I have a series of illuminance values recorded using HOBO pendant loggers. The loggers record illuminance (lux). We used them about a meter off of the ground to record both air temp and illuminance at 5 - 15 minute intervals for three years during a plot based study of soil carbon flux. I have been parsing through my data and I am struggling to find what is the most useful way to present said data. In our design, we had allotted for three different vegetation cover types across a watershed. I have toyed with using daily or hourly maximum values, daily averages, hourly averages . . . but I am curious as to what others might think about the best way to present this data.
I would like to be able to use this to show differences in plots/vegetation types, more than an actual explanatory variable--however I am open to all or any suggestions. Thanks.
Kobe and Hogarth has a useful table comparing methods of measuring and presenting understory light dynamics. We've found the most reliable and representative way to look at our data is to select the mean light reading every ten minutes for two hours on either side of solar noon - there's still enough variation to represent the light environment for the full day, and it adequately captures the diffuse light that is so crucial in our forest type.
Article Erratum: Evaluation of irradiance metrics with respect to pr...
Shawn this is great, thanks! Do you know of a short-hand name for that variable?
We call that measurement an estimate of daily transmittance for our work. Be careful with lux, though - its weighted for human vision and might not give you as much information about plant-relevant light conditions as might a PAR meter.
Yeah, that seems to have been the problem all along. I think we will just end up using more of a quantitative measure of vegetation differences among plots . . i.e. differences in shade cover or something, not directly relating it to anything directly. More comparison.
Your data have a very high time resolution. If the measuring points are situated in forest areas you could use them as an index for determining LAI and its seasonal fluctuation. LAI is a key parameter for crown interception of precipitation and thus one of the most important plant variables for water modeling
We measured LAI using a LiCor instrument. The problem with using the light data for LAI was that the loggers were rotated under plots of similar treatments over the course of the summer so I cannot pinpoint exactly which plot data at any point was collected under since there were multiple replicates--a mistake I will avoid in the future as I see how valuable this could be now! Thanks for the insight.
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