Information Technology Reference
In-Depth Information
The maps are produced conform to the OGC standards, thus can be used in other
systems.
In addition to the GIS functionalities of zooming and panning, it is possible to scroll through
the maps of the last ten days. This gives an excellent overview of the temporal development
of the pest or disease risk.
The system is supplemented by a spatial three-day weather forecast 3 day offered by the
German Meteorological Service. It is expected that this further supports the decision and
management processes of the farmer.
4. Model validation and evaluation in crop protection warning service
Whereas in the previous two chapters the management, validation and preparation of
meteorological data which are essential for the forecasting models were discussed the next
chapter will address the complex issue concerning the validity of the simulation models
used in pest integrated control.
Considering the general mathematical simulation of real events or specific models for plant
disease epidemiology, there are several definitions of model validation (Kranz & Royle,
1978, Racca
, et al.
, 2010b, Reynolds
, et al.
, 1981, Sargent, 1998, Schlesinger, 1979, Teng, 1985,
Welch
, et al.
, 1981). The validation process can be summarised as the comparison between
the virtual (simulated) and the real (actual) system. According to (Balci & Sargent, 1984) the
model validation of a generic model will be separated in two methods: the subjective
validation techniques and the statistical techniques. In other words, the model validation
strictly depends on the modelled system, the model output and the availability of observed
field data for the validation.
According to the classification due to ZEPP (Racca
, et al.
, 2010b) the simulation models can
be summarised in:
Pests and disease models:
Type 1: Models predicting first appearance of a disease or a pest.
Type 2: Complex simulation models predicting the epidemiological development or
population dynamics like the disease severity, the disease incidence or pest abundance.
Type 3: Models predicting a target event like the overriding of an action threshold or
periods with high risk for an epidemiological development of the disease or of pest
population dynamic.
Ontogenesis models:
Ontogenesis models are able to simulate the crop-growing. These models can be used in
combination with the diseases or corresponding pest models.
For each kind of these models a subjective and/or a statistical validation is possible.
The evaluation of the model performance depends on the aim and the type of model and is
strictly correlated with the validation results. Generally, based on the ZEPP experience, a
model has a good performance when during the validation phase a quote of correct
prognoses up to 75% is overridden and/or the underestimations are less than 15%.
4.1 Validation of type 1 models
Type 1 models forecast the first appearance of a disease or a pest at the beginning of the
growing season. They are mainly used by advisors to determine the beginning of the
regional monitoring activities and by farmers to do the initial checks on their fields. The
results are generally given on a regional level considering the region as the area
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