1.5 diffusb.aml

This AML enables the user to calculate diffuse short-wave radiation for a terrain of choice (Kumar et al., 1997) using a batch job mode. There is no difference to the coding of diffuse.aml, except that diffusb.aml has no user interface. Rather, the necessary parameters are passed when starting the AML. It might be appropriate to read the instructions for diffuse.aml and for shortwavc.aml first. The usage of the routine is as follows:
 
&r diffusb  <dem>  <out>  <lat>  <dstart>  <dend>  <timeint>


where: trn = the DEM grid; out  = is the radiation output grid; dem = file name of DEM; out = base name of outgrid file names; lat = latitude of study site (DEM) in decimal degrees; dstart = the start day (in Julian day); dend = the time interval in minutes to calculate sun positions (used for interpolating the energy budget; timeint = the time interval in minutes to calculate sun positions (used for interpolating the energy budget.

If dend is set equal to dstart then a single day is calculated with this routine. .

All the other requirements are the same as for running the shortwavc.aml

This is a complementary calculation to the direct radiation modeling. The portion of diffuse solar radiation relative to the global radiation varies between summer and winter, and is a function of solar altitude and terrain reflectance, among other. Global radiation (the sum of direct and diffuse radiation) is often used in other biophysical modeling application (e.g. modeling of potential evapotranspiration, 3.1 – 3.3).
 

Modifications:

This AML had to be adjusted to a bug in ArcInfo 8.0.2, where the raise to fractional powers causes the program to crash. This reported bug is supposed to be fixed for AI 8.2. Calvin Tolkamp proposed an interim "fix", which is included in the version you download here. Attention: This "fix" has been updated Sept. 14th, 2000!
 
 
 

General specifications of the AML:

Command: &r diffuseb
Required input: DEM
Output units: kJ/m2/time period
Speed of calculations: Very fast due to parsimonious programming
Flexibility of the routine: Medium; can’t go beyond 1 day
User interface: Limited, but simple and easy
Known errors:  -
Corrections 9/14/2000: Adjustments to bug in ArcInfo 8.0.2
Programmer L. Kumar (original coding)
N.E. Zimmermann (code adjustments)
Download: diffuseb.aml       (use: "save link as")
Contact: niklaus.zimmermann @ wsl.ch

 

References:

Kumar, L., Skidmore, A.K. and Knowles, E., 1997. Modelling topographic variation in solar radiation in a GIS environment. International Journal for Geographical Information Science, 11(5): 475-497.
 
 

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Last Updated: 9/24/03
By Niklaus E. Zimmermann