Eliel Villa-Aleman

Dependence of Surface-Enhanced Infrared Absorption (SEIRA) Enhancement and Spectral Quality on the Choice of Underlying Substrate: A Closer Look at Silver (Ag) Films Prepared by Physical Vapor Deposition (PVD)

Silver (Ag) films of varying thickness were simultaneously deposited using physical vapor deposition (PVD) onto six infrared (IR) substrates (BaF2, CaF2, Ge, AMTIR, KRS-5, and ZnSe) in order to correlate the morphology of the deposited film with optimal SEIRA response and spectral band symmetry and quality. Significant differences were observed in the surface morphology of the deposited silver films, the degree of enhancement provided, and the spectral appearance of para-nitrobenzoic acid (PNBA) cast films for each silver-coated substrate. These differences were attributed to each substrates chemical properties, which dictate the morphology of the Ag film and ultimately determine the spectral appearance of the adsorbed analyte and the magnitude of SEIRA enhancement. Routine SEIRA enhancement factors (EFs) for all substrates were between 5 and 150. For single-step Ag depositions, the following ranking identifies the greatest SEIRA enhancement factor and the maximum absorption of the 1345 cm−1 spectral marker of PNBA at the optimal silver thickness for each substrate: BaF2 (EF = 85 ± 19, 0.059 A, 10 nm Ag) > CaF2 (EF = 75 ± 30, 0.052 A, 10 nm Ag) > Ge (EF = 45 ± 8, 0.019 A, 5 nm Ag) > AMTIR (EF = 38 ± 8, 0.024 A, 15 nm Ag) > KRS-5 (EF = 24 ± 1, 0.015 A, 12 nm Ag) > ZnSe (EF = 9 ± 5, 0.008 A, 8 nm Ag). A two-step deposition provides 59% larger EFs than single-step depositions of Ag on CaF2. A maximum EF of 147 was calculated for a cast film of PNBA (surface coverage = 341 ng/cm2) on a 10 nm two-step Ag film on CaF2 (0.102 A, 1345 cm−1 symmetric NO2 stretching band). The morphology of the two-step Ag film has smaller particles and greater particle density than the single-step Ag film.

Observations and model predictions of water skin temperatures at MTI core site lakes and reservoirs

The Savannah River Technology Center (SRTC) measured water skin temperatures at four of the Multi-spectral Thermal Imager (MTI) core sites. The depression of the skin temperature relative to the bulk water temperature ((Delta) T) a few centimeters below the surface is a complex function of the weather conditions, turbulent mixing in the water and the bulk water temperature. Observed skin temperature depressions range from near zero to more than 1.0 degree(s)C. Skin temperature depressions tend to be larger when the bulk water temperature is high, but large depressions were also observed in cool bodies of water in calm conditions at night. We compared (Delta) T predictions from three models (SRTC, Schlussel and Wick) against measured (Delta) Ts from 15 data sets taken at the MTI core sites. The SRTC and Wick models performed somewhat better than the Schlussel model, with RMSE and average absolute errors of about 0.2 degree(s)C, relative to 0.4 degree(s)C for the Schlussel model. The average observed (Delta) T for all 15 databases was -0.7 degree(s)C.

Measurements of the Skin Temperature on Small Lakes

Abstract An apparatus to measure the skin temperature and related variables on inland lakes is described. The apparatus is a transparent frame with sensors to measure the skin and bulk water temperature, the wind velocity, and the air temperature and humidity for periods of several days. The sensors are positioned within 1 m of the air–water interface and sample boundary layer variables every 2 s. Data for a 4-h period at midday are discussed, and the vertical fluxes of heat and momentum are calculated using bulk relationships for 1- and 5-min periods. It is shown that the measured water temperature at a depth of 1 cm correlates well with estimates based on the bulk heat flux. The skin temperature depression is calculated from the bulk heat and momentum fluxes and is found to vary between 0.4° and 0.5°C for the 4-h period and was in good agreement with the measured values. However, the calculated and measured skin temperatures were poorly correlated for both the 1- and 5-min averages. This is believed to ...

MTI thermal bands calibration at Ivanpah Playa with a Fourier transform infrared spectrometer

The Savannah River Technology Center (SRTC) is currently calibrating the Multispectral Thermal Imager (MTI) satellite sponsored by the Department of Energy. The MTI is a research and development project with 15 wavebands in the 0.45-11.50 micrometers spectral range. The reflective bands of the MTI satellite are calibrated in desert playas such as Ivanpah Playa in the Nevada/California border. The five MTI thermal bands are calibrated with targets of know emissivity and temperature such as power plant heated lakes. In order to accomplish a full calibration at the desert playas, a Fourier transform infrared spectrometer was used to measure soil surface radiance and temperature during the satellite overpass. The results obtained with the mobile FTIR during the ground truth campaign at Ivanpah Playa will be presented.

Electrochemical degradation of butyltrimethylammonium bis(trifluoromethylsulfonyl)imide for lithium battery applications

Ionic liquids (ILs) are being considered as electrolytes for lithium ion batteries due to their low volatility, high thermal stability, and wide electrochemical windows which are stable at the strongly reducing potentials present in Li/Li+ batteries. Lithium metal deposition occurs under strongly reducing conditions and the effect that Li metal and any overpotential has on the stability of ILs is important in furthering the application of ILs in lithium based batteries. Here, N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide was exposed to various potential differences in order to collect and characterize the volatile products. The IL produced more volatile products when exposed to strong reducing potentials which included reactive products such as hydrogen, alkanes, and amines. Water is a known contributor to hydrogen production in reducing environments, but the IL is also a source of hydrogen. If Li+ was present, the preferred pathway of reduction was plating of the lithium onto the working electrode, thus decreasing the reaction rate of degraded ILs.

Thermal targets for satellite calibration

The Savannah River Technology Center (SRTC) is currently calibrating the Multispectral Thermal Imager (MTI) satellite sponsored by the Department of Energy. The MTI imager is a research and development project with 15 wavebands in the visible, near-infrared, short-wave infrared, mid-wave infrared and long-wave infrared spectral regions. A plethora of targets with known temperatures such as power plant heated lakes, volcano lava vents, desert playas and aluminized Mylar tarps are being used in the validation of the five thermal bands of the MTI satellite. SRTC efforts in the production of cold targets with aluminized Mylar tarps will be described. Visible and thermal imagery and wavelength dependent radiance measurements of the calibration targets will be presented.

DIRECT MEASUREMENT OF HEAT FLUX FROM COOLING LAKE THERMAL IMAGERY

Laboratory experiments show a linear relationship between the total heat flux from a water surface to air and the standard deviation of the surface temperature field, σ, derived from thermal images of the water surface over a range of heat fluxes from 400 to 1800 Wm-2. Thermal imagery and surface data were collected at two power plant cooling lakes to determine if the laboratory relationship between heat flux and σ exists in large heated bodies of water. The heat fluxes computed from the cooling lake data range from 200 to 1400 Wm-2. The linear relationship between σ and Q is evident in the cooling lake data, but it is necessary to apply band pass filtering to the thermal imagery to remove camera artifacts and non-convective thermal gradients. The correlation between σ and Q is improved if a correction to the measured σ is made that accounts for wind speed effects on the thermal convection. Based on more than a thousand cooling lake images, the correlation coefficients between σ and Q ranged from about 0.8 to 0.9.

Radiometric modeling of cavernous targets to assist in the determination of absolute temperature for input to process models

Determining the temperature of an internal surface within cavernous targets, such as the interior wall of a mechanical draft cooling tower, from remotely sensed imagery is important for many surveillance applications that provide input to process models. The surface leaving radiance from an observed target is a combination of the self-emitted radiance and the reflected background radiance. The self-emitted radiance component is a function of the temperature-dependent blackbody radiation and the view-dependent directional emissivity. The reflected background radiance component depends on the bidirectional reflectance distribution function (BRDF) of the surface, the incident radiance from surrounding sources, and the BRDF for each of these background sources. Inside a cavity, the background radiance emanating from any of the multiple internal surfaces will be a combination of the self-emitted and reflected energy from the other internal surfaces as well as the downwelling sky radiance. This scenario provides for a complex radiometric inversion problem in order to arrive at the absolute temperature of any of these internal surfaces. The cavernous target has often been assumed to be a blackbody, but in field experiments it has been determined that this assumption does not always provide an accurate surface temperature. The Digital Imaging and Remote Sensing Image Generation (DIRSIG) modeling tool is being used to represent a cavity target. The model demonstrates the dependence of the radiance reaching the sensor on the emissivity of the internal surfaces and the multiple internal interactions between all the surfaces that make up the overall target. The cavity model is extended to a detailed model of a mechanical draft cooling tower. The predictions of derived temperature from this model are compared to those derived from actual infrared imagery collected with a helicopter-based broadband infrared imaging system collected over an operating tower located at the Savannah River National Laboratory site.

Comparison of MTI Satellite-Derived Surface Water Temperatures and In-Situ Measurements

Temperatures of the water surface of a cold, mid-latitude lake and the tropical Pacific Ocean were determined from MTI images and from in situ concurrent measurements. In situ measurements were obtained at the time of the MTI image with a floating, anchored platform, which measured the surface and bulk water temperatures and relevant meteorological variables, and also from a boat moving across the target area. Atmospheric profiles were obtained from concurrent radiosonde soundings. Radiances at the satellite were calculated with the Modtran radiative transfer model. The MTI infrared radiances were within 1% of the calculated values at the Pacific Ocean site but were 1-2% different over the mid-latitude lake.

Ground truth collections at the MTI core sites

The Savannah River Technology Center (SRTC) selected 13 sites across the continental US and one site in the western Pacific to serve as the primary or core site for collection of ground truth data for validation of MTI science algorithms. Imagery and ground truth data from several of these sites are presented in this paper. These sites are the Comanche Peak, Pilgrim and Turkey Point power plants, Ivanpah playas, Crater Lake, Stennis Space Center and the Tropical Western Pacific ARM site on the island of Nauru. Ground truth data includes water temperatures (bulk and skin), radiometric data, meteorological data and plant operating data. The organizations that manage these sites assist SRTC with its ground truth data collections and also give the MTI project a variety of ground truth measurements that they make for their own purposes. Collectively, the ground truth data from the 14 core sites constitute a comprehensive database for science algorithm validation.