The Possibilities of New Satellite Image Types in the Control of Area-based Subsidies and in Ragweed Monitoring System

In the assessment of the effectiveness of a remote sensing based land cover or land use mapping application, it is desirable to survey as large area as possible at a given spatial resolution, and with high thematic accuracy. To achieve these goals, remote sensing is usually supported by classical on-the-spot check, either in advance, with ground truth data collection, orafter, with the validation of remote sensing mapping results.

In the various applications there is a huge difference in the ratio between classical field survey and remote sensing. In our article the connection between field and GIS work will be presented in the frame of two operational projects, together with the changes in the ratio of these approaches and the future possibilities.

The first project is Control with Remote Sensing of Area-based Agricultural Subsidies. This kind of subsidies exist in EU for about two decades. Traditionally, the crop cultivated and its area are principal questions. There is a change in the task of control: since a reform in the subsidy system after 2000, the preservation of environment gained much moreimportance. This resulted in the involvement of a new set of standards in the control, which is called Good Agricultural and Environmental Conditions (GAEC). For example, preventing soil erosion and fighting against unwanted vegetation belong to these standards. The change in regulations and the development of technology results in a continuous evolution of control methods. Besides, methods differ from country to country. The two major approaches are classical field inspection and remote sensing control. Within remote sensing, there are several possibilities depending on the number, properties and dates of images. There is also a possibility to carry out so-called Rapid Field Visits, which complement remote sensing: in some cases - mainly in the determination of crop type - it gives more reliable answer, or it confirms remote sensing results. In past years, it is compulsory to use very high resolution (VHR) satellite images (or ortho-photos) for area measurement. This is because of the strict rules on positional accuracy and area measurement precision. The sensitivity of this project enforces the
usage of the most precise remote sensing data. It is also important to involve VHR images in the control of GAEC. For example the detection of appearance and encroachment of unwanted vegetation and its exact delimitation can be carried out much more efficiently with VHR images.

The other project is ragweed monitoring. Due to the increasing pollen contamination in Hungary, Ragweed Control Program has grown to a priority project of past years. Ragweed detection with remote sensing has been introduced formerly as one of the high-tech components of this program. Due to the spatial and temporal behavior of ragweed and the difficulties in its recognition it is very important to use a good quality remote sensing data set. A necessarily dense time series plays a crucial role, as ragweed must be recognized and exempted before pollen scattering in order to successfully block pollen spread. However, it has been proven during the control program carried out in past years that the accuracy of spots
delineated with remote sensing has also a principal role in order to effectively collaborate with on-the-spot inspection. In the past years the Institute of Geodesy, Cartography and Remote Sensing used medium and high resolution satellite images in this task, which provided sufficient accuracy. Nevertheless, it is seen now that introducing very high resolution images would further increase spatial accuracy and thus the effectiveness of monitoring, and would give stronger support to on-the-spot checks. The procedure that has been used with proven efficiency for several years in the subsidy control, and especially, in the control of GAEC standards, seems to be a promising opportunity in ragweed reconnaisance, as well. In case financial conditions allow, we are technologically ready to its introduction.

It is demonstrated by these two projects that increasing demands and the change of regulatory background requires the continuous development of technology. An important element of this is getting acquinted with integrating into survey tasks of newly introduced remote sensing data sets and the utilization of their mutually advantageous properties.