Metadata:
  Identification_Information:
    Citation:
      Citation_Information:
        Originator: Patrick Caldwell
        Originator: NOAA/NESDIS/NODC/NCDDC
        Publication_Date: Unknown
        Title: Scaled photographs of surf over the full range of
breaker sizes on the north shore of Oahu and Jaws, Maui, Hawaiian Islands
        Series_Information:
          Series_Name: None
          Issue_Identification: None
        Publication_Information:
          Publication_Place: Unpublished Material
          Publisher: Unpublished Material
        Online_Linkage: http://www.nodc.noaa.gov
    Description:
      Abstract: Digital surf photographs were scaled using surfers as height 
benchmarks to estimate the size of the breakers.  Historical
databases for surf height in Hawaii are recorded in Hawaii Scale 
Feet (HSF), and these photographs have been used to translate
HSF to trough-to-crest heights.  Results show the trough-to-crest 
heights to be double the HSF within a 10-20% margin of error over 
the full range of possible breaker sizes.  This assumes 1) the trough-
to-crest height is defined as the highest height reached in the 
vertical between the crest and the preceding trough at any point 
along the wave front during breaking and 2) zones of high 
refraction on outer reefs are included for extreme days when Waimea 
Bay was the reporting location.
      Purpose: To better understand wave heights reported in Hawaii Scale Feet.
      Supplemental_Information: NOAASupplemental:
Entry_ID: Unknown
Sensor_Name: digital cameras  
Originating_Center: NOAA/NESDIS/NODC/NCDDC   
Storage_Medium: jpeg
Online_size: 9190 kbyte
    Time_Period_of_Content:
      Time_Period_Information:
        Range_of_Dates/Times:
          Beginning_Date: 19980128
          Ending_Date: 20040524
      Currentness_Reference: ground condition
    Status:
      Progress: Complete
      Maintenance_and_Update_Frequency: None Planned
    Spatial_Domain:
      Bounding_Coordinates:
        West_Bounding_Coordinate: -158.108
        East_Bounding_Coordinate: -156.323
        North_Bounding_Coordinate: 21.692
        South_Bounding_Coordinate: 20.950
    Keywords:
      Theme:
        Theme_Keyword_Thesaurus: None
        Theme_Keyword: Coastal studies
        Theme_Keyword: surf height
        Theme_Keyword: wave height
        Theme_Keyword: scaled photograph
      Place:
        Place_Keyword_Thesaurus: None
        Place_Keyword: North Pacific,
        Place_Keyword: Hawaiian Islands,
        Place_Keyword: Oahu,
        Place_Keyword: North Shore,
        Place_Keyword: Waimea Bay,
        Place_Keyword: Sunset Point,
        Place_Keyword: South Shore,
        Place_Keyword: Ala Moana,
        Place_Keyword: Jaws (Peahi), Maui
      Stratum:
        Stratum_Keyword_Thesaurus: None
        Stratum_Keyword: surface
    Access_Constraints: None
    Use_Constraints: Dataset credit required
    Point_of_Contact:
      Contact_Information:
        Contact_Person_Primary:
          Contact_Person: Mr. Patrick C. Caldwell
          Contact_Organization: NOAA/NESDIS/NODC/NCDDC
        Contact_Position: Hawaii/US Pacific Liaison
        Contact_Address:
          Address_Type: mailing
          Address: 1000 Pope Road, MSB 316
          Address: Dept. of Oceanography
          Address: University of Hawaii at Manoa
          City: Honolulu
          State_or_Province: Hawaii
          Postal_Code: 96822
          Country: USA
        Contact_Voice_Telephone: (808)-956-4105
        Contact_Facsimile_Telephone: (808) 956-2352
        Contact_Electronic_Mail_Address: caldwell@hawaii.edu
        Hours_of_Service: 8 AM to 5 PM weekdays
        Contact_Instructions: check services@nodc.noaa.gov if not available
    Data_Set_Credit: Hawaii Liaison Office
National Coastal Data Development Center
NOAA/NESDIS/NODC/NCDDC
    Native_Data_Set_Environment: jpeg files
  Data_Quality_Information:
    Logical_Consistency_Report: see lineage, process step
    Completeness_Report: none
    Lineage:
      Process_Step:
        Process_Description: Surf Observations
=================
With the growth of surfing in the 1960s on the north shore, Oahu, came 
routine observations made by surfers, and later in the 1970s, by 
lifeguards and commercial surf report ventures.  Observations were 
reported in Hawaii Scale Feet (HSF). 
 
Observations are reported as a height range.  Observers ignore the 
smaller waves.  As a simplified example, assume a given day has 
dominant wave energy in the 14-17 second wave period range with 
negligible energy outside this band.  Assume five waves catch the 
eye of an observer every four minutes, or 100 waves every 80 minutes.  
This takes into account the time periods of varying length without 
waves arriving.  The upper end of the reporting range is approximately
equivalent to the H1/10, the average of the highest 10 waves, which if 
evenly distributed in time, would occur every 8 minutes.  The lower 
end of the observing range is near the H1/3, or the average of the 
highest 1/3 waves, which if evenly distributed in time, would occur 
every 3 minutes.  The highest wave over this nominal 80-minute period 
with 100 waves, or H1/100, would be equivalent to the observers use 
of occasional heights in their reports.

A digital database of surf observations, referred to as the 
Goddard-Caldwell (GC) set, dates back to August 1968 for the north 
shore, and to March 1972 for the south shore of Oahu.  It is described 
in more detail in Caldwell (2005).  Data are recorded in HSF.  The daily 
values in the GC database refer to the surfing location along the given 
coast with the highest reported breakers.  For the north shore, most 
observations are taken at Sunset Point, which is usually one of the 
highest surf spots along the coast under the dominant northwest swell 
direction.  For days of extreme surf with heights greater than roughly 
15 HSF, visual observations are reported at Waimea Bay, where breakers 
are much closer to shore relative to most of the north shore, which is 
fringed with offshore reefs.  The surf reports are typically made 
several times per day.  The daily value in the GC set represents the 
upper end of the reported height range for the observing time with the 
highest breakers.  This number aims to be equivalent to H1/10.  Comparisons 
of the GC database to 1981-2002 data from NOAA buoy 51001, which is 
located roughly 400 km west-northwest of Oahu, show the surf observations 
are temporally consistent with the shoaling-only, buoy-estimated breaker 
heights and have an uncertainty of 10 to 15% of the surf 
height (Caldwell, 2005).  

Photograph analysis
===================
A breaker or surf is defined at the moment in time when some portion of 
the front face of a wave becomes vertical and unstable due to a decrease 
in water depth.  The trough to crest surf height is defined as the vertical 
distance between the crest and the preceding trough at the moment and 
location along the wave front of highest cresting, which has been shown 
in models and observations to be at the time and location of breaking.  For 
locations with high refraction, such as Sunset Point, where most of the 
visual observations are made, the breaker often forms an A-shape.  The 
trough to crest height refers to the center of the A, i.e., the point 
along the wave front with the highest height.
	
Photographs were obtained from Internet sites or directly from photographers.  
Location and date was a prerequisite.   Photographs showing the highest waves 
of a given day were chosen from the available pool of pictures.  Pictures 
were sorted by size in HSF matching the date to the GC database.  Typically,
 15 images for each size category were selected (Table 1).

Each photograph requires a surfer or some other identifiable object to use 
as a benchmark in estimating wave height.  Dashed lines were superimposed 
on each photograph to indicate the approximate trough and crest.  An arrow 
was overlaid next to each benchmark to denote a 5 unit.  The benchmark 
arrow was duplicated and subsequent arrows were stacked from trough to 
crest to gauge the wave size (Figure 3). 

Photographs capture a two-dimensional image of a three-dimensional world 
and distortions of shapes and sizes are inherent.  Shots taken from a high 
vantage point, such as a cliff or helicopter, make detection of the wave 
trough difficult.  Wave size is distorted in pictures taken by a swimming 
photographer near the surfer.  Priority in selecting shots was given to 
images taken by a photographer standing close to mean sea level either on 
shore or on a floating craft.  Distortion of perception decreases as the 
distance between the camera and the surfer/wave increases. 

There are various sources for errors in this exercise.  The error associated 
with trough identification has been estimated at 10% of the wave height.  
The surfers height is not known in most images.  It is assumed that the 
average surfer height is 5'9 and a typical surfer stance is roughly 
5 with a 6 uncertainty, which leads to an error of 10% in the surf 
height estimate.  For both cases, the errors average out as the number 
of photographs increases.  Since the photographs were selected from still 
images, it is not certain that any given picture represents the highest 
height reached by that wave during breaking, or if these few select waves 
represent H1/10, which is assumed in the GC database.  With the small 
number of available pictures per day, the translation based on these 
pictures likely underestimates the heights in the GC database.

Each scaled photograph was examined to estimate the height to the nearest 
tenth of a foot.  For each size category, a mean and standard deviation 
of the estimated trough to crest heights were computed (Table 1).  
Using two standard deviations as a proxy for uncertainty, the margin of error 
is within 10-20% of a given size for categories with at least 15 photographs, 
disregarding the lowest and highest percentage values.  For days 
with surf heights of 15 HSF or less, most photographs are taken at spots 
from Log Cabins to Sunset Beach, which typically has the highest surf on 
the north shore (Figure 2a).  For days with surf heights greater than or 
equal to 15 HSF, photographs were further sorted by location: Waimea Bay, 
Oahu outer reefs, and Jaws (Peahi), Maui.  Under northwest swell with 
17-20 second wave periods, the travel time from Oahu to Maui is roughly 
three hours, which makes comparisons of daily data appropriate.  Fewer 
photographs were available for the Oahu outer reefs than for Waimea Bay.  
The paired HSF and trough to crest heights are plotted in a scatter 
diagram (Figure 4).    

For surf heights of two to six HSF the translation shows the trough to 
crest heights are more than double the HSF observations (Table 1, last 
column).  From six to twelve HSF, the translation is close to double.  An 
inadequate supply of photographs were available of Sunset Point for heights 
in the 13-15 HSF range, when the offshore-most breaking point is roughly 
one km from shore and strong currents impede water photography.  The 
available images suggest the translation of 15 HSF to trough to crest 
heights is slightly less than double.  For the entire range from two to 
fifteen HSF, the translation can simply be defined as double within the 
margin of error.

For surf above 15 HSF, the wave energy at Sunset Point becomes overwhelming 
and the resultant breakers occur unpredictably over a wide area both parallel 
and perpendicular to shore.  This makes surfing dangerous due to difficulties 
in maintaining a safe wave-entry point.  Under such extreme conditions, 
surfers historically challenged Waimea Bay, where the take-off zone is 
narrower and the proximity to shore allows landmark referencing for more 
precise wave-entry positioning.

Numerous photographs are available for Waimea Bay during surf in the 
12-30 HSF range.  The surfers enter the wave about 50-100 m outside the 
point on the northeast side of the bay and surf at an angle toward the 
safety of the deep waters in the center of the bay.   The wave-entry point 
shifts northwest of the northeast point of the bay with increasing wave size.  
At approximately 30 HSF, the entire wave front cascades nearly simultaneously 
across the breadth of the bay, ending a surfers chance for a safe ride.

The photographs at Waimea Bay suggest the trough to crest heights are 
roughly 1.5 times HSF during days with observations in the 15-30 HSF range.  
Within the collection of photographs, there are several occasions when 
images were available for the same day from both Waimea Bay and outer reefs 
of Oahu and Maui, where tow-in surfing (motor-powered-watercraft-assisted 
breaker entry) has gained popularity over the past decade.  Over the submerged 
ridges of the offshore reefs to either side of Waimea Bay, the SWAN output 
(Figure 2b) shows increased heights due to convergence of wave rays, i.e. 
refraction.  Photographs of tow-in surfers on outer reefs validate the 
larger heights relative to Waimea Bay.   

In summary, the translation of HSF to trough to crest heights is a factor 
of two within the 10-20% margin of error for the full range of breaker sizes 
encountered in Hawaii.  This assumes the height is defined as the highest 
height reached in the vertical from the trough to crest at any point along 
the wave front during breaking and zones of high refraction (outer reefs) 
are included for extreme days when Waimea Bay was the reporting location.  
The HSF, or simply dividing trough to crest height by two, has been adopted 
by other big wave enthusiasts around the globe as seen in pictures and 
dialogue from extreme surf contests in California, Peru, and South Africa.  
It is important for scientists and the general public to understand this 
relationship for utilizing surf observations reported in HSF.

Acknowledgments.
Larry Goddard is recognized for establishing the surf observation database 
from 1968-87.  Great appreciation is given to the north shore surf observers, 
surfers, and photographers.  Special thanks are given to photographers Claudia 
Ferrari (claudiaferrari.com), Jamie Ballenger, (HawaiianWaterShots.com), and 
Ian Masterson.  Warm regards go to photographers of Oahu outer reefs 
(Justin Langlais, John Bilderback, and Hankfotos.com) and Jaws, Maui (Eric 
Aeder, Steve Kornreich, Les Walker, C. Levy, and C. Oreve).
        Source_Used_Citation_Abbreviation: Caldwell, P. and J.Aucan, 2004: Translation of surf observations from Hawaii 
        Source_Used_Citation_Abbreviation: scale to trough to crest heights based on photographic evidence. Poster.  8th 
        Source_Used_Citation_Abbreviation: International Workshop on Wave Hindcasting and Forecasting,  North Shore, 
        Source_Used_Citation_Abbreviation: Oahu, Hawaii, November 2004.
        Source_Used_Citation_Abbreviation: Caldwell, P. and J.Aucan, 2004:  AN EMPIRICAL METHOD FOR ESTIMATING SURF 
        Source_Used_Citation_Abbreviation: HEIGHTS FROM DEEP WATER SIGNIFICANT WAVE HEIGHTS AND PEAK PERIODS IN 
        Source_Used_Citation_Abbreviation: COASTAL ZONES WITH NARROW SHELVES, STEEP BOTTOM SLOPES, AND HIGH 
        Source_Used_Citation_Abbreviation: REFRACTION. 8th International Workshop on Wave Hindcasting and Forecasting,  
        Source_Used_Citation_Abbreviation: North Shore, Oahu, Hawaii, November 2004.
        Source_Used_Citation_Abbreviation: Caldwell, P., 2005: Validity of North Shore, Oahu, Hawaiian Islands surf 
        Source_Used_Citation_Abbreviation: observations. Journal of Coastal Research, 21(1), 2005.
        Process_Date: Unknown
        Process_Contact:
          Contact_Information:
            Contact_Person_Primary:
              Contact_Person: Mr. Patrick C. Caldwell
              Contact_Organization: NOAA/NESDIS/NODC/NCDDC
            Contact_Position: Hawaii/US Pacific Liaison
            Contact_Address:
              Address_Type: mailing
              Address: 1000 Pope Road, MSB 316
              Address: Dept. of Oceanography
              Address: University of Hawaii at Manoa
              City: Honolulu
              State_or_Province: Hawaii
              Postal_Code: 96822
              Country: USA
            Contact_Voice_Telephone: (808)-956-4105
            Contact_Facsimile_Telephone: (808) 956-2352
            Contact_Electronic_Mail_Address: caldwell@hawaii.edu
            Hours_of_Service: 8 AM to 5 PM weekdays
            Contact_Instructions: check services@nodc.noaa.gov if not available
  Entity_and_Attribute_Information:
    Overview_Description:
      Entity_and_Attribute_Overview: A summary of files is given in ../../data/readme.txt

The scaled photographs are sorted by size in Subdirectories, which have 
names as xx_Hsf or xx_xx_Hsf, where xx denotes a size and xx_xx denotes
a size range.

Within each subdirectory, filenames of each photograph vary yet all contain
the date (mmddyy) and the recorded size in the Goddard-Caldwell dataset as
_Cxx, where xx is the size in Hsf.
      Entity_and_Attribute_Detail_Citation: none
  Distribution_Information:
    Distributor:
      Contact_Information:
        Contact_Organization_Primary:
          Contact_Organization: NOAA/NESDIS/NODC/NCDDC (National Coastal Data Development Center)
        Contact_Address:
          Address_Type: Mailing and Physical Address
          Address: National Coastal Data Development Center, Building 1100
          City: Stennis Space Center
          State_or_Province: MS
          Postal_Code: 39529
        Contact_Voice_Telephone: 866-732-2382
        Contact_Facsimile_Telephone: 228-688-2968
        Contact_Electronic_Mail_Address: ncddcgetdata@noaa.gov
        Hours_of_Service: 8am-5pm, Monday through Friday
    Distribution_Liability: NOAA makes no warranty regarding these data,expressed or implied, nor does the fact of distribution constitute such a warranty.  NOAA, NESDIS, NODC and NCDDC cannot assume liability for any damages caused by any errors or omissions in these data, nor as a result of the failure of these data to function on a particular system.
  Metadata_Reference_Information:
    Metadata_Date: 20041012
    Metadata_Contact:
      Contact_Information:
        Contact_Person_Primary:
          Contact_Person: Mr. Patrick C. Caldwell
          Contact_Organization: NOAA/NESDIS/NODC/NCDDC
        Contact_Position: Hawaii/US Pacific Liaison
        Contact_Address:
          Address_Type: mailing
          Address: 1000 Pope Road, MSB 316
          Address: Dept. of Oceanography
          Address: University of Hawaii at Manoa
          City: Honolulu
          State_or_Province: Hawaii
          Postal_Code: 96822
          Country: USA
        Contact_Voice_Telephone: (808)-956-4105
        Contact_Facsimile_Telephone: (808) 956-2352
        Contact_Electronic_Mail_Address: caldwell@hawaii.edu
        Hours_of_Service: 8 AM to 5 PM weekdays
        Contact_Instructions: check services@nodc.noaa.gov if not available
    Metadata_Standard_Name: FGDC CSDGM
    Metadata_Standard_Version: FGDC-STD-001-1998

