TrueWind

calculate True Wind from Apparent Wind

• AWA Apparent Wind Angle (relative to H) environment.wind.angleApparent
• H Heading (relative to true north) navigation.headingTrue
  • AWD Apparent Wind Direction (relative to true north) environment.wind.directionTrue
  • AWD = MOD(H+AWA;360)

• AWS Apparent Wind Speed environment.wind.speedApparent
• COG Course Over Ground navigation.courseOverGroundTrue
• SOG Speed Over Ground navigation.speedOverGround
  • TWS True Wind Speed (relative to ground) environment.wind.speedOverGround
  • TWSx = SOG * Sin (COG) - AWS * Sin (AWD)
  • TWSy = SOG * Cos (COG) - AWS * Cos (AWD)
  • TWS= SQRT (TWSx*TWSx + TWSy*TWSy)
  • TWD True Wind Direction (relative to true north) ???
  • TWD = ATAN ( TWSx / TWSy )
• STW Speed Trough Water navigation.speedThroughWater
  • DFT Current Drift (relative to ground) environment.current.drift
  • DFTx = SOG * Sin (COG) - STW * Sin (H)
  • DFTy = SOG * Cos (COG) - STW * Cos (H)
  • DFT= SQRT (DFTx*DFTx + DFTy*DFTy)
  • SET Current Set (relative to true north) environment.current.setTrue
  • SET = ATAN ( DFTx / DFTy )

simplified, assuming H=COG

• COG Course Over Ground navigation.courseOverGroundTrue
• SOG Speed Over Ground navigation.speedOverGround
• AWA Apparent Wind Angle (relative to H) environment.wind.angleApparent
• AWS Apparent Wind Speed environment.wind.speedApparent
  • AWSx = AWS * Cos (AWA)
  • AWSy = AWS * Sin (AWA)
  • TWA True Wind Angle (relative to H) environment.wind.angleTrueGround
  • ATAN2(AWSy, -SOG + AWSx)
  • TWS True Wind Speed (relative to ground) environment.wind.speedOverGround
  • SQRT (POWER(AWSy,2) POWER(-SOG + AWSx,2))

see also

• http://davidburchnavigation.blogspot.com/2013/04/true-true-wind-from-apparent-wind.html
• https://coaps.fsu.edu/woce/truewind/paper/index.html