Patrick Caldwell - NOAA/NESDIS/NODC/NCDDC
Unknown
Scaled photographs of surf over the full range of breaker sizes on the north shore of Oahu and Jaws, Maui, Hawaiian Islands (NODC Accession 0001753)
None
None
Unpublished Material
Unpublished Material
https://www.ncei.noaa.gov/archive/accession/0001753
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.
To better understand wave heights reported in Hawaii Scale Feet.
NOAASupplemental:
Entry_ID: Unknown
Sensor_Name: digital cameras
Originating_Center: NOAA/NESDIS/NODC/NCDDC
Storage_Medium: jpeg
Online_size: 9190 kbyte
Resource Description: NODC Accession Number 0001753
19980128
20040524
ground condition
None Planned
-158.108
-156.323
21.692
20.950
NCEI Geoportal FilterCoRIS_Metadata
ISO 19115 Topic Category
oceans
014
CoRIS Discovery Thesaurus
Numeric Data Sets > Oceanography
CoRIS Theme Thesaurus
EARTH SCIENCE > Oceans > Ocean Waves > Wave Height
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Coastal studies
surf height
wave height
scaled photograph
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North Pacific
Hawaiian Islands
Oahu
North Shore
Waimea Bay
Sunset Point
South Shore
Ala Moana
Jaws (Peahi), Maui
CoRIS Region
MHI
CoRIS Place Thesaurus
OCEAN BASIN > Pacific Ocean > Central Pacific Ocean > Hawaiian Islands > Oahu Island > Oahu (21N157W0003)
COUNTRY/TERRITORY > United States of America > Hawaii > Honolulu > Oahu (21N157W0003)
OCEAN BASIN > Pacific Ocean > Central Pacific Ocean > Hawaiian Islands > Maui Island > Maui Island (20N156W0004)
COUNTRY/TERRITORY > United States of America > Hawaii > Maui > Maui Island (20N156W0004)
None
surface
None
Dataset credit required
Mr. Patrick C. Caldwell
NOAA/NESDIS/NODC/NCDDC
Hawaii/US Pacific Liaison
mailing
1000 Pope Road, MSB 316
Dept. of Oceanography
University of Hawaii at Manoa
Honolulu
Hawaii
96822
USA
(808)-956-4105
(808) 956-2352
caldwell@hawaii.edu
8 AM to 5 PM weekdays
check services@nodc.noaa.gov if not available
Hawaii Liaison Office
National Coastal Data Development Center
NOAA/NESDIS/NODC/NCDDC
jpeg files
see lineage, process step
none
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 observer's 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 surfer's 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 surfer's 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).
Caldwell, P. and J.Aucan, 2004: Translation of surf observations from Hawaii
scale to trough to crest heights based on photographic evidence. Poster. 8th
International Workshop on Wave Hindcasting and Forecasting, North Shore,
Oahu, Hawaii, November 2004.
Caldwell, P. and J.Aucan, 2004: AN EMPIRICAL METHOD FOR ESTIMATING SURF
HEIGHTS FROM DEEP WATER SIGNIFICANT WAVE HEIGHTS AND PEAK PERIODS IN
COASTAL ZONES WITH NARROW SHELVES, STEEP BOTTOM SLOPES, AND HIGH
REFRACTION. 8th International Workshop on Wave Hindcasting and Forecasting,
North Shore, Oahu, Hawaii, November 2004.
Caldwell, P., 2005: Validity of North Shore, Oahu, Hawaiian Islands surf
observations. Journal of Coastal Research, 21(1), 2005.
Unknown
Mr. Patrick C. Caldwell
NOAA/NESDIS/NODC/NCDDC
Hawaii/US Pacific Liaison
mailing
1000 Pope Road, MSB 316
Dept. of Oceanography
University of Hawaii at Manoa
Honolulu
Hawaii
96822
USA
(808)-956-4105
(808) 956-2352
caldwell@hawaii.edu
8 AM to 5 PM weekdays
check services@nodc.noaa.gov if not available
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.
none
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Downloadable Data
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jpg
https://accession.nodc.noaa.gov/0001753
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20210106
20090810
Mr. Patrick C. Caldwell
NOAA/NESDIS/NODC/NCDDC
Hawaii/US Pacific Liaison
mailing
1000 Pope Road, MSB 316
Dept. of Oceanography
University of Hawaii at Manoa
Honolulu
Hawaii
96822
USA
(808)-956-4105
(808) 956-2352
caldwell@hawaii.edu
8 AM to 5 PM weekdays
check services@nodc.noaa.gov if not available
FGDC CSDGM
FGDC-STD-001-1998
20090810062540
None
19980128
20040524
https://www.coris.noaa.gov/metadata/records/html/scaled_surf_fotos_fgdc_0001753.html
2771