Add referenceHumidity and observedHumidity parameters to altitudeFromPressureDifference

[Copilot]

Description

Enhances altitudeFromPressureDifference to accept separate humidity values at reference and observed altitudes. Since humidity varies with altitude, using distinct values for each level and averaging their virtual temperatures provides more accurate altitude calculations than a single uniform humidity.

Type of Change

• New formula/feature (non-breaking change that adds functionality)

Related Issue

Addresses the question: "Could altitudeFromPressureDifference be improved even more having a referenceHumidity and a observedHumidity?"

Changes Made

• Added referenceHumidity and observedHumidity optional parameters to altitudeFromPressureDifference
• When both provided, calculates virtual temperature at each level using its respective pressure and humidity, then averages them
• Maintains backward compatibility: existing relativeHumidity parameter still works unchanged
• Priority order: separate humidities > single humidity > dry air

// Existing usage (unchanged)
const altitude = altitudeFromPressureDifference(101325, 89874, 0, 288.15, 60);

// New: separate humidity at each level (80% at reference, 40% at observed)
const altitude = altitudeFromPressureDifference(101325, 89874, 0, 288.15, undefined, 80, 40);

Formula Details (if applicable)

Formula Name

Hypsometric equation with humidity-varying virtual temperature

Scientific Source

• Source: Virtual Temperature approach for moist air density
• Link: https://en.wikipedia.org/wiki/Virtual_temperature

Input Parameters

• referencePressure: Pressure at reference altitude (Pa)
• observedPressure: Pressure at observed altitude (Pa)
• referenceAltitude: Known altitude (m), default 0
• temperature: Average temperature (K), default 288.15
• relativeHumidity: Single humidity for both levels (%), optional
• referenceHumidity: Humidity at reference altitude (%), optional
• observedHumidity: Humidity at observed altitude (%), optional

Output

• Altitude in meters (m)

Validation

• Tested against known reference values
• Compared to scientific literature

Testing

Test Coverage

• Added tests for new functionality
• All tests pass locally (npm test)
• Build succeeds (npm run build)

Test Results

Test Suites: 15 passed, 15 total
Tests:       229 passed, 229 total

Manual Testing

Added 8 new tests covering: separate humidity values, equal humidity matching single-humidity behavior, fallback to dry air when only one humidity provided, priority over single humidity, and extreme humidity differences.

Documentation

• Added/updated JSDoc comments
• Added usage examples (if applicable)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have used the correct units (Kelvin for temperature, SI units for others)
• I have verified backward compatibility (or documented breaking changes)

Breaking Changes

• This PR introduces breaking changes

Performance Impact

• No performance impact

Dependencies

• No new dependencies

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Reviewer Notes

• Key files to review: src/formulas/altitude.ts, tests/formulas/altitude.test.ts
• Areas needing special attention: Virtual temperature averaging approach for the layer

Original prompt

Could altitudeFromPressureDifference be improved even more having a referenceHumidity and a observedHumidity?

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