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From:
Jeffrey Normandin <[log in to unmask]>
Reply To:
Jeffrey Normandin <[log in to unmask]>
Date:
Mon, 5 May 2014 14:03:17 +0000
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Thanks Mike, that is a lot of great information!

Jeff

From: Maine GeoNews [mailto:[log in to unmask]] On Behalf Of Smith, Michael
Sent: Monday, May 05, 2014 9:44 AM
To: [log in to unmask]
Subject: Re: Maine GeoLibrary ortho-imagery and infrared light

Thanks Joseph.

I believe this stems from a question at the MMA/MEGUG meeting on Thursday, during our orthoimagery session.  That question had to do with knowing whether the IR band provided by the GeoLibrary imagery was indeed suitable for the applications we were discussing (mapping vegetation, imperviousness, and wetlands - particularly vernal pools).

A little history for context first if I may.  The LandSat MultiSpectral Sensor (MSS) has been around since 1972 and captured earth reflectance data until 1999 (and then resurrected for a few months in 2012).  It used a series of four bands which ranged from green to near-IR (0.5 um to 1.1 um).  The fourth band was designed to capture differences in vegetation based on water content and used a range of 0.8-1.1 um.  LandSat's Thematic Mapper (TM) sensor and the follow-up enhanced TM (ETM+) sensed in greater detail the infrared and added thermal energy to the array.  For infrared bands it carried a narrower near-IR band than MSS (0.76-0.9 um), and added a mid-IR band (1.55-1.75um) and a farther mid-IR band (2.08-2.35um).  These are designed for sensing vegetation, soil water content, and wetlands.

Additionally, NOAA's Advanced Very High Resolution Radiometer (AVHRR) uses a similar range of 0.73-1.0 um for determining land/water boundaries.

The Leica ADS-80 near-IR sensor carries on this same lineage of near-IR reflectance capture, using a range that is slightly narrower than the LandSat TM near-IR band 4, and quite a bit narrower than the old MSS band 4.  Now I am not an expert on energy reflectance, but from what I have read, this is the range that is best utilized for determining surface moisture , both for vegetation and surface water (while the mid-IRs can be more useful for sensing water a bit deeper in the land like hydric soils).  This is also followed up by NOAA's choice of that range for land/water delineations.

So Leica's choice of an infrared band is on par with best practices in the remote sensing industry for capturing surface moisture content in both vegetation and standing water, and thus is entirely suitable for delineating vegetation, imperviousness, and wetlands (especially vernal pools).  Now, for forestry purposes, the timing of our leaf-off collect is useful for delineating deciduous vs. coniferous, but probably not useful for determining variations within deciduous stands.  That would require additional collects during the growing season.  As the primary mission of our program is municipal orthoimagery, the leaf-off collection date was the most suitable.  This time period is also ideal for delineating wetlands as they will have the most water in the Spring, after snowmelt.

For more info on infrared data, see this tutorial provided by NASA and Utah State University:
http://extension.usu.edu/nasa/htm/on-target/near-infrared-tutorial

LandSat band designations:  http://landsat.usgs.gov/band_designations_landsat_satellites.php
AVHRR band designations: http://noaasis.noaa.gov/NOAASIS/ml/avhrr.html
Wikipedia: http://en.wikipedia.org/wiki/Multispectral_image
WorldView 2 satellite bands (good discussion of band ranges): http://satimagingcorp.s3.amazonaws.com/site/pdf/WorldView-2_8-Band_Applications_Whitepaper.pdf


===============================
Michael Smith MS GISP
State GIS Manager, Maine Office of GIS
State of Maine, Office of Information Technology
michael.smith _at_ maine.gov 207-215-5530

Board Member, Maine GeoLibrary
Education Chair, Maine GIS Users Group
State Rep, National States Geographic Information Council
[cid:image001.jpg@01CF6848.D9AD21D0]

State House Station 145
51 Commerce Drive
Augusta, ME 04333-0145
69o 47' 58.9"W  44o 21' 54.8"N
From: Maine GeoNews [mailto:[log in to unmask]] On Behalf Of Joseph R LaBranche
Sent: Saturday, May 03, 2014 11:14 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Maine GeoLibrary ortho-imagery and infrared light

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<http://www.labranchelandsurveys.com>


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