PNNL-13501 - Pacific Northwest National Laboratory

Study Control Number: PN00057/1464
Infrared Polarization Signatures
Thomas A. Blake, John F. Schultz
This project will produce a laboratory database of infrared reflectance and polarization spectra of liquid phase chemical
compounds coated onto terrestrial surfaces such as rocks, minerals, sands, clays, etc. The database will be indispensable
in understanding remote sensing data of the terrain surrounding suspected weapons of mass destruction proliferation sites.
Such a database could also be extended to detecting changes in soil salinity and moisture as well as surface pollution such
as petroleum spills.
Project Description
The purpose of this project is to set up a Fourier transform
infrared spectrometer that can then be used to record
reflectance spectra of low volatility organic and
organophosphorous compounds coated onto terrestrial
surfaces. In the second year, the spectrometer will be
modified to include an ellipsometry capability, so that
changes in the state of polarization as light reflects off
these coated surfaces can be measured. The database of
infrared reflectance and polarization spectra of a select
group of compounds on a select group of surfaces will be
invaluable in interpreting remote sensing data of soils
surrounding suspected proliferation sites. To date, we
have set up the Fourier transform spectrometer, and a
reflectance accessory for holding our samples and
recording spectra at variable reflectance and detection
angles. We have begun recording reflectance spectra of
several surfaces such as rough cut quartz crystal, and
quartz and feldspar sands. The spectra agree nicely with
reflectance spectra recorded for geological spectral
databases, and we are now coating quartz and feldspar
sands with dimethyl methylphosphonate, which is a
benign simulant of the G class of chemical weapon
compounds, and recording reflectance spectra of these
coated surfaces. The spectra show that there is a
significant change in the spectra in going from the
uncoated to coated surface. Such changes will provide a
“smoking gun” signature of the presence of this
compound. This work is now expanding to other
compounds and other surfaces.
Introduction
The objective of this project is to explore unpolarized and
polarization-resolved reflectance spectra for detecting the
presence of liquids and particulates related to the
production of weapons of mass destruction on surfaces
around suspected facilities. It will be possible to detect
changes in the reflectance spectra as a surface is coated
with liquids, thus providing information about the
operational status of a facility and likely locations for
physical sampling. By comparing how the reflectance
spectra change as a compound accumulates and ages on a
surface, it may also be possible to identify classes of
compounds, and perhaps even specific chemicals. We
will determine whether such spectral features can be
found for each compound-substrate combination and if
the signatures will be pronounced enough to detect from a
remote sensing platform. If this work indicates that the
polarization-resolved reflectance spectra can be used to
detect weapons-related compounds on surfaces, we see
immediate extension to a number of important battlefield
chemical warfare and environmental applications.
Field data will be collected using multispectral passive
remote sensing systems similar to NASA’s Airborne
Visible and InfraRed Image Spectrometer (wavelength
coverage 0.4 to 2.45 µm) or Thermal Infrared
Multispectral Scanner (wavelength coverage 8 to 12 µm).
These instruments operate from NASA’s ER-2 and Lear
Jet aircraft, respectively, and have instantaneous ground
fields of view of about 10 meters. As an example of
sensitivity, the Thermal Infrared Multispectral Scanner
uses liquid nitrogen cooled HgCdTe detectors and has a
noise equivalent temperature difference of 0.1 K at 300 K.
This figure of merit can be related to a noise equivalent
reflectance difference of 0.002 at a wavelength of 8 µm.
Since most terrestrial materials have a reflectance
between 0.2 and 0 the instruments are sensitive to
reflectance changes of 1 part in 100. The laboratory
measurements will allow us to quantify reflectance
changes with amounts of coverage of our target
compounds (Asrar 1989; Wolfe and Zissis 1985).
Tailings and effluents pumped from mines (Barettino et
al. 1999), petroleum ground spills (Brodskii and Savchuk
Sensors and Electronics 401