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The Field Research Facility (FRF) has entered into a cooperative study to test air visibility sensors with the US Coast Guard (USCG) and the National Oceanic and Atmospheric Administration's (NOAA) National Ocean Service (NOS) Center for Operational Oceanographic Products and Services (COOPS). The testing involves inter-comparison of air visibility sensors from different manufacturers in support of USCG and COOPS operations. The initial evaluation period is for one year, beginning March 2008, with possible future years that will be determined after completion of the first year.


In addition to comparing visibility measurements the units are being tested for maintenance requirements. Two identical sensors will be evaluated for cleaning requirements - one will be periodically cleaned, the other will not be cleaned until the instrument reports an alarm. Observations will be made to determine the nature of the maintenance alarm (e.g., salt accumulation, cobwebs, or corrosion).

Data are collected in 6-minute averages, centered on reported time, every 6 minutes starting at the top of the hour (i.e., 0, 6, 12 minutes). Some instruments operate in polled mode and others in auto-transmit mode. The table below lists the sampling parameters for each instrument.

Three video cameras mounted on the FRF observation tower provide ground-truth data for verification of instrument visibility readings. The camera elevations are 3.4, 15.5, and 19.5 m (11, 51, and 64 ft) above ground level (4.6m , 15 ft NGVD). The upper two cameras are used for visibility estimates, the lowest camera is for viewing the immediate area around the sensors. Snapshot video images are also collected every 6 minutes at the mid-point of the visibility averages.

From these web pages you can link to instrument descriptions, the most recent data from each sensor, a 3-day gauge inter-comparison plot, weekly archived plots, and past camera images.