NOAA Technical Report NOS CO-OPS 38

Triaxys Directional Wave Buoy for Nearshore Wave

Measurements - Test and Evaluation Plan

Silver Spring, Maryland

January 2003

noaa National Oceanic and Atmospheric Administration

U.S. DEPARTMENT OF COMMERCE

National Ocean Service

Center for Operational Oceanographic Products and Services
Center for Operational Oceanographic Products and Services

National Ocean Service

National Oceanic and Atmospheric Administration

U.S. Department of Commerce

The National Ocean Service (NOS) Center for Operational Oceanographic Products and

Services (CO-OPS) collects and distributes observations and predictions of water levels

and currents to ensure safe, efficient and environmentally sound maritime commerce.

The Center provides the set of water level and coastal current products required to

support NOS' Strategic Plan mission requirements, and to assist in providing operational

oceanographic data/products required by NOAA's other Strategic Plan themes. The

Center manages the National Water Level Observation Network (NWLON), and a

national network of Physical Oceanographic Real-Time Systems (PORTSTM) in major

U.S. harbors. The Center: establishes standards for the collection and processing of

water level and current data; collects and documents user requirements which serve as

the foundation for all resulting program activities; designs new and/or improved

oceanographic observing systems; designs software to improve CO-OPS' data processing

capabilities; maintains and operates oceanographic observing systems; performs

operational data analysis/quality control; and produces/disseminates oceanographic

products.
NOAA Technical Report NOS CO-OPS 38

Triaxys Directional Wave Buoy for Nearshore Wave

Measurements - Test and Evaluation Plan

H.H. Shih

January 2003

noaa National Oceanic and Atmospheric Administration

U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration

Don Evans, Secretary Vice Admiral Conrad C. Lautenbacher, Jr., U.S. Navy (Ret.)

Undersecretary of Commerce for Oceans and Atmosphere and 

NOAA Administrator

National Ocean Service

Jamison Hawkins, Acting Assistant Administrator for 

NOAA Oceans and Coasts

 

Center for Operational Oceanographic Products and Services

Michael Szabados, Director
NOTICE

Mention of a commercial company or product does not constitute

an endorsement by NOAA. Use for publicity or advertising

purposes of information from this publication concerning proprietary

products or the tests of such products is not authorized.
iii

Table of Content

 Page

ABSTRACT .......................................................................................................................... 1

1. INTRODUCTION ............................................................................................................... 1

1.1 Needs for Wave Information ................................................................................... 1

1.2 Existing Wave Measurement Systems .................................................................... 1

1.3 Available Instruments .............................................................................................. 2

1.4 NOS Application Environment ............................................................................... 4

1.5 Test and Evaluation Objectives ............................................................................... 5

2. THE TRIAXYS DIRECTIONAL WAVE BUOY .............................................................. 7

2.1 Principle of Operation ............................................................................................. 7

2.2 Major Components and Manufacturer’s Specifications .......................................... 7

3. TEST AND EVALUATION ............................................................................................... 15

3.1 Scope ....................................................................................................................... 15

3.2 Approaches ............................................................................................................. 15

3.2.1 General Guidelines ......................................................................................... 15

3.2.2 Type of Test .................................................................................................... 16

 A. Acceptance Test ........................................................................................ 16

B. Subsystem/Module/Component Test ........................................................ 17

C. System Performance Test .......................................................................... 19

D. Data Quality Assurance Test .................................................................... 19

E. Operational Test ........................................................................................ 19

3.3 System Issues to Be Verified .................................................................................. 20

3.4 Responsibility ......................................................................................................... 20

3.5 Test Facilities .......................................................................................................... 20

3.6 Schedule .................................................................................................................. 21

4. DOCUMENTATION, REVIEW AND PLANNING ........................................................ 23

4.1 Test Report .............................................................................................................. 23

4.2 Review and Planning .............................................................................................. 23

ACKNOWLEDGMENTS ....................................................................................................... 25

REFERENCES ........................................................................................................................ 25

APPENDICES ......................................................................................................................... 27

A. Triaxys Factory Check Sheets ................................................................................... 28

B. Triaxys Sensor Validation Sheets .............................................................................. 31

C. Triaxys Field Checkout/Deployment Sheet ............................................................... 34
iv
1

ABSTRACT

A Triaxys directional wave buoy was acquired by CO-OPS with funds from the NOS

Partnership, “Tools and Technical Guidance to Improve Restoration of Coastal Habitat”.

It is to be deployed at Barren Island and other sites in the Chesapeake Bay in support of

marsh restoration. In the future, it may be used to support other CO-OPS programs,

such as PORTS® and other coastal programs. The buoy contains three solid state

accelerometers, three angular rate sensors, and a fluxgate compass, and derives directional wave

information from dynamic motion measurements and six degrees of freedom buoy motion

equations. The technique is relatively new and requires validation by NOS for operational use

by NOS. This document outlines a test and evaluation plan which provides a framework for

developing detailed test procedures that can be carried out in- house or via contractual

arrangement. 

 

1. INTRODUCTION

1.1 Needs for Wave Information 

Surface waves provide principle energy inputs to many near shore processes such as long shore

currents, changes in beach profiles, longshore transportation of sand. There has been growing

interest in coastal wave information from maritime commerce, environmental managers, and

engineering and scientific communities. Previous user surveys have found that the surface wave

observations and forecasts are usually one of the top three variables requested or used by marine

users. The other two variables are surface winds and currents. The Oceans.US Phased

Implementation Plan for the US IOOS [1] also identifies waves as number 3 priority under

physical observations, following temperature and salinity.

Identified areas of application include wave nowcast/forecast model verification, marsh

restoration and shore erosion, hazardous material spill response, coastal storm induced flooding,

engineering design and construction, dredging, ship routing and scheduling, cargo loading and

unloading, and recreational boating. Wave observation networks in ports and harbors have been

established in several countries including Japan, Netherlands, and Spain.

In the U.S., user groups include Federal agencies (NOAA, USCG, USACE, Navy, EPA, and

USGS), State and local governments (Port Authorities, Civil Defense, Public Work, Recreation,

and Natural Resources), private industry and general public [2].

There is an identified gap in NOS in operational observing system capabilities for waves in

ports, harbors, and bays. 

 

1.2 Existing Wave Measurement Systems 

Several wave measurement systems/networks are presently installed in the U.S. The

NOAA/National Data Buoy Center (NDBC) maintains and operates a network of large wave

buoys in order to gather wave information in deeper ocean basins as well as in the Great Lakes.

Some of NDBC’s coastal C-MAN stations also are equipped with water level sensors which

produce non-directional wave information [3]. The U.S. Army Corps of Engineers (USACE)
2

together with the Scripps Institution of Oceanography (SIO) maintain and operate pressure

transducer arrays and Waverider buoys for directional and non-directional wave measurements

in shallower coastal waters [4]. 

There are also other special research programs, such as the Navy’s North Gulf Littoral Initiative

and Louisiana State University’s Wave-Current-Surge Information System [5]. Wave monitoring

near shore such as in and around ports, harbors and bays, however, is not common. 

1.3 Available Instruments

Available instruments can be categorized into two groups: in situ and remote sensing. A brief

description and comments about commonly used sensors or technologies are given below.

A. In Situ Instruments

In situ techniques are ideal for collecting large quantities of wave data at a specific point.

However, deployment and maintenance for long term services are expensive. Commonly used

instruments, their advantages and disadvantages are listed below.

a) Surface piercing type 

a1. Resistance gauges - The gauge consists of two vertical parallel conducting wires. The

two wires are insulated from one another at the lower ends. Water will short the wires and

creates a circuit. The resistance of this circuit is related to the depth of submergence of the

wires and hence the water surface elevation. 

 Advantages: high frequency response; easy to install; widely used in laboratory.

Disadvantages: non-directional wave data; changes in the water salinity will affect the

calibration of the gauge; fouling of wires also present a problem; requires continual

maintenance. 

a2. Capacitance gauges - the gauge consists of a single Teflon coated wire. The

conducting wire and the water form the two plates of a capacitor, separated by the

insulating coating. The dielectric constant of the capacitor varies with the length of

submergence. 

 Advantages: high frequency response; insensitive to salinity changes; easy to install;

widely used in laboratory.

Disadvantage: non-directional wave data; marine fouling and damage of insulating coating

of the wire often affect the gauge performance; requires continual maintenance.

a3. Transmission line gauges (such as the Baylor wave staff) - The gauge consists of two

inductive wire ropes held vertically in parallel under tension. These wires form an electric

transmission line terminated by the water surface. The impedance of the transmission line

varies with the water surface elevation and can be easily measured. The gauges have an

accuracy and resolution of 1 and 0.1 percent full scale, respectively. 

 Advantages: rugged, easily to install and maintain; used widely by offshore oil industry. 

Disadvantages: non-directional wave data; 

b) Bottom mounted instruments
3

b1. Pressure transducer array - compute surface elevation and direction from water

pressure and phase measurements.

Advantages: less susceptible to damage from dynamic water surface; 

Disadvantages: measures depth attenuated pressure; uses linear wave theory to derive

correct pressure; needs water density and barometric pressure data in water surface height

conversion; need data telemetry to shore; has relatively poor high frequency response due

to water depth pressure attenuation. 

b2. Acoustic Doppler Current profiler (ADCP) - derive surface wave information from

wave orbital velocity and pressure measurements.

 Advantages: measure both current profiles and directional wave information; more

compact and rugged than bottom pressure array.

Disadvantages: High frequency wave measurements may be limited due to water depth

pressure attenuation. The instrument uses linear wave theory for pressure correction. 

b3. PUV sensor – This includes the SonTek Acoustic Doppler Profiler and Velocity Meter

(ADP and ADV) and InterOcean’s S4 electromagnetic current meter. Statistics of sea surface

elevation are derived from pressure measurements at a point and wave direction is computed

from phase differences between surface elevation and orbital velocities (U and V).

 Advantages: measure both current profiles and directional wave information; more

compact and rugged than bottom pressure array.

Disadvantages: Uses linear wave theory for pressure correction and has low directional

resolution.

c) Surface buoys 

c1. Slope-following buoys - Heave-pitch-roll buoy such as NDBC disc and torous buoys.

 Advantages: rugged and used often in deep water.

Disadvantages: hull and mooring system are expensive; accurate measurement requires that

the buoy be designed to follow water surface and the accelerometer remains vertical

c2. Particle following buoys – These include Datawell’s Waverider and AXYS’ Triaxys

buoy. Typically spherical shape; uses a compliant mooring system; The Waverider sensing

package consists of a gyroscopically stabilized platform, accelerometers (heave), surface

slope (pitch and roll) and compass. The Triaxys sensing package consists of

accelerometers, rate gyros, and compass.

 Advantages: less expensive; portable; widely used.

Disadvantages: susceptible to theft, vandalism and damage from shipping; could be

overturned by steep breaking waves (often occur in shallow waters less than 8 m); accurate

measurement requires that the buoy be designed to follow water particles; accuracy

degrades in very highest waves or short crest seas, and measuring nonlinear wave

properties.

B. Remote Sensing Techniques

Remote sensing techniques, ground-based, aircraft borne, or satellite borne, are capable of

measuring the surface wave field (locally or global). However, only limited instruments are
4

operational or quasi operational. Several others are in the developmental phase and require

adequate validation. Existing technologies are briefly listed below.

a) Ground-based, ship-based, or aircraft-borne:

a1. Microwave radar - Mostly are used in scientific experiments (such as NOAA, U.S.

Naval Research Lab). Several European products are in the market (such as Miros, SAAB,

MAREX microwave radar, and GSK marine radar).

 Advantage: above sea surface, provide wave pattern information, useful in research and

site specific studies. 

Disadvantage: performance has not been adequately validated. 

a2. Laser and sonic - Several ranging instruments have been used for non-directional wave

measurement (such as IR laser wave height sensor by Schwartz electro-Optics used by

NDBC, THORN/EMI wave height sensor used in Europe, Western Marine Electronics’

sonic sensor).

 Advantage: non-contact with water surface

Disadvantage: non-directional and performance has not been adequately validated.

b) Satellite-borne: 

b1. Radar altimeter (1986-1990 GEOSAT, 1992-present TOPEX, 1991 - present ERS1,

1995-present ERS2) - not applicable to coastal area where wave field has significantly

spatial variability (due to large footprint, approximately 10 km in diameter), ocean

coverage and repeat paths are relatively course; no wave period or direction can be

obtained; requires validated signal transfer functions; typical accuracy is about + 0.5 m or

10% in significant wave height, whichever is greater. 

b2. Synthetic Aperture Radar (SAR, installed on SEASAT, ERS1, ERS2, RADRSAT) - A

coherent radar that looks at right angles to the flight path. Swath path is about 100 km

wide and offset from the satellite track by about 250 km. ERS1 and 2 are capable of

providing 10 km x 5 km wave-mode images every 200 km along the satellite track. 

Advantage: potentially global directional wave spectra, providing wave pattern

information. 

Disadvantage: Mechanisms in deriving wave information from SAR images are complex

and are still under study. Application to near coast area (ports, harbors and bays) is limited.

 

1.4 NOS Application Environment 

The requirement to provide wave information for safe and efficient navigation in major ports as

well as for marsh restoration and other environmental management programs in estuaries and

marine sanctuaries could lead to a new service area, either by NOS alone, or through cooperative

efforts with other partners. 

Since winds in enclosed or semi-enclosed waters are limited in fetch, locally wind generated

waves are typically of short periods. However, ocean waves and swells coming from open

oceans may produce large surface oscillations, especially when the periods are close to the
5

resonant oscillation periods of the enclosed waters. Very long period swell, seiches, and tsunami

waves can significantly impact ship operations. 

Other environmental characteristics in ports, harbors and bays include the presence of a large

tidal range, strong currents, storm surges, varying water densities of the surface layer, varying

water depth, bottom topography and sediment types, and floating ice. Another feature often

observed at entrances to rivers, harbors, and bays is steeper waves due to wave-current

interactions. These areas should be of higher priority for wave (and current) measurements.

Long term wave monitoring at strategic locations in and around bays and ports will provide

valuable data sets for wave nowcast/forecast model development and validation. Its importance

is similar to the PORTS water level data that are integral part of the hydrodynamic nowcast and

forecast model operation and evaluation. 

The relatively small water body, the intense utilization of the water and its densely populated

shoreline may require much tighter requirements for wave measurements compared to that for

Open Ocean and coastal waters. Suggested accuracy requirements are + 10 cm in wave heights,

+ 3 degrees in wave direction, and + 1 second in wave period. 

1.5 Test and Evaluation Objectives

The data and experiences gained from test and evaluation will be used for detailed assessment of

the suitability of the Triaxys buoy for NOS operations.

Specific objectives for test and evaluation are:

A. to obtain and validate data on technical performance of the Triaxys system and critical

components and major subsystems.

B. to obtain operational data (such as measurement limitations, reliability, maintainability) for

determining that Triaxys system is suitable for NOS application.

C. to obtain data for developing data quality assurance procedures and to verify data quality.

D. to evaluate system performance in terms of critical technical, operational and logistical

requirements (such as calibration, handling, setup, inspection, site selection, deployment, etc.).

E. to identify system malfunction/failure/breakdowns/problems such as mooring failure,

component aging, solar/battery charging, radio interference, system work-hardening effects, and

impacts of physical modifications (change in battery weight and mooring line configurations

etc.) for developing corrective measures and system improvements. 

F. to verify the adequacy of technical manuals and other documents for operational use.

G. to evaluate overall performance based on NOS coastal wave measurement requirements, and

to develop an operational plan.
6
7

2. THE TRIAXYS DIRECTIONAL WAVE BUOY

2.1 Principle of Operation

The Triaxys Wave Buoy, like the widely used Datawell Directional Waverider Buoy, is a water

particle-following buoy that measures the water particle motion in three orthogonal directions.

However, the wave measuring techniques for the two instruments are different. The Triaxys

buoy uses three accelerometers to measure total accelerations along the mutually orthogonal X,

Y, Z axes of the buoy; three angular rate sensors to measure rotation rates about the roll, pitch

and yaw axes, and a gimbaled compass to measure sensor heading. An algorithm for a 6-

degrees-of-freedom non-linear equation of motion of sensor and a Maximum Entropy Method

are used to derive wave height and directional frequency spectra. In comparison, the Waverider

buoy uses heave-pitch-roll sensors, two horizontal hull-fixed accelerometers, and compass to

determine directional wave information. 

The Triaxys buoy also differs from the traditional NDBC disc buoy, a surface slope following

buoy, which uses a similar sensor package as Waverider. 

The Triaxys buoy wave measuring technique is claimed to be more flexible and accurate.

However, its accuracy and reliability have not been fully evaluated.

2.2 Major Components and Manufacturer’s Specifications 

The major system components consist of the sensor and telemetry module (TAS), the Triaxys

Digital Receiver (TDR) and antenna, a power supply subsystem consisting of solar panel

assembly and batteries (TAB), navigation light, antenna, and an infrared serial port, upper dome

cover and clamping ring, lower hull (including purge port, lifting bridle, and magnetic key),

rubber fender, and mooring hardware. A User’s manual, WaveView software, and spares kit are

also included in the delivered package. 

Sensors and data processing software include compass, accelerometers (along X, Y, and Z axes),

angular rate gyros (about X, Y, and Z axes), and PC104 wave processor. Other measurements

include water temperature, system voltages and currents, solar currents, and battery currents.

Data telemetry subsystems include VHF radio system and antenna, GPS and ARGOS. An

internal PCMCIA RAM stores data up to 128 MB. The WaveView software allows the user to

monitor data collection in real-time.

 

Figs. 1 and 2 show the major components of the Triaxys buoy and manufacturer suggested

standard mooring configuration, respectively. Manufacturer’s specifications and acceptable

ranges for sensors at static, level, and upright position and static tilt positions are summarized in

Tables 1 and 2, respectively.
8

Figure 1. Major components of Triaxys directional wave buoy [5]

 
9

Figure 2. Triaxys standard mooring configuration in deep water [5]
10

Table 1. Triaxys Directional Wave Monitoring System Specifications [5]

ITEM SPECIFICATION

Physical Description

Diameter nominal, around bumper - 1.10 m (43.5 inches) O.D.

Stainless steel hull - 0.91 m (36 inches)

Weight 197 kg (including 4 batteries); 90 kg (excluding batteries) 

Purge port 3/4" - 16 UNF with Swagelock hex plug

Obstruction light Amber LED source; programmable flash sequence, three miles visibility

Materials

Hull Stainless steel

Dome Polycarbonate Cyrolon ZX (tested to ASMT D3763 and ISO 6603-2

impact specifications)

Solar panel

assembly

Fiberglass over foam

Clamping ring Stainless steel

Sensors/Processor

Water temperature Thermilinear composite network

Accelerometers Flexure suspension servo (range: + 2g)

Rate Piezoelectric vibrating gyroscope (max. angular velocity: + 80 deg. /s)

Compass Microprocessor controlled fluxgate (accuracy: + 0.5 deg.)

A/D and sampling

frequency

8 channel 14 bit at 4 Hz

Microprocessor PC104 and 80C552

GPS 12 channels

Resolution/Accuracy

Range Resolution Accuracy

Heave + 20 m 0.01 m better than 2%

Period 1.56 to 33.33 seconds

Direction 0 to 360 degrees + 1 degree

Water temperature -5 to +50 deg. C + 0.1 degree C
ITEM SPECIFICATION

11

Power System

Operational system

voltage

11.0 to 14.1 VDC

Batteries 4 @ GNB SunLyte 5000X 12 volt, 100 amp hr

Solar panels 10 @ 6 watt Siemens SM6

Smart charger Sunsaver-6

On/off switch Turn buoy on when Magnetic Key is removed

Telemetry

30 to 50 MHz Synthesized VHF transmitter (standard)

Effective radiated

output

0.5 watts

Data Format Binary transmission

Transmission rate 2400 Baud

Maximum range

(VHF line-of- sight)

16 km (10 miles) over water (less over land)

Optional

transmission

ARGOS

Optional watchcircle beaconARGOS or INMARSAT D+

 Input/output power and data through Belgian connector; frequency bands up to 123

 Operating

 temperature

 -30 to +60 degree C

 Storage/transit

 temperature

 -40 to +70 degree C

 Data

 transmission

 standard: multiple transmissions of each data set; directional wave

 characteristics and spectra; wave statistics; SST; battery voltage; solar

 current; error checking.

 optional: VHF (30-39 MHz, or 39-50 MHz, synthesized frequency

 selection), or ARGOS;

 real-time; programmable configuration

 communication: 19,200 baud, 8 bits, 1 stop, no parity

 Power supply: +12 to 14 VDC

 consumption: 0.134 amp-hr per 20-min sample 

 transmission: 3 watts @ 12 VDC; VHF range to 10 nautical miles

 battery: 4 gel cells

 solar panel: 10 @ 6 watts

 Position GPS/ARGO (optional)
12

Table 2. Acceptable ranges for sensors at rest position (still, level, and upright)

Sensor Range Check Procedure

Compass Heading 0 to 359 check against hand held compass

Accelerometer X near 0 + 0.06 g’s x axis is north

Accelerometer Y near 0 + 0.06 g’s y axis is east

Accelerometer Z near -1 + 0.06 g’s z axis is positive downward

Water Temperature -5oC to 50oC

(0 to 25oC with dummy plug)

check with measured value of air

temperature

System Voltage 11 to 14.1 volts measure before installing the dome

System Current1 20 to 50 milliamps PC104, motion sensors & transmitter

not powered

550 to 750 milliamps PC-104 only powered

120 to 200 milliamps motion sensors only powered

100 to 200 milliamps transmitter only, powered on but not

transmitting

Rate Gyro X near 0 + 6 o

/sec

Rate Gyro Y near 0 + 6 o/sec

Rate Gyro Z near 0 + 6 o/sec

Solar Current 1.1 to 1.5 amps bright sunshine

0.5 to 0.8 amps shade

0.0 to 0.2 amps overcast

Battery Current2 -1.0 to +1.8 amps battery current = solar current - system

current, check that the battery current

is correct as per the above formula

Notes: 

1. System current = Solar current - Battery current. If there is no solar current then the Battery current (negative) will

approximately equal the System current (positive).

2. These values for currents assume daylight conditions and do not include any current draw that might be associated

with the operation of the light.
13

Table 3. Acceptable ranges for accelerometers at static tilt position

Sensor Range in g (+ 0.03g) Procedure

Accelerometer X -sin 2 (for 2 = 20o

, value = - North down

Accelerometer Y 0 North down

Accelerometer Z -cos 2 (for 2 = 20o , value = - North down

Accelerometer X +sin 2 (for 2 = 20o

, value = North up

Accelerometer Y 0 North up

Accelerometer Z -cos 2 (for 2 = 20o , value = - North up

Accelerometer X 0 West up

Accelerometer Y -sin 2 (for 2 = 20o

, value = - West up

Accelerometer Z -cos 2 (for 2 = 20o , value = - West up

Accelerometer X 0 West down

Accelerometer Y +sin 2 (for 2 = 20o

, value = West down

Accelerometer Z -cos 2 (for 2 = 20o , value = - West down
14
15

3. Test and Evaluation 

3.1 Scope

Since the Triaxys system is being considered for deployment as an operational system, the focus

of the tests will be:

A. to verify system performance and functionality of subsystems.

B. to demonstrate the suitability of the system to NOS applications.

C. to establish that the data quality satisfies NOS requirements.

3.2 Approaches

3.2.1 General Guidelines

The followings are general guidelines for tests and evaluations:

A. System to be tested and evaluated includes all hardware, software, internal and external

interfaces and documents.

B. System will be inspected/checked after delivery from manufacturer, tested/checked prior to

deployment, and calibrated/tested after 1-2 years of service.

C. Test requirements, plans, and procedures will be evaluated to ensure compatibility between

tests.

D. Determine whether the delivered system meets NOS requirements.

E. Existing well accepted instruments and methods will be used as references for evaluating

the performance of the instrument and its components.

F. Components testing will be kept to a minimum whenever valid test data exist. Duplication

of testing will be kept to minimum (except those for deployment and acceptance).

G. Data to be evaluated consists of those obtained by manufacturers, other users, from

laboratory, field tests, and service records. 

H. It is assumed that the manufacturer has conducted all necessary design tests after burn-in,

prior to delivery. These include functional tests in service configurations, environmental tests

under extreme conditions, reliability tests, maintainability tests, subsystem integration tests.

These tests will not be repeated unless test records are not available or new design

modifications are made. Sample manufacturer’s factory test records (for the NOS Buoy S/N

TAB00311) are shown in Appendix A.

I. Documents will be reviewed by operating personnel and users for accuracy and clarity.

J. Software will be reviewed and tested for accuracy and functionality.
16

3.2.2 Type of Test

Several types of test will be conducted in order to meet the test and evaluation objectives. These

are described below. A description of some of the associated test facilities are given in Section

3.5

 

A. Acceptance Test 

An acceptance test will be performed after receiving of product. It will be done mostly in the

laboratory to verify that the delivered system meets contractual requirements. Recommended

tests include:

a) Sensor range value test under static level and tilt positions (Tables 2 and 3). Fig. 3 shows

the buoy convention for heading, and roll axes used in the range value tests.

b) Visual inspections (S/N of major components, cleanness and scratches, and cracks

around the dome flange area; lifting bridle, magnetic key, and other attachments).

c) Verification and documentation of contractor provided items (S/N and other pertinent

data of hardware, software, user’s manual, spares kit, IR device/harness, antenna cable and

3 db antenna, etc.)

Figure 3. Buoy conventions for heading and roll axes

 
17

B. Subsystem/Module/Component Test

This is to verify that subsystems, modules, components, and interfaces function properly. These

will be conducted when anticipated operational conditions are close to the limits of the specified

range (such as operating temperature), a new design modification or change has been made, the

sensors’ function needs to be validated, or special issues identified in the field tests are to be

investigated. Recommended tests include:

 a) Validation of sensor range values under static level and tilt positions. 

b) Validation of angular rate gyros via pendulum test (Fig. 4).

Sample form is shown in Section 7.4 of Triaxys sensor validation sheets in Appendix B.

c) Calibration of wave height and period measurements using rotating arm facility (or

Rotating/or Swing Calibrator, Fig. 5). 

It is recommended that tests (a) and (b) be conducted whenever there is concern about the

functions of the system. Test (c) should be performed by the manufacturer prior to return from

repair. 

Figure 4. Pendulum test setup

 
18

Figure 5. Rotating arm test (swing calibrator) setup

d) Wave processor (PC104) test – This is to check the processor for accuracy. It is

desirable to check the processor outputs using simulated sensor inputs (compass,

accelerometers and angular rates). The Triaxys Wave Processing Diagnostics Menu allows

user to check the processor using simulated sinusoidal wave amplitudes and periods.

e) Radio base station subsystem test/check. The subsystem includes the Triaxys Digital

Receiver (TDR), antenna, and associated software. If the received signal is affected by RF

interference the antenna should be relocated and/or reconfigured. Typical acceptable

background noise level is around 2 dB and signal strength is around 3 dB. The VHF radio

operating frequency is set at the factory (42.6 MHz for NOS buoy S/N TAB00311). This

value is indicated on the receiver panel. For a minor frequency change, a channel change is

sufficient. When a major frequency shift occurs, a complete realignment of the radio

should be done at the factory.

The manufacturer should be contacted for problems related to other subsystems such as ARGOS

and GPS. 
19

C. System Performance Test

Inter comparison tests using accepted reference instruments provide the ultimate performance

validation. System performance tests will be conducted in event driven pilot projects due to

limitations in budget and staff resources. As shown in Table 3, the planned system performance

tests are:

a) Field tests at Duck, NC - A cooperative effort with NDBC and Army Corps of

Engineers’ Field Research Facility (FRF) will enable us to inter compare with FRF’s

reference wave instruments in high energy coastal area. Ancillary data include wind,

current (low) and temperature.

b) Field deployments in the Chesapeake Bay - This is to support marsh restoration, wave

modeling, hazardous material spill analysis, and to evaluate advanced underwater data

telemetry technology through the NOS Partnership program. Ancillary data include water

level and current measurements. NOS’ tide station and other bay monitoring network (such

as EPA and University of Maryland at Hines Point) in the vicinity provide other

environmental data such as wind, air and water temperature.

c) Other special wave measurement projects - There are a few other PORTS® sites and

coastal navigation waterways where wave information is of importance to mariners. These

include, Los Angles/Long Beach harbor complex, Puget Sound, Chesapeake Bay entrance,

Cape Cod Canal, etc. and are potential test sites when resources are available.

The varied environmental conditions at these sites offer excellent opportunity to fully evaluate

the Triaxys’ performance.

D. Data Quality Assurance Test

The time series data and results of statistical analyses obtained from tests will be studied to

assess the data quality. 

To facilitate data processing and analysis and maintain high quality of data the following tasks

should be performed.

a) Develop automated methods and procedures for real-time data quality check, analysis

(wave energy spectra, zero crossing, and statistics) and data storage. 

b) Analyze failure and faults to identify causes and to develop correction procedures.

c) Perform Inter comparisons with reference instruments and/or wave model hindcasts.

d) Develop methods and formats for data products and dissemination.

E. Operational Test

This is to verify that the delivered system performs its required functions in a wide range of NOS

operational environments and situations when operated and maintained by NOS personnel. To

ensure that system is well prepared for the test, a manufacturer recommended field checkout

procedure (Appendix C) should be followed prior to each deployment. Detailed setup and check

out procedures are also described in Section 8 of the user’s manual [5]. 
20

3.3 System Issues to Be Verified 

The unique PORTS® requirements dictate that certain system performance and design issues be

evaluated. These include:

A. Measurement accuracy

a) Current effect - measurements in strong currents where buoy is in a pulled down

altitude,

b) Frequency response to long waves - a common concern for this type of buoy.

B. Reliability of mechanical components

a) Rubber fender attachment, hull leakage, fouling and corrosion, and elastic mooring cord.

b) Mooring dynamic performance and design variations for different site and environment

(such as requirement of sub-surface floatation in deeper water).

C. Reliability of sensing and electrical components

a) Flash light and sensor assembly.

b) Antenna and other data transmission system components.

D. Power supply

a) Performance of solar power system in wave environment.

b) Efficiency of battery charging 

E. Mooring design and analysis

Since the mooring dynamics will affect the Triaxys buoy response characteristics, a capability of

conducting mooring analysis and modify design to adapt to different deployment site is needed.

F. GPS positioning system

a) Multi-path problem due to low antenna elevation and wave environment.

3.4 Responsibility

CO-OPS personnel will be responsible for preparing and approval test plans, conducting and /or

monitoring tests, reviewing test results, and conducting or supporting operational tests.

3.5 Test Facilities

Facilities that are applicable to the various tests described in above sections include:

A. Environmental chamber test - to test system or component in simulate temperature and

humidity conditions. Available facilities include the NWS’ Sterling laboratory in Sterling,

VA. 

B. Static tests - to validate Triaxys sensor function under static conditions (see Appendix B).

These tests can be easily done with buoy placed on the shipping cradle or similar structure.

C. Pendulum test - to validate sensor function under quasi-dynamic conditions (see Appendix B).

Fig. 4 illustrates a simple setup for this test.
21

D. Rotating arm (or swing calibrator) test - to validate wave measurement accuracy under

simulated sinusoidal wave conditions. Fig. 5 illustrates a conceptual setup configuration.

Various wave amplitudes (maximum value is limited by the available facility), periods (short

to long in order to check the sensitivity and stability of accelerometers and integrators), and

directions (via orientation of the sensor/telemetry box, limited) can be simulated. Such

equipment are available at NDBC, AXYS (amplitude: 2m, periods: 5-25s), and Scripps

Institute of Oceanography (to be constructed, amplitude: 6m).

E. Wave basin test - Laboratory wave basins with appropriate water depth (say, 6m and

above) could be used for testes under controlled wave conditions. These include the U.S.

naval David Taylor Model Basin (DTMB, 110m long x 73 m wide x 6.1 m deep) at

Cardercok, MD, deep water wave basin at Texas A&M University at College Station, and

wave tank (76m long x 10 m wide x 5.4m deep, with 9 m pit) at CBI Industries, Inc.

 

3.6 Schedule

The planed and anticipated events for field testing are shown in Table 4.

Table 4 Planed and anticipated field testing events 

Deployment/Test Site Reference Instruments Environment Partnership

Duck, NC 12/01-3/02 Waverider, pressure

transducer array,

Baylor staff

Depth 8m, mean tide range: 1m

Alongshore currents: <30 cm/s

NDVC,

USACE

Chesapeake Bay

Barren Is. (10/9/02-

1/9/03)

Eastern Neck (1/22-

4/22/03)

Taylor Is. (4/1-8/31)

Bay entrance (?)

ADCP and NDBC

buoy near the Bay

entrance

Depth: 6 – 10m

Mean tide range: 1m

Mean tidal currents: <50 cm/s

NDBC, U.

MD

Puget Sound, WA (?) ADCP Depth: Deep

Mean tide range: to 3m,

Mean tidal currents: 1.5 m/s

TBD

LA/LB Harbor (?) ADCP Depth: 15m

Mean tide range: 1.2 mean tidal

currents: < 50 cm/s

TBD

Cape Cod Canal, MA ADCP Depth: TBD
22
23

4. DOCUMENTATION, REVIEW, AND PLANNING

To achieve the full value of test and evaluation program, the following activities should be

performed.

 

4.1 Test Report

At the conclusion of the tests appropriate documents such as a test report and evaluation sheets

should be completed. Contents should include test results, notes and comments which will be

helpful in identifying problem areas and formulate future solutions.

 

4.2 Review and Planning

Test results will be reviewed by a panel consisting of users (NOS/CO-OPS) and invited advisors

(such as NDBC, Triaxys, USACE/FRF, U. of Penn, U.S. Navy, and other users). Corrective and

preventative actions will be developed by the CO-OPS review panel and recommended to the

manufacturer and field personnel for implementation.
24
25

ACKNOWLEDGMENTS

Several of my colleagues contributed to this work: Kristen Tronvig arranged funds for the

purchase of NOS’ first Triaxys buoy; Mark Bushnell acquired the system, Maureen Kenny,

Kristen Tronvig, Kate Bosley, Mark Bushnell, and Tom Mero reviewed the manuscript; and

Brenda Via and Gina Stoney provided publication support. The writer is also grateful to 

Dr. C. C. Teng of NDBC and William Birkemeier of the Field Research Facility of the Coastal

Engineering Research Center (CERC), U.S. Army Corps of Engineers for useful discussions.

 

REFERENCES

1. Oceans.US Phased Implementation Plan for the US IOOS, Dec. 2002.

2. Baer, L. 1981. Operational needs for wave data, p, 14-27, in Measuring Ocean Waves, Proc.,

 Symposium and Workshop on Wave-Measurement Technology, April 22-24, 1981, 

 Washington, D.C., National Academy Press, 249 pp.

3. NDBC network (web site: www.ndbc.noaa.gov)

4. USACE/SOI network (web site: cdip.ucsd.edu)

5. Louisiana State University, Coastal Studies Institute: Wave-Current –Surge Information

 System (WAVCIS) (web site: wavcis.csi.isu.edu)

6. TriaxysTM Directional Wavy Buoy: User’s Manual, V. 08, November 20001, Axys

 Environmental Systems, Canada, 102 pp.

7. Barstow, S.F., Krogstad, H.E., Torsethsugen, K., and Audunson, T., 1985. “Procedures and

 problems associated with the calibration of wave sensors,” Advances in Underwater

Technology and Offshore Engineering, Vol. 4 London, Graham and Trotman, 267pp. 

(Buoy/mooring ling effects).

8. Skey, S. G. P. and Miles M.D., “Advances in buoy technology for wind/wave data collection

 and analysis.”

9. Teng, C.C., 2001. “A field test of buoy dynamics and measurements,” Proc., Waves2001
26
27

APPENDICES

A. Triaxys Factory Check Sheets

B. Triaxys Sensor Validation Sheets

C. Triaxys Field Checkout/deployment Sheets
28

A. Triaxys factory check sheets
29
30
31

B. Triaxys sensor validation sheets
32
33
34

C. Triaxys field checkout/deployment sheets