The Savannah River National Laboratory (SRNL) collected thermal imagery and ground truth data at two commercial
power plant cooling lakes to investigate the applicability of laboratory empirical correlations between surface heat flux
and wind speed, and statistics derived from thermal imagery. SRNL demonstrated in a previous paper  that a linear
relationship exists between the standard deviation of image temperature and surface heat flux. In this paper, SRNL will
show that the skewness of the temperature distribution derived from cooling lake thermal images correlates with
instantaneous wind speed measured at the same location. SRNL collected thermal imagery, surface meteorology and
water temperatures from helicopters and boats at the Comanche Peak and H. B. Robinson nuclear power plant cooling
lakes. SRNL found that decreasing skewness correlated with increasing wind speed, as was the case for the laboratory
experiments. Simple linear and orthogonal regression models both explained about 50% of the variance in the skewness
- wind speed plots. A nonlinear (logistic) regression model produced a better fit to the data, apparently because the
thermal convection and resulting skewness are related to wind speed in a highly nonlinear way in nearly calm and in
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.
The Savannah River Technology Center (SRTC) conducted four reflectance vicarious calibrations at Ivanpah Playa, California since July 2000 in support of the MTI satellite. The multi-year study shows temporal, spatial and spectral variability at the playa. The temporal variability in the wavelength dependent reflectance and emissivity across the playa suggests a dependency witt precipitation during the winter and early spring seasons. Satellite imagery acquired on September and November 2000, May 2001 and March 2002 in conjunction with ground truth during the September, May and March campaigns and water precipitation records were used to demonstrate the correlation observed at the playa.
The Savannah River Technology Center (SRTC) conducted four vicarious reflectance calibrations at Ivanpah Playa, California since July 2000 in support of the MTI satellite. The potential of the playa as a thermal calibration site was also investigated in the campaigns with a mobile Fourier transform infrared spectrometer. The multi-year study shows time and spatial variability in the spectral emissivity. The ground truth temperature and emissivity correlate quite well with the data from the MTI satellite imagery. The research paper will show the time-dependent emissivities measured during our ground truth campaigns and the corresponding satellite imagery.
A survey of surface temperatures of the Mauna Loa caldera during 7/14/00 and 7/15/00 was made by SRTC in conjunction with a MTI satellite image collection. The general variation of surface temperature appears quite predictable responding to solar heating. The analysis of detailed times series of temperature indicates systematic variations in temperature of 5 C corresponding to time scales of 3-5 minutes and space scales of 10-20 m. The average temperature patterns are consistent with those predicted by the Regional Atmospheric Modeling System (RAMS).
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.
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.
The Tropical Pacific Island of Nauru is a US DOE ARM observation site that monitors tropical climate and atmospheric radiation. This observation site is ideal for validating MTI images because of the extensive deployment of continuously operating instruments. MTI images are also useful in assessing the effect of the island on the ocean climate and on the ARM data. An MTI image has been used to determine the spatial distribution of water vapor and sea-surface temperature near the island. The results are compared with a three-dimensional numerical model simulation.
Natural bodies of water have several advantages as IR calibration targets in remote sensing. Among these are availability, homogeneity, and accurate knowledge of emissivity. A portable, low-cost, floating apparatus is described for calibration of remote IR sensors to within 0.15 C. The apparatus measures the surface and bulk water temperature as well as the wind speed, direction, temperature, and relative humidity. The apparatus collects data automatically and can be deployed for up to 24 hours. The sources of uncertainty, including the effects of skin temperature and waves are discussed. Data from several field campaigns to calibrate IR bands of DOE's Multi-Spectral Thermal Imager are described along with estimates of error.
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.
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) T's 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.
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.
Remote sensing temperature measurements of water bodies is complicated by the temperature differences between the true surface or `skin' water and the bulk water below. Weather conditions control the reduction of the skin temperature relative to the bulk water temperature. Typical skin temperature depressions range from a few tenths of a degree Celsius to more than one degree. In this research project, the Savannah River Technology Center used aerial thermography and surface-based meteorological and water temperature measurements to study a power plant cooling lake in South Carolina. Skin and bulk water temperatures were measured simultaneously for imagery calibration and to product a database for modeling of skin temperature depressions as a function of weather and bulk water temperatures. This paper will present imagery that illustrates how the skin temperature depression was affected by different conditions in several locations on the lake and will present skin temperature modeling results.
Sandia National Laboratories (SNL), Los Alamos National Laboratory (LANL) and the Savannah River Technology Center (SRTC) have developed a diverse group of algorithms for processing and analyzing the data that will be collected by the Multispectral Thermal Imager (MTI) after launch late in 1999. Each of these algorithms must be verified by comparison to independent surface and atmospheric measurements. SRTC has selected 13 sites in the continental U.S. for ground truth data collections. These sites include a high altitude cold water target (Crater Lake), cooling lakes and towers in the warm, humid southeastern U.S., Department of Energy (DOE) climate research sites, the NASA Stennis satellite Validation and Verification (V&V) target array, waste sites at the Savannah River Site, mining sites in the Four Corners area and dry lake beds in Nevada. SRTC has established mutually beneficial relationships with the organizations that manage these sites to make use of their operating and research data and to install additional instrumentation needed for MTI algorithm V&V.