#HIGH TIDE GRAPH INSTALL#

Oceanographers are also developing continuous GPS systems-which relay location information all the time rather than occasionally-to measure sea level while taking into account a factor they hadn’t understood well until recently: the motion of the land. A small GPS antenna enables precise timekeeping-not elevation tracking-and a second antenna transmits data to geostationary satellites. That’s a testament to the painstaking, detail-obsessed work done by generations of tide gauge observers, technicians taking care of the equipment, and NOAA analysts putting together the results from all the nation’s gauges every month, according to Gill.Ī NOAA water level monitoring station with an acoustic sensor on Dauphin Island, Alabama. In fact, the accuracy of the monthly mean sea level observations-which most climate scientists use as a starting data point when looking at long-term ocean trends-as calculated using measurements from the microwave sensors is almost exactly the same as what scientists calculated using tide gauges in the 1800s, Bushnell says. However, the data they provide is only marginally more accurate.

#HIGH TIDE GRAPH INSTALL#

NOAA will operate both types of sensors side by side for several months before disassembling the old sensors to check for any discrepancies in the data, Gill says.Ĭompared with the old technologies, the microwave sensors are more reliable and much cheaper to install and maintain-no boats, divers or regular manual attention required. The microwave sensors, in contrast, can operate without any protection from waves, noise or weather. Most of the older sensors were installed in the early ‘90s and work similarly, but use sound waves instead of microwaves-and therefore must be enclosed in protective tubes that extend into the water. territories with microwave sensors, says Steve Gill, chief scientist at NOS/CO-OPS. NOAA is in roughly the first year of a four-year project to replace most of the sensors in its 210-strong network covering the nation and many U.S. The higher the water, the quicker return echo. The radar, encased in the white plastic housing in the foreground, sends a pulse of microwave energy down toward the water surface and listens for the echo. For one thing, scientists later replaced analog gauges with punched-paper tape systems that computers could read and tabulate.Ī microwave radar attached to a bridge over the Dog River in Alabama.

Several other types of tide gauges arose in the following decades, each gradually improving on the amount of manual labor required, the cost or the accuracy of the data collection. Then it could be several weeks before repairs were made. The early tide gauges were expensive and difficult to maintain-and if they stopped working, the local tide observer would have to contact Coast Survey field parties by mail to inform them. “The past two directors of NOS/CO-OPS like to quote Alexander Dallas Bache, the second superintendent of the Coast Survey, 1854: ‘It seems a very simple task to make correct tidal observations but, in all my experience, I have found no observations which require such constant care.’” “They worked well when they worked,” says Mark Bushnell, an oceanographic consultant at CoastalObsTechServices, LLC, and a former NOAA oceanographer. Rigg) checking a tide gauge on western Greenland as part of the MacMillan Arctic Expedition in 1926.

High tide graph