Typical and Potential Applications
The instruments have been used for a variety of applications, including military test support and climate research. We feel that they are also ideal for observatory support.
For military applications, the most common use is to detect the presence of clouds, and use these to assess the results of classified and unclassified tests. This is particularly useful because the Day/Night imager can provide excellent results both at night, detecting clouds that cannot be seen visually, as well as during the day. Several examples are as follows.
a) On some of the systems, the data are acquired remotely, and transferred to a processing computer, which processes the data in near-real time, to yield the cloud decision image which shows the presence of clouds. At the same time, a third computer can be linked in, and provide the location of moving regions of interest (ROI). The WSI can then provide the cloud decision results over these ROIs, as well as over the full sky.
b) One of the systems is used primarily to provide raw imagery, particularly at night. In this instrument, the data acquisition rate can be enhanced for specific tests, and the raw images are used to visually assess sky conditions during the test.
c) Another system had the capability of inputting a test satellite track in advance, and could be used to determine the locations of clouds along the tracks. This could easily be automated to provide continually updated satellite tracks, and assessments along these tracks.‹ In this particular application, the imager was used to assess when the satellite lock-on was lost due to clouds and/or enhanced background sky radiance.
d) We processed a library of WSI data, to determine cloud free line of site statistics, as well as the persistence of the cloud free line of sight. This used a data set acquired at 1-minute intervals over two years.
For climate research applications, such as the ARM program, perhaps the most important output is the absolute radiance distribution in conjunction with the cloud distribution. This can potentially enable the evaluate of models, and aid an understanding of the impact of the cloud distribution on the radiance distribution.‹ The cloud decision images may also be processed through additional software developed by Kegelmeyer at Sandia National Labs. This software generates the following cloud spatial statistics from the cloud decision images:
The sector cloud cover values are the fraction of the sector containing cloud pixels. The cloud statistical quantities have the units of pixels if no cloud height is assumed; otherwise, they are in the same units as the cloud height.
New and potential applications include the following:
Determination of earth-to-space beam transmittance distributions at night
Support of test sites and observatories in choosing the most productive part of the sky to image
Support of observatory measurements, in documenting the sky radiance and beam transmittance during critical measurements.
Documentation of sky brightness conditions, for use in site selection.
Determination of cloud free line of site statistics for military site selection
Monitoring of sky conditions to enable decisions of when to close observatories, when to start tests, and so on
A broad variety of research applications in which knowledge of the clouds or sky radiances have improved.
by the Marine Physical Laboratory, SIO.