NOAA Marine Environmental Buoy Data (F291) Wave Measurement Errors

U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Data Buoy Center
Stennis Space Center, Mississippi 39529-6OOO
May 4, 1995 F1804-06
DB3:95-118
DBG:fcw

MEMORANDUM FOR: E/OC11 - Philip R. Hadsell, E/CC22 - Michael J. Changery

FROM: W/DB3 - David B. Gilhousen

SUBJECT: Wave Measurement Biases

The National Data Buoy Center (NDBC) has discovered biases in wave data from certain, identifiable moored buoy stations during select time periods. As a result, the following message will be placed on our home page to inform the users of biases in our wave measurements. I suggest a similar statement be added to NODC's home page and all CD-ROMs containing uncorrected data.

The wave spectra and significant wave heights were underreported at about a dozen NDBC stations for periods ranging from several months to two years. The bias is a result of an overzealous noise correction for systems that transmitted an acceleration spectrum. Most NDBC systems transmit a displacement spectrum and are not affected. The bias was discovered during comparisons with other wave measurement systems in field experiments.

The bias is significant only at low wave heights and becomes negligible (less than 0.15 m) above 2 m wave heights. Significant wave heights reported as 0.2 m could have a bias as large as 0.4 m, e.g., the value 0.2 m should be 0.6 m. More bias occurs when the spectrum is bimodal, in other words, when both swells and wind waves exist.

NDBC has developed an improved noise correction for these biased reports. Data from the following stations and times will be reprocessed and corrected at the National Oceanographic Data Center and the National Climatic Data Center within the next year:

cc: E/CC22 - Joe Elms