The following subject areas are covered: microburst detection, location and measurement; thermal alerter for microbursts prototypes (TAMP); sensor-transmitters (Senstrans) design; TAMP installation; and DAPAD software

Eccles, Peter J.

English

NASA Technical Reports Server

Background
Microbursts + other factors
crash aircraft taking off or landing
close runways
cause delays
force alternative airport landings.
• Microburst detection, location and measurement
-- will enhance airport usage and safety.
Microbursts,streams of rapidlymoving,downwardlydirectedair, are a principalcause of wind shear
hazards. The air withina microburstcools rapidlydue to water dropevaporationand meltinghall, both of
which maintain negative buoyancyin the air and propelit to the ground. Microburstsare always associated
with cloudsand principallywith severe convective storms,though microbursts have been observed beneath
virga-likeprecipitation. Microburstsare typicallyellipticalin shape and initiaterelativelyhigh inthe
atmosphere where heavily water-laden air can have diameters of ten km or more. The negatively-buoyantly
maintained rapiddownward acceleration of this water-laden air causes a microburst to become narroweras
it approaches the groundso that it may have a diameter of less than a k_lometernear the ground. When
the air in a microburststrikes the ground,itscootsout horizontallyina divergingpattern from a central point
(or nadir).
Due to the stronglydivergent air, a moving aircraft first experiencesa headwind,which increases lift, rapidly
followed by a tailwincl,which reduces liftby reducingthe relative speed of the aircraft. A significantloss of
altitudecan occur which, depending onthe altitudeof the aircraft,can cause a crash.
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https://ntrs.nasa.gov/search.jsp?R=19910014866 2020-03-19T18:17:11+00:00Z
LONG TERM IMPACT
- HIGH CONFIDENCE OF DETECTING, LOCATING ALL MICROBURSTS
- ECONOMIC OBJECTIVE: AFFORDABLE LOW COST
- WORLDWIDE CONSCIOUSNESS OF MITRE'S COMMITTMENT
TO AIRPORT SAFETY
- POTENTIAL SPONSORS
- GOVERNMENT AGENCIES RESPONSIBLE FOR AIRPORT SAFETY
-FAA
-MAJOR AIRPORTS
- MINOR AIRPORTS
- AIRPORT MANAGEMENT, WORLDWIDE
MITRE
Since its formation, the MITRE Corporation has been associated withAir Traffic Control (ATC). We are
aware of the absolute requirement for high quality in the reliability,accuracy,precisionand availabilityof
equipment for ATC in that these provide conf_ence to the users: flight specialistsincluding ATC specialists
and air crew. Our objectivewas to show that both the equipment and the associated algorithmscomputing
0E had these properties. The sensorsand the equipmentwould be inexpensive,solidstate, and solar
powered. The equipment, displaysand archivingwouldbe based on standardIBM-compatiblepersonal
computers (PCs). The success of this very simplifiedwind shear detectionsystemwouldaffirmthe
company's interest in sensible, simplifiedbutconfidence-inspiringATC equipment.
The experimental LLLLLLLLL_nwas to deploy a tight array of reliable solid-statemeteorologicalsensorsaround an
airport, to set up a i:ligitaldata recordingsystemand to operate this in a hands-off mode. In this first
instance the data would be analyzed off-line,though it could be used for operationalpurposes, given the
appropriate analysisand displaycapabilities.
Other objectivesof this MITRE-funded research were to have a high confidence of detecting and locating
all microbursts,and to work to deploy operational eE-measuring arrays in placeswhich there are no plans
to detect microburstsat thistime, such as secondary, General Aviationand thirdworld airports.
355
APPROACH
° MODELS
° ALGORITHM
° PATrERN RECOGNITION
° DEFINE PROCESSING REQ.
- COMPUTER SURVEY
° DESIGN - PURCHASE -
FABRICATE - TEST
• SENSOR SURVEY
° DESIGN - PURCHASE - OTS -
FABRICATE BREAD BOARD
- TEST
= BRASS BOARD
- TEST
BEST
NETWORK SIZE,
DENSITY
NEAR
PROGRAM TASKS
DEPLOYMENT, TEST
OPERATION
MITRE
FALSE
ALARM
RATES
FALSE
SAFE
RATES
The MITRE approach to this problemwas very standard. One of the firstproductswas the development of
a complete system specif_,ation. The sJideis self-explanatory. It setsout the variousmajor objectives
includingthe detailed planning,purchasingand equipmentrefinement for the developmentand testof any
large system includingthis thermodynamic alerter for microbursts.
356
Thermal Alerter for Microbursts Prototype (TAMP)
CLOSED
OPEN
NEW AIR POTENTIALTEMPERATURE
DECREASE
INCREASE
TAMP
ALERTS
ALGORITHM-'_
MICROIURST J
PRESENT
OR
APPROACHING
CLOSED
- DELAY
- ALTERNATIVE
AIRPORTS
MITRE
WIND
rNCREASE
MICROBURST
PRESENT
Since eE is conservative, new air from aloftwill have a different0Efrom air at the ground. Therefore, a pool
of different (almostinvariablylower) 0 E willappear as a rapidlyexpandingpoolwithinthe currentlypresent,
nearly uniform,OE._Proctor has shown models of near-surfacechanges of thistype due to temperature
alone. - -- •
In additJon,_e movement of the boundariesof the pool yielda measure of shear, microburststrength, or
the so-calle_lmaximum expected lossacross the microburst. The depth of the change will also give a
measure of the change, much likethe relation given by Proctorof 8v (m/s) = 2.5 _T°C.
35'/
//'__- --Pressure
{'/ _ .r,p Input
L./'_'
=k_'#s_Lolc?m_or.
The sensor-transmitters(Senstrans) in the array have wind speed sensors similarto the Bedard-Fujita
design shown, but modifiedby MITRE to includedirectionsensors,which are straingaugesmounted
directlyon the rodwhich holdsthe Bernoullisphere. When the ball moves,the directionis measured by
resistance changes in the s_'aingauges. In the MITRE design, the pressureswitchis replacedby a solid
state pressure transducer soldered to the printedcircuitboard (PCB). The wind shear is then potentially
obtainable in three ways, direct measurement, inference from the temperaturedepression,and
geometrically,from the rate of expansionof the pool of new air.
Further, totalpressure change, defined as the sum of the scalar pressure change and the dynamic
pressurecomputed from the kineticenergy of the moving air, gives yet a thirdpotential indicatorof the
presence ofa mj¢'lR)urst(Fujita). Changes in the staticpressure over short periods of time (infrasound)
have been postulatiBdby Be(lard as indicatorsof the presence of microbursts, butare nota possible output
from the Senstrans array.
358
MITRE
The plan for the operationalair trafficcontroller(ATC) displayis for a simple nested family of non-
overlappingthreat-indicatingellipses. Ellipsesare very simplydefined:five bytes completelydescribethe
location and size of an ellipse. Therefore sixteen bytes completely descdbe three ellipses, sinceonly one
byte is needed forcolor. Given this economy of informationto be transferred, the inner ellipsewouldbe
filledwith red, indicatingthe highestthreat, probably impenetrableby any aircraft on landing or departure.
The area between that and the next ellipse, which totally surroundsthe former, would be amber, indicating
considerable threat, but possiblysuccessfullypenetrable by a microburst-experienced pilot. The finally
enclosed area would be green indicating a moderate threat, butpenetrable by all pilots except those who
have no wind shear train=ng. There would be no confusing overlappingof ellipses. However, there might
be a small number of red ellipseswithin one amber ellipse,and there mightsimilarlybe multipleamber
ellipseswithin one green ellipse. However, for transmission to f_ht decks, a simpler, three nested ellipse
family for any one airportwouldbe generated from the availabledata.
The advantage of ellipses is that they simplifythe overly-complexshape of meteorological iso-lines or
contours(such as radar echoes) which describe random noisephenomena and are not meaningful in
detail. Where threals are defined, however, the selected ellipseis guaranteed to be the smallest ellipse
which contains the defined threat, and does notoverlap any innerellipse.
Sixteen byt_ of_claracan be transmitted in one informationpacket of Mode S data. In addition,at the low
transmissiorrrateof 1200 baud, 16 bytes of data can be transmitted anywhere in the world in a tenthof a
second. Thus, the functional informationof the locationand size of a microburst on an airportcan be
transmitted ingraphical form more economically than the ASCII format of the current controller verbal
transmissions.
On the flightdeck a colordisplayof threats shouldfacilitatepilot intentions,and an appropriate choice. In
addition,a smart flight-deck computercould generate a probabilityof survival number between zero and 1
(1 beingsurvival, 0 being impact} since it conlains the aircraftconfigura_oninformation.
359
Senstrans - Field Equipment
Sensors and their sensitivities
Temperature sensor: O.ldeg C in 7 s; shelter air limits rate.
Pressure sensor: 0.1 mb, no time limit.
- V,/ill sense pressure changes ahead of descending air.
- AIIc'NS estimate of temperature change due to pressure.
Wind speed sensor (Bedard-Fujita design, modified): 1 m/s above
5 m/s, no time limits.
- Uses the same sensor as the pressure sensor.
Relative humidity sensor: 3% RH in 5 minutes.
- Water content change will cause temperature change.
- Sensor siow, but look-ahead and nowcasting possible.
Solar insolation
- "Free": From output voltage of solar power supply.
Adequateaccur.a_isachievedbyacceptingsmallagsinseveralparametersthataremeasured.
Pressureandwir_ speedareavailableinstantaneously,incetheyaremeasuredon-chipbya sensorwith
a deflectingsiliconmembrane.Winddirectionhassimilarqualities.Temperaturehasa slightlagbecause
ofthethermaJmassofthesensor.Humidity,witha lagoftheorderofa minute,becauseoftheneedfor
waterconcentrationchangeina thinfilm,hasthelongestlagofthevitalparameters.
Accuraciesand lagsare givenin thefollowingtable:
Parameter Sensor Accuracy Lag
Temperature Thermistor .1°C 7 seconds
Differential Siliconwafer .1 millibar zero
WindSpeed Siliconwafer 1 nYs zero
Relative _ _;Thinfilm 3% 5 minutes
Humidity _
Insolation_ Solararray
Comment
wrtPressure
Above5m/s
zero Accuracy
N/A
Generallythesensors,themicrocontroller,the transmitterare solderedononetwo-sidedPCB, thus
eliminatingmanycablesandconnectorswhichare themosttroublesomeportionofcomplexequipment.
Thisis mounted insidea standardinstrumentshelterwhichyieldsadequateexposuretothecomponents
withinit. However,thesolarpanel,the battery,andthe windsensormustbeelsewhere,sostandard
telephonecableswith their gold-platedandsprungconnectorsareusedwhereconnectorsarerequired.
360
SENSTRAN
Pressure
Temperature VT INTEL
Humidity
Battery
Input
DESIGN
FM
TRANSMITTER
MITRE ,-
The microcontroller containsan ND converterand has eight multiplexed analog inputs. These include one
digitalvoltmeter whichcan be attachedto any pointon the PCB, and readsremotely. It feeds synthesized
frequency shiftkeyed (FSK) tones to a 2.0 watt FM transmitter.
Unfortunately,the microcontrolleralso contains a fatal flaw which will notbe addressed nor correctedby
the manufacturer. Accordingly,many Senstrans exhibit"gracefulfailure', a tendency towards sparser
transmission, and incorrectresults. This could be detected and correctedby occasional visitsto the
variousSenstrans. While this is notcommon to all microcontrollers, itsunadvertisedpresence inthe
chosen chip was discovered too late to alter the design to accommodate some other chip.
Future Senstra_ _11be designed around permanentlyenergized low-currentmicrocontrollersto simplify
designana_t0circumventa similar fatal flaw should it be present in any of the low-currentmicrocontrollers.
361
TAMP Installation at Stapleton
LLWAS ,_m_or (FAA)
1lOft
TAMP
Sens_r/Tmnsmlttsr
(Senstrmt)
Low level
Wind Sheer
Alert System
Tower (LLWAS)
LLWAS SoW Panel
'up to 7 km
Spare LLWAS Antenna (FAA) .-D,,.I
I
I
t Col_
. J (_)
I TAMP Data
I Acquisition
I proc_slng
I Analysis
I Display
l unlt
I (DAPAD)
!
TRACON .
Equipment
"Room
Security Fence _T_
The receivingantenna is aspare LLWAS antenna on the roofof the ATC Tower,which feeds a receiver in
the FAA equipment room. This isconnected to a standardcommunicationsport ona PC via a 1200 baucl
demodulator. The decodingand archivingsoftware isa Basicprogram.
With permissionof the StapletonFacilitiesSection,each of thirteen Senstrans is mounted on an LLWAS
tower withina few feet of the operational LLWAS unit,and is up to 7 km from the receiver in the ATCT. It
has no impact on the operationof LLWAS.
Operation was achieved on June 26, 1990 and continues.
362
DAPAD Software
RECEIVER
DECODER
STATION
EXTRACTION METEOROLOGICAL ]
VARIABLE COMPUTATION
AND PLOTTING
Ir
Nffl"RE
DOS
The softwarewithinthe data acquisitionprocessing analysis and display unit (a PC) is a simple Basic
language program. The archive is initially the hard-drive in the PC. Files are occasionallywritten to 3.5"
floppy disks and are then sent to MITRE.
Results
One comparison has been made with the 11 August 1990 microburst. At this time there were only three
remaining operational Senstrans, but its presence was detected by all of them.
Acknowledgments
The author is particularlygrateful for the collaborationof the North West MountainRegion FAA,specifically
the Denver Hub AirportFacilitiesSector led by Mr. Jack McCormick.
363
364
Session VI. Heavy Rain Aerodynamics
365
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Thermodynamic Alerter for Microbursts (TAMP)

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