Struct Ussa76

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pub struct Ussa76 { /* private fields */ }

Expand description

The U.S. Standard Atmosphere, 1976, optionally offset in temperature and sea-level pressure.

It serializes as its two parameters, temperature_offset_k and sea_level_pressure_pa, and re-checks them when deserialized.

Implementations§

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impl Ussa76

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pub fn standard() -> Self

The standard itself: no offset and P₀ = 101325 Pa.

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pub fn with_offset( temperature_offset_k: f64, sea_level_pressure_pa: f64, ) -> Result<Self, AtmosError>

The standard with its molecular-scale temperature offset by temperature_offset_k at every geopotential height, and hydrostatic pressure from sea_level_pressure_pa at H = 0.

§Errors

AtmosError::Domain if the offset is not finite or would make the temperature anywhere in the model zero or negative (it must exceed −186.9 K), or if the sea-level pressure is not finite and positive.

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pub fn anchored( height_msl_m: f64, temperature_k: f64, pressure_pa: f64, ) -> Result<Self, AtmosError>

The offset standard that passes through a measured kinetic temperature_k and pressure_pa at geometric height_msl_m: ΔT makes the temperature match there, and P₀ scales the pressure profile to match. Launch-site conditions are the usual use.

The offset holds all the way up, which a real hot or cold day does not: anchoring +20 K at a 1400 m field (at the standard’s field pressure) makes the air 5.7% thinner at 3 km but 14% denser at 20 km and 30% denser at 30 km than the standard (validation/oracles/atmosphere/conventions.py). For flights far above the field, prefer a sounding.

§Errors

AtmosError::Domain if the height is not finite or not above −r₀, the temperature or pressure is not finite and positive, or the implied offset or sea-level pressure is out of range (see Ussa76::with_offset).

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pub fn temperature_offset_k(&self) -> f64

The temperature offset ΔT, K.

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pub fn sea_level_pressure_pa(&self) -> f64

The pressure at H = 0, Pa.

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pub fn sample(&self, height_msl_m: f64) -> Result<AirSample, AtmosError>

The air at geometric height height_msl_m (see Atmosphere::air).

§Errors

AtmosError::Domain if the height is not finite or not above −r₀.

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pub fn pressure_altitude_m(&self, pressure_pa: f64) -> Result<f64, AtmosError>

The geopotential altitude H (m′) at which this atmosphere’s pressure is pressure_pa: its pressure altitude. Of the standard itself, this is what a barometric altimeter reads.

It inverts eqs. 33a and 33b in the layer whose base pressures bracket P:

H = H_b + (T_M,b / L_M,b) [(P / P_b)^(−R* L_M,b / (g₀′ M₀)) − 1]      L_M,b ≠ 0
H = H_b − (R* T_M,b / (g₀′ M₀)) ln(P / P_b)                         L_M,b = 0

Above sea-level pressure it extends the lowest layer, and below the 86 km top’s it continues isothermally, as Ussa76::sample does. In the troposphere of the standard it is the altimeter formula H = 44330.8 m [1 − (P / 101325 Pa)^0.190263].