When
the sunshine duration is known, the global radiation is calculated using
the Ångström-Prescott formula. Constants depend on the geographic
location.

where |
Rg |
: |
Incoming daily global solar radiation |
[MJ m-2 d-1] |
|
Ra |
: |
Daily extra-terrestrial radiation |
[MJ m-2 d-1] |
|
Aa |
: |
Empirical constant |
[-] |
|
Ba |
: |
Empirical constant |
[-] |
|
n |
: |
Bright sunshine hours per day |
[hr] |
|
Ld |
: |
Astronomical day length |
[hr] |
When sunshine
duration is not available but minimum and maximum temperature and cloud
cover are known, the Extended Hargreaves (a.k.a. Supit ) formula is applied.
Constants depend on geographic location:

where |
Rg |
: |
Incoming daily global solar radiation |
[MJ m-2 d-1] |
|
Ra |
|
Daily extra-terrestrial radiation |
[MJ m-2 d-1] |
|
CC |
|
Mean total cloud cover during daytime |
[octa] |
|
Tmax |
|
Maximum temperature |
[°C] |
|
Tmin |
: |
Minimum temperature |
[°C] |
|
As |
: |
Empirical constants |
[°C-0.5] |
|
Bs |
: |
Empirical constants |
[-] |
|
Cs |
: |
Empirical constants |
[MJ m-2 d-1] |
When only
minimum and maximum temperatures are known, the Hargreaves equation is
applied. Again, the constants depend on geographic location:

where |
Rg |
: |
Incoming daily global solar radiation |
[MJ m-2 d-1] |
|
Ra |
|
Daily extra-terrestrial radiation |
[MJ m-2 d-1] |
|
Tmax |
|
Maximum temperature |
[°C] |
|
Tmin |
: |
Minimum temperature |
[°C] |
|
Ah |
: |
Empirical constants |
[°C-0.5] |
|
Bh |
: |
Empirical constants |
[MJ m-2 d-1] |
For more information contact Privateers
N.V. / ParBleu Technologies
1CGMS
is the Crop Growth Monitoring System as applied by the European Commission