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|LIMITATIONS OF DRYMON
As any validated and tested method DRYMON has limitations. These limitations are related to the global coverage, data continuity and detail.
DRYMON does not perform well in:
- High mountains: there is hardly any soil moisture to monitor or it is covered by snow and ice;
- Deserts: the very low quantities of soil moisture are hidden under shifting sands;
- Rain forests: the soil is hidden under 20-40 meters of vegetation cover and is always so wet, that it is not useful to speak of droughts;
- Arctic zones where there are no well-developed soils, and where soils are frozen (e.g., permafrost).
DRYMON performes less at all these landscape types, but drought is usually not an environmental problem or a bottle-neck in crop production here.
A mask is applied to DRYMON-products where no meaningful information can be obtained. The mentioned problems do not reduce the value of DRYMON: it performs well within the area where 99.9% of agricultural production occur, 95% of the livestock products comes from and 90% of the forest products.
The method is based on the ERS-SCAT and is used on the METOP-ASCAT. The SCAT- instrument has been flown on ERS-1 (1991-1999) and on ERS-2 (1995-2011). The ASCAT is onboard the METOP series of satellites of whim the first was launched October 2006.
The ASCAT provides a signal averaging data over areas of 12.5 * 12.5 km. Of course this is a problem if one wants to monitor soil moisture in a particular field. Alternatively the scale of rainfall events and therefore of soil moisture evolution over time is very much in harmony with the sampling distance of the ASCAT.