View Full Version : Infrared Reflectance of conifer Needels?
11-24-2008, 12:17 PM
I have a digital camera with IR capability. If you take a landscape picture, you notice that the needles of pine trees appear very bright. Why do these specied reflect IR-would'nt it be useful to extract the most energy they can from sunlight? So why do they refelect the infrared/
11-25-2008, 10:44 AM
Plants primarily use sunlight for photosynthesis, and probably infrared photons have too little energy to drive any chemistry. Chemical reactions often involve energies of around 2 to 4 ev per event, and the digicam IR photons are probably half an ev to maybe a bit over one ev. There might be some evolutionary advantage to absorbing less NIR, such as reducing drying out during hot weather, or maybe it never mattered.
11-25-2008, 11:20 AM
Plants have special sensors (Phytochromes) that react to the ratio between red light (620-710nm) and near IR light (far-red, 710-810nm). They use this to orient leafs and flowers to the sun and to regulate their circadian rythm.
11-25-2008, 03:50 PM
Did you recently get this? Is it winter where you are? If you take that out in summer, you'll find that grass and most tree leaves will be bright white also.
11-26-2008, 12:08 AM
Healthy vegetation has a high reflectance in the near-infrared due to the air spaces in the mesophyll layer of it's leaves. Age, health and different species of vegetation can often be picked out in aerial and satellite imaging due to the difference rates reflectivity. Here (http://pirlwww.lpl.arizona.edu/research/biosphere/Lesson/) is something I found that might help explain it.
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