What To Measure And How; Experiment Design - Delta-T Devices SunScan SS1 User Manual

What to Measure and How

Experiment Design

This section discusses the factors that bear on your experimental
objectives. It should help you answer questions like:

What equipment do I need?

What readings must be taken?

Will I have to wait for particular times of day or weather conditions?
The type of study you propose to do will determine the time of year and
duration of the experiment, and whether you are interested, for example,
in monitoring growth by interception of solar radiation, or perhaps in the
canopy structure as well.
Some canopies types (the non-uniform ones) preclude the use of the
SunScan's direct LAI readout. You could, however, characterise the 3-
dimensional light distribution within your canopy at different heights, or
along transects through it. For brevity we call this approach "PAR
mapping" in the discussion below.
Answers to the above questions are complicated, but the following should
give you a good appreciation of the main issues involved.
Above-canopy reference requirements
This refers to measurements of PAR incident on the canopy, made at the
same time as the below-canopy measurements. The question is whether
to use a beam fraction sensor (BFS).
Use of a Beam Fraction Sensor e.g. BF5 Sunshine
Sensor
A BF5 connected to the SunScan probe provides the best option, because
you can operate with fewest restrictions. However, with some canopy
types this may not be practical.
The next best option is to use the SunScan probe (without the BF5)
sequentially above and below the canopy, but you may be restricted to
times when the light levels are not changing fast.
See also Take LAI Readings on page17.
32  What to Measure and How
SS1 User Manual v3.3