18
••••
SunScan Tutorial
Document code: SS1-UM-1.05
Setting up a measurement session
Working through the menu options
In normal use the SunData software calculates Leaf Area Index (
LAI
) based on
readings from the SunScan probe and from the Beam Fraction Sensor (if fitted).
These calculations also require information about the distribution of leaf angles and
absorption of light by leaves within the canopy and knowledge of the solar angle
calculated from the time of day and local latitude and longitude.
SunScan probe
Average PAR within canopy
Beam fraction
PAR above canopy
ïïïï
Ratio of Direct to Total light
ïïïï
ELADP setting
Leaf Angle Distribution
Leaf Area Index
Absorption setting
Leaf PAR Absorption
ïïïï
Time and date
üüüü
ïïïï
Latitude setting
Solar zenith angle
Longitude setting
Before it can make sensible calculations of the Leaf Area Index, SunData needs to
know what values to use for the above settings.
♦
Press
Menu
, use the
←
←
←
←
→
→
→
→
arrow keys to
select the
Settings
menu, and the
↑↑↑↑↓↓↓↓
keys to highlight
Site
, and press
Enter
.
Type in a
Name
for your present site, and
set the
Latitude
and
Longitude
by
pressing
Del
and typing in the
appropriate values. When everything is
correct, to accept it
♦
Press
Menu
again, then select
Time & Date
and press
Enter
. Now set the local
time and date in the dialog box. You also need to set the appropriate offset from
GMT for your time zone. Set
Local time is GMT
to between -12.0 and +13.0
hours. Remember to make allowance for any special seasonal offsets, such as
“Summer Time”, “Daylight Saving”. For example: British Summer Time is
GMT+1, India is GMT+5.5, and USA EST is GMT - 5.0.
♦
Press
Enter
to accept the settings and return to the Title screen.
Note: The date and time formats can be changed, but for the moment just get the
information correct. To change am to pm, select it, and press
p
(or
a
).
♦
Use the
←
←
←
←
→
→
→
→
arrow keys to set the
Absorption
to
0.85
. Set the
ELADP
(
E
llipsoidal
L
eaf
A
ngle
D
istribution
P
arameter) to
1
. Press
Enter
to accept
these settings.
Later sections in
Measurement Options
and
LAI Theory
give explanations and
advice on choosing values for these parameters.
♦
Set the
Display
format to
LAI
. Leave the
‘Sample’
and
‘Plot’
names unchanged.
The options for
Display
(
LAI
,
PAR
and
All
) have an important effect on the display
of readings but they also interact with the setting for
Ext sensor
(
BFS
or
none
) to
determine the sequence of readings required.
