[Show abstract][Hide abstract] ABSTRACT: The Multispectral Thermal Imager (MTI) is a 15-band satellite-based imaging system. Two of the bands (J, K) are located in the mid-infrared (3-5 μm) wavelength region: J, 3.5-4.1 μm and K, 4.9-5.1 μm, and three of the bands (L, M, N) are located in the thermal infrared (8-12 μm) wavelength region: L, 8.0-8.4 μm; M, 8.4-8.8 μm; and N, 10.2-10.7 μm. The absolute radiometric accuracy of the MTI data acquired in bands J-N was assessed over a period of approximately three years using data from the Lake Tahoe, CA/NV, automated validation site. Assessment involved using a radiative transfer model to propagate surface skin temperature measurements made at the time of the MTI overpass to predict the vicarious at-sensor radiance. The vicarious at-sensor radiance was convolved with the MTI system response functions to obtain the vicarious at-sensor MTI radiance in bands J-N. The vicarious radiances were then compared with the instrument measured radiances. In order to avoid any reflected solar contribution in the mid-infrared bands, only nighttime scenes were used in the analysis of bands J and K. Twelve cloud-free scenes were used in the analysis of the data from the mid-infrared bands (J, K), and 23 cloud-free scenes were used in the analysis of the thermal infrared bands (L, M, N). The scenes had skin temperatures ranging between 4.4 and 18.6°C. The skin temperature was found to be, on average, 0.18 ± 0.36°C cooler than the bulk temperature during the day and 0.65 ± 0.31°C cooler than the bulk temperature at night. The smaller skin effect during the day was attributed to solar heating. The mean and standard deviation of the percent differences between the vicarious (predicted) at-sensor radiance convolved to the MTI bandpasses and the MTI measured radiances were -1.38±2.32, -2.46 ± 1.96, -0.04 ± 0.78, -1.97 ± 0.62, -1.59 ± 0.55 for bands J-N, respectively. The results indicate that, with the exception of band L, the instrument measured radiances are warmer than expected.
Full-text · Article · Oct 2005 · IEEE Transactions on Geoscience and Remote Sensing
[Show abstract][Hide abstract] ABSTRACT: Since shortly after launch the radiometric performance of band 6 of the ETM+ instrument on Landsat 7 has been evaluated using vicarious calibration techniques for both land and water targets. This evaluation indicates the radiometric performance of band 6 has been both highly stable and accurate. Over a range corresponding to a factor of two in radiance (5 to 55 C in kinetic temperature terms) the difference between the in-situ derived radiance and the image derived radiance is on average 0.5% or less. Water targets are the easiest to use but are limited to the temperature range from 0 to about 32 C. Land targets can reach 55 C or more but are far less spatially homogeneous than water targets with respect to both local surface temperature and spectral emissivity. The techniques used and the results are described.
Preview · Article · Aug 2005 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: The absolute radiometric accuracy of the thermal infrared band (B6) of the Thematic Mapper (TM) instrument on the Landsat-5 (L5) satellite was assessed over a period of approximately four years using data from the Lake Tahoe automated validation site (California-Nevada). The Lake Tahoe site was established in July 1999, and measurements of the skin and bulk temperature have been made approximately every 2 min from four permanently moored buoys since mid-1999. Assessment involved using a radiative transfer model to propagate surface skin temperature measurements made at the time of the L5 overpass to predict the at-sensor radiance. The predicted radiance was then convolved with the L5B6 system response function to obtain the predicted L5B6 radiance, which was then compared with the radiance measured by L5B6. Twenty-four cloud-free scenes acquired between 1999 and 2003 were used in the analysis with scene temperatures ranging between 4°C and 22°C. The results indicate L5B6 had a radiance bias of 2.5% (1.6°C) in late 1999, which gradually decreased to 0.8% (0.5°C) in mid-2002. Since that time, the bias has remained positive (predicted minus measured) and between 0.3% (0.2°C) and 1.4% (0.9°C). The cause for the cold bias (L5 radiances are lower than expected) is unresolved, but likely related to changes in instrument temperature associated with changes in instrument usage. The in situ data were then used to develop algorithms to recover the skin and bulk temperature of the water by regressing the L5B6 radiance and the National Center for Environmental Prediction (NCEP) total column water data to either the skin or bulk temperature. Use of the NCEP data provides an alternative approach to the split-window approach used with instruments that have two thermal infrared bands. The results indicate the surface skin and bulk temperature can be recovered with a standard error of 0.6°C. This error is larger than errors obtained with other instruments due, in part, to the calibration bias. L5 provides the only long-duration high spatial resolution thermal infrared measurements of the land surface. If these data are to be used effectively in studies designed to monitor change, it is essential to continue to monitor ins- trument performance in-flight and develop quantitative algorithms for recovering surface temperature.
Preview · Article · Jan 2005 · IEEE Transactions on Geoscience and Remote Sensing
[Show abstract][Hide abstract] ABSTRACT: In 1999, four monitoring stations were permanently moored on Lake Tahoe. California-Nevada. Each monitoring station provides near-real-time measurements of the surface skin temperature and bulk temperature on a near-continuous basis. Day and night data, acquired over Lake Tahoe from March to August 2000 with the second Along-Track Scanning Radiometer (ATSR-2), have been analyzed, and sets of coefficients for recovering the skin temperature and bulk temperature of the lake have been derived. The field measurements indicate that there is a noticeable difference between the bulk and skin temperatures (skin effect). which varies over the diurnal cycle. At the time of the ATSR-2 daytime overpass, the skin temperatures are on average 0.11°C cooler than the daytime bulk temperatures. At the time of the nighttime ATSR-2 overpass. the skin temperatures are on average 0.46°C cooler than the nighttime bulk temperatures. The smaller skin effect during the day is attributed to strong solar heating and low wind speeds at the site in the morning. The standard errors for recovering the daytime bulk and nighttime bulk temperatures, by regressing the in situ measurements against the average ATSR-2 nadir 11- and 12-μm channel brightness temperatures, are 0.40° and 0.18°C, respectively. By comparison the standard errors for recovering the daytime skin and nighttime skin temperatures by the same approach are 0.33° and 0.28°C, respectively. The lower standard error obtained for recovery of the skin and bulk temperatures at night is attributed to the lake surface being more homogeneous with the absence of solar heating. A comparison between the measured skin temperatures, skin temperature recovered by an ATSR-2 two-channel sea surface temperature algorithm, and the in situ regression indicates that the ATSR-2 algorithm has a similar scatter to the in situ linear regression but is offset with respect to the measured skin temperatures.
No preview · Article · Apr 2003 · Journal of Atmospheric and Oceanic Technology
[Show abstract][Hide abstract] ABSTRACT: Calibration of the five EOS ASTER instrument emission bands (90 m pixels
at surface) is being checked during the operational life of the mission
using field measurements simultaneous with the image acquisition. For
water targets, radiometers, temperature measuring buoys and local
radiosonde atmospheric profiles are used to determine the average water
surface kinetic temperature over areas roughly 3 X 3 pixels in size. The
in-band surface leaving radiance is then projected through the
atmosphere using the MODTRAN radiation transfer code allowing an at
sensor radiance comparison. The instrument at sensor radiance is also
projected to the water surface allowing a comparison in terms of water
surface kinetic temperature. Over the first year of operation, the field
measurement derived at sensor radiance agrees with the image derived
radiance to better than plus/minus 1% for all five bands indicating both
stable and accurate operation.
No preview · Article · Dec 2001 · Proceedings of SPIE - The International Society for Optical Engineering