Verified and improved the airodynamic resistance code now with a minimum

	pSD->checkUnit("s/m");

	cropHeight_ = pSD->existingPath("/plants/canopyHeight", "cm");

	if (!cropHeight_) msg::warning("AerodynamicResistance: /plants/canopyHeight not found. Assuming 0.5 m");

	cropHeight_->checkUnit("cm");

	windSpeed_ 		 = pSD->existingPath("/environment/atmosphere/windSpeed"); //, "m/s"

	windSpeed_->checkUnit("m/s");

}

std::string AerodynamicResistance::getName() const {

	/// exchange of vapor at the surface when air is calm. This effect occurs when the wind speed is small and

	/// buoyancy of warm air induces air exchange at the surface. Limiting u2 >= 0.5 m/s in the ETo equation improves

	/// the estimation accuracy under the conditions of very low wind speed.

	double windSpeed; // Windspeed at measurement height, which we assume to be 2 meters.

	double windSpeed(2); // Windspeed at measurement height, which we assume to be 2 meters.

	if (windSpeed_) {

		/// --- Wind speed ---  /// --- Weibull distributed ---

		windSpeed_->get(t, windSpeed); ///< U2 being the wind speed at 2-m height in m/s

		// The aerodynamic resistance equation for open air estimations reduces to r_a = 208./U2;

		// An alternative, semi-empirical, equation of ra (Thom and Oliver, 1977)

		// is used for greenhouse conditions (Stanghellini equation), characterized by low wind speed (<1 m s-1)

		// There is always a little bit of wind or convection

		if (windSpeed < 0.5) windSpeed = 0.5;

	} else {

		windSpeed = 2.;

		msg::warning("AerodynamicResistance: No wind speed is set by user. Assuming a wind speed of 2 m/s.");

	}

	// There is always a little bit of wind or convection

	if (windSpeed < 0.5) windSpeed = 0.5;

	// Allen, Richard G., et al. "Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56." Fao, Rome 300.9 (1998): D05109.

	// See also http://www.fao.org/3/X0490E/x0490e06.htm

	double vonKarmanConstant = 0.41;

	const double vonKarmanConstant = 0.41;

	double measurementHeight = 2;

	double zeroPlaneDisplacementHeight = 50;

	double cropHeight = 0.50; //m

	if (cropHeight_) {

		cropHeight_->get(t, zeroPlaneDisplacementHeight);

		if(zeroPlaneDisplacementHeight<1)zeroPlaneDisplacementHeight=1;

		cropHeight_->get(t, cropHeight);

		cropHeight/=100; //cm to m

		if(cropHeight<0.1)cropHeight=0.1; //asume crop height is at least 10 cm, given that the soil will be uneven.

	}

	zeroPlaneDisplacementHeight = zeroPlaneDisplacementHeight/100.; // Convert from cm to m

	double roughnessLengthMomentumTransfer = 0.123*zeroPlaneDisplacementHeight;

	double roughnessLengthHeatAndVapour = 0.1*0.123*zeroPlaneDisplacementHeight;

	zeroPlaneDisplacementHeight *= 2./3.;

	measurementHeight=std::max(measurementHeight,cropHeight+1);// make sure the measurement height is at least 1 m above the crop.

	const double zeroPlaneDisplacementHeight = 2./3. * cropHeight; // Convert from cm to m

	const double roughnessLengthMomentumTransfer = 0.123*cropHeight;

	const double roughnessLengthHeatAndVapour = 0.1*0.123*cropHeight;

	r_a = log((measurementHeight - zeroPlaneDisplacementHeight)/roughnessLengthMomentumTransfer)*log((measurementHeight - zeroPlaneDisplacementHeight)/roughnessLengthHeatAndVapour)/(vonKarmanConstant*vonKarmanConstant*windSpeed);

	if (std::isnan(r_a)) msg::error("AerodynamicResistance: NaN value");

	if (std::isinf(r_a)) msg::error("AerodynamicResistance: inf value");

	if (r_a <= 0) msg::error("AerodynamicResistance: Aerodynamic resistance smaller than or equal to 0. Check if crop height is less than 2, if not, adjust measurement height in the code.");

}