Providing weather satellite images to a classroom using the World Wide Web (WWW).
Widespread study of weather in a classroom would not only improve the scientific literacy of students but would also provide a useful means for introducing information technology into the classroom.
In Japan, 5th-grade students learn that weather change can be predicted using weather information, and 8th-grade students learn how weather changes when a front passes through an area. Basic meteorology, including the motion of air, clouds and precipitation, and seasonal variations in weather are also taught as part of the earth science curriculum in high schools in Japan. The results of the questionnaire survey showed that about 85% of 5th-grade students in Japan had often seen a weather forecast on TV or in a newspaper and that 75% of them had made use of the information in their everyday lives. These results indicate that students direct attention to daily weather, which will provide a helpful beginning for weather study. Availability of weather data, including satellite images, the Internet being one of the best sources of such data, is necessary to further encourage students to study weather. Satellite images are particularly important for the study of weather because the images have a strong visual appeal to students and thus the application of such images would result in an expansion of a student's perspective from a local-scale view of the weather seen through the student's own eyes to a synoptic-scale view or a planetary-scale view of a weather system. Various companies in Japan, such as TV stations and weather service companies, provide the latest images from a geostationary satellite on Internet sites as useful information for weather forecasting. However, satellite images displayed on the Internet sites are usually not of fine quality due to lossy data compression, a reduction process in which some information is discarded. This was the reason for constructing a new system.
In this article, a web-based system and a software program that have been developed for using satellite images as teaching material in a classroom are described.
PREPARING IMAGES FOR A CLASSROOM
Components of the System
Figure 1 shows a schematic diagram of the system that has been developed for making satellite images available in a classroom through the Internet. The system consists of three computers linked together using TCP/IP. The computers are used for receiving satellite image data, converting the data format into a format suitable for users, and as a WWW/file server.
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A commercially available system (Nippon Hakuyo GMSP-W) consisting of a parabolic antenna, a down-converter, and a personal computer was used to receive images in WEFAX format (Conway & The Maryland Space Grant Consortium, 1997) from a Japanese geostationary satellite. The satellite is positioned at longitude 140 degrees east and directly above the equator and provides imagery of the west Pacific, eastern Asia, and Oceania. The antenna was set up on the roof of the Integrated Center for Educational Research and Training, Hokkaido University of Education, Japan.
The raw satellite data were received in the data-receiving computer and then transferred to and stored in a data-converting computer using Windows 2000 server software that converts the data into a more useful form. The raw data has 800x800 pixels and 8 bits (i.e., 64 tones); therefore, the file size of each image is 640 KB. Hence, the size of the file should be reduced to shorten the time needed to download the image. Also, to make the global infrared image easier to analyze, an integrated image was made from the four original images that each covered a single zone. A data conversion software program for the computer was developed using the C++ language (Borland). The data could be automatically processed at any set time interval.
Finally, the converted data were sent to and stored in another computer using Linux software, which was linked to the Windows 2000 machine by Samba software. This Linux computer also functioned as a WWW server. The accumulated data were saved on a CD-ROM.
The raw satellite data that were stored in the data-converting computer included infrared images of eastern Asia (updated hourly), visible images of eastern Asia (updated hourly during daylight hours), infrared images of the globe divided into four zones (updated every 3 hours), and water vapor images of the globe divided into four zones (updated every 12 hours). Infrared, visible, and water vapor images are derived from emissions by the Earth and its atmosphere at thermal-infrared wavelengths, from reflected sunlight at visible wavelengths, and from water vapor emission, respectively. An infrared image is a picture of the cloud top or earth's surface temperature: the colder, that is, higher, cloud tops appear whiter. In a visible image, areas of higher reflectivity appear whiter: thick clouds appear whiter. The angle of sunbeams also affects the brightness: an image with a low sun angle is less bright. Water vapor images, which show moisture in the middle and upper troposphere, were not included in this system, because the image is not common, and students might become confused if they use these three different types of images.
In the data-converting computer, the data were processed in the following sequence:
1. After the overlapping areas had been removed, four images, each representing one of the four zones into which the earth is divided, were pasted together to produce a full-disk image of the globe. The values of four adjacent pixels were averaged to display the image of the entire globe on a monitor screen with a resolution of 1024 by 768 pixels, and then the file size was reduced to 404 KB. This process is shown in Figure 2.
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2. The 8-bit raw data were converted into 4 bits, thereby reducing the size of the file by half, that is, 320 KB (infrared and visible images of eastern Asia) and 202 KB (full-disk images of the globe). This conversion process actually had almost no effect on the quality of images.
3. The data files were compressed by Run Length Encoding (Barron & Orwig, 1997) in which all of the original information in the images was preserved to maintain a clear image. On average, this decreased the file sizes of the above-mentioned 4-bit data by 48% for infrared images of eastern Asia, by 32% for visible images of eastern Asia, and by 32% for infrared images of the globe obtained in the year 2000.
The final file sizes of the 8,157 infrared images of eastern Asia, the 3,113 visible images of eastern Asia and the 2,687 infrared images of the globe in the year 2000 ranged from 125 to 226 KB, 90 to 303 KB, and 124 to 150 KB, respectively, and the average final sizes were 166, 219, and 137 KB. The average final file size of visible images was largest because of the high resolution of a visible image compared with that of an infrared image, while the file size of a visible image taken in the morning and evening was small because the shaded areas all had the darkest pixel value.
PROVIDING IMAGES ON THE WWW
Figure 3 shows the web pages for satellite data, which are available in both English and Japanese. The pages were produced using HTML. The user can select an image from a daily list of images. When a user accesses the web site, the CGI, which was written by Perl software, automatically updates the list to provide the latest information. To view an image from a previous day, a user simply enters the appropriate date and then selects the image from the list of that day's images. The following kinds of geostationary satellite images are available at this website: (a) infrared images of eastern Asia (updated hourly); (b) visible images of eastern Asia (updated hourly during daylight hours); (c) infrared images of the globe in full-disk form (updated every 3 hours).
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Tests on accessing the web pages through an Internet provider using an analog telephone line with a data modem were carried out. When the communication speed was 52.0 kbps, it took 23, 31, and 16 seconds to download an infrared image (184 KB), a visible image (246 KB), and an infrared image of the globe (143 KB) obtained at 03 GMT (12 JST), July 1, 2001. The results of these tests showed that this system works well even if an analog telephone line is used.
SOFTWARE FOR PRESENTING IMAGES
The software for viewing satellite images is available in both English and Japanese on the Web for Windows 95, 98, NT, 2000, Me, and Xp operating systems. This software, which was developed using C++ programming language (Borland), enables images to be displayed, images to be stored in a bit-mapped format, and images to be enlarged twofold or reduced by half. Figure 4 shows how the software appears on a monitor screen. The images can be displayed with 16 tinted tones from dark blue to white. Figure 5 shows the three kinds of satellite images that are available at this website, as stated in a previous section. An infrared image of eastern Asia (a) and a visible image of eastern Asia (b) were obtained at the same time. Those images showed that large tropical cyclones had hit Japan (a, b) and Australia (c). There was no cloud in India owing to the dry season (c). Because of the lossless compression and 16 tones, the quality of these images is higher than that of images presented on other web sites.
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A software program enabling students to perform various functions such as image animation, coloring by temperature or brightness, displaying cloud top temperatures, and superimposing an infrared image on a visible image has also been developed. The animation is especially useful for weather study because students can intuitively and easily understand the movement of clouds that are associated with a particular weather system, such as a cyclone or a typhoon, or can view global air circulation through the motion of clouds. A CD-ROM package containing the software and about 4,000 annual satellite images with daily surface weather charts is now commercially available.
A web-based system in which weather satellite data are automatically processed and stored at regular time intervals was constructed. This system was designed to be used in a classroom to teach students about the science of weather and show them a useful application of information technology.
Reduction of the file sizes of the satellite image data is essential for shortening the time required to download them. The 8-bit raw image data received from a satellite are converted into 4-bit data. This process actually had little effect on image quality. The data files are compressed using Run Length Encoding, but the information in the original file is retained to maintain clarity of the image. On average, the file sizes of the 4-bit data were reduced by 48% for infrared images of eastern Asia, by 32% for visible images of eastern Asia, and by 32% for infrared images of the globe throughout a year. A full-disk image of the globe is made by combining four regional images and then reducing in size by averaging the pixel values of four adjacent dots to display an image of the entire globe on a monitor screen with a resolution of 1024 by 768 pixels. Infrared images of eastern Asia (updated hourly), visible images of eastern Asia (updated hourly during daylight hours), and infrared images of the globe showing the west Pacific, eastern Asia and Oceania (updated every 3 hours) are sent to a web site. This web site can be accessed, and an image can be selected from a list of images automatically renewed by CGI.
A software program to enable display, storage in the form of a bit map, and enlargement and reduction of the images has been developed, and is available for educational purposes on the Internet. Because of the lossless compression and 16 tones, the quality of images obtained using this new system is much higher than that of images presented at other websites. The homepage address for the web page including the software developed here is http://wing.sap.hokkyodai.ac.jp.
I would like to thank Tatsuya Hirono for his contribution in the early stage of this study. Earlier reports of this study were presented at the International Conference on Mathematics/Science Education and Technology, San Antonio, TX, USA in March 1999 and at the International Conference on Computer Education, Seoul, Korea in November 2001.
Barron, A.E., & Orwig, G.W. (1997). New technologies for education: A beginner's guide. Englewood, CO: Libraries Unlimited.
Conway, D., & the Maryland Space Grant Consortium (1997). An introduction to satellite image interpretation. Baltimore, MD: The Johns Hopkins Press.
Sapporo Utsukushigaokamidori Elementary School
Sapporo Satunaekita Elementary School
Integrated Center for Educational Research and Training