Irrigation Management

Remote sensing can be used as a very efficient tool for managing irrigated agricultural areas. A number of different applications can be used for operational management and planning for irrigated schemes and usually it is necessary to develop local adaptations to existing methods. Applications include crop mapping during the growing season, assessment of water abstraction and assessment of crop yields and productivity. It is usually an important component in water resource assessment.

Water abstraction - semi bio-physical vegetation productivity approach
An assessment of vegetation photosynthetic activity will be made at different points in time. Vegetation water consumption will then be determined as a function of vegetation photosynthetic activity expressed as a function of NDVI and/or fAPAR (fraction of absorbed photosynthetically active radiation) and weighted relative to the per cent vegetation cover of the irrigated fields. Three times during the growing season (using three different satellite scenes) the accumulated water consumption will be estimated from different vegetation production and vegetation cover measures and evaluated against reference data.

Water abstraction - empirical approach
From optical remote sensing data different measures of wetness using mid- and near- infrared information can be used, e.g. the Tasselled Cap transformation. Radar data can equally provide different information on humidity. Together with the vegetation growth information derived from NDVI and/or fAPAR, a statistical analysis will identify possible empirical models for water abstraction. Multiple regression analysis will be used. The results will be compared with the reference data.

Crop Yield
The approach of the well known light use efficiency model (LUE) will be tested (Kumar & Monteith 1982, Rasmussen, 1998). This can be done using fAPAR as an input to assess crop yield and using single high or medium resolution remote sensing data (maximum three different images).

Capacity building is an important part of GRAS's activities. The implementation activity includes the transfer of technology and methods to the client. This will be done through on-the-job training and more formal training about the used methods and techniques to relevant staff at the client's organisation. Once this is achieved the trained local remote sensing staff will make their own first assessment of water abstraction and crop yield for a new growing season. GRAS will provide technical backstopping and if necessary, follow-up missions can be arranged for solving problems, supervision and quality control.