Standard Atmosphere Lapse Rate Model mechanism

Model scope

The forward ISA concept is standard, but the specification needs review before implementation because altitude convention, supported range, complete layer table, boundary behavior, and the promised inverse calculation are unspecified. The honest label correctly states that this is an idealized standard atmosphere and not a real-time atmospheric model.

• The stated T=T0-L·h formula is valid only within a single constant-lapse-rate layer; the implementation must select the correct ICAO/ISO 2533 layer and use that layer's base temperature and pressure.
• The barometric formula is underspecified: for a nonzero lapse-rate layer it is p=p_b·(T/T_b)^(g0/(R·L)), while for an isothermal layer it is p=p_b·exp[-g0(h-h_b)/(R·T_b)].
• Density must be explicitly computed as rho=p/(R·T); it is not determined by the lapse-rate equation alone.
• The spec mentions inversion from pressure/temperature but provides no inversion algorithm, layer-selection rule, or handling of multiple possible inputs.
• The standard atmosphere table is valid over defined altitude ranges; the supported range and behavior outside the ICAO/ISO 2533 layers are not specified.

Units and conventions

• Test inputs use geopotential altitude in metres unless explicitly stated otherwise; ICAO Standard Atmosphere layer altitudes are geopotential altitudes.
• Temperature is in kelvin, pressure in pascals, density in kilograms per cubic metre, gravitational acceleration in metres per second squared, and the specific gas constant for dry air in joules per kilogram-kelvin.
• The dry-air gas constant is R=287.05287 J/(kg·K), and g0=9.80665 m/s².
• Displayed expected values are rounded; production output should document numerical precision and tolerances.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "altitude_m": 0
  },
  "expected_outputs": {
    "temperature_K": 288.15,
    "pressure_Pa": 101325,
    "density_kg_m3": 1.225
  },
  "reference_data": {
    "source_convention": "ICAO Standard Atmosphere 1976 / ISO 2533:1975; widely tabulated standard value",
    "sea_level": {
      "geopotential_altitude_m": 0,
      "temperature_K": 288.15,
      "pressure_Pa": 101325,
      "density_kg_m3": 1.225
    },
    "g0_m_s2": 9.80665,
    "R_dry_air_J_kgK": 287.05287
  },
  "working": "At h=0 m, use the exact sea-level standard row directly: T=288.15 K; p=101325 Pa. Then rho=p/(R·T)=101325/(287.05287·288.15)=101325/82713.5≈1.225 kg/m³. This is the zero-altitude boundary case and the widely memorized ISA sea-level entry."
}

Failure boundary

• Altitude units are ambiguous in the instrument spec; treating feet as metres would produce materially incorrect results.
• Geometric altitude versus geopotential altitude is not specified. ISA/ICAO layer boundaries conventionally use geopotential altitude.
• Division by zero or invalid results can occur if temperature is zero or nonpositive, especially in an inversion or out-of-range input.
• A zero lapse rate causes division by zero in the power-law barometric formula; the isothermal exponential branch is required.
• Negative altitude, altitude above the supported table range, and exact layer-boundary selection are unspecified.
• Real atmospheric pressure, temperature, and density vary with weather, latitude, season, and composition; the existing idealized-atmosphere honest label is necessary and appropriate.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche7/tranche7-results.json