Detailed Description

Models the 1976 U.S.

Standard Atmosphere, with the ability to modify the temperature and pressure. A base feature of the model is the temperature profile that is stored as an FGTable object with this data:

GeoMet Alt    Temp      GeoPot Alt  GeoMet Alt
   (ft)      (deg R)      (km)        (km)
 ---------  --------    ----------  ----------
       0.0    518.67 //    0.000       0.000
   36151.6    390.0  //   11.000      11.019
   65823.5    390.0  //   20.000      20.063
  105518.4    411.6  //   32.000      32.162
  155347.8    487.2  //   47.000      47.350
  168677.8    487.2  //   51.000      51.413
  235570.9    386.4  //   71.000      71.802
  282152.2    336.5; //   84.852      86.000

The pressure is calculated at lower altitudes through the use of two equations that are presented in the U.S. Standard Atmosphere document (see references). Density, kinematic viscosity, speed of sound, etc., are all calculated based on various constants and temperature and pressure. At higher altitudes (above 86 km (282152 ft) a different and more complicated method of calculating pressure is used.

The temperature may be modified through the use of several methods. Ultimately, these access methods allow the user to modify the sea level standard temperature, and/or the sea level standard pressure, so that the entire profile will be consistently and accurately calculated.

Properties

atmosphere/delta-T
atmosphere/T-sl-dev-F

Author: Jon Berndt

See also: "U.S. Standard Atmosphere, 1976", NASA TM-X-74335

Definition at line 98 of file FGStandardAtmosphere.h.

#include <FGStandardAtmosphere.h>

Inheritance diagram for FGStandardAtmosphere:

Collaboration diagram for FGStandardAtmosphere:

Public Member Functions
	FGStandardAtmosphere (FGFDMExec *)
	Constructor.

virtual	~FGStandardAtmosphere ()
	Destructor.

bool	InitModel (void) override

Temperature access functions.
There are several ways to get the temperature, and several modeled temperature values that can be retrieved. The U.S. Standard Atmosphere temperature either at a specified altitude, or at sea level can be retrieved. These two temperatures do NOT include the effects of any bias or delta gradient that may have been supplied by the user. The modeled temperature and the modeled temperature at sea level can also be retrieved. These two temperatures DO include the effects of an optionally user-supplied bias or delta gradient.
double	GetTemperature (double altitude) const override
	Returns the actual modeled temperature in degrees Rankine at a specified altitude. More...

virtual double	GetStdTemperature (double altitude) const
	Returns the standard temperature in degrees Rankine at a specified altitude. More...

virtual double	GetStdTemperatureSL () const
	Returns the standard sea level temperature in degrees Rankine. More...

virtual double	GetStdTemperatureRatio (double h) const
	Returns the ratio of the standard temperature at the supplied altitude over the standard sea level temperature.

virtual double	GetTemperatureBias (eTemperature to) const
	Returns the temperature bias over the sea level value in degrees Rankine.

virtual double	GetTemperatureDeltaGradient (eTemperature to)
	Returns the temperature gradient to be applied on top of the standard temperature gradient.

void	SetTemperatureSL (double t, eTemperature unit=eFahrenheit) override
	Sets the Sea Level temperature, if it is to be different than the standard. More...

void	SetTemperature (double t, double h, eTemperature unit=eFahrenheit) override
	Sets the temperature at the supplied altitude, if it is to be different than the standard temperature. More...

virtual void	SetTemperatureBias (eTemperature unit, double t)
	Sets the temperature bias to be added to the standard temperature at all altitudes. More...

virtual void	SetSLTemperatureGradedDelta (eTemperature unit, double t)
	Sets a Sea Level temperature delta that is ramped out by 86 km. More...

virtual void	SetTemperatureGradedDelta (double t, double h, eTemperature unit=eFahrenheit)
	Sets the temperature delta value at the supplied altitude/elevation above sea level, to be added to the standard temperature and ramped out by 86 km. More...

virtual void	ResetSLTemperature ()
	This function resets the model to apply no bias or delta gradient to the temperature. More...

Pressure access functions.
double	GetPressure (double altitude) const override
	Returns the pressure at a specified altitude in psf.

virtual double	GetStdPressure (double altitude) const
	Returns the standard pressure at the specified altitude.

void	SetPressureSL (ePressure unit, double pressure) override
	Sets the sea level pressure for modeling an off-standard pressure profile. More...

virtual void	ResetSLPressure ()
	Resets the sea level to the Standard sea level pressure, and recalculates dependent parameters so that the pressure calculations are standard.

Density access functions.
virtual double	GetStdDensity (double altitude) const
	Returns the standard density at a specified altitude.

Public Member Functions inherited from FGAtmosphere
	FGAtmosphere (FGFDMExec *)
	Constructor.

virtual	~FGAtmosphere ()
	Destructor.

bool	Run (bool Holding) override
	Runs the atmosphere forces model; called by the Executive. More...

virtual double	GetTemperature () const
	Returns the actual, modeled temperature at the current altitude in degrees Rankine. More...

virtual double	GetTemperatureSL () const
	Returns the actual, modeled sea level temperature in degrees Rankine. More...

virtual double	GetTemperatureRatio () const
	Returns the ratio of the at-current-altitude temperature as modeled over the sea level value.

virtual double	GetTemperatureRatio (double h) const
	Returns the ratio of the temperature as modeled at the supplied altitude over the sea level value.

virtual double	GetPressure (void) const
	Returns the pressure in psf.

virtual double	GetPressureSL (ePressure to=ePSF) const

virtual double	GetPressureRatio (void) const
	Returns the ratio of at-altitude pressure over the sea level value.

virtual double	GetDensity (void) const
	Returns the density in slugs/ft^3. More...

virtual double	GetDensity (double altitude) const
	Returns the density in slugs/ft^3 at a given altitude in ft.

virtual double	GetDensitySL (void) const
	Returns the sea level density in slugs/ft^3.

virtual double	GetDensityRatio (void) const
	Returns the ratio of at-altitude density over the sea level value.

virtual double	GetSoundSpeed (void) const
	Returns the speed of sound in ft/sec.

virtual double	GetSoundSpeed (double altitude) const
	Returns the speed of sound in ft/sec at a given altitude in ft.

virtual double	GetSoundSpeedSL (void) const
	Returns the sea level speed of sound in ft/sec.

virtual double	GetSoundSpeedRatio (void) const
	Returns the ratio of at-altitude sound speed over the sea level value.

virtual double	GetAbsoluteViscosity (void) const
	Returns the absolute viscosity.

virtual double	GetKinematicViscosity (void) const
	Returns the kinematic viscosity.

virtual double	GetDensityAltitude () const

virtual double	GetPressureAltitude () const

Public Member Functions inherited from FGModel
	FGModel (FGFDMExec *)
	Constructor.

	~FGModel () override
	Destructor.

virtual SGPath	FindFullPathName (const SGPath &path) const

FGFDMExec *	GetExec (void)

const std::string &	GetName (void)

unsigned int	GetRate (void)
	Get the output rate for the model in frames.

virtual bool	Load (Element *el)

void	SetPropertyManager (FGPropertyManager *fgpm)

void	SetRate (unsigned int tt)
	Set the ouput rate for the model in frames.

Public Member Functions inherited from FGModelFunctions
std::string	GetFunctionStrings (const std::string &delimeter) const
	Gets the strings for the current set of functions. More...

std::string	GetFunctionValues (const std::string &delimeter) const
	Gets the function values. More...

FGFunction *	GetPreFunction (const std::string &name)
	Get one of the "pre" function. More...

bool	Load (Element el, FGFDMExec fdmex, std::string prefix="")

void	PostLoad (Element el, FGFDMExec fdmex, std::string prefix="")

void	PreLoad (Element el, FGFDMExec fdmex, std::string prefix="")

void	RunPostFunctions (void)

void	RunPreFunctions (void)

Public Member Functions inherited from FGJSBBase
	FGJSBBase ()
	Constructor for FGJSBBase.

virtual	~FGJSBBase ()
	Destructor for FGJSBBase.

void	PutMessage (const Message &msg)
	Places a Message structure on the Message queue. More...

void	PutMessage (const std::string &text)
	Creates a message with the given text and places it on the queue. More...

void	PutMessage (const std::string &text, bool bVal)
	Creates a message with the given text and boolean value and places it on the queue. More...

void	PutMessage (const std::string &text, int iVal)
	Creates a message with the given text and integer value and places it on the queue. More...

void	PutMessage (const std::string &text, double dVal)
	Creates a message with the given text and double value and places it on the queue. More...

int	SomeMessages (void) const
	Reads the message on the queue (but does not delete it). More...

void	ProcessMessage (void)
	Reads the message on the queue and removes it from the queue. More...

Message *	ProcessNextMessage (void)
	Reads the next message on the queue and removes it from the queue. More...

void	disableHighLighting (void)
	Disables highlighting in the console output.

Humidity access functions
double	StdSLtemperature
	Standard sea level conditions.

double	StdSLdensity

double	StdSLpressure

double	StdSLsoundspeed

double	TemperatureBias

double	TemperatureDeltaGradient

double	GradientFadeoutAltitude

double	VaporMassFraction

double	SaturatedVaporPressure

FGTable	StdAtmosTemperatureTable

FGTable	MaxVaporMassFraction

std::vector< double >	LapseRates

std::vector< double >	PressureBreakpoints

std::vector< double >	StdPressureBreakpoints

std::vector< double >	StdDensityBreakpoints

std::vector< double >	StdLapseRates

static constexpr double	EarthRadius = 6356766.0 / fttom
	Earth radius in ft as defined for ISA 1976.

static constexpr double	a = 611.2/psftopa
	Sonntag constants based on ref [2]. More...

static constexpr double	b = 17.62

static constexpr double	c = 243.12

static constexpr double	Mwater = 18.016 * kgtoslug / 1000.0
	Mean molecular weight for water - slug/mol.

static constexpr double	Rdry = Rstar / Mair

static constexpr double	Rwater = Rstar / Mwater

void	SetDewPoint (eTemperature unit, double dewpoint)
	Sets the dew point. More...

double	GetDewPoint (eTemperature to) const
	Returns the dew point. More...

void	SetVaporPressure (ePressure unit, double Pv)
	Sets the partial pressure of water vapor. More...

double	GetVaporPressure (ePressure to) const
	Returns the partial pressure of water vapor. More...

double	GetSaturatedVaporPressure (ePressure to) const
	Returns the saturated pressure of water vapor. More...

void	SetRelativeHumidity (double RH)
	Sets the relative humidity. More...

double	GetRelativeHumidity (void) const
	Returns the relative humidity in percent.

void	SetVaporMassFractionPPM (double frac)
	Sets the vapor mass per million of dry air mass units. More...

double	GetVaporMassFractionPPM (void) const
	Returns the vapor mass per million of dry air mass units (ppm).

virtual void	PrintStandardAtmosphereTable ()
	Prints the U.S. Standard Atmosphere table.

void	Calculate (double altitude) override
	Calculate the atmosphere for the given altitude.

void	CalculateLapseRates ()
	Recalculate the lapse rate vectors when the temperature profile is altered in a way that would change the lapse rates, such as when a gradient is applied. More...

void	CalculatePressureBreakpoints (double SLpress)
	Calculate (or recalculate) the atmospheric pressure breakpoints at the altitudes in the standard temperature table.

void	CalculateStdDensityBreakpoints ()
	Calculate the atmospheric density breakpoints at the altitudes in the standard temperature table.

double	GeopotentialAltitude (double geometalt) const
	Convert a geometric altitude to a geopotential altitude.

double	GeometricAltitude (double geopotalt) const
	Convert a geopotential altitude to a geometric altitude.

double	CalculateDensityAltitude (double density, double geometricAlt) override
	Calculates the density altitude given any temperature or pressure bias. More...

double	CalculatePressureAltitude (double pressure, double geometricAlt) override
	Calculates the pressure altitude given any temperature or pressure bias. More...

double	CalculateVaporPressure (double temperature)
	Calculate the pressure of water vapor with the Magnus formula.

void	ValidateVaporMassFraction (double geometricAlt)
	Validate the value of the vapor mass fraction.

void	CalculateSLDensity (void)
	Calculate the SL density.

void	CalculateSLSoundSpeedAndDensity (void)
	Calculate the SL density and sound speed.

void	bind (void) override

void	Debug (int from) override

Additional Inherited Members
Public Types inherited from FGAtmosphere
enum	ePressure { eNoPressUnit =0, ePSF, eMillibars, ePascals, eInchesHg }
	Enums for specifying pressure units.

enum	eTemperature { eNoTempUnit =0, eFahrenheit, eCelsius, eRankine, eKelvin }
	Enums for specifying temperature units.

Public Types inherited from FGJSBBase
enum	{ eL = 1, eM, eN }
	Moments L, M, N.

enum	{ eP = 1, eQ, eR }
	Rates P, Q, R.

enum	{ eU = 1, eV, eW }
	Velocities U, V, W.

enum	{ eX = 1, eY, eZ }
	Positions X, Y, Z.

enum	{ ePhi = 1, eTht, ePsi }
	Euler angles Phi, Theta, Psi.

enum	{ eDrag = 1, eSide, eLift }
	Stability axis forces, Drag, Side force, Lift.

enum	{ eRoll = 1, ePitch, eYaw }
	Local frame orientation Roll, Pitch, Yaw.

enum	{ eNorth = 1, eEast, eDown }
	Local frame position North, East, Down.

enum	{ eLat = 1, eLong, eRad }
	Locations Radius, Latitude, Longitude.

enum	{ inNone = 0, inDegrees, inRadians, inMeters, inFeet }
	Conversion specifiers.

Static Public Member Functions inherited from FGJSBBase
static const std::string &	GetVersion (void)
	Returns the version number of JSBSim. More...

static constexpr double	KelvinToFahrenheit (double kelvin)
	Converts from degrees Kelvin to degrees Fahrenheit. More...

static constexpr double	CelsiusToRankine (double celsius)
	Converts from degrees Celsius to degrees Rankine. More...

static constexpr double	RankineToCelsius (double rankine)
	Converts from degrees Rankine to degrees Celsius. More...

static constexpr double	KelvinToRankine (double kelvin)
	Converts from degrees Kelvin to degrees Rankine. More...

static constexpr double	RankineToKelvin (double rankine)
	Converts from degrees Rankine to degrees Kelvin. More...

static constexpr double	FahrenheitToCelsius (double fahrenheit)
	Converts from degrees Fahrenheit to degrees Celsius. More...

static constexpr double	CelsiusToFahrenheit (double celsius)
	Converts from degrees Celsius to degrees Fahrenheit. More...

static constexpr double	CelsiusToKelvin (double celsius)
	Converts from degrees Celsius to degrees Kelvin. More...

static constexpr double	KelvinToCelsius (double kelvin)
	Converts from degrees Kelvin to degrees Celsius. More...

static constexpr double	FeetToMeters (double measure)
	Converts from feet to meters. More...

static double	PitotTotalPressure (double mach, double p)
	Compute the total pressure in front of the Pitot tube. More...

static double	MachFromImpactPressure (double qc, double p)
	Compute the Mach number from the differential pressure (qc) and the static pressure. More...

static double	VcalibratedFromMach (double mach, double p)
	Calculate the calibrated airspeed from the Mach number. More...

static double	MachFromVcalibrated (double vcas, double p)
	Calculate the Mach number from the calibrated airspeed.Based on the formulas in the US Air Force Aircraft Performance Flight Testing Manual (AFFTC-TIH-99-01). More...

static bool	EqualToRoundoff (double a, double b)
	Finite precision comparison. More...

static bool	EqualToRoundoff (float a, float b)
	Finite precision comparison. More...

static bool	EqualToRoundoff (float a, double b)
	Finite precision comparison. More...

static bool	EqualToRoundoff (double a, float b)
	Finite precision comparison. More...

static constexpr double	Constrain (double min, double value, double max)
	Constrain a value between a minimum and a maximum value.

static constexpr double	sign (double num)

static double	GaussianRandomNumber (void)

Public Attributes inherited from FGAtmosphere
struct JSBSim::FGAtmosphere::Inputs	in

Static Public Attributes inherited from FGAtmosphere
static constexpr double	StdDaySLtemperature = 518.67

static constexpr double	StdDaySLpressure = 2116.228

static const double	StdDaySLsoundspeed = sqrt(SHRatioRengStdDaySLtemperature)

Static Public Attributes inherited from FGJSBBase
static char	highint [5] = {27, '[', '1', 'm', '\0' }
	highlights text

static char	halfint [5] = {27, '[', '2', 'm', '\0' }
	low intensity text

static char	normint [6] = {27, '[', '2', '2', 'm', '\0' }
	normal intensity text

static char	reset [5] = {27, '[', '0', 'm', '\0' }
	resets text properties

static char	underon [5] = {27, '[', '4', 'm', '\0' }
	underlines text

static char	underoff [6] = {27, '[', '2', '4', 'm', '\0' }
	underline off

static char	fgblue [6] = {27, '[', '3', '4', 'm', '\0' }
	blue text

static char	fgcyan [6] = {27, '[', '3', '6', 'm', '\0' }
	cyan text

static char	fgred [6] = {27, '[', '3', '1', 'm', '\0' }
	red text

static char	fggreen [6] = {27, '[', '3', '2', 'm', '\0' }
	green text

static char	fgdef [6] = {27, '[', '3', '9', 'm', '\0' }
	default text

static short	debug_lvl = 1

Protected Member Functions inherited from FGAtmosphere
double	ConvertToRankine (double t, eTemperature unit) const
	Converts to Rankine from one of several unit systems.

double	ConvertFromRankine (double t, eTemperature unit) const
	Converts from Rankine to one of several unit systems.

double	ConvertToPSF (double t, ePressure unit=ePSF) const
	Converts to PSF (pounds per square foot) from one of several unit systems.

double	ConvertFromPSF (double t, ePressure unit=ePSF) const
	Converts from PSF (pounds per square foot) to one of several unit systems.

Protected Member Functions inherited from FGModel
bool	Upload (Element *el, bool preLoad)
	Uploads this model in memory. More...

Static Protected Member Functions inherited from FGJSBBase
static std::string	CreateIndexedPropertyName (const std::string &Property, int index)

Protected Attributes inherited from FGAtmosphere
double	SLtemperature

double	SLdensity

double	SLpressure

double	SLsoundspeed

double	Temperature

double	Density

double	Pressure

double	Soundspeed

double	PressureAltitude

double	DensityAltitude

double	Viscosity

double	KinematicViscosity

Protected Attributes inherited from FGModel
unsigned int	exe_ctr

FGFDMExec *	FDMExec

std::string	Name

FGPropertyManager *	PropertyManager

unsigned int	rate

Protected Attributes inherited from FGModelFunctions
FGPropertyReader	LocalProperties

std::vector< FGFunction * >	PostFunctions

std::vector< FGFunction * >	PreFunctions

Static Protected Attributes inherited from FGAtmosphere
static constexpr double	SutherlandConstant = 198.72

static constexpr double	Beta = 2.269690E-08

static constexpr double	Rstar = 8.31432 * kgtoslug / KelvinToRankine(fttom * fttom)
	Universal gas constant - ft*lbf/R/mol.

static constexpr double	Mair = 28.9645 * kgtoslug / 1000.0
	Mean molecular weight for air - slug/mol.

static constexpr double	g0 = 9.80665 / fttom
	Sea-level acceleration of gravity - ft/s^2. More...

static double	Reng = Rstar / Mair
	Specific gas constant for air - ft*lbf/slug/R.

static constexpr double	SHRatio = 1.4

Static Protected Attributes inherited from FGJSBBase
static Message	localMsg

static std::queue< Message >	Messages

static unsigned int	messageId = 0

static constexpr double	radtodeg = 180. / M_PI

static constexpr double	degtorad = M_PI / 180.

static constexpr double	hptoftlbssec = 550.0

static constexpr double	psftoinhg = 0.014138

static constexpr double	psftopa = 47.88

static constexpr double	ktstofps = 1.68781

static constexpr double	fpstokts = 1.0 / ktstofps

static constexpr double	inchtoft = 1.0/12.0

static constexpr double	fttom = 0.3048

static constexpr double	m3toft3 = 1.0/(fttomfttomfttom)

static constexpr double	in3tom3 = inchtoftinchtoftinchtoft/m3toft3

static constexpr double	inhgtopa = 3386.38

static constexpr double	slugtolb = 32.174049
	Note that definition of lbtoslug by the inverse of slugtolb and not to a different constant you can also get from some tables will make lbtoslug*slugtolb == 1 up to the magnitude of roundoff. More...

static constexpr double	lbtoslug = 1.0/slugtolb

static constexpr double	kgtolb = 2.20462

static constexpr double	kgtoslug = 0.06852168

static const std::string	needed_cfg_version = "2.0"

static const std::string	JSBSim_version = JSBSIM_VERSION " " __DATE__ " " __TIME__

static int	gaussian_random_number_phase = 0

Member Function Documentation

◆ CalculateDensityAltitude()

double CalculateDensityAltitude	(	double	density,
		double	geometricAlt
	)

overrideprotectedvirtual

Calculates the density altitude given any temperature or pressure bias.

Calculated density for the specified geometric altitude given any temperature or pressure biases is passed in.

Parameters

density
geometricAlt

See also: https://en.wikipedia.org/wiki/Density_altitude https://wahiduddin.net/calc/density_altitude.htm

Reimplemented from FGAtmosphere.

Definition at line 494 of file FGStandardAtmosphere.cpp.

 {
   // Work out which layer we're dealing with
   unsigned int b = 0;
   for (; b < StdDensityBreakpoints.size() - 2; b++) {
     if (density >= StdDensityBreakpoints[b + 1])
       break;
   }
  
   // Get layer properties
   double Tmb = StdAtmosTemperatureTable(b + 1, 1);
   double Hb = StdAtmosTemperatureTable(b + 1, 0);
   double Lmb = StdLapseRates[b];
   double pb = StdDensityBreakpoints[b];
  
   double density_altitude = 0.0;
  
   // https://en.wikipedia.org/wiki/Barometric_formula for density solved for H
   if (Lmb != 0.0) {
     double Exp = -1.0 / (1.0 + g0/(Rdry*Lmb));
     density_altitude = Hb + (Tmb / Lmb) * (pow(density / pb, Exp) - 1);
   } else {
     double Factor = -Rdry*Tmb / g0;
     density_altitude = Hb + Factor * log(density / pb);
   }
  
   return GeometricAltitude(density_altitude);
 }

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◆ CalculateLapseRates()

void CalculateLapseRates ( )

protected

Recalculate the lapse rate vectors when the temperature profile is altered in a way that would change the lapse rates, such as when a gradient is applied.

This function is also called to initialize the lapse rate vector.

Definition at line 422 of file FGStandardAtmosphere.cpp.

 {
   unsigned int numRows = StdAtmosTemperatureTable.GetNumRows();
   LapseRates.clear();
  
   for (unsigned int bh=0; bh < numRows-1; bh++)
   {
     double t0 = StdAtmosTemperatureTable(bh+1,1);
     double t1 = StdAtmosTemperatureTable(bh+2,1);
     double h0 = StdAtmosTemperatureTable(bh+1,0);
     double h1 = StdAtmosTemperatureTable(bh+2,0);
     LapseRates.push_back((t1 - t0) / (h1 - h0) - TemperatureDeltaGradient);
   }
 }

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◆ CalculatePressureAltitude()

double CalculatePressureAltitude	(	double	pressure,
		double	geometricAlt
	)

overrideprotectedvirtual

Calculates the pressure altitude given any temperature or pressure bias.

Calculated density for the specified geometric altitude given any temperature or pressure biases is passed in.

Parameters

pressure
geometricAlt

See also: https://en.wikipedia.org/wiki/Pressure_altitude

Reimplemented from FGAtmosphere.

Definition at line 525 of file FGStandardAtmosphere.cpp.

 {
   // Work out which layer we're dealing with
   unsigned int b = 0;
   for (; b < StdPressureBreakpoints.size() - 2; b++) {
     if (pressure >= StdPressureBreakpoints[b + 1])
       break;
   }
  
   // Get layer properties
   double Tmb = StdAtmosTemperatureTable(b + 1, 1);
   double Hb = StdAtmosTemperatureTable(b + 1, 0);
   double Lmb = StdLapseRates[b];
   double Pb = StdPressureBreakpoints[b];
  
   double pressure_altitude = 0.0;
  
   if (Lmb != 0.00) {
     // Equation 33(a) from ISA document solved for H
     double Exp = -Rdry*Lmb / g0;
     pressure_altitude = Hb + (Tmb / Lmb) * (pow(pressure / Pb, Exp) - 1);
   } else {
     // Equation 33(b) from ISA document solved for H
     double Factor = -Rdry*Tmb / g0;
     pressure_altitude = Hb + Factor * log(pressure / Pb);
   }
  
   return GeometricAltitude(pressure_altitude);
 }

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◆ GetDewPoint()

double GetDewPoint ( eTemperature to ) const

Returns the dew point.

Parameters

to	The unit of measure that the dew point should be supplied in.

Definition at line 595 of file FGStandardAtmosphere.cpp.

 {
   double dewpoint_degC;
   double VaporPressure = Pressure*VaporMassFraction / (VaporMassFraction+Rdry/Rwater);
  
   if (VaporPressure <= 0.0)
     dewpoint_degC = -c;
   else {
     double x = log(VaporPressure/a);
     dewpoint_degC = c*x / (b - x);
   }
  
   return ConvertFromRankine(1.8*(dewpoint_degC + 273.15), to);
 }

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◆ GetSaturatedVaporPressure()

double GetSaturatedVaporPressure ( ePressure to ) const

Returns the saturated pressure of water vapor.

Parameters

to	The unit of measure that the water vapor should be supplied in.

Definition at line 630 of file FGStandardAtmosphere.cpp.

 {
   return ConvertFromPSF(SaturatedVaporPressure, to);
 }

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◆ GetStdTemperature()

double GetStdTemperature ( double altitude ) const

virtual

Returns the standard temperature in degrees Rankine at a specified altitude.

Parameters

altitude The altitude in feet above sea level (ASL) to get the temperature at.

Returns: The STANDARD temperature in degrees Rankine at the specified altitude.

Definition at line 273 of file FGStandardAtmosphere.cpp.

 {
   double GeoPotAlt = GeopotentialAltitude(altitude);
  
   if (GeoPotAlt >= 0.0)
     return StdAtmosTemperatureTable.GetValue(GeoPotAlt);
   else
     return StdAtmosTemperatureTable.GetValue(0.0) + GeoPotAlt*LapseRates[0];
 }

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◆ GetStdTemperatureSL()

virtual double GetStdTemperatureSL ( ) const

inlinevirtual

Returns the standard sea level temperature in degrees Rankine.

Returns: The STANDARD temperature at sea level in degrees Rankine.

Definition at line 135 of file FGStandardAtmosphere.h.

135 { return StdSLtemperature; }

◆ GetTemperature()

double GetTemperature ( double altitude ) const

overridevirtual

Returns the actual modeled temperature in degrees Rankine at a specified altitude.

Parameters

altitude The altitude above sea level (ASL) in feet.

Returns: Modeled temperature in degrees Rankine at the specified altitude.

Implements FGAtmosphere.

Definition at line 244 of file FGStandardAtmosphere.cpp.

 {
   double GeoPotAlt = GeopotentialAltitude(altitude);
  
   double T;
  
   if (GeoPotAlt >= 0.0) {
     T = StdAtmosTemperatureTable.GetValue(GeoPotAlt);
  
     if (GeoPotAlt <= GradientFadeoutAltitude)
       T -= TemperatureDeltaGradient * GeoPotAlt;
   }
   else {
     // We don't need to add TemperatureDeltaGradient*GeoPotAlt here because
     // the lapse rate vector already accounts for the temperature gradient.
     T = StdAtmosTemperatureTable.GetValue(0.0) + GeoPotAlt*LapseRates[0];
   }
  
   T += TemperatureBias;
  
   if (GeoPotAlt <= GradientFadeoutAltitude)
     T += TemperatureDeltaGradient * GradientFadeoutAltitude;
  
   return T;
 }

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◆ GetVaporPressure()

double GetVaporPressure ( ePressure to ) const

Returns the partial pressure of water vapor.

Parameters

to	The unit of measure that the water vapor should be supplied in.

Definition at line 622 of file FGStandardAtmosphere.cpp.

 {
   double VaporPressure = Pressure*VaporMassFraction / (VaporMassFraction+Rdry/Rwater);
   return ConvertFromPSF(VaporPressure, to);
 }

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◆ ResetSLTemperature()

void ResetSLTemperature ( )

virtual

This function resets the model to apply no bias or delta gradient to the temperature.

The delta gradient and bias values are reset to 0.0, and the standard temperature is used for the entire temperature profile at all altitudes.

Definition at line 464 of file FGStandardAtmosphere.cpp.

 {
   TemperatureBias = TemperatureDeltaGradient = 0.0;
   CalculateLapseRates();
   CalculatePressureBreakpoints(SLpressure);
  
   SLtemperature = StdSLtemperature;
   CalculateSLSoundSpeedAndDensity();
 }

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◆ SetDewPoint()

void SetDewPoint	(	eTemperature	unit,
		double	dewpoint
	)

Sets the dew point.

Parameters

dewpoint	The dew point in the units specified
unit	The unit of measure that the specified dew point is supplied in.

Definition at line 585 of file FGStandardAtmosphere.cpp.

 {
   double altitude = CalculatePressureAltitude(Pressure, 0.0);
   double VaporPressure = CalculateVaporPressure(ConvertToRankine(dewpoint, unit));
   VaporMassFraction = Rdry * VaporPressure / (Rwater * (Pressure - VaporPressure));
   ValidateVaporMassFraction(altitude);
 }

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◆ SetPressureSL()

void SetPressureSL	(	ePressure	unit,
		double	pressure
	)

overridevirtual

Sets the sea level pressure for modeling an off-standard pressure profile.

This could be useful in the case where the pressure at an airfield is known or set for a particular simulation run.

Parameters

pressure	The pressure in the units specified.
unit	the unit of measure that the specified pressure is supplied in.

Reimplemented from FGAtmosphere.

Definition at line 225 of file FGStandardAtmosphere.cpp.

 {
   SLpressure = ConvertToPSF(pressure, unit);
   CalculateSLDensity();
   CalculatePressureBreakpoints(SLpressure);
 }

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◆ SetRelativeHumidity()

void SetRelativeHumidity ( double RH )

Sets the relative humidity.

Parameters

RH	The relative humidity in percent.

Definition at line 645 of file FGStandardAtmosphere.cpp.

 {
   double altitude = CalculatePressureAltitude(Pressure, 0.0);
   double VaporPressure = 0.01*RH*SaturatedVaporPressure;
   VaporMassFraction = Rdry * VaporPressure / (Rwater * (Pressure - VaporPressure));
   ValidateVaporMassFraction(altitude);
 }

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◆ SetSLTemperatureGradedDelta()

void SetSLTemperatureGradedDelta	(	eTemperature	unit,
		double	t
	)

virtual

Sets a Sea Level temperature delta that is ramped out by 86 km.

The value of the delta is used to calculate a delta gradient that is applied to the temperature at all altitudes below 86 km (282152 ft). For instance, if a temperature of 20 degrees F is supplied, the delta gradient would be 20/282152 - or, about 7.09E-5 degrees/ft. At sea level, the full 20 degrees would be added to the standard temperature, but that 20 degree delta would be reduced by 7.09E-5 degrees for every foot of altitude above sea level, so that by 86 km, there would be no further delta added to the standard temperature. The graded delta can be used along with the a bias to tailor the temperature profile as desired.

Parameters

t	the sea level temperature delta value in the unit provided.
unit	the unit of the temperature.

Definition at line 371 of file FGStandardAtmosphere.cpp.

 {
   SetTemperatureGradedDelta(deltemp, 0.0, unit);
 }

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◆ SetTemperature()

void SetTemperature	(	double	t,
		double	h,
		eTemperature	unit = `eFahrenheit`
	)

overridevirtual

Sets the temperature at the supplied altitude, if it is to be different than the standard temperature.

This function will calculate a bias - a difference - from the standard atmosphere temperature at the supplied altitude and will apply that calculated bias to the entire temperature profile. If a graded delta is present, that will be included in the calculation - that is, regardless of any graded delta present, a temperature bias will be determined so that the temperature requested in this function call will be reached.

Parameters

t	The temperature value in the unit provided.
h	The altitude in feet above sea level.
unit	The unit of the temperature.

Implements FGAtmosphere.

Definition at line 327 of file FGStandardAtmosphere.cpp.

 {
   double targetTemp = ConvertToRankine(t, unit);
   double GeoPotAlt = GeopotentialAltitude(h);
  
   TemperatureBias = targetTemp - GetStdTemperature(h);
  
   if (GeoPotAlt <= GradientFadeoutAltitude)
     TemperatureBias -= TemperatureDeltaGradient * (GradientFadeoutAltitude - GeoPotAlt);
  
   CalculatePressureBreakpoints(SLpressure);
  
   SLtemperature = GetTemperature(0.0);
   CalculateSLSoundSpeedAndDensity();
 }

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◆ SetTemperatureBias()

void SetTemperatureBias	(	eTemperature	unit,
		double	t
	)

virtual

Sets the temperature bias to be added to the standard temperature at all altitudes.

This function sets the bias - the difference - from the standard atmosphere temperature. This bias applies to the entire temperature profile. Another way to set the temperature bias is to use the SetSLTemperature function, which replaces the value calculated by this function with a calculated bias.

Parameters

t	the temperature value in the unit provided.
unit	the unit of the temperature.

Definition at line 345 of file FGStandardAtmosphere.cpp.

 {
   if (unit == eCelsius || unit == eKelvin)
     t *= 1.80; // If temp delta "t" is given in metric, scale up to English
  
   TemperatureBias = t;
   CalculatePressureBreakpoints(SLpressure);
  
   SLtemperature = GetTemperature(0.0);
   CalculateSLSoundSpeedAndDensity();
 }

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◆ SetTemperatureGradedDelta()

void SetTemperatureGradedDelta	(	double	t,
		double	h,
		eTemperature	unit = `eFahrenheit`
	)

virtual

Sets the temperature delta value at the supplied altitude/elevation above sea level, to be added to the standard temperature and ramped out by 86 km.

This function computes the sea level delta from the standard atmosphere temperature at sea level.

Parameters

t	the temperature skew value in the unit provided.
unit	the unit of the temperature.

Definition at line 383 of file FGStandardAtmosphere.cpp.

 {
   if (unit == eCelsius || unit == eKelvin)
     deltemp *= 1.80; // If temp delta "t" is given in metric, scale up to English
  
   TemperatureDeltaGradient = deltemp/(GradientFadeoutAltitude - GeopotentialAltitude(h));
   CalculateLapseRates();
   CalculatePressureBreakpoints(SLpressure);
  
   SLtemperature = GetTemperature(0.0);
   CalculateSLSoundSpeedAndDensity();
 }

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◆ SetTemperatureSL()

void SetTemperatureSL	(	double	t,
		eTemperature	unit = `eFahrenheit`
	)

overridevirtual

Sets the Sea Level temperature, if it is to be different than the standard.

This function will calculate a bias - a difference - from the standard atmosphere temperature and will apply that bias to the entire temperature profile. This is one way to set the temperature bias. Using the SetTemperatureBias function will replace the value calculated by this function.

Parameters

t	the temperature value in the unit provided.
unit	the unit of the temperature.

Reimplemented from FGAtmosphere.

Definition at line 363 of file FGStandardAtmosphere.cpp.

 {
   SetTemperature(t, 0.0, unit);
 }

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◆ SetVaporMassFractionPPM()

void SetVaporMassFractionPPM ( double frac )

Sets the vapor mass per million of dry air mass units.

Parameters

frac	The fraction of water in ppm of dry air.

Definition at line 662 of file FGStandardAtmosphere.cpp.

 {
   double altitude = CalculatePressureAltitude(Pressure, 0.0);
   VaporMassFraction = frac*1E-6;
   ValidateVaporMassFraction(altitude);
 }

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◆ SetVaporPressure()

void SetVaporPressure	(	ePressure	unit,
		double	Pv
	)

Sets the partial pressure of water vapor.

Parameters

Pv	The vapor pressure in the units specified
unit	The unit of measure that the specified vapor pressure is supplied in.

Definition at line 612 of file FGStandardAtmosphere.cpp.

 {
   double altitude = CalculatePressureAltitude(Pressure, 0.0);
   double VaporPressure = ConvertToPSF(Pa, unit);
   VaporMassFraction = Rdry * VaporPressure / (Rwater * (Pressure - VaporPressure));
   ValidateVaporMassFraction(altitude);
 }

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Member Data Documentation

◆ a

constexpr double a = 611.2/psftopa

staticconstexprprotected

Sonntag constants based on ref [2].

They are valid for temperatures between -45 degC (-49 degF) and 60 degC (140 degF) with a precision of +/-0.35 degC (+/-0.63 degF)

Definition at line 365 of file FGStandardAtmosphere.h.

The documentation for this class was generated from the following files:

Detailed Description

Properties

Public Member Functions

Humidity access functions

Additional Inherited Members

Member Function Documentation

◆ CalculateDensityAltitude()

◆ CalculateLapseRates()

◆ CalculatePressureAltitude()

◆ GetDewPoint()

◆ GetSaturatedVaporPressure()

◆ GetStdTemperature()

◆ GetStdTemperatureSL()

◆ GetTemperature()

◆ GetVaporPressure()

◆ ResetSLTemperature()

◆ SetDewPoint()

◆ SetPressureSL()

◆ SetRelativeHumidity()

◆ SetSLTemperatureGradedDelta()

◆ SetTemperature()

◆ SetTemperatureBias()

◆ SetTemperatureGradedDelta()

◆ SetTemperatureSL()

◆ SetVaporMassFractionPPM()

◆ SetVaporPressure()

Member Data Documentation

◆ a