ESRL Global Systems Division
Japan Earthquake Affects NOAA GPS Water Vapor Measurements
One of the 2,000 Global Positioning System (GPS) receivers in the Japan GPS network (MIZU) is located in the city of Oshu about 100 km (60 miles) north of Sendi Province and it bore the brunt of the recent earthquake and subsequent tsunami. MIZU provides real-time data that are used by GSD to "anchor" NOAA GPS-met sites in the Western Pacific. When the earthquake struck, electrical power and communications were interrupted and we abruptly stopped receiving data from this site. The loss of data from MIZU did not seriously affect the accuracy and reliability of the water vapor estimates from the other sites in the Western Pacific Subnetwork because the data processing system built by OAR has sufficient redundancy to deal with the loss of data from several individual sites at the same time.
When power and communications were restored to the site on March 16, we started to receive observations again from MIZU, but we soon discovered that there was a serious problem: the GPS receiver was not where it was supposed to be.
MIZU had moved approximately 4 meters to the east of its presumably "permanent" location, along with the rest of this part of Honshu Island. This change in location caused the GPS-Met data processing system in Boulder to mismodel the atmosphere at every station in the same subnetwork as MIZU. Simultaneously, quality control software built to automatically detect errors caused by large (greater than 10 cm or about 4 inch) changes in position stopped sending water vapor estimates from every station in the Western pacific subnetwork to modelers and forecasters. To restore data flow to NCEP and NWS Western Region, we manually removed MIZU from the network until a new "permanent" position can be determined.
Clearly, GSD has learned valuable lessons from this tragedy: nothing is permanent and any reliable system has to deal with change.
Name: Seth Gutman