One-Angstrom microscope update (open access)

One-Angstrom microscope update

The One-Angstrom Microscope project has attained its goal, and is now producing images down to 1 Angstrom resolution. We have demonstrated transmission electron microscopy of defect structures down to a resolution of 1.1 Angstrom, with evidence that 0.89 Angstrom will be possible. This level of resolution will soon be made available to all those NCEM users who have a requirement for sub-Angstrom resolution.
Date: April 4, 1999
Creator: O'Keefe, Michael A.
Object Type: Report
System: The UNT Digital Library
Comparing robust and physics-based sea surface temperature retrievals for high resolution, multi-spectral thermal sensors using one or multiple looks (open access)

Comparing robust and physics-based sea surface temperature retrievals for high resolution, multi-spectral thermal sensors using one or multiple looks

With the advent of multi-spectral thermal imagers such as EOS's ASTER high spatial resolution thermal imagery of the Earth's surface will soon be a reality. Previous high resolution sensors such as Landsat 5 had only one spectral channel in the thermal infrared and its utility to determine absolute sea surface temperatures was limited to 6-8 K for water warmer than 25 deg C. This inaccuracy resulted from insufficient knowledge of the atmospheric temperature and water vapor, inaccurate sensor calibration, and cooling effects of thin high cirrus clouds. The authors will present two studies of algorithms and compare their performance. The first algorithm they call robust since it retrieves sea surface temperatures accurately over a fairly wide range of atmospheric conditions using linear combinations of nadir and off-nadir brightness temperatures. The second they call physics-based because it relies on physics-based models of the atmosphere. It attempts to come up with a unique sea surface temperature which fits one set of atmospheric parameters.
Date: April 4, 1999
Creator: Borel, C. C.; Clodius, W. B.; Szymanski, J. J. & Theiler, J. P.
Object Type: Article
System: The UNT Digital Library
Using Perspective to Model Complex Processes (open access)

Using Perspective to Model Complex Processes

The notion of perspective, when supported in an object-based knowledge representation, can facilitate better abstractions of reality for modeling and simulation. The object modeling of complex physical and chemical processes is made more difficult in part due to the poor abstractions of state and phase changes available in these models. The notion of perspective can be used to create different views to represent the different states of matter in a process. These techniques can lead to a more understandable model. Additionally, the ability to record the progress of a process from start to finish is problematic. It is desirable to have a historic record of the entire process, not just the end result of the process. A historic record should facilitate backtracking and re-start of a process at different points in time. The same representation structures and techniques can be used to create a sequence of process markers to represent a historic record. By using perspective, the sequence of markers can have multiple and varying views tailored for a particular user's context of interest.
Date: April 4, 1999
Creator: Kelsey, R.L. & Bisset, K.R.
Object Type: Article
System: The UNT Digital Library
Practical Atmospheric Correction Algorithms for a Multi-Spectral Sensor From the Visible Through the Thermal Spectral Regions (open access)

Practical Atmospheric Correction Algorithms for a Multi-Spectral Sensor From the Visible Through the Thermal Spectral Regions

Deriving information about the Earth's surface requires atmospheric corrections of the measured top-of-the-atmosphere radiances. One possible path is to use atmospheric radiative transfer codes to predict how the radiance leaving the ground is affected by the scattering and attenuation. In practice the atmosphere is usually not well known and thus it is necessary to use more practical methods. The authors will describe how to find dark surfaces, estimate the atmospheric optical depth, estimate path radiance and identify thick clouds using thresholds on reflectance and NDVI and columnar water vapor. The authors describe a simple method to correct a visible channel contaminated by a thin cirrus clouds.
Date: April 4, 1999
Creator: Borel, Cristoph C.; Villeneuve, Pierre V.; Clodium, William B.; Szymenski, John J. & Davis, Anthony B.
Object Type: Article
System: The UNT Digital Library