TSI-880 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 available to any user via the web.
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.
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.
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 archival or reprocessing.
System setup can be performed quickly: connect AC power and its ground wire to a ground rod, aim the system geographically north, and bolt it down to a stable, level surface (such as a table or concrete paver) via four 1/4-20 fasteners. Next, using a terminal emulator such as HyperTerm, connect a PC's serial port to the system's console port and follow user prompts that walk you through assigning a unique TCP/IP address. Next, connect a networked PC to the system's Ethernet port. Point your web browser to the system's URL to set the system time, site latitude, and longitude. (Note: these steps can be performed prior to arriving at the site). Finally, check that the imager is properly aligned to the center of the mirror via the web-based alignment step shown below. The system now runs automatically.
Data Storage and Display Options
For remote sites that are not practical to connect directly to a telephone line or the Internet, the optional DSM-420 provides nearly a half-gigabyte (1/2 GB) of non-volatile, removable local storage. It permits operators to periodically retrieve data from a TSI-880 at a remote site and play it back on PCs or workstations. Typical image size is about 30 KB; the rate at which storage is used up depends on the capture interval and the current number of daylight minutes. For example, worst case, with 30 second samples and 16 hour days, the system will save about 29 MB of images a day.
The optional Data Visualization Engine with its YESDAQ database permits reprocessing of stored TSI-880 data as well as real-time playback and display of animations to one or more workstations via the web. (See the YESDAQ data sheet for more information).
A TSI-880 can be directly connected to a LAN or telephone line to support real-time display, storage and backup to remote hosts. To support a wide variety of configurations it is equipped with these interfaces: