Automatic Total Sky Imager

The Total Sky Imager Model TSI-880 is an automatic, full-color sky imager system that provides real-time processing and display of daytime sky conditions.

At many sites, the accurate determination of sky conditions is a highly desirable yet rarely attainable goal. Traditionally, human observers reported sky conditions, resulting in considerable discrepancies from subjective observations. In practice, the use of human observers is not always feasible due to budgetary constraints. The TSI-880 now replaces the need for these human observers under all weather conditions.

An onboard processor computes both fractional cloud cover and sunshine duration, storing the results and presenting data to users via an easy-to-use web browser interface. The self-contained design makes it well suited for mission-critical applications such as aviation and military meteorology monitoring. It captures images into standard JPEG files that are analyzed into fractional cloud cover; if networked via TCP/IP (10/100BaseT) or PPP (modem) it becomes a sky image server to remote any user via the web.

Features:

• Embedded processor; no external workstation is required to operate system
• Open architecture uses JPEG file format and TCP/IP protocols; real-time data via the Internet permits remote monitoring
• Web browser-based interface supports MS-Windows, Macintosh, and UNIX users
• Reliable solid-state CCD technology with heavy duty removable imager assembly
• Readily interfaced to existing weather data collection systems via RS-232 or TCP/IP
• Environmentally sealed for long life
• Optional Data Storage Module permits remote operation and rapid data retrieval

Applications:

•  Cloud cover and present weather conditions
• General aviation meteorology
• Military border and air space monitoring
• Remote sensing and atmospheric research
• UV-B, pollution, and research

Principle of Operation

Images from the sky are captured via a solid-state CCD imager looking downward onto a heated, rotating hemispherical mirror. A shadowband on the mirror blocks the intense direct-normal light from the sun, thereby protecting the imager optics. An embedded image-processing algorithm captures and displays the images. Results are presented in real time via a web server, both statically and via panoramic views and animations.

The TSI-880 is a daytime imager. Once the sun rises above a user-selectable minimum solar zenith angle, image acquisition begins. The analysis step first masks out obstructions-the imager, its arm, and the sun-blocking band. Fractional cloud cover is determined by a sophisticated embedded algorithm. The system can be configured to operate either standalone or networked. In standalone mode, it can be interfaced directly to existing surface weather systems via its RS-232 serial interface. Or it can be networked to the Internet via its 10/100-BaseT or telephone modem (PPP) interfaces. Networked, users can view real-time processed images locally or remotely via a web browser.

Raw Sky Image Processed Sky Image

Side-by-side cloud images show a raw sky image before any processing, and the same image after a software filter is applied. The filter algorithm clearly defines the clouds so that fractional cloud cover can be readily calculated. TSI-880 users can fine-tune the algorithm in real time to meet special local requirements or adapt to local weather characteristics.

Software Architecture

The TSI-880 uses a sophisticated server-based embedded processing architecture that can support multiple networked systems via the Internet. Because the TSI-880 contains its own onboard image processor, users only need a web browser to adjust the cloud cover extraction algorithms remotely, without any need for special software and without taxing the display workstation. Images can be displayed as panoramic views using the optional Data Visualization Engine (DVE); images are stored as JPEG files in YESDAQ for later for later archival or reprocessing.