SYSTEM GLOSSARY
System Sensors
PARAMETER SENSOR TYPE RANGE AND ACCURACY
Wave Data

Not Installed

Not Applicable

Water Current Data

Not Installed

Not Applicable

Air Temperature

FG-SEN-P-300

Range -40°C to +60°C Accuracy ±0.1°C

Relative Humidity

FG-SEN-P-300

Range 0% to 100% Accuracy ±1% to 2%

Barometric Pressure

FG-SEN-P-300

Range 500hPa to 1100hPa Accuracy ±0.2hPa

Wind Speed Sensor

Gill IS Wind Sensor

Range 0 - 60 m/S

Wind Direction Sensor

Gill IS Wind Sensor

Range 0 - 359 deg

Cloud Height

FG-SEN-C-31

Range 0 to 25000ft Accuracy ±1%

Horizontal Visibility / Present Weather

FG-SEN-VPW-22-UH

Range 10 to 20000m
Accuracy: ±10% to 10Km     ±15% to 20Km

Vessel Motion

FG-SEN-HRP-10

Heave Range -10m to +10m Accuracy 5cm or 5%
Pitch/Roll Range -90° to +90° Accuracy 0.1°
GPS

AIRMAR

TBA

Gyro

Existing Equipment

Not Applicable

Helideck Monitoring Software

FG-WM-XP-SU/XML

Not Applicable

Date of Last Service
All above sensors meet the relevant requirements of CAP437 and the Relevant Norwegian Standard

Glossary

Wind

All wind parameters are calculated from a 2-minute sample (unless otherwise specified). Speeds are measured in knots and directions are measured in degrees from true north.

 

Wind Speed: (Mean wind Speed) The average wind Speed over the averaging period.
Wind Gust: (Maximum gust Speed) The highest 3-second wind Speed at any time during the averaging period.
Wind Direction:  (Mean wind direction) The average wind direction over the averaging period.

 

Atmospheric Temperature

All temperatures are calculated from a 1-minute sample and are measured in Celsius.

 

Dry Air Temp: (Dry air temperature) This is the temperature measured by a normal thermometer.
Wet Air Temp:  (Wet air temperature) This is the temperature measured by a normal thermometer whose bulb is covered by a wet wick. The difference between wet and dry temperatures is due to evaporation which lowers the temperature reading and is largely dependent upon humidity. The wet air temperature should always be less than or equal to the dry air temperature.
Dew Point: The temperature at which cloud will form in the current atmospheric conditions. Mist or fog is more likely to form when dew point is near the dry air temperature. Dew point should always be less than or equal to wet air temperature.
Humidity:  (Relative Humidity) This is a measure of air saturation. As relative humidity approaches 100%, the air becomes fully saturated and water vapour condenses out as cloud, mist or fog.

 

Atmospheric BP

All pressures are calculated from a 1-minute sample and are measured in millibars. Barometric pressure is the pressure at the sensor and is corrected to provide pressures at sea level and helideck.

 

QNH: (Air pressure at mean water level) The relationship between QNH and barometric pressure as illustrated in Figure 2.
QFE: (Air pressure at the helideck). The relationship between QFE and barometric pressure is illustrated in Figure 2.

 


Figure 2 : Relationship between measured pressure, QNH and QFE

The equation used to convert the pressure measured at sensor height, Z, to QNH is Kempe’s formula.

Equation :


This equation can also be used to convert from sensor height to QFE.
 

 

Cloud and Visibility

All cloud and visibility parameters are calculated from a 10-minute sample. Cloud is measured in feet and visibility in metres.

 

Cloud Base 1:  The height of the lowest cloud layer above long term mean water level, measured in feet.
Cloud Base 2: . The height of the bottom of the second distinct cloud layer above long term mean water level, measured in feet.
Visibility:  The horizontal distance at which the light intensity from a standard source would drop to 5%. This is calculated by measuring the amount of infra-red scatter in a small volume of air at the sensor location and assuming this sample has similar properties to the surrounding air mass. Contaminants in the air will lower the inferred visibility.

 

 

Waves

All wave parameters are calculated from a 34-minute sample. Constants are measured in metres and periods in seconds.

 

Sig Wave_Radar: (Significant wave height) This is 4 times the standard deviation of the sea surface over  the averaging period and is approximately equal to the average of the 1/3 highest waves.
Max Wave_Radar: (Maximum wave height) This is the largest individual wave within the averaging period. It is defined as the greatest vertical distance between a wave crest and its succeeding trough.
Crest Ht: (Maximum crest height) This is the highest wave crest above the mean water level over the averaging period. Since waves are rarely exactly symmetrical about the mean water level this is not necessarily associated with the largest wave.
Mean Period: (Mean zero-crossing period) This is the average wave period. 

 

 

Water Levels

All water levels are calculated from a 30-minute sample. Constants are measured in metres.

 

Tide Level: The mean height of the sea surface over the averaging period with respect to the long term mean water level.
Extreme Level: The highest individual sea surface height over the averaging period with respect to the long term mean water level.
Air Gap: The smallest distance between the bottom deck and the sea surface over the averaging period. It is related to Extreme Level as illustrated in Figure 1.

 


Figure 1 : Relationship between air gap and extreme level