applications of aircraft weather data sensor development and characteristics. ralph petersen, univ....

Applications of Aircraft Weather Data

SENSOR DEVELOPMENT AND CHARACTERISTICS.

Ralph Petersen, Univ. of Wisconsin-Madison

American Meteorological Society Short CourseSan Antonio, Texas January 14, 2007

Randy Baker – UPS AirlinesRalph Petersen – University of Wisconsin-Madison, CIMSSStan Benjamin, Bill Moninger – NOAA ESRLDave Helms, Kevin Johnston, Rich Mamrosh – NOAA NWS

• In the mid-1980s, Stan Benjamin and I had the opportunity to participate in the FAA’s Aviation Weather Forecasting Task Force led by John McCarthy.

• At that time, flight level wind and temperature forecast errors were costing airlines major losses. e.g., Trans-oceanic flights were often forced to make unscheduled refueling stops in route, requiring overnight

lodging for passengers and equipment rescheduling

A Brief Historical Perspective

• Airlines offered to help.– Several airlines were

already downlinking automated temperature and wind data for their own internal use

• At this time, most major airlines had in-house meteorological staffs – and used the aircraft wind/temperature data to update their own systems flight plans

– Resulted in financial advantage to airlines collecting data– Airlines were reluctant to share data with airlines that didn’t

invest in down-linking costs.– Relied upon existing digital air-to-ground communincations

Aircraft Data Collection has been a Joint Industry/Government effort

• Airlines offered to help.– Basic AMDAR Data

(Flight Level (Pressure),

Temperature and Wind)

are, for the most part,

copies of observations taken for other purposes – Commercial aircraft need accurate temperature and wind

observations to operate most efficiently while in flight• Pressure to determine altitude• Jet Engine performance is related to the temperature difference

between the engine and the atmosphere• Flight efficiency depends on minimizing head winds

Aircraft Data Collection has been a Joint Industry/Government effort

The benefits of AMDAR data are global and large for forecasts out to 48 hour.

Results from ECMWF data denial experiments show benefits at all levels, but most

in regions where observations are made.

Impact of AMDAR Temp / Wind data

depends on number of reports

Impact of local detail present in

AMDAR Temp / Wind reports is greatest in

shorter range forecasts –

Satellite data dominates longer ranges ( >48 hrs)

The benefits of AMDAR data are global and large for forecasts out to 48 hour.

The benefits of AMDAR data are global and large for forecasts out to 48 hour.

Profiles from aircraft ascent/descent improve forecasts further over US

THE Reference for AMDAR data

“On-board” Data Processing

Cost of aircraft-to-ground data transmission shared by government and airlines- About 1¢ per report- Data available in real time to research community and government

- Airlines consider real-time data to be proprietary for others

Observations possible using “Standard” Aircraft Instrumentation

Available Aircraft Data Systems

Deriving Meteorological Variables from Aircraft Data Systems

Observation Accuracies• The observations are dependent upon each other

– Pressure is measured by an electronic barometer connected to static pressure ports in the “pitot-static”’ probe

• Note: All measurement devices mounted on fast jet aircraft must be small to reduce drag and minimize associated fuel costs

Observation Accuracies• The observations are dependent upon each other

– Pressure is converted to Flight Levels using the ICAO Standard Atmosphere for down-linking as part of the meteorological report

• Pressure-altitude conversions can produce errors of 2-4 hPa

Note: Lower Flight Levels are obtained from a radio-altimeter and are reported in geometric units

Observation Accuracies

• The observations are dependent upon each other

– Temperature observations are made via small tubes protruding from the front sides of the aircraft

Observation Accuracies

• The observations are dependent upon each other

– Temperature observations are made via small tubes protruding from the front sides of the aircraft

• At high air speeds, the force of the air entering the tubes can increase the pressure in the tube, and therefore bias temperatures through “dynamic” (compressional) heating

– Corrections for this dynamic heating are made on-board

Observation Accuracies

• Observation accuracy can vary from one aircraft type to another and depend on locations of instrumentation on the aircraft– “Determine optimal instrument location is still an art form”

Sample of temperature differences between co-located radiosonde and UPS 757 reports

Observation Accuracies• The observations are dependent upon each other

– Indicated air speed is determined using pressure sensors pointing along the direction of the aircraft and sometimes located at various locations on the aircraft

• Temperature can affect the pressure/speed relationships

Observation Accuracies

• The observations are dependent upon each other

– Pressure is measured by an electronic barometer connected to static pressure ports in the “pitot-static”’ probe

– Temperature observations are made via small tubes protruding from the front sides of the aircraft

• At high air speeds, the force of the air entering the tubes can increase the pressure in the tube, and therefore bias temperatures

– Corrections for this dynamic heating are made on-board

– Indicated air speed is determined using pressure sensors pointing along the direction of the aircraft and sometimes located at various locations on the aircraft

• Temperature can affect the pressure/speed relationships

– Moisture can also affect the latter two types of observations

Observation Accuracies – Converting Air Speed to Wind Speed -

• Indicated air speed is determined using pressure sensors pointing along the direction of the aircraft and located at various locations on the aircraft

• Temperature can affect the pressure/speed relationships

– Larger impacts during maneuvers (direction changes – actually changes in aircraft ‘yaw’)

• Airplanes normally don’t ‘point’ in the direction they are headed– Usually are ‘pointed’ slightly in the direction of any cross-wind– As long as ‘wind-relative’ direction of airplane doesn’t change,

pressure on sensors remains constant– However, as an aircraft changes directions relative to the wind (or the

wind changed direction very rapidly), the pressure of the air hitting the sensors changes – producing unreliable results

– Data taken during maneuvers are flagged before transmission» Roll angle is used as an indicate that maneuvers may be occurring

A review of aircraft orientation terminology

Effect of Aircraft Maneuvers on Wind Calculations

– Data taken during maneuvers are flagged before transmission

• Indicated Air Speed must be converted to Wind Speed and Direction (Vector) – assuming no cross-winds– Done by combining Indicated Air Speed with motion of the

aircraft (Ground Speed and Direction). – Ground Speed (actually a vector) accuracy depends on the

accuracy of aircraft navigation systems.– Ground Speed calculated from difference in aircraft locations over

short time intervals– In late 1960’s, inertial navigation systems (complex gyroscopic

instruments) were developed to determine precise earth locations without the need for a ‘navigator’ on the aircraft.

– Later, these systems were replaced by simpler (less costly and lighter) LORAN and GPS systems

– Accuracy of Ground Speed calculation depends on:» Accuracy of navigation systems and» Precision of navigation system and Indicated Air Speed outputs

– Wind Report made in terms of Speed and Direction» Precision of output Speed and Direction affects final Wind Vector

Observation Accuracies – Converting Air Speed to Wind Speed -

Observation Accuracies – Temperature and Wind Speed -

More discussions of observed data quality

will follow Comparison of AMDAR and GPS radiosonde winds

AMDAR Data Reporting Precision and Desired Accuracy – Primary Observations

Many: ±0.7ºInst. Precision

100’ = 30mTemp error

Truncated <±0.3ºNearest <±0.15º

AMDAR Data Reporting Precision and Desired Accuracy – Additional Observations

Measuring Moisture

• Efforts underway for over a decade– Research instruments not appropriate for “day-to-

day”, “real world” application– Initial experiments were made using a “stand-

alone” Temperature/Relative Humidity sensor called the Water Vapor Sensing System (WVSS-I)

• Used humidity sensors “similar” to those used on radiosondes

– Test results showed:» Substantial Biases and RMS values that exceeded WMO

specification» Systems became contaminated by everyday airport

“gunk”, e.g. deicer, dirt on runways, etc.

Measuring Moisture

• Efforts underway for over a decade– Second-generation Water Vapor Sensing System

(WVSS-II) measures Mixing Ratio directly• Uses a laser-diode system to measure number of water

molecules passing sensor• Testing on UPS 757s

– Initial tests in Spring 2005– Second version tested last fall

Measuring Moisture

• Efforts underway for over a decade– Second-generation Water Vapor Sensing System

(WVSS-II) measures Mixing Ratio directly• Uses a laser-diode system to measure number of water

molecules passing sensor• Testing on UPS 757s

– Initial tests in Spring 2005– Second version tested last fall

• Initial results for ascent data

from both tests agree– Some descent reports still questionable

Other Measurements• Turbulence

– “Eddy Dissipation Rate” derived from high-resolution air speed and vertical accelerometer taken from flight data recorder (“black box”) data feed

• Binned into approximately 10 data divisions• Available primarily from a select number of UAL aircraft for

research purposes only

• Icing– “Ice indicator” indicates presence of ice, not the process of

icing– Icing detectors under development

Other Data Sources - TAMDAR• Efforts underway for nearly a decade

– Objective – To fill in data between major airports using commuter airlines

• A private venture – Built upon concept supported – by FAA and NASA

• Originally intended for slower-flying aircraft• Does not need airlines to subscribe (pay for) ARINC digital

communications services• Consists of:

– Self contained observing system» Temp, Wind, Pressure, Icing, Turbulence, …

– Satellite-based air-to-ground communications» Requires new comms systems

• All data are proprietary

Other Data Sources - TAMDAR

Improvements in NWP over past 10 yearsAMDAR data have made a difference

SAA pilot said recently thatflight times from

South Africa to Australiaare now typically within

1 minute of predictions

1996 2006

Other observations made from Aircraft can be interesting too!!

©Ralph Petersen 2006