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National Weather Service - ASOS Intranet Connectivity and Near Real-time Weather Data Acquisition

 
   
NOAA ASOS Intranet Connectivity and Near Real-time Weather Data Acquisition
Problem
The National Weather Service (NWS, a division of NOAA) is the key federal agency responsible for weather forecasts and weather modeling across USA. The Automated Surface Observing Systems (ASOS) program is a joint effort of NWS, the Federal Aviation Administration (FAA), and the Department of Defense (DOD). The ASOS systems serve as the nation’s primary surface weather observing network. ASOS is designed to support weather forecast activities; aviation operations; and of the Meteorological, hydrological and climatological research communities. More than 800 units of unmanned ASOS units are deployed throughout the United States.

With such a diverse group of end users, and such a large number of stations, it would be highly desirable to gather all ASOS weather observations into a central Data Reservoir, so users may access to the full range of current and historical data. It is also desirable that this data be gathered in near real time, since for some applications (aviation, severe weather alerts) weather data is very time-sensitive. Finally, a high-speed standard interface to the ASOS stations would ease many maintenance tasks. Currently, the only way to upgrade an ASOS station with the latest software is for a technician to visit the site; a remote software download facility, plus a more proactive way to gather system log and alert data, would be most helpful.

NWS enlisted PCI to build a prototype of the Near Real-Time Data Acquisition and Internet Connectivity function for ASOS. Our task was to implement a Data Reservoir system which would collect observations from up to five ASOS sites over an indefinite period, and also facilitate the remote software upgrade capability.

Solution
NWS had previously engaged PCI to upgrade the ASOS processor from Motorola 68K-on-Xycom to Motorola PPC-750-on-Synergy’s VGMD board; thus, we were very familiar with the ASOS hardware platform and pSOS+ real-time operating system. PCI also has extensive experience with standard network communication protocols, such as TCP/IP, FTP, PPP, etc. Lastly, because PCI has worked with NWS since 2000, we are conversant with the field conditions an ASOS station is expected to encounter, and are sensitive to the requirements of the various NWS user communities.

In the first phase, Prism undertook a Requirements Study, to understand the needs of the user groups involved, and to identify the weather products to be transmitted – temperature, cloud, lightening, etc. Prism analyzed the composition of these weather products, the frequency with which they should be transmitted, and the format of their transmission.

Prism designed a strategy for the near real-time transmission, which uses a PPP connection on a dial-up network to connect to the Internet. At that point, the ASOS station uses a modified FTP protocol to transfer weather data to the central Data Reservoir (DR) once per minute. FTP was chosen because it is a standard protocol for sending discrete messages from many clients to a central server system. All major operating systems support FTP, so there is a wealth of existing code and real world experience to draw on, thus reducing effort and risk; also, standard FTP clients and servers were successfully used to support testing.

PCI modified the protocol to read from memory segments instead of files at the ACU, and to write the information to a database at the DR. The DR runs on Windows 2000 platform and uses Microsoft Access Database to implement the database into which ASOS weather products and system messages are stored.

The above design allowed the ASOS station to be available over the Intranet. Building on 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 the ASOS system or logon to the custom OID screen (Operator Interface Device screen). A TFTP transfer is used to download the new application software from a central Software Reservoir (SR). The TFTP connection is established over the existing PPP link. Based on the user inputs, the software will be burnt into one of the available FLASH memory segments.

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

View solution diagram

Architecture
· Multiple ASOS systems 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 system 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.

View architecture diagram

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. PCI rewrote and modified the stacks to suit the needs of the project. Similarly, the FTP server customization on Windows 2000 platform involved lots of rework.

The result is the ASOS Intranet (called ASOSi) that lets all the ASOS systems connect to the Intranet and send real-time data to a central Data Reservoir. This database provides immediate access to weather data transmitted by all participating ASOS stations, without requiring the data consumer to connect individually to each ASOS station by 1200-bps phone line. Also, ASOSi functionality lets the user upgrade the software remotely using TFTP, thus greatly reducing the need for site visits.

The architecture is scalable and hence expanding the prototype to a full scaled system wide functionality is easy. The modular architecture allows ASOSi to easily accommodate new weather products. Also, the introduction of Internet capability opens the door for any number of future ASOS functions, such as

· Receive alarms and SYSLOG messages in near real time
· Check the status and current weather conditions at a site
· “Chat client” for field operators reporting problems to ASOS Operations Center

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

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