(Difference between revisions)
| Revision as of 12:46, 15 June 2006 Peter (Talk | contribs) (→'''Two basic modelling options''') ← Previous diff |
Revision as of 12:47, 15 June 2006 Peter (Talk | contribs) (→'''Two basic modelling options''') Next diff → |
||
| Line 1: | Line 1: | ||
| + | <blockquote> | ||
| ='''Two basic modelling options'''= | ='''Two basic modelling options'''= | ||
| Line 31: | Line 32: | ||
| gridding before modelling, and modelling before gridding. Advantages and disadvantages in terms of errors, labour and accuracy of forecasts. | gridding before modelling, and modelling before gridding. Advantages and disadvantages in terms of errors, labour and accuracy of forecasts. | ||
| + | </blockquote> | ||
Revision as of 12:47, 15 June 2006
Two basic modelling options
A crop monitoring program has to be based on data from different locations inside the country of region that needs to be monitored.
Technically these monitoring locations are points. Points can be pinpointed at the earth’s surface with coordinates. The coordinate system that is used in crop forecasting is called a geographic coordinate system whereby the coordinates are expressed in Longitude - Latitude pairs.
Example : the geographic coordinates of Pnom Penn (Cambodia) are:
- Longitude: 104.917445
- Latitude : 11.558831
Normally expressed as 104.917445, 11.558831 (longitude always first). Read more: Geographic Coordinates
Depending on the circumstances, the crop forecasting network can be based on:
- An irregularly spaced network based on real-world stations. As an example below part of the rainfall recording stations in Africa (Type 1). This type of network has a preference over the second type when station data to run the water balance are available. The main advantages of this type of monitoring network are:
- Input and output of the water balance model can be checked against the real situation in the field.
- Station weather data are more accurate than gridded data in the vicinity of the stations themselves.
Type 1. Rainfall stations in Africa
- A regularly spaced grid (Type 2). In this case, grid points do not coincide with meteorological stations.
Type 2. Grid example for Afghanistan (0.5 degree distance)
Within the crop forecasting tools these locations areWhen setting up a crop monitoring program two basic approaches exist
gridding before modelling, and modelling before gridding. Advantages and disadvantages in terms of errors, labour and accuracy of forecasts.
