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Integrated Remote Sensing and GIS for Natural Resources Management
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Asian applications of the 'WETNET' concept - A personal computer network to receive daily global satellite data sets and derived geophysical products
James C. Dodge
NASA Headquarters, Washington,
DC 20546
(USA)
Introduction
Wet Net is a name given to an experimental NASA computer network that will allow participating scientists to receive daily global satellite images related to studies of physical processes within the Earth's global hydrologic cycle. The remote sensing data will be acquired, processed, and distributed automatically in standardized GIS format images which will allow the scientists to browse the content of numerous satellite channels as well as derived global products such as precipitation rate, atmospheric moisture, cloud liquid water, cloud-free vegetation distribution from the traditional AVHRR "greenness" index and a new microwave "Wetness" index, wind stress over the oceans, land surface and sea surface temperatures, oceanic evaporation, and sea ice extent. Also, accumulated quantities such as estimates of monthly to enable visualization of regional variations. Slowly - varying quantities such as sea ice margins and boundaries of vegetation extent will be illustrated buy making difference maps of mosaic, cloud -free images. If a particular segment of the full-resolution data is desired at the time, the scientist may highlight the region on his computer screen and have it sent to him electronically over phone lines. This mode of high-resolution data transfer is limited to selected regions the global data set because of the data bandwidth of telephone lines.
While this system is designed to enable rapid data selection for the study of interacting physical processes within the Earth's global environment, it also; can lead to discovery of unanticipated relationships between the interacting geophysical variables. From an Asian point-of view, a similar system using some of the same methodologies could help in the study of regional environmental interactions and in the solution of problems which extend beyond the geographical boundaries of any particular country.
Specifics of the WetNet System
In order to evaluate the presumed utility of such a system of daily electronic image delivery to working scientists, we have selected a primary data set and several related ancillary data sets from other satellites observing the Earth during the same time intervals. As the primary data source, we have chosen the microwave imager (SSM/I) carried on all of the DMSP series of U.S. satellites. Its seven channels consist of vertical and horizontal polarizations of 19, 37, and 85 GHz and the vertical polarization of 22 GHz . These particular channels, in various linear combinations, can yield information on various moist processes in the Earth's atmosphere and at the surface. If ancillary information from other satellites, including the
U.S. GOES and NOAA satellites as well as the Japanese GMs and Europe's Meteosat, and still other information from surface radar composites is added to the database, then a wide range of algorithms can be developed for various geophysical parameters. With the additional information and available computer power to calculate different algorithms for various scene conditions, latitudes, and seasons, it is presumed that and optimum set of conditional algorithms can be developed for each parameter so that when the set of algorithms is applied to the full global and seasonal data set, the resulting derived physical quantities will have the greatest possible accuracies from remotely sensed data at this time. The reason that such emphasis is being placed on changing physical process involved, and seasonal variations is that we are looking of long-term variations in the Earths environment, so we want to be certain that we have accounted for as many of the remote-sensing algorithm sensitivities as possible.
All data from the SSM/I passive microwave sensor will be collected and processed for quality control in order to insure a properly time-ordered and non-redundant data sequence for image generation. The data source at first will be magnetic tapes from NOAA/NESDIS with eventual data flowing, hopefully, over NSFNET in near-real time. The SSM/I data will be received at NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama, USA; entered automatically into a large database and assembled for the calculation of numerous daily, weekly, and monthly output product maps. The maps will be transmitted via a scheduler program at the user's terminal so that each scientist need only collect products related to interests. Adequate computer disk space has been provided so that four days worth of data products can reside on the designated disk space available until the oldest data is overwritten. This procedure will allow scientists to return from several days absence from the office and still be able to search the browse products for interesting physical events to study. The transmitted browse products may be selectively saved to permanent memory media such as floppy disks so that either key physical situations are thereby noted for future study or a climatology of browse products themselves is accumulated.
In addition to the basic SSM/I data. related ancillary data-- including geostationary images in visible and infrared wavelengths at the times of SSM/I passage over the nadir longitude, manually digitized radar composites over the U.S., and reduced resolution (27 km) AVHRR global data sets -- will be accessed from the satellite data banks of the Space be accessed from the satellite data banks of the Space Science and Engineering Center of the University of Wisconsin and forwarded through a 56 kbaud phone line to the MSFC.
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