The NASA ER-2 aircraft is used as a platform for high altitude atmospheric missions. The Meteorological Measurement System (MMS) was designed specifically for atmospheric research to provide accurate, fast response, in situ measurements of pressure, temperature, and the three dimensional wind vector. The MMS consists of three subsystems: an air motion sensing system to measure the velocity of the air with respect to the aircraft, a high resolution Inertial Navigation System (INS) to measure the velocity of the aircraft with respect to the Earth, and a Data Acquisition System, to sample, process and record the measured quantities. Details of each of these systems are given. The location of the MMS instrumentation is illustrated. The calibration of the MMS is discussed and results on an intercomparison of MMS measurements, Vaisala radiosonde observation and radar tracking data are given. An illustration of the MMS measurement of vertical wind is given

Bowen, Stuart W.

Bui, T. Paul

Chan, K. Roland

Scott, Stan G.

English

NASA Technical Reports Server

B.6 The NASA ER-2 Meteorological Measurement Sysicm:
N91-22658
51
TIlE NASA ER-2 METEOROLOGICAL MEASUREMENT SYSTEM:
INSTRUMENTATION, CALIBRATION AND INTERCOMPARISON RESULTS
K. Roland Cban I , Stuart W. Bowen 2, Stan G. Scott I , and T. Paul Bui I
1. NASA Ames Research Center, Moffett Field, California 94035, U.S.A.
2. San Jose State University, San Jose, California 94192, U.S.A.
Abstract
The NASA ER-2 aircraft is used as a platform for high-altitude atmospheric missions. The
Meteorological Measurement System (MMS) was designed specifically for atmospheric research to
provide accurate, fast-response, in situ measurements of pressure (+0.3 mb), temperature (_+0.3°C),
and the 3-dimensional wind vector (_+1 m s-I). Developed over a period of years and operational
since early 1986, the MMS has participated in three major scientific expeditions: the Stratospheric-
Tropospheric Exchange Project (STEP) based in Darwin, Australia in January and February of
1987, the Airborne Antarctic Ozone Experiment (AAOE) based in Punta Arenas, Chile in August
and September of 1987, and the Airborne Arctic Stratopsheric Expedition (AASE) based in
Stavanger, Norway in January and February of 1989.
The MMS consists of three subsystems: (1) an air motion sensing system to measure the
velocity of the air with respect to the aircraft, (2) a high-resolution inertial navigation system (INS)
to measure the velocity of the aircraft with respect to the earth, and (3) a data acquisition system to
sample, process and record the measured quantities. The location of the MMS instrumentation is
shown in Fig. 1. Detailed discussion of the instrumentation is reported by Scott et al. [1989].
(1) The air motion sensing system consists of sensors which measure pressures, tempera-
ture, and airflow angles (angle of attack and angle of sideslip). Static and total pressure measure-
ments are obtained from precision pressure transducers, using existing aircraft pressure ports and
plumbing. Total air temperature is obtained from two tot',.d temperature probes with matching signal
conditioners installed on the lower hatch of the equipment bay. A radome differential pressure
system, similar to the one developed for a NASA Convair-990 aircraft [Chaussee et al., 1983;
Bowen et al., 1985], is installed in the ER-2 aircraft to measure the airflow angles.
(2) The inertial navigation system normally used by the ER-2 aircraft is a Litton LTN-72
INS. While this INS is satisfactory for aircraft navigation, it does not meet the stringent require-
ments of data rate and accuracy for MMS measurements. With a standard INS, the accuracy of
wind computation is adversely affected by the internal digital filters of the INS, and the resolution is
limited by the INS data bus update rate of only 3 s l. A high-resolution Litton LTN-72RH INS,
configured for scientific applications, was selected for the MMS because of its compatibility (with
the aircraft installation), higher altitude specification (usable up to cabin pressure altitude of 26,000
https://ntrs.nasa.gov/search.jsp?R=19910013345 2020-03-19T17:59:50+00:00Z
52 AppendixB.ExtendedAbstracts
ft),precision( odigitalfilters),timeresolution(dataupdaterateof25s-l),andspecialprovisions
forMMSmeasurements(verticalvelocityandinertialltitudewithinternalbaro-inertialloop).This
INSisinstalledintheaircraftupperequipmentbay,whichismaintainedat=28,000-ftpressure
altitudewhentheaircraftisat65,000ft. Temperatureintheequipmentbaywithafullcomplement
ofoperatingequipmentistypically5to25°C.
(3)Thedatacquisitionsystem(DAS)samples45independentvariablesatarateof5s-I
(maximum:10s-l),accommodatesvariousmodesofdata(analoganddigital,serialandparallel,
synchronousandasynchronous),storesthedataontwomedia(discandtape),andmeetsaircraft
constraintsofcompactness,lightweight,andsafety.Commerciallyvailableboardproductswere
utilizedwherepossible.TheDASisinstalledintheupperequipmentbayoftheaircraft,nexttothe
inertialnavigationu it.Majorcomponentsof heDASconsistofasingle-boardcomputer,mass
datastoragesystems,acommunicationandmemoryboard,anINSreceiver,clockandterminal
interfaces,analog-to-digital(A/D)interfaces,input/output(I/O)interfaces,andpowersupplies.
Thedatacquisitionsoftwareishighlycustomizedandmodularizedtomeetthefollowing
requirements:flexibilityinmodifyingthedataframeandsamplingrate(1toI0s-I);redundancyof
massdatastorage(tapeand isc);simultaneityofsampling45variables(<0.01sbetweenthefirst
sampledvariableandthelast);asynchronousinterfacewithINSdigitaldatastreams;controlfdisc
turn-onandturn-offduringlandingandtakeofftoavoidpossibledamagetothediscdrive;handling
ofread/writeerrorstominimizedataloss;handlingofdataloggingincaseoftemporarypowermai-
function;andspecialutilityand iagnosticprogramsforprefightcheckoutandpostflightcommand.
SoftwareisakeyelementoftheMMS;itwaswrittenintheMC68000microprocessora sembly
languageforcompactnessandpeed.Thedatacquisitionsoftwarecodesizeis34Kbytes.
The DAS has twooperating_modes: stand-alone (flight mode) and interactive (ground mode).
In the flight mode the DAS runs the acquisition routine at power turn-on and logs data conti-
nuously. Pilot interaction is limited to a power on-off switch in response to a fail-light indicator. In
the interactive mode the user can execute any of the modular routines, including flight-mode
acquisition, through an external terminal. Postflight data can be downloaded from the DAS to a
ground system in two ways: through a heavily shielded and terminated parallel cable and through a
pair of communication boards. The second method has a fast transfer rate of--- 100 kBaud. For an
8-hour flight, MMS raw data (= 15 Mbytes) can be downloaded to the ground station in 15-20 min.
The MMS ground station consists of several portable and desktop computers. Our current research
effort has been primarily in the development and improvement of the data analysis software.
;. The calibration of the MMS instrumentation consists of (1) sensor calibration, (2) system and
transducer response tests, (3) inflight calibration, and (4) laboratory INS calibration. First,
pressure and temperature sensors, signal conditioners, transducers are individually and periodically
calibrated either in-house or by the manufacturer. Second, the frequency response of the radome
B.6 The NASA ER-2 Meteorological Mcasurcmcnt Syslcm: 53
differential pressure system was measured a,_d determined to be satisfactory even at high altitudes in
the range of interest up to 10 Hz. The dynamic response of the radome system, including the short
feeder tubing, has been measured in the laboratory. Third, inflight calibration requires the pilot to
fly the aircraft in square patterns and to induce yaw and angle-of-attack maneuvers at several
altitudes. These inflight maneuvers are used to establish the calibration constants of the differential
pressure system which measures the airflow angles and to determine the angular offset between the
differential pressure system and the INS. The calibration constants are Mach-number (0.35 - 0.72)
dependent. Finally, the calibration of the INS is conducted on a physical pendulum of = 2 m in
length. The pendulum is tilted and positioned in such a way that pitch, roll, heading, N-S velocity,
E-W velocity, and vertical acceleration can all be measured in each swing. Various time delays are
introduced in the data processing, and Lissajous diagrams for each INS variable are plotted. This
calibration procedure can determine the time delay of each INS output variable to the nearest 0.01 s.
For the Litton LTN-72RH INS, there is = 0.045 s time delay for the heading signal, = 0.39 s for
the vertical accelerometer output, = 0.08 s for N-S and E-W velocities, and none for the pitch and
roll signals. Time delays, caused by the INS internal electronics and/or the external antialiasing
filters of the DAS, have been determined in the laboratory, and the appropriate time shift is applied
to the data stream of each MMS measured variable during processing. _ "J )_
Intercomparison of MMS measurements, Vaisala radiosonde observation, and radar tracking
data was conducted]n April I986at theCrows Landing facility in California. Data were processed
so that time and altitude of the three sets of data were properly matched. Measurements of pressure,
temperature and the horizontal wind vector by the MMS, balloonsonde and radar were compared.
The difference between the mean MMS and balloonsonde/radar meausurements is within the speci-
fied accuracy of the instruments; the variability of these measurements is larger than the difference
of the mean. The variability is primarily due to spatial and temporal difference between the aircraft
and the balloons. This intercomparison indicates that the overall MMS accuracy is very good.
The vertical wind is the most difficult measurement of the MMS. As an illustration of the , .
MMS response to a significant natural atmospheric phenomenon, the vertical wind measurement on :
September 22, 1987 during the AAOE mission is shown in Fig. 2. The ER-2 aircraft was stationed
at Punta Arenas, Chile (53°S, 72°W), flew southward on an isentropic surface (= 420K), descended
and ascended at the southern terminus (= 72°S) over Antarctica, and returned northward on the
same isentropic surface. The vertical wind measurement over the 6-hour period is shown in Fig. 2a
with time and corresponding latitude indicated on the bottom and top of the figure, respectively.
For most of the flight the atmosphere was smooth, and vertical winds generally average to zero over
any section of the flight. However, large perturbations are observed on both the southbound and
northbound legs at = 69°S latitude. These perturbations have been noted as possible mountain lee
waves over the Antarctic Palmer Peninsula [Chan et al., 1989; Gary, 1989]. Two 20-rain sections
• °
54 Appendix ft. Extended Abstracts
of the data in Fig. 2a are shown in Fig. 2b and 2c with the time scale expanded. In Fig. 2b (58,000
- 59,200 s) the amplitude of ttle vertical wind is very small and close to zero throughout this 20-min
period. In Fig. 2c (58,000 - 59,200 s), the mountain lee wave signature is shown in more detail.
Although the amplitude of the vertical wind data has large excursions during this 20-min period, the
vertical wind measurement is well defined and returns to the mean value after the perturbation.
;" The MMS meets the science requirements for in situ airborne measurements of free-stream
_. pressure, temperature and wind for atmospheric missions. The customized DAS provides the flexi-
bility to adapt the MMS to changing scientific needs. Special attention has been given to sensor and
' system calibrations. Future development will involve spectral analyses of MMS variables to further
' reduce the aircraft motion feed-through in the wind measurement and computation.
References
Bowen, S. W., S. G. Scott, K. R. Chan, and J. G. Borucki, Yaw and angle of attack measurements on the CV-990
aircraft, Paper 85-0341, A/AA 23rd Aerospace Science Meeting, Reno, NE, 1985.
Chan, K. R., S. G. Scott, T. P. Bui, S. W. Bowen, and J. Day, Temperature and horizontal wind measurements on
the ER-2 aircraft during the 1987 Airborne Antarctic Ozone Experiment, J. Geophys. Res., 94, 11573-11587, 1989.
Chaussee, D. S., P. G. Buning, and D. B. Kirk, Convair 990 transonic flow-field simulation about the forward
fuselage, Paper 1785, AIAA Applied Aerodynamics Conference, Danvers, MA, 1983.
Gary, B. L., Observational results using the microwave temperature profiler during the Airborne Antarctic Ozone
Experiment, J. Ceophys. Res., 94, 11223-11231, 1989.
Scott, S. G., T. P. Bui, K. R. Chan, and S. W. Bowen, The Meteorological Measurment System on the NASA ER-2
aircraft, submitted to J. Atmospheric and Oceanic Technology, 1989.
INERTIAL NAVIGATION AOA AND SIDE SLIP
SYSTEM {LITTON LTN-72) (INS) DIFFERENTIAL
,_'_"7_ PRESSURE AND PT
MMS DATA SENSOR PORTS -
ACQUISITION /
SYSTEM {DAS]
/ U, ERO:..Y(-
/ RACK
a r_ "" ('\'"
_IFFERENTIAL AND PT
/ "_ / \1 \ .RESSURE
LOWER O-BAY / /1 / Y \ TRANSDUCERS
HATCH / / PITOT-STATIC _ {INSIDE,
-- PRESSURE
TOTAL TEMPERATURE I PRESSURE AIRCR"FT
....... / SENSORS AIR DATA
p.OBES / C'_M;_TER(ADC)
Po" Pt TRANSDUCERS
{INSIDE)
Fig. I. Location of the MMS instrumentation on the ER-2 aircraft.
FL6 The NASA FR-2 Meteorological Measurement System: 55
LATITUDE (°S)
54 56 58 60 62 64 66 68 70 7272 70 68 66 64 62 60 58 56 54
20 - , .... ,
10
I
_n
g
rl
z 0
o
"=' I
> -10 1 '--'
52,000 53,200
-20'_ ' ' ' " '
50,000 55,000
i i_
i
i i
55,000 59,200
Fig. 2a
, , i [ i , i i =_ *_.
60,000 65,000 70,000 72,000
UNIVERSAL TIM E (sec)
_-- 10
I
8
en
g
._ °I
w
,,=,
> -10
52,000
___ , i ............. _ig,2b, t
52,300 52,600 52,900 53,200
UNIVERSAL TIME (sec}
I
E
Z 0
o
w
-10
58,000
f .,3 ,;.
i \ -, -
,.. f '-_.-_..
_," Fig. 2c
' i _ i. i l i i i . f i I i _ i, ' , • ,
58,300 58,600 58,900 59,200
UNIVERSAL TIME (sec)
Fig. 2a. Vertical wind results on September 22, 1987 during the
Airborne Antarctic Ozone Experiment (AAOE) mission.
Fig. 2b. Expanded section (52,000 - 53,200 s) of Fig. 2a.
Fig. 2c. Expanded section (58,000 - 59,200 s) of Fig. 2a.


The NASA-ER2 meteorological measurement system: Instrumentaion, calibration and intercomparison results

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