National Ocean Service (Continued) 
Tides, Monthly Mean Summaries, are the records of the average monthly and 
yearly water level heights. These include monthly and yearly averages for 
mean tide level, mean sea level, diurnal tide level, mean higher high water, 
mean high water, mean lower low water, mean range, diurnal mean range, Green- 
wich mean high water time intervals, and Greenwich mean low water time inter- 
vals. Summary tide records are maintained for approximately 200 past and 
present stations in the NTON. 
Tidal Bench Mark Sheets with Tidal Datums provide vertical elevations and 
descriptions of tidal bench marks at tide observation stations. The bench- 
marks are referenced to the tidal datums of mean lower low water and mean high 
water. Information is also provided to reference tidal benchmarks to other 
tidal datums and to the National Geodetic Vertical Datum (NGVD) of 1929 when 
available. 
Frequency and Duration of Tidal Inundations is a summary report of a 
detailed statistical analysis of historic records of tide action at NOS tide 
stations. This analysis may be performed relative to either high or low 
waters. The report shows the frequency and duration of inundation of every 
10th of a foot of elevation over a period of years. Results of the analysis 
are reported in five tabular columns: (a) elevations above station datum in 
feet and meters at increments of every 10th of a foot over the total range of 
water level at the station; (b) frequency of inundations--the number of times 
the water level has equaled or exceeded each incremental elevation for a 
period of the analysis; (c) percent frequency of inundation--the number of 
inundations in item b, expressed as a percentage of the total number of 
inundations occurring in the period of the analysis; (d) duration of 
inundation--the total hours at which the water level remained at or exceeded 
each incremental height for the period of the analysis; and (e) percent 
duration of inundation--the number of hours in item d, expressed as a 
percentage of the total number of hours in the period of the analysis. This 
service was started in 19/9, involving the analysis of long-term tide data for 
each NOS tide station. Reports are added to the station data file as they are 
completed. 
Tidal Zoning (Area Tide Prediction Factors) is a new category of tide 
data that provides the tidal corrections for predicting height and time over 
large areas of US and Caribbean coastal and continental shelf waters. Tidal 
corrections, in the form of time differences in minutes and tide height fac-— 
tors, are determined by historical tidal characteristics and comparing ob- 
served tide data which has been related to the 19-year Metonic cycle. These 
corrections when applied to the tide predictions for a control tide station 
determine the predicted time and height of the tides over the area. These 
computations are based on tide behavior at tide station locations and are pre- 
pared by NOS on request. 
Special Services includes development of harmonic constants for predic-— 
tion of tides; long-term tidal mean and extreme data analysis; technical 
advice on methods for conducting tidal surveys; plots of hourly or 6-min tidal 
heights; plots of daily, monthly, or yearly mean sea level; and simultaneous 
plots of two stations or a plot of observed verses predicted tidal heights. 
III-6 
