Taking a Surf Observation
(SUROB)

Remember:  Sea State Observations are taken from the ocean's perspective--not yours!

     Taking a Surf Observation

• bucket
• rope
• thermometer
• large piece of drift wood (for Littoral Current)
• Surf observation worksheet
• pencil
• time keeping device, with a second hand

B. Before beginning a surf observation, the observer must have a basic understanding of waves and their dynamics. The surf zone is defined as the area between the first breaker shoreward to the beach. Breakers form as a wave enters water which is shallower than half its wave length. The water near the bottom of the wave begins to feel bottom, and is retarded by friction, causing the wave to increase in height until it becomes too high for its motion, and falls over into the preceding trough.

There are three types of breakers in the surf zone; spilling, plunging, and surging. The slope of the beach and the types of waves approaching the surf zone determine which type of breaker is going to be predominant.

Spilling: breaks gradually over a distance. White water forms as the crest and expands down the face of the breaker. Only the top portion of the wave curls over however. Light foam may wash gently up the shore. This type of wave is normally found with a flat bottom beach. It is usually the most observed type of wave.

Plunging: the wave peaks up until it is an advancing vertical wall of water. The crest advances faster than the base of the breaker, curls, and then descends violently into the trough. This type of breaker sometimes causes an explosive sound as trapped air escapes behind the wave. It is usually found on a medium to steep sloping beach, with little wind or an offshore wind.

Surging: advances at the same rate as the base of the breaker, it surges up the beach as a wall of water. It may or may not be accompanied by white water, and is usually found on very steep beaches. 

C. Taking the Surf Observation

(Please refer to the surf observation form for the following section on correctly filling out the form.)

1. Begin by filling in the surf ob number and the beach or port the observation is being taken in.
   
2. Record the day and time of the beginning of the observation to the nearest second.
   
3. In the grid provided, record the type and estimated height (nearest half foot) of 100 consecutive breakers. As soon as the 100 breakers are recorded, place the time the observation ended, to the nearest second on the form. Add the minutes and seconds from start to finish, and place on the observation form.
   
4. The next section is Alpha, find the height of the highest 33 breakers. A small section for computation is provided in the lower right corner. If, for example, 6 feet was the highest breaker and it occurred twice, you would record 6 feet in the height section and 2 in the occurrence category, multiply these together and 12 would be the total product. Find the next highest height and the number of occurrences and record them in the chart also. Do this until the highest 33 waves have been recorded. Add the total products together and divide by 33 to get your Alpha total. Record it to the nearest half foot.
   
5. Bravo section is the next category. Record the highest breaker recorded from the observation to the nearest half foot.
   
6. Charlie is the total number of seconds the observation took, divided by 100. This gives the wave period. It is recorded to the nearest half second.
   
7. The next section is Delta, simply count the number of plunging, spilling, and surging waves that occurred and record them in the proper place.
   
8. Echo is the breaker angle. It is the angle the breaker makes with the beach. It is always determined as moving toward the right or left flank, and is always referred to as seen from the boats and landing craft. If you can’t remember this, just imagine being out over the water facing the beach and land and determining what angle the waves are rolling in. If they are parallel to the beach you would record 0 to the right/left flank.
   
9. Foxtrot is the littoral current. It is the current that moves parallel or adjacent to the shoreline. To determine the current, throw a piece of driftwood, or an object that will float, directly in front of the innermost breaker, and pace off the distance (in feet) the object moves in one minute. Each ten feet of movement is equal to one-tenth of a knot of littoral current. (ex. if the driftwood moved 90 feet, then the littoral current would be 0.9 knots) Note the direction of movement also. Remember that the direction of movement is as seen from a boat or ship in the water, facing land. If time permits, do this several times and take an average reading for greater accuracy.
   
10. Golf is the size of the surf zone. The surf zone extends from the outermost breaker to the limit of the uprush on the beach. Simply count the number of breakers and estimate the width of the surf zone, and record on the form.
    
11. Hotel is used to report anything the observer feels is significant to operations. The relative wind direction and speed in relation to right or left flank is recorded here, as is weather and visibility.  If a secondary wave system is visible anywhere, also record it here, with its height, period, and angle if known.
    
    
12. To determine the temperature of the water, take the bucket with the rope tied to the handle and toss   it out as far you can. Pull the bucket back in and place the thermometer in the water. Record the temp in case it is needed.

• MSI = 3.6

• ALPHA - Significant Breaker Height
• BRAVO - Maximum Breaker Height
• CHARLIE - Breaker Period

• DELTA - Breaker Types

• ECHO - Angle of breaker with beach

• FOXTROT - Littoral (Longshore Current)

• GOLF - Surf Zone
• HOTEL - Info important to landing operation. Wind speed and direction, visibility, debris in the surf, obstacles, etc. (additional remarks)
  

MODIFIED SURF INDEX     

      The Modifed Surf Index or MSI is a single dimensionless number which provides a relative measure of the conditions likely to be encountered in the surf zone.  For the reported or forecast conditions, the Modified Surf Index provides a guide for judging the feasibility of landing operations for each type of landing craft.

     When applied to a known or forecast surf condition, the Modified Surf Index calculation provides the commander with an objective method of arriving at a safe and reasonable decision with respect to committing landing craft and amphibious vehicles.  Limiting surf conditions for training operations shall be set by the commander concerned.  These limits shall not exceed conditions acceptable for routine operations as calculated by the tables in the JOINT SURF MANUAL Chapter 11. Once you obtain all elements on the surf observation form you would get the Modified Surf Index calculation sheet located in Chapter 11 and fill in the appropriate columns and add them up to get the correct Modified Surf Index. 

     For now, we are not going to teach this technique, but just be aware that it exists and how to calculate it from the above listed reference if necessary.