stratum (arable or permanent crops).
Main features of the methodology:
adoption of the modal value of the distribution of the potential donors;
selection of the donor set that minimizes the cost function:

13. Data processing: Estimator
Two-phase estimator for stratification was used to derive estimates of land cover and land use rates
Estimates for LC and LU rates derived at NUTS2 level.
Surfaces derived applying rates at official NUTS2 areas
Upper level geographical estimates (NUTS1 and NUTS0) obtained summing up lower level geographical estimates.
h = stratum h=1, … , H;
= first phase sample size (total, by strata);
= second phase sample size (total, by strata);
= first phase sample weight;
= rate of the land cover j in stratum h-th

14. How to interpret results
Distinction between land cover and land use in nomenclature;
Main definitions as much as possible coherent with the international ones;
Territorial coverage (points with elevation below 1000m, mainland and islands connected by bridges to mainland)
6 out of 248 regions were not surveyed
some strata in specific NUTS2 have been under-sampled (e.g. bareland in Trentino)
Effect on completeness and precision not on the accuracy

15. Preliminary results Three sets of results are presented:
An overview of land cover at NUTS2 level (rates and surfaces)
An overview of land use at NUTS2 level (rates and surfaces)
Diversity indexes based on transect land cover changes
They take into consideration both:
the number of different land covers (m)
their relative occurrences (Pi).