GEOLIBRARY-L Digest - 15 Apr 2014 to 20 Apr 2014 (#2014-17)Good morning all,

There has been some discussion as of late regarding the use of the infrared spectral bands for measuring relative turgidity, or the water content of the spongy mesophyll portion of a plant leaf.  I would like to clarify a few of the points being made.

There are several spectral bands that are sensitive to the amount of water in a plant leaf and they are middle-infrared, thermal infrared and passive microwave.  The Leica ADS80, the sensor used by Woolpert to collect the latest 4-band ortho-imagery graciously provided by the Maine GeoLibrary, apparently uses a near-infrared band (833-887 nanometers) in addition to the typical red, green, blue bands.

Additionally, while middle-infrared (e.g 1550-1750 nanometers) can be used to measure moisture content, it is accomplished by examining a lack of reflectance not an increase in reflectance.  This is due to the fact that infrared light in general is absorbed by water, not reflected.  The use of middle-infrared is helpful because water is an especially good absorber of middle-infrared light.

Please excuse the lack of context and supporting information.  For those of us privy to, and making use of, the information that is being disseminated I suggest we take a closer look at our literature regarding the matter.  

Have a great weekend.

Kind regards,

Joseph R. LaBranche, P.L.S.
LaBranche Land Surveys
27 Oak Street
Rockland, Maine 04841
(207) 594-4206
(207) 691-3218
www.labranchelandsurveys.com


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