Calibration of aircraft instruments using a laser sensor

1. A method for correcting an ambient pressure measurement outside an aircraft, comprising the steps of:

receiving an airspeed measurement v from a laser sensor;

receiving an ambient pressure measurement from a first sensor, the first sensor being an absolute transducer in fluid communication with a static port;

calculating an ambient pressure correction p c or the first sensor using the airspeed measurement v from the laser sensor and the ambient pressure measurement p m from the absolute transducer, where the ambient pressure correction

p

c

=

q

m

-

p

m

⁢

χ

1

+

χ

,

where

χ

⁡

(

v

,

T

)

=

(

v

2

2

⁢

c

p

⁢

T

-

1

)

c

v

/

R

α

-

1

,

q m is a dynamic pressure measurement, T is a temperature, c v is a respective specific heat of air at constant volume, and R a is a gas constant for air; and

calculating a corrected ambient pressure using the ambient pressure measurement p m and the ambient pressure correction p c , wherein the ambient pressure correction p c corrects for a flow angle with respect to the static port.

2. The method of claim 1 , wherein the ambient pressure measurement is determined using a transducer.

3. The method of claim 1 , further comprising the steps of:

receiving a plurality of airspeed measurements corresponding to a plurality of total pressure measurements;

calculating a plurality of ambient pressure corrections p c using the plurality of airspeed measurements and the plurality of total pressure measurements p c ; and

generating a numerical fit to the plurality of ambient pressure corrections p c .

4. The method of claim 3 , further comprising the step of:

calculating an interpolated ambient pressure correction using the numerical fit.

5. The method of claim 1 , further comprising the step of:

correcting the airspeed measurement v from the laser sensor to determine a longitudinal airspeed measurement corrected for a side-slip angle.

6. The method of claim 1 , further comprising the step of:

receiving an independent airspeed measurement; calculating a corrected dynamic pressure using the corrected ambient pressure and a total pressure measurement; and

calculating a corrected airspeed using the corrected ambient pressure, the corrected dynamic pressure, and the independent airspeed measurement.

7. The method of claim 1 , further comprising the steps of:

calculating a first corrected ambient pressure using the ambient pressure measurement and the ambient pressure correction p c at a first altitude;

calculating a second corrected ambient pressure using the ambient pressure measurement and the ambient pressure correction p c at a second altitude;

receiving a height between the first altitude and the second altitude; and

calculating a calculated temperature using the first corrected ambient pressure, the second ambient corrected pressure, and the height between the first altitude and the second altitude.

8. The method of claim 1 , further comprising the steps of:

receiving a plurality of sensor temperatures, each respective sensor temperature of the plurality of sensor temperatures corresponding to a respective measured altitude of a plurality of measured altitudes;

receiving a plurality of total pressure measurements from the aircraft instrument, each total pressure measurement of the plurality of total pressure measurements corresponding to a respective measured altitude of the plurality of measured altitudes;

calculating a plurality of corrected ambient pressures corresponding to the plurality of total pressure measurements and the plurality of corresponding ambient pressure corrections p c at each of the plurality of measured altitudes; calculating a mean temperature using the plurality of corrected ambient pressures and the plurality of measured altitudes; and

validating a temperature sensor using the mean temperature.

9. The method of claim 1 , further comprising the steps of:

calculating a time series of corrected ambient pressure values, each corrected ambient pressure value of the time series of corrected ambient pressure values corresponding to a measured altitude of a plurality of measured altitudes;

calculating a time series of calculated altitudes using the time series of corrected ambient pressure values;

generating a numerical fit to the time series of corrected ambient pressure values by minimizing the difference between the plurality of measured altitudes and the time series of calculated altitudes;

calculating a calculated temperature using the numerical fit;

receiving a sensor temperature; and

comparing the calculated temperature to the sensor temperature to validate a temperature sensor.

10. The method of claim 9 , wherein each corrected ambient pressure of the time series of corrected ambient pressure values is calibrated for a horizontal pressure gradient.

11. A method for calculating a calculated temperature outside an aircraft, comprising the steps of:

receiving an airspeed measurement v from a laser sensor;

receiving an ambient pressure measurement p m from a first sensor, the first sensor being an absolute transducer in fluid communication with a static port;

calculating an ambient pressure correction p c for the first sensor using the airspeed measurement v from the laser sensor and the ambient pressure measurement p m from the absolute transducer, where the ambient pressure correction

p

c

=

q

m

-

p

m

⁢

χ

1

+

χ

,

where

⁢

⁢

χ

⁡

(

v

,

T

)

=

(

v

2

2

⁢

c

p

⁢

T

-

1

)

c

v

/

R

α

-

1

,

q m is a dynamic pressure measurement, T is a temperature, c v is a respective specific heat of air at constant volume, and R a is a gas constant for air;

calculating a corrected ambient pressure using the ambient pressure measurement p m and the ambient pressure correction p c , wherein the ambient pressure correction p c corrects for a flow angle with respect to the static port;

receiving a total pressure measurement; and

calculating the calculated temperature using the corrected ambient pressure, the total pressure measurement, and the airspeed measurement v from the laser sensor.

12. The method of claim 11 , further comprising the step of:

correcting the airspeed measurement v from the laser sensor to determine a longitudinal airspeed measurement corrected for a side-slip angle.

13. The method of claim 11 , further comprising the steps of:

receiving a sensor temperature; and

comparing the calculated temperature to the sensor temperature to validate a temperature sensor.

14. The method of claim 11 , further comprising the step of:

providing the calculated temperature when a sensor temperature is not available.

15. An apparatus for calculating a calculated temperature in flight, comprising:

a laser sensor configured to provide an airspeed measurement v;

a first aircraft instrument configured to provide an ambient pressure measurement p m , the first aircraft instrument being an absolute transducer in fluid communication with a static port; and

a processing system usable to calculate an ambient pressure correction p c for the first sensor using the airspeed measurement v from the laser sensor and the ambient pressure measurement p m from the absolute transducer, where the ambient pressure correction

p

c

=

q

m

-

p

m

⁢

⁢

χ

1

+

χ

,

where

⁢

⁢

χ

⁡

(

v

,

T

)

=

(

v

2

2

⁢

⁢

c

p

⁢

T

-

1

)

c

v

/

R

α

⁢

-

1

,

q m is a dynamic pressure measurement, T is a temperature, c v is a respective specific heat of air at constant volume, and R a is a gas constant for air; and calculate a corrected ambient pressure using the ambient pressure measurement p m and the ambient pressure correction p c , wherein the ambient pressure correction p c corrects for a flow angle with respect to the static port.

16. The apparatus of claim 15 , further comprising:

a temperature sensor, wherein the processing system is usable to verify a sensor temperature by comparing the calculated temperature to the measured temperature.

17. The apparatus of claim 16 , wherein the processing system is further able to provide the calculated temperature when the sensor temperature is not available.

18. The apparatus of claim 15 , wherein the laser sensor further includes an optical window in thermal contact with a heater.