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NOAA/National Weather Service - ASOS Intranet Connectivity

 
   
Department of Commerce/NOAA/NWS NOAA/National Weather Service -ASOS Intranet Connectivity
Problem
NOAA National Weather Services (NWS) is the key federal agency responsible for weather forecasts and weather modeling across the USA. The Automated Surface Observing Systems (ASOS) program is a joint effort of the NWS, the Federal Aviation Administration (FAA), and the Department of Defense (DOD).
ASOS serves as the nation's primary surface weather observing network. ASOS is designed to support weather forecast activities, aviation operations and the needs of the meteorological, hydrological and climatological research communities. More than 800 units of unmanned ASOS units are spread across the USA.

Having such a diverse group of end users necessitates a central data reservoir accumulated at near real-time, so as to facilitate the users in accessing both current and backlog data. Presently, in order to upgrade the ASOS application software, it was necessary for the technician to visit the actual site and do it on-site.

Having worked with Prism previously, the NWS enlisted Prism to carry out the task of building a prototype of the Intranet to connect the different units of ASOS to a central data reservoir. The NWS further engaged Prism to develop a scheme to remotely upgrade the application software running on ASOS.
 
Solution
Since we at Prism had done the processor upgrade of ASOS from Motorola 68K-on-Xycom to Motorola PPC-750-on-Synergy's VGMD board, we were aware of the hardware resources available and having worked with the NWS since 2000, we were aware of the actual field conditions and the requirements of the end user communities.

As a first phase, Prism undertook a requirement study to understand the actual needs of the user groups and the different weather products that need to be transmitted. Also, Prism analyzed the different weather products and the frequency in which they need to be transmitted and the format of their transmission.

Prism designed a scheme to use PPP connection on a dial-up network to connect to the Internet. Once on the Internet, ASOS does a FTP transfer of the weather data to the central Data Reservoir (DR). In order to overcome the fact that ASOS does not have a file system and to reduce the processor loading, the FTP client software was modified to send the data directly from the memory rather than from a file, as it's done in a traditional FTP client.

The DR runs on Windows 2000 platform and uses Microsoft Access Database to implement prototype DR Database. DR was developed using Microsoft Visual C++. The FTP server runs on the DR and in order to achieve optimal usage, the FTP server was modified to write directly into the Microsoft Access database rather than into the files, as done in the conventional FTP servers.

The above scheme allowed ASOS to be available over the Intranet. Exploiting this, Prism developed a scheme to remotely upgrade the application software. In order to start the software upgrade remotely, the user can either open a telnet session to ASOS or logon to the custom OID screen (Operator Interface Device screen). TFTP transfer is used to download the new application software from a central software reservoir. The TFTP connection is setup over the existing PPP link. Based on the user inputs, the software will be burnt into one of the available FLASH memory.

ASOS has dual-redundant processor boards. The two-processor boards have separate memory and communicate over the VME bus. The software upgrade scheme upgrades the application software on the redundant board too, thereby maintaining consistency.

 
Architecture
Multiple ASOS connect to the Internet using a dial-up line and the local ISP.

Once on the Internet, the ACU systems transmit different weather data at almost real time to the Data Reservoir.

Data reservoir, running assimilates the data it receives into the database instantly, enabling the user community to use it instantly.

Data Reservoir acts as the focal point for letting systems access it thereby providing security.

The ASOS-to-DR communication protocol is simple but robust. The design of the protocol needed changes in the FTP command/response format in order to optimize.

Any link downtime has minimal impact. On the link being up again, all the backlog data is sent to the DR, thereby having zero data loss.

The software upgrade functionality is transparent and does not impact the running of the current build.

The following figure explains the message flow between ASOS and the ACU. The message flow was developed to support the existing format of the weather products and also the exploit the rich features of FTP protocol. This did require some customization on the FTP command/response format.
Result
Prism developed all of the above features on top of the existing code base, which itself runs to about 300K LOC. The development activity posed some unique challenges. The PPP and FTP stacks used for the development had some limitations in a real-time environment. We at Prism rewrote/modified the stacks to suit the needs. Similarly, the FTP server customization on Windows 2000 platform involved lots of rework.

The result is the ASOS Intranet (called ASOSi) that lets ASOS connect to the Intranet and send real-time data to a central data reservoir. Also, ASOSi functionality lets the user upgrade the software remotely.

The architecture is scalable and hence expanding the prototype to a full-scale system wide functionality is easy. The modular architecture ensures that adding new weather products is taken care of. Also, the architecture is transparent to additions or deletions of weather sensors to ASOS.

ASOSi has chalked a clear path for ASOS into the realm of Internet, thereby increasing the utility of these key weather systems by manifolds.
 
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