Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for...

46
SAFGL-TR-LR?.0079 INtSTRUM9NTATION PAPERX. NO. 310 Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER 24 FEBRUARY 1982 Approved for public release; distributlor "uIlmitod. C) AERONOMY DIVISION PROJECT 6687 AIR FORCE GEOPHYSICS LABORATORY HANSCOM APB, MASSACHUSETTS 01731 AIR FORCE SYSTEMS COMMAND, USAF 144

Transcript of Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for...

Page 1: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

SAFGL-TR-LR?.0079

INtSTRUM9NTATION PAPERX. NO. 310

Sonde Experiments for Comparative Measurementsof Optical Turbulence

J.H. BROWNR.E. GOODP.M. BENCHG. FAUCHER

24 FEBRUARY 1982

Approved for public release; distributlor "uIlmitod.

C)

AERONOMY DIVISION PROJECT 6687

AIR FORCE GEOPHYSICS LABORATORYHANSCOM APB, MASSACHUSETTS 01731

AIR FORCE SYSTEMS COMMAND, USAF

144

Page 2: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

REPORT DOCUNENTATIO?4 PAGE j FFRE (t0MLNSTICG FOR

",~iclentiui, . 11 1 U'lis).A v A I: I-X~ II (NJ* )L ( 0A)MPAI 1 LX iVMI.ASUIII;MYNTS 0V 1"I'M AI 'L TUIMlULVYfi1% Tn "'Y..

I H-' No. 31'4~~ CONTR., ,ACT OR CRANr nUM3FR

.1. HI. Brown G,. 1'aucilurT1%. Goodl

P. M. 1pc

Air Force Geophysics Laboratory (1,1W) I .. *R NIOP

Hjanscom A Vi) (;2 11) F'M a s.a chusetts 0 j,:31 fifr 8- 0T8

Aitr Yarce Geophyipics I-aboratory (LKI)) 2 4 February CBHanscom AFB F ;MR E 0,Massachusetts 01731 ________46 ____

M7*, , '4 .' A.' ¶ O'i S 'fI4**4 7, M~n.,I, . "-f ,- SECURIT4, CL4ASS. 'ýI 11

.1W 10 - N' IE

I'lefr'active Htrur~ure cous.tatit Scintilloinnftrilarlay, turbulerice RadiosondeIIerl-rIIsrl)dJIre T'urbulenice

t . ~AV(IU thesiistd art() aizx-raft tr ox-u -thermnal rnfaSUrerncnt5. DescribedI:le11i thle radiousrinde and thurtios'jnduý etectrunieni arid their calibrations.

Thie data i-'v'Ju,:tiun kS (Intr k f descriloed and a b~rif-f program desr:ription isgiveti. Altisungh the differersnt lnsti'urijunt.j gaive mecasu-remeýnts somewhat

DD 1473 Unclassified

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UnclassifiedSECURITY CLASSIFICATION OF THIS PAOE(WIhe DlI*e EntIr'ed)

20. Abstract (Continued)

separated in space and time, first results show good agreement between theradar, scintl.ometer, and thermosonde measurements.\ý

UnclassifiedSECUAITY CLASSIFICATION OF THIS PACOE(Whs., Date Entered)

-A

.1

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i-'-mu w - , ' . - - .... .

i .. ei"n".: , ...

IT

\.)

~i~ivt

Preface

This program owes its success to the dedication of numerous individuals.

These include:

Thermosonde construction and Mr. Hans Laping, LCCRadiosonde modification Mrs. Eovelyn Hnyni-, L].(

MSGT N. K. Newijian, LCCMr. G. Murphy, Tri-Con Assoc., Inc.

Radiosonde tuning and tracking Mr. J. Griffin, LCRMr. K. Walker, LCR

Radar observations Dr. Brenton Watkins, Univ. of AlaskaMr. G. Loriot, NEROCDr. Prabhat Rostogi, NEROC

Scintillometer observations Dr. A. Quesada, LED

Radiosonde balloon launch Mr. G. McPhetres, LCCMSGT J. Gordon, 1,CCC

Tracking data reduction Mr. Brian Sullivan, Boston College

Theoretical discussions Dr. Edmond Dewan, LKD

We sincerely thank the many named and unnamed individuals who in large or

small part contributed of themselves so willingly.

3

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Contents

i. INTRODUCTION 7

2. RAWINSONDE 8

2. 1 hawinsond( Moditications 92. 1. 1 Met Circuit Card 92. 1. 2 Transponder Receiver 92.1.3 Transmitter 10

2.2 Resistance Calculation 102.2. 1 Temperature Calibration 112.2.2 Humidity Calibration 112. 2. 3 Pressure Calibration 12

3. THERMOSONDE 14

3. 1 Thermosonde Description 143.2 Sensor Heating Effects 173.3 Sensor Frequency Response 203.4 Therrnosonde Calibration 213.5 Thermosonde Environment 21

4. DATA REDUCTION 23

4. 1 Time Period Records 244.2 Reference Frequency ID 244. 3 Segment Window ID 244.4 Tracker Data 25

5. PROGRAM DESCRIPTION 26

6. IIESULTS 31

REFERENCES 45

knzczg~iMG PAGE RANK-NOT FlJ

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S.. . ... .... .. , **,., T Ir-Illustrations

1. Sample Output of Reduced Radioaonde/Thermosonde Data iS2. Photograph of Thermosonde and Micro-thermal Probe 16

3. Schematic of Thermosonde Sensor Convective Heat TransferTest Circuit 18

4. Heat Transfer Coefficient Curve of Thermosonde Sensor as aFunction of Altitude 19

5. Calibration Curve of Thermosonde Sensor AR as a Function

of Radiosonde Frequency 226. Calibration Curve of Thermosonde (AT)RMS as a Function of

Radiosonde Frequency 22

7. Sample Output of Reduced Tracker Data 278. Typical Temperature Profile Plot 319. Typical Relative Humidity Profile Plot 32

10. Typical Balloon Velocity Analysis - East Profile Plot 3311. Typical Balloon Velocity Analysis - North Profile Plot 33

12. Typical Horizontal Vector Shear Analysis Profile Plot 3413. Expanded View of Horizontal Vector Shear 34

14. Power Spectral Density Analysis of Horizontal Vector Shear 35

15. Raw ThermosoNde C2 Analysis -- Profile Plot 37

16. Expanded Vie- of Raw Thermosonde C• Profile Plot 38

17. Smoothed Thermosonde Cý Profile Plot 39

18. Cumulative ProbabUity Distribution Curve of Log C2 4019. Comparison of Radar C2 and Scintillometer C2 41

N N Profiles 4

20. Scintillometer Weighting Functions 42

21. Comparison of Thermosonde C2 and Scintillometer C2

Profiles N 4322. Comparison of Thermosonde C2 and Radar C2 Profiles 44

24

Tables

1. Optical CR (Turbulence) Measurement Program 28

61

I

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Sonde Experiments for Comparative

Measurements of Optical Turbulance

I. INTRODUCTION

Atmospheric properties ot temperature, pressurc, humidity, and wind speed,

as measured by meteorological radiosondes, offer a means of estimating the fluc-

tuations in the atmospheric optical index of refraction. Fluctuations of the index

of refraction, characterized as C are important to numerous DOD optical sys-

tems being both planned and developed. Direct measurements of C are possible

with optical systems such as those used to evaluate sites for astronomical tele-

scopes. These measurements have been limited to a few locations, and this tech-

nique is not suitable for assembling a world wide data base of C2 . Given that CN

determined from meteorological data can be an accurate measure of optical turbu-

lence, the best promise for economically assembling a large data base is through

the use of the archived meteorological sounding data obtained from sondes.

The present rawinsonde measurements are usually achieved with altitude

resolution of 300 m or larger. This scale is generally accepted as being larger

than the vertical scales of turbulence that produce the C2 . Thus, in order to de-

velop an analytical model predicting CN from the standard rawinsonde, it is nec-

essary to have a statistical base relating the actual turbulence scales to the rawin-sonde observed scales. New sondes (artsondes) have been developed by VIZ

Corporation for the National Weather Service to measure the meteorological

(Received for publication 19 February 1982)

7

S-t.AV''W----X

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variables at smaller altitude resolution. These sondes were modified at AFGL to

provide data for a CN intercomparison test. The program objective is to compare

C as determined from standard rawinsondes, the AFOL modified artsondes,

AFGL built thermosondes. stellar scintillometers0 aircraft-mounted commercial

thermosondes, and UHF radar.

The dttailed description of the AFGL artsonde and thermosonde is presented in

this report. Also presented is the calibration procedure and the computer analysis

used to derive the meteorological values from the recorded telemetry signal. The

sonde tracking and ranging system is described along with the data processing pro-

cedures used to smooth the data and determine the winds as a function of altitude.

A brief description of experimental results is shown as comparisons of C 2 meas-AN

urements obtained with radar, optical scintillometer, and thermosonde.

2. RAWINSONDE

The rawinsonde used in these experiments consists of meteorological measuring

elements coupled to a radio transmitter and assembled into a small lightweight

plastic case. The device is carried aloft by a 1200-gm balloon filled with heliumgas. Included in the train is a small parachute to slow the descent of the device

after the balloon bursts. An automatic launching reel is attached to the train, which

lowers the radiosonde until the train is fully extended to about 20 m. As the balloon

ascends at about 5 m/see, measurements of pressure, temperature, and relative

humidity are transmitted to a ground station where the data are recorded. As the

balloon rises, it is followed electronically by radio direction-finding equipment that

tracks the transmitted signal. Measurements of the balloon position relative to the

ground station are recorded in terms of azimuth, elevation, and slant range. These

measurements ax'e converted to X, Y, and Z distances. The data are filtered as

described in Section 4. 4 to remove extraneous signals and then time differenced

to obtain wind velocity profiles.

Fifty (50) state-of-the-art radiosondes were purchased from VIZ Corporation,

Philadelphia, Pa. These! are called by them the "Artsonde-Phase 11, " and they

carry VIZ part number, 1499-311. This is a 1680-MHz amplitude modulated sonde

with a 403-MHz receiver used for tra.nsponder ranging. The transmission ofmeteorological (MET) data serially switches by solid-state circuitry from pressure

to temperature, to relative humidity, to reference, and back to pressure with a

segment dwell time of 250 msec. Premium sensor elements are used for the

aneroid baroswitch, thermistor, and hygristor. Depending upon the sensor inputresistance, a frequency of 30 to 1000 Hz is produced that modulates the 1680 MHztransmitter. The reference frequency is set close to 1000 Hz. It provides the

A i4 h

• . • '1• " , , ...... , •i: " .... : ..... " .. . •.. . .| " • " " .. ... ...i . ....... •.......... 'i .. ... ... ',

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identification of segment position, and it allows for data correction of tenipcraturu

induced frequency drifts.

2.1 Ralinsornde NMoifications

After delivery of the radiosondes, sv,'.,. in-house modifications were re-

quired. Because greater temporal and spatial data resolution were desired than

were available from a standard radiosonde and its associated GMD tr-acker, special

payload and ground equipment changes were implemented. Additionally, a sepa-

rate instrument to mneasure small temperature fluctuations (thermosonde) was

attached physically and electrically to the radiosonde. The modification included

changes in the radiosonde transmitter, receiver, solid-state switching, and MET

oscillator circuit boards.

.MET CIRCUIT CARD

In order to transmit the additional thermosonde data, the number of commuta-

tion data segments was increased from the standard four to eight. To accomplish

this, a second quad-bilateral switch (p/n 4060) was added to the MET circuit iboard. This was facilitated uy the existing 4017 IC clock, which allows serial

switching of up to ten segments. Two of the additional segments were used for

thermosonde information and two were used as auxilliary segments. The auxillary

segmcnts allowcd supcr-commutation, uf tim MET dta ou r the reporting of electron-

ics temperature.

To accomplish calibration and ground-base checks the eight lock-up and one

common test points were brought to an eight-position rotary switch. During cali-

bration the normally free-running segment switch was stopped on a segment cor-

responding to the position of the switch. The frequency of each segment was

examined. in turn, by rotating the switch from one position to the next. The

measured frequency was then recorded along with the measured temperature,humidity, pressure commutator position, and thermosonde test value. The baro-switch that forms one part of the MET board transmits one of four unique fre-

quencies depending upon the position of the baroswitch armature. The original

separation of frequencies was only 10 or 20 Hz. In order to provide a separation

of 100 Hz between each frequency, three new resistors replaced existing ones with

appropriate values. 'This reduced confusion over contact identification.

2, 1.2 TIRANSPONDER RECEIVER

The balloon borne 403-MHz transponder receiver is used to derive the slant

range in the following manner: Ground-base equipment generates a PCM code that

is synchronized with the start pulse of a time interval counter. This code modulates

the ,k03-MHz uplink transmitter. The receiver transponder uses this code to

9 1

So.. .... ..... ..., ..... . ....:''- 1 . ... " . ... .... -'" ...

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modulate a 70-kHz subcarrier oscillator. This subcarrier is mixed with the MET

data and used to modulate the balloon-borne transmitter. Ground-base equipment

retrieves and decodes the PCM code, which then @ends a stop pulse to the inter-

val counter. Since slant range is calibrated vs interval, a direct digital coded

range output it produced.

2.1.3 TRANSMITTER

Normally the transmitter is 100 percent amplitude modulated b" .Ae MET data

pulses. When the MET data pulse is high, the transmitter is -hut down. This

results in an AM pulse repetition frequency that is measured by ground receiving

equipment to determine the sensor input resistance.

The on-board 403-MHz receiver frequency modulates the transmitter. Since

this information is lost when the MET signal is high (because the transmitter is

shut down), difficulty In holding synchronization to the ranging signal develops.

Consequently the evaluation of slant range data contains associated errors. To

eliminate this problem, the ac-coupling AM input to the transmitter was removed.

Instead, the MET data was ac-coupled to the transmitter in the same manner and

to the same junction point as the ranging signal. This results in MET data fre-

quency modulation of 30 to 1000 Hz and ranging modulation of 70 ldiz.

2.2 Resktance Calculation

This section presents the MET data transfer equations as given by VIZ

Corporation (document nos. VIZ 800721 and 761101B). The form of these ex-

pressions as well as the constants depend on the sensor type and manufactu.ring

lot number. The input resistance to the radiosonde corresponding to the measured

MET frequency is:

Rinput e R it (refifmeas- D

where fref is the average measured reference frequency and I raas is the average

measured segment frequency when the baroswitch in on a space (that is, between

two discrete contact points).

The thermistor or pressure resistance is the input resistance when on a tern-

perature or pressure segment.

The input resistance when on a humidity segment is the equivalent parallel

resistance of a I-M resistor and the hygristor resistance; thus,

Rinput X 10 6

1RH - 6_- X 10 -input

10

S. .. ..... - ... i ..... i l' ........i .. .i ...... ...... i.... i" " i 'i= T " - ' ' ....

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2.2.1 TEMPERATURE CALIBRATION

Temperature is calculated from L,.t. thermistor resistance hiT as follows:

Ii -273.15t 3

ý A k Ii, M T/R30)

ko

where R30 is the acculok lock-in resistance at 300 C. The coefficients for pre1Cit..i,

temperature element lot P6,7, as provided by VLZ are:

A 3.2987 E-03

A,= 4. 7610 E-04

A2 = 2.8417 E-06

A 3 = 1.5691E-06

2.2.2 HUMIDITY CALIBRATION

Relative humnidity is calculated from the hygristor resisiance R as follows:

}'•. k [ fIRH)H69.RH 11 A-

k0 RH

where

f(R RH)= f(t) in (1RH/R 33)

R is the acculok lock-in resistance at 33 percent 1L1 and 25

and

3

f(t) = W C. (t)k (t = °Celsius)

k=o

The coefficients fo-" premium humidity element lot 2265 as provided by VIZ are:

for RHRH/R 3 3 _: 1: for ,RH/R33 '1 1:

C = 7.885 E-01 C = 9.243 E-01o 0

C 9.286 E-03 C1 = 3. 059 E-03

C2 = -2.462 E-05 C2 = -1. 188 E-06

C3 = -3. 368 E-07. C3 = 0.

3I

it i I ..I I 1... ..i ...i i. . '

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r

for f(R]RH) 2t -0.2: for MR.H) < -0.2:

P i. a -2. 0909 E00

D! * 7. 1454 E-01 D, a 9.2406E00

D 2 & -7. 9163 E-02 D2 = 2.1693 E01

D13 a 3.2555 E-02 D3 = 2.2214 E01

D4 a 3. 9255 E-03 D4 - -6. 1926 BOO

A * 102. A - 0.

2.2.3 PRESSURE CALIBRATION

Each radiosonde is provided with pressure calibration values for the leading

edge of 160 contact positions of the baroswitch by VIZ Corporation. Four discrete

frequencies can be transmitted by the baroswitch, depending upon at which of the four

classifications of contacts the baroswitch is located. The four frequencies were

adjusted to provide approximately 500-, 600-, 700-, and 800-Hz signals. Approxi-

mately 500 Hz is transmitted when the baroswitch is located between any two dis-crete contact points. Approximately 600 Hz is transmitted for the following contact

numbers: 30, 45, 60, 75, 00, 105, 120, 135, 140, 145, 150, 155, and 160. These

start at contact number 30 and increase by 15 for contact numbers less than 135 arid

increase by five fui contact numbers grester than 135. Approximately 700) Hz is

transmitted for the following contact numbers: 5, 10, 15, 20, 25, 35, 40, 50, 55,65, 70. 80, 85, 95, 100, 110, 115, 125, 1301, 136, 137, 138, 139, 141, 142, 143,

144, 146, 147, 148, 149, 151, 152, 153, 154, 156, 157, 158, and 150. These start

at contact number 5 and increase by five for contact numbers less than 135 and

increase by one for contact numbers gieater than 135, Approximately 800 lfz is

transmitted for all other contacts. Before each launch the baroswitch is manuallyset to the contact position corresponding to the ambient station pressure. During

analysis the computer identifies groups and subgroups of contacts and defines aparticular contact within a larger group. Thus, if transmission is lost for a short

time, the computer redefines the location of the baroswitch and estimates the pres-

ent contact number. Pressure is defined at the leading edge of each contact and is

logarithmnically interpolated between contacts based on altitude.Sample results of the pressure, temperature, humidity, and CN calculations

are presented in Figure 1. The first column is the record number. "Timne" isdefined as seconds after launch. "CTEMP" is the corrected temperature based un

inferred time lags. No correction is made to humidity below -400C. Pressure

contacts are split into classes 0 to 3. Column 11 shows that a contact number is

defined at the first encounter of a new contact. Columns 14 and 16 show that

12iA

• *..... - .i.iT T~•= -'•~ " i I •Ii I ii " !'4

Page 13: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

-~ ~ ~~~ . .JW J W M 4 b f .1 .114 ?U c14-F.ClM0~l'@~lt ~ V4C, -1 V *O 0- 010 t0410Oi4C 0 0 Q

-00-01 000 0- 0 0 -c ý0 M -fl c 0 ~ ~ .0 m ..... . I00 n000In 000-00 I

- 0 0 0 - 0 .-"Ta 0 00 0 O *- 0 O 0 T02

o S. n - - -- - - 0 0 "

Illý II! I!11 I!I !InI

a wow*EI.4-~-U il.0lM 1 *l2t.a*11g~e~ *S,10C~i* *ro-. ono~q..c~q oc Orlq * 0C~nO . 7-04*00*l M o-o oooV cn -- 'M O T c.-oo M .0 0 . .pwc~

* . .4 . .* . . a ... . (.Ad

I a.2))0lW ~ W 0 .4a41. a7.iC'041 -- a%.C74 0 q0a0-a,4 . V

ooooooooooo -oo~ oooooo C(a qqqn~~~oo~o~~r~r~r..-----t I00 0 7 1 70 6 4 4 0 W Nrl--N41O 4 W

wz7- m74 mmm 212ýl0 4 mw

Me- 000P)12 00 0 912C7.0470.0' q141.41C'70-C,)fl21217444 0 n0) 44 0

15 w 0 . 0 7 7 4 . 1 7 ? S 2 c 1 J 0 v r o z ~ - b t t 2 0 c ' 1 . ~ ~ ~ -7* oo vv voo

0 o~ 1241414o41A .7m " " m

o4) 1 1 o 0 b 2 4 0 ) t 0 t 4 0 0 t ) 4 1 m0l

Cl I ~ ~ ~ ~ N .... I2 00 0 0 0 0 0 0 00 0 0 0 0 0 0 0 000 0 0 0 0 0 0

7 . -13

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( rT)mras is undefined for values less than 0. 0020. The "* ' in the last column

flag values of (AT)rms low gain that are greater than 0. 035°. The corresponding

high gain value in not valid for this condition.

3. THERMOSONDE

The thermosonde is a small, lightweight, temperature-sensing electronic

unit that attaches to the radiosonde. It measures the difference In temperature of

the ambient atmosphere between two probes mounted horizontally I m apart. As

the balloon ascends or descends, the temperature differences are processed and

routed to the radiosonde MET segments. The received data is used to calculatethe atmospheric temperature structure parameter C2 . These data, together with

I Tpressure and temperature, are used to calculate the refractive index structure

parameter CN. Fundamentally, C2 is defined as: 1

C x [n() - 2)]/r

for n(r.) the index of refraction at point r1 and r = ri--i I. This parameter in thit

key unknown in estimating the performance cf laser systems through the clear.2atmosphere. Among those -xplicit or indirect dcpendencie-s on the Cpr'ile ar.. ..

log-amplitude of light fluctuations, wave structure function, receiver diaieter for

heterodyne detection, and modulation transfer function.

In flight, the thermosonde passes its temperature difference measurcre,:,t (if

T 2 - T 1 through a root mean square (rms) module. Ground-based procensi, g con-

verts this to the mean square temperature fluctuation (T, - T1)2, which over oric2 1

meter separation equals Cj. This is converted to CjN through the equation:

2 = 79.9 P(h)X X 10 2CN(h) CT Q()

where P(h) is pressures in mbar and h is altitude. 1

The original lightweight thermosonde system was developed by GTE' Sylvania

Inc. , Electro-optics Organization for the Goddard Space Flight Center in 117 1.2 . 3

1. Tatarski, V.I. (1961) Wave Propagation In a Turbulent Medium, McGraw-11111Co., New York.

2. 1litterton, P. J. , Mallery, L. E. , and Arken, T. A. (1.971) IhtwegyhtTh'ermosonde System., GTE Sylvania, Inc., l"inal l ~eport-NA•-114 93.

3. GTE Sylvanda, Inc. (1972) Lighhtieight Therrnosondc System Model 140(Instruction Manual), Mountain View, Caornia, fl4i-0

14

S. . . ... . . . .. .

. , . . .. :• . . .. .... , ,..

Page 15: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

Thisi jaxotttyj'. rsynti''nt Witt)flow IJWIy till Witilomi w0iof. till Al,(It 1i,of

1 U N'uvcrnl ru 11171 I Lt U.bl.', 11it. hod li iio ith nx 'twult~. wniklyZit it fy .11,'•k I .. IHilie'l

of the Goddard Space Flight Center, NASA. 4

Mudlbatlonu 1',m fi Wilvi -)utit( ojprittlon ojf thiin hypitiri, v, ert railfti In If7'?" by tlt-i

j~Alit Fuitt cWcapo:'i Luji'vz miiy. liizti I mr Avii, V.. M tx. %&iUk cnntintanrie orji

ft orrlnul rl-illu JDyliaaitt lonl Cl~ '~wallot'. A imw L-1 Ovml 't6~ A oard I t yout afil cutin-

juiuit.Iirt 1t:julk- i'u t til 4. In wt '1 1''* ii.t. di Ilt A I(;I In l Io fii,- £ t Itttrx% 1"1 1

id I 'liltuI 1:t vwith it !P1 tll fI111,imfl v tf't t

t001 W ~lt (-it qut 4 -di ' It W.14n 11 f it' tnfty Wt tuft1

ritl f .L Urej'I;1A;:Ill V.; It' Ioill u r Lnjif ;yipta 0 (Hymir: 2) vib 10, ; gfu i nign fi,;'ift'ai -

tit Ituti 11th Y'C2( tmhfitI.Il.Wd waut tuatjtltyti lt- tirall1rtzIrg, n'rv1'vntu ;it lm hu f

tilt- A)-(.c;sIU liuiivi brartn' 1.

:i. I1 In ,frmintifusei Ir 1-11 uijt'llu

The theirmomonde monsists of lt.u fise-wirs twigastan probes vxpoflrd tu thit

ambient atmospherv and ueparated by I m, Each probe ham a reaiubanoo definedlit ulp I Ille [IIi I i' a ~ ttt? diffi ci' ti I.* IV 1-t . till `LAu I~ 6eTh,A'

In (it 't-i ,iiio (I fj n; , if w,(,u l o I'i vi-d duff': i, * ;i It. vltn utme'

0.1'li ki I . litU Ahtb t. . I 'I hliti n -t I 11jut li Lit Li'~ ' t -tI . 1 9.' iHiIf aw1ý 0 it it'

nunt Iu Iii tin 's Ar a ili.I blttru I flu"' t'atal''t hi .i II. lit hI'i l1j ie''J'lit V, titI' l

jtari tVId It oJuw ti; 'J:u;,''lt ';til ,1- t1 iIttiia 1, .'li', 1.1: i'ft, I t it't li-uj:.hii, itt P Iiol, it

;w m uit te 14cl't i' t It' Ti ft ' t ' ,V II I'll tii','ha l t- 1 h'Ill. t l 111' 1 (t Utlj T ll to tt I 1' IN'

42 Hu'i' i~ttz vI Y U01 tai l '311 v1.Y -)kfhl filtt I li't 'fI Y. I'N'.t: -3 01J1 1 utolii'L tfi'I itta MIl 11

4 li fto, .1. 1 , ('17:5) 1 tiit I itie Jiridf Alv'tt I ii Wto bidtltt;'t !Iata v.l it

til--i ut jowt Ill njtli' il' -t Ill~I tilt~ t AS ol ' Nli 711.7

7. Mu: jihy, P;. (;~i V, 'I 'It Itleirti- Mill IStV ' th b I fillQ~j bt/u~~~~

AIt1ý1 ~io~, 5

Page 16: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

mOp,

1F:I'ure 2. Phot',graph of "T'hermoFbonde and Micro .Thermal Probe, Tungsten wire(Iatrnitr!r 3.45 min. Effective length is 0. 45 cm. Nominal ice point resistance is27 uht,, awl itst t e.i.pcrature co efficient of resistance is 0. 0u375OC-1. Sensorwireretou:hed for Iettor photographing

IwoO 1iz and 0.2 liz, respectively. A 1-sec rma average is performed on the

filtered signal.

In tile cas e of a squar'e wave Fignal, the rms resistance is one-hall the peak-

to-peak rensitance and Eq. (2) becomes

rms )(/(2crl })

T'ihe fijri 99. f8 zi , rCeit palre tungtiten wire is m anufactured by the: Sigm ond

Colc, wCorp,. Mt. Vernon, N.Y. , and the wire is attached to a probe assembly

by Datumetricus, Inc. The normil at wirv diaine'ier Is 3.45 pn, A 0.45-cm length

of the wire is mounted hetwccrn two 0. 5-cm long wire supports extending out from

the probe holder (Figure 2). Its nominal ice point resistance, R10, is 27 ohms at

0()C. "J'hin bets thie elctrical resistivity at 5. 9 uQ2 - em. The cemperature coef-

fitient of 2,11 tarlcC was imiCEIsured at 0. 00375)C-1. Note that the electrical

If-;

.1.

r%.y.

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resistivity and temperature coefficient differ from tabulated values. This is pro-

bably due to a low annealing temperature of the drawn wire. 8

Opthnum performance of the thermosonde can be achieved by passing a current

through the wire that is large enough to enhance the temperature response, but

small enough to avoid significant velocity response. Since a cool ambient fluidflowing over a warmer body will lower the temperature of the body toward the

fluid temperature, it is desirable to keep the current-Induced temperature dif-ference below the minimum detectable value of 0. 0020 C rms. The maximum cur-

rent allowed for not exceeding this temperature difference can be estimated from

a heat transfer analysis. The current generated temperature difference, tTw.can be determined as

•P.

ATwYKJi * (4)

where1 w P is the electrical power input between two conditions

J is the mechanical equivalent of heat 4. 18 (Joule/Cal)

As is the surface area of the wire = 5 X t0-4 (cmr2 )

h is the heat transfer coefficient (Cal - es . - LI).

The power input is P = 12(RA+-P,) where RA is the sensor resistance in the ab-

sence of an applied current and AR is the change in resistance due to applied

current.The heat transfer coefficient of the actual thermosonde probe was determined

in the laboratory by the temperature difference between two power levels. A spe-

cial bridge test circuit (Figure 3) was built to provide a constant current across

the bridge. This current alternatively can be stepped high and low, depending upon

the input voltage E. The bridge output, E0 , was amplified by a factor of 83. 33.The additional wire resistance, R, caused by the current heating was determined

from the observed voltages and current as

t1 - E /83.331i (5)

The current converter input voltages were stepped from 0. 5 V to 5 V, which pro-

duced pjibe currents, Ii. of 0. 5 mA and 5 m.A, respectively. The observed

8. Sm itnc2)ls, C.J. (1952) Tungsten, A Treatise on Its Metallurgy, PropertiesAnd Appblcat ions, Chapman & Hall, London, 3rd ed.

I'r

17J

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I

°106k 160K-

lOOK 1 2KK,.-K A

50RIDGE " W500 OHM

-

Figure 3. Schematic of Thermosonde Sensor Convective Heat Transfer TestCircuit. For a given input voltage, Ein, the LH004I circuit produces a con-stant probe current of (Ein/(2 X500)) amps. The 725 amplifier provides an out-put, E - 83 33 X Bridge potential difference. Thus the differential resistanceof the gridge due to probe 12 R heating is: R = Eo/83. 33 Ii

outputs were 0. 01 V and 0. 32 V. The temperature difference produced ini the

wire, ATW, is

ATw = (R5.0 - 0. 5 )/ aR , (6)

where in this case R =26.28 0, AR 5.0 -R0.5 H 0.528 0, and ATW = 5.360C.

The difference in power between the two test conditions was determined as

AP z P5.0 - PO. 5 = (24.75 RA + 60 E 5. 0 - 6E 0 . 5 )puW with a measured RA = 28.25 Q,

AP = 718 pW. From Eq. (4), the experimentally determined heat transfer coef-

ficient is found, h = 0.064 cal , s"1 . cm- 2 . oK-1.

In flight, using a probe power of 1/3 MW rms produces a self-heating temper-

ature rise [using Eq. (4)] of

AT = 0.00250C (rms)

Consequently, self-heating effects set the thermosonde noise level at 0. 002 C. The

actual flight condition heat transfer coefficient depends upon air velocity and den-

sity. A study was performed to determine the convective heat transfer coefficient

18

• .a. -s

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as a function Reynolds number. The heat transfer coefficient h is described in

terms of the Nusselt number Nud as h a Nudk/d, where k is the thermal conductivity

of the air and d is the characteristic length. The Nusselt number can be calculated

from the Reynolds number Red over limited regions.9 Calibrations of h vs pressure

and wind velocity were performed in a bell jar/blower vacuum system at conditions

corresponding to the surface level, that is, p = 760 mmHg, T = 24°C,

velocity= 5m - s- (corresponding to the vertical balloon ascent rate) Re 1 1. 2;

h is evaluated to be 0. 12 cal - s-I • cm"2 . o°KI or double the "no-wind" condition.

At lower pressures, the bell jar density is correlated with the standard atmosphere

to obtain altitude. An altitude profile of h is constructed from these calibrations

(Figure 4). Above 29-km altitude molecular flow occurs. Here, the free molecular

heat conductivity given by Dushman is used.' 0 It is clear that an increase in velo-

city (Reynolds number) at standard conditions enhances the value of h and lowers

self-heating even below the specified 0. 0020 C. At the maximum expected altitude

of about 30 kIn, h 0.031 cal. s- cmI 2' °.K', and self-heating can be ex-

pected to approach a noise value of 0. 005 0 C.

4 0 \%

4f4

0.031

30 :I

t320-

10 REYNOLDS<EFFECTLOWER LIMIT FOR----

VISCOSITY FLOW

0-3 10-2 0.064 10-I

HEAT TRANSFER COEFFICIENT, (vol. s-, cn" 2- kOli)

Figure 4. Heat Transfer Coefficient Curve of Thermo-sonde Sensor as a Function of Altitude. Bell jar cali-bration. At STyf, h is _measured at0.064, cal ' - cm-2 °K-I. With air §peed5 m "-, h- 0.12 oa1l cm- - °K-` at 30 km,h .0.31 cal. s- •cm .K . Above 30kin,free molecular conductivity applies

9. Maron, L. (1981) Fluid Dynamics, Academic Press, New York, Vol. 18,Part A, p. 27 1.

10. Dualhman. S. (1962) Scientific Foundations of Vacuum Techniques, John Wiley,New York, p. 47, mair

19

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I3.3 Seno Frequency Respons

If the temperature of the environment T. suddenly changes, one wishes to know

how fast the sensor will follow the environmental changes. Assume that the wire

initially has a temperature Ti and is to be brought to an environment temperatureTe, The time for the wire temperature to recover a given fraction of the environ-

mental temperature is given as:I1

0 -2abt (7)r

where.

00 Tmax - T e

0i Ti - Te

r wire radius (cm)

a thermal diffusivity of the wire (cm 2 /see)

b h/k

h - convective heat transfer coefficient (cal s- 1 . cm 2 °K'l)

- the maximum temperature in the wire after time, t

k = thermal conaurtivityof tungsten (cal -s- I cm- 1 o K-l)

x 0.426 cal- s- cm-1- OK-1

a --

Pw tungsten density - 19.3 g cm 3

a heat capacity of tungsten = 0. 032 cal• g 1 OK-1

2.-a 0. 69 cm s

b 0. 16 cm 1

t - time (sec)Thus, the response time required to recover 0./0i 50 percent and 0 0 /9 = 90 per-

cent is 0.4 msec and 0. 72 msec, respectively.

This was verified experimentally. The sensor was placed in , bell jar vacuumchamber. A current pulse train of 0. 5- to 5- mA amplitudes was applied to the

sensor and the ac bridge signal response was displayed on an oscilloscope. It wasobserved that the bridge output approached 1/2 of its full-scale change in 0. 3 msec.

This gives a frequency response fl/ 2 - 3570 Hz. It is clear that the sensor has an

adequate temperature frequency response for the purpose of turbulence

meaaurements.

11. Jakob, M. (1949) Heat TransfeL, John Wiley, New York. Vol. 1, p. 291.

20

IA

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3.4 Thermosonde Calibration

The thermosonde measurement is transmitted as a frequency value, nominally

ranging between 30 and 700 Hz. Each frequency is related to a resistance which

is defined by the observed temperature difference using Eq. (3). The relationship

between frequency and resistance is determined by actual observations. A thermo-

sonde test box was fabricated that alternately switches a test resistor in and out

across one of the pair of matched 27 Ii resistors to simulate the probes. Any one of

12 precision resistors ranging from 1. 4 M 0 to 20 k Q can be inserted for the test

resistor. These parallel resistors establish a known equivalent resistance. The

differential resistance (AR) across the bridge is then,

,AR R -Rps eq

where R is the simulated probe resistor 27 Q, andps

R XRR eq RPs +a

ps s

where Rs is the inserted test resistor. Thus,

2

R = R

ps s

For each thermosonde a table is constructed for AR vs radiosonde frequency.

6Trms is calculated from Eq. (3) and a polynomial fit is performed on this data

in order to provide the transfer function. Typical calibrations are shown in Fig-

ures 5 and 6.

3.5 Thermoeonde Environment

The thermosonde was suspended 18 m below the sonde balloon. The balloon

diameter expands from approximately 2 m at launch to about 10 m at 30 krn.

A working rule is to locate experiments at least five diameters below the bal-

loon to avoid wake effects. The 18-m suspension length is a compromise. A

longer length can enhance a pendulum motion that would interfere with measure-

inents. Thus, it is expected that the therroosonde will be located inside the balloon

wake except during instances of large shears. However, even with the thermosonde

inside the balloon wake, it is not clear what type of thermosonde error, if any, the

wake would produce.

21

'I

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R91

.008 R

"I RG.007

' R7 HIGH GAIN

S-R6 ,1RIP.-z__ . 5 RII1- -.05

-.04R5 oR0.04

R5-

.001 HIG GAIN4 .01

.0 R6 RI3

I00 200 300 400 500 600 700FREQUENCY (Hz)

Figure 5. Calibration Curve of Thermosonde Sensor6F% as a Function of Radiosonde Frequency. Testresistors are switched quickly across simulatedprobes. This prnvide.s a calibration frequency foreach lmown differential resistance

.05 - .25h e HIGH GAIN CALIBRATION

.4 LOW GAIN CALIBRATION.20

LOW GAIN IS-.03 15

-�3 nHIGH GAIN 10

.01 _ .05

/]Hr I 1I, I I J

100 200 300 400 500 600 700FREQUENCY (Hz)

Figure 6. Calibration Curve of Thermosonde(AT)rms as a Function of Radiosonde Frequency. Fora probe of given resistance and temperature coeffi-cient, the resistance vs frequency calibration curveis converted to (OT)rms vs frequency

22

L I --

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The existence of R wake behind a slow moving balloon (Re - 105) could gener-

ate a temperature fluctuation due tc two mechanisms. The first is due to turbulent

mixing of the atmospheric ternperFture structure over some vertical scale length.

The second could arise as a companion to compressible flow fluctuations of the

velocity in the wake.

In the troposphere, the sonde is usually in supercritical flow, and the sepa-

rated flow produces organized vortices. At about ll-kms. the flow becomes sub-

critical and the flow around the balloon turns into a randomized separation and a

uniform turbulent wake. Analysis of the thermosonde data reveals no significant

differences between tropospheric and stratospheric data. The thermosonde data

indicates the probability of C2is log normally distributed. Power spectral analy-

sis of CT shows that no frequency spikes or features exist over the measurement

range of 2- to 200-sec periods. This implies that any wake effects arising from

atmospheric structure would have to arise from scales smaller than 10 m. The2thermosonde observes layers of high CT over scales larger than 20 m as well as

undetectable C T (S/N < 1) for scales larger than 10 m. This strongly suggests

that the existence of a wake does not cause false signals.

The explanation of why there is no wake effect could be due to the rapid dis-

sipation of wake gradients. The small scale of the wake (length less than 10 m)

allows rapid mechanical mixing to a still smaller scale followed by rapid thermal

dissipation. We have made measurements of the rate of energy dissipation, F, in

the wake of high altitude aircraft. Film density analysib of aircraft wakes marked

by creating a smoke trail of titanium oxide hydrates shows the energy decay rate-4

to follow a t dependence. Thus, for a vertical rise rate of 5 m/see, the balloon

wake energy should be expected to dissipate to 1/256 of its original value by the

time it reaches the thermosonde.

Confidence in the absence of wake effect will be developed as more of the data

is analyzed and C2 comparisons are made with the scintillometer and radar.

4. DATA REDICCION

The "raw" transmitted MET signal is bandpass filtered at 400 Hz and 5000 Hz,

after which it triggers a "one shot" comparator. This results in a "clean" train

of constant-amplitude/constant-width pulses equivalent to the MET frequencies.

A Hewlett-Packard model 5326b timer/counter measures the time period of every

other frequency period and transfers these times in a binary coded decimal format

to a Honeywell computer, model316. The computer packs a magnetic tape eight

bits per word in a pre-determined record size and format. These tapes are then

unpacked and converted to CDC 6600 computer compatible 9 track tapes.

23

.1

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4.1 Time Period Records

N Running time is determined by setting the algorithm time e Header time +

2 E T where header time is the actual Zulu time at the start of each compu-im true'

ter record. The factor 2 appears because the counter measures every other peri-

od. The true time period is:

T tape speed input to countertrue =tape" apeed of original recording X measured counter time

For this series, the tape speed counter input was 1/2 the original tape speed. If

any T true is less than 0. 91 msec, it is considered a data glitch and dropped from

the summation and analysis.

4.2 Reference Frequency ID

The unpack routine is initialized to the measured reference frequency at launch.

A forward test searches for three successive data periods with a frequency of the

initialized value : 5 percent. When this criterion is achieved, a backwards test

searches in reverse from the first of the three found frequencies to the first en-

counter of the initialized reference frequency ±50 Hz. Once aloft, the reference

frequency is allowed to drift slow"' 'om its initialized value.

4.3 Segment Windnw ID

After locating the last reference period of the previous reference segment, the

time interval of the entire eight segment commutation frame is measured by sum-

ming each period and multiplying the result by two as described before. This de-

fines the frame time. Since there are eight segments, the frame time is divided by

eight to identify each segment interval. Since the frame rate is set at approximate-

ly 2.0 sec, the segment dwell time is approximately 250 msec per segment. Only

the center 60 percent of each time segment is used in the frequency determination

for that segment. The first and last 20 percent of the segment time is dropped and

the remaining periods are averaged. Inverting the average period provides the

average frequency for the segment. The standard deviation of each segment inter-val is calculated, and if aref exceeds t 10 Hz, or if a temp a.., or apress exceeds

± 5 Hz, the two smallest time periods are dropped. In most cases this removes

spurious pulses. A new average and a are redetermined, and if aref exceeds

+ 10 Hz, the entire commutation frame is dropped from analysis. If utemp, 0 RH,

or Upress exceeds ± 5 Hz, the calculated segment frequency is considered erron-

eous, and individual bad segments are dropped from analysis. In addition, if at

least two time periods are not found in a particular segment, that segment is

dropped from analysis. The segment sequence per frame is, in most cases:

24

• =• . ... . I .. . -

Page 25: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

reference, thermosonde high gain, temperature, relative humidity, thermosonde

low gain, pressure, temperature, and relative humidity. When the thermosonde is

not flown, those segments usually contain second samples of pressure and relative

humidity.

4.4 Tracker Data

Due to the intrinsically low signal sensitivity of the on-board receiver, and

to tracker hunting errors, large fluctuations occurred in the instantaneous position

measurements of azimuth, elevation, and slant range. These data were refined

after each flight on a CDC 6600 computer. The data. which were recorded every

0. 1 see, was edited by passing through a first difference software routine. Dif-

ferences between adjacent points greater than two standard deviations from the

average deviation were flagged. The average first difference is defined by:

n (X -xi..1

7- X n- IP2

Where n is the number of points and X. is the value of the ith point. The standard

deviation is:

-n ]

a = 1 - 1 -2 ý Xi xi I(i i- il) i=2

i2: -L

To smooth through the flagged data, a search was made to find four statistically

acceptable points on either side of the flagged values. Once found, least squares

polynomials were generated through this eight point array. Root-mean-square and

Durbin-Watson criteria were used to automatically select the optimal fit, up to

fifth degree. Polynomial interpolation then replaced the flagged data,

Smoothing of data within ± 2 a was performed by replacing centered data with

a 3 X 3 moving average of neighboring points. The average is defined by:

X -/9Xi- 2 + 2/9xi. 1 + 1/3Xi + 2/9Xi+1 + 1/9X11+2

Simultaneously, a second arithmetic running average was performed on the

resulting data to create 10-sec averages spaced at 2-see intervals. Furthermore,

the data went through a low-pass digital filter having a -3 dB band edge at 0. 01 Hz

that drops to -60 dB at 0.02 Hz.

25

Page 26: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

The smoothed azimuth, elevation, and slant range were then transposed to X,

Y, and Z Cartesian and geodetic coordinates. Using data time spacings of 30 sec,

north, east, vertical, horizontal balloon speeds, and horizontal wind shears were

calculated.

Sample results of the balloon position, velocity, and horizontal wind shear

calculations are presented in Figure 7. The data are interpolated for even spac-

ings of time every 2. 0 second.

5. PROGRAM DESCRIPTION

The general researci, objective of this program is to compare the measure-

ments of atmospheric turbu!ence of several different experimental designs. The

primary instruments consisted of the MIT Lincoln Laboratory 440 MHz 12 turbu-

lence scatter radar and an Air Force Weapons Laboratory Stellar Scintillometer.1 3

In addition to the primary instrumentation, radiosonde, thermosonde, and air-

craft instrumentation were used to provide a broader comparison base. AFGL

operated the sondes and scintillometer, while personnel from the Northeast Radio

Observatory Corporation (NEROC) operated the raar. Aircraft measurements

were provided by Airborne Research Associates, Bedford, Mass., under contract

to AFGL.

From 10 Feb 1081 until 8 Aug 1981, over 30 radiosondes were frown. Twenty-

nine of these are listed in Table 1. The preliminary qualification flights, up until

21 May 1981, were launched from AFGL. The remainder of the experimnents (22)

were launched near the NEROC Haystack Observatory at Millstone Hill, Westford,

Mass., during the month of July.

Scheduling conflicts, time of day, and equipment availability dictated, to some

extent, the particular experiment on a given day. The scintillometer could be

operated only on cloudless nights. The aircraft required co-ordination with the

FAA, and it was further constrained by bad weather and other scheduling difficulties.

The radar was shared by other groups at Millstone, and it was available for these

measurements only on those dates pre-arranged weeks in advance. The radiosonde

*As of this printing, a detailed description of the positional data was beingprepared for publication as an AFGL technical memorandum. The title is:Analysis of Balloon Trajectory for the Calculation of Wind Velocities and Shears,by Sullivan, B., et. al.

12. Watkins, B.J. (1!81) Millstone Hill Doppler Radar Observations of Winds andTurbulence, Middle- trpheric Program, Handbook for M•P, Extendedabstracts from Int. Sym. on Middle Atm. Dyn. 2:30-36.

13. Ochs, G.R., Lawrence, 1.S.,. and Wang, T. (1976) Stellar scintillationmeasurement of the vertical profile of refractive--index turbulence in theatmosphere, Proc. Soc. of Photo-optical Inst. Eng. 75:48-54.

26

,:$

Page 27: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

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Page 28: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

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28

S< =l •I • ' ' ' ' ' , ; ?

--- - -, - - --- -, - ,--- -- I- ... ------ t ... iI ;.a. ; -.aMI •, , ' •, 's. -I-

Page 29: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

"I.:; ; Ap l ii Aa il

I - I . 04.. , I

9I , . I ,p ,. I • . I .. . , .

IKol i II •., -,k-I v i I ib .. , I' f) 1,

jI * I , , ,

I T - - I... l.. . *--I - - - -- 4- - .. .9-9- - ,- -I .. L ' I :L : .,L.. N 4

, , ,F MLII , V V L Li I .I , , : , , , I , I

r- .. .• - Is . .I. . . . i ..... 4 4 I - ! . . -IF - . - -I

'. 4 '4 I i ' 4 '4 i'" ' i

. II I II ',* I .- • •, •

.. . ... I .. . . . I C.. .. , .

.-. ,. - , , . I .. .. . . . -

I- I-. . . .. - - -. . . • . . . . F.. . • . . . .. . • - '.. . .. 4 --,. . .

• ,,s : ' i .. : : o , .- ; A

! , . , ., • • ., • . . , ., I , • l2-,

1I

Page 30: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

i PI .. n '.. "

i2*'o, Q Q- lt I ,.,<*• o5I '<I I I +

I• , - " > I . : , I ' ,I

I i

1,1,

8 ---- 1 -- --; ----- - -- H-- -- ;.-H--H -- •-I-- --k--I

Q , ' : :. :. . . . .-.

•. -; .. ,

"I-_, ;- • [ ... . . . _ • _ • • + ,C, ' ' I

'- -------H--- • -------- ---- ----- I- -- L- F- --- -- I

ۥ- " .4<1

I'i • -, r-" -, • I F-. " -~*-• - - - - - • - - - - - - H r- - - -H----

* .t-•H m H- . ,

L' • I ' I-d- .. . .. T.. - - - • - ' . . .'I-

- " Ii ... ,+ I I , I

C , I ,- ' , C , ,

I ,,

...I I . . .II I . .. . .. .. .II. . .. ..I

Page 31: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

and thermosonde had no constraints other than availability of tracking personnel.

As it turned out, the scintIllometer and radar operated together only on one even-

ing. 31 July 1981. Good quality experiments using three techniques, radar,

thermosonde, and aircraft were accomplished twice. Good quality radar and radio-

sonde measurements were completed on fifteen occasions. Good quality radiosonde

and thermosonde experiments were operated on eighteen occasions. Radar, radio-

sonde, and thermosonde operated successfully on eleven occasions.

6. RESULTS

Results of typical experimental runs are presented in the following plots.

Figures 8 and 9 show temperature and relative humidity profiles obtained 31 July.

A small temperature inversion is found at 3 km that roughly corresponds with a

high negative gradient in relative humidity. A more pronounced temperature

inversion is found at 12 km, defining the tropopause.

QO2O MT DTA

24.0-

21.0-

18.0-

I S. a- ,

S12.0"

9.0"

6.0-

3.0

-si -4.0 -31.S -A-00.5 1.o0 1.5 2s .0TEMP (DEG C)

Figure 8. Typical Temperature Profile Plot. Processed result

31

• (

Page 32: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

¢QM~ MET CPTYA1.0. T

7.0

6.0

7.0

6.0

S.0

S4.D

.- , 3.O

2.0

10 20 30 ZO so 60 70 so

RELATIVE HUMIDITY (PERCENT)

Figure 9. Typical Relative Humidity Profile Plot. Processedresult

Figures 10 and 11 show the east and north balloon velocity component profiles.

The maximum horizontal wind occurs at 10.7 km at 35 m/sec. The detailed wind

structure is clearly evident.

Figure 12 shows the horizontal vector wind shear, SHR profile to 30 km. SH

is defined as the resultant of the east and north horizontal component shears, or

SH2 =N + S2. Figure 13 is an expanded view of Figure 12 in the altitude range-1

from 20 krn to 25 lun and shows the mean shear at about 0.02 sec . This plot

shows structuring of the wind shear down to the spatial filter wavelength of about

120 m. The power spectral density of the winds are plotted in Figure 14. The

slope is about -2. 5, which compares well with other measurements. 14

14. Endlich, R. M., and Singleton, H. C. (1969) Spectral analysis of detailedvertical wind speeds profiles, j. Atmos. Sci. 26:1030-1041.

32

Page 33: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

QIX002 FINIA TRIO4rT 4NOLVSIS

6.7O

S11.z

3.7,

S-is -o -is A -'s w a mVELOCITY - EAST (M/SEC)

Figure 10. Typical Balloon Velocity Analysis -East Profile Plot. Edited and filtered

QXOOM FINAL Tq••T ANALYSIS

•I•.O

3 .S!1.2

-AS A-0 -is tj its 1' 4VELOCITY - N0RTH (M/IS:ll

Figure 11. Typical Balloon Velocity Analysis -North Profile Plot. Edited and filtered

33 i

Page 34: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

XOMOO FINAL TRlMT ANAYSIS

3.7

-. i 6)1 .&si 5.6-m 6.8-w 0.WS 5.1% . o.8- co

514 ,VERTICAL 1141HAR OF I4OIZONTAL WIM

Figure 12. Typical Horizontal Vector Shear Analysis.Profile plot. Shear is calculated over a 30-sec dataspacing

OX0M0 FINAL TRAOT ANALYSIS

M HVETIA OHEA OFM ZNTLWN

Figur 13. xaddVewo7oiotl etr er

Th sher aliuersltoni bu 2

Z3.IZ34

ZZ.~ so,

Page 35: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

02(20 MGO 126 POINT FFT. *IHING S'TOOIEO.

to

S101

(-I

-. . . .. It,-

WAVE NO. (CY/M1)

Figure 14. Power Spectral Density Analysis of HorizontalVector Shear. The slope iss about -2. 5

Figure, 15 shows "RAW" thermosonde C2 values as a function of altitude. The

2 N

mean C• tends to decrease logarithmically with altitude. Figure 16 is an expanded

N

view of Figure 15 in the altitude range from 10 km to 15 kin. A large-scale max-

mum shows up at 11. 5 km while the fluctuations in C- Npert edet h ml2

sampling interval. C N smoothed to 120 m is plotted in Figure 17 for comparison.Figure 18 plots the cumulative frequency distribution of C 2. Th~e data follows a

UT

straight line, except at the endpoints, which confirms the log normal distributionof C2N"

IL The purpose of the optical turbulence program was to compare various tech-

niques of observing C N. Sonde measurements were important in the low altitude

comparison between radar, scintillometer, and thermosonde. The radar-received2

power, scattered by refractive index fluctuations, can be related to a CN. This

C• is caused by turbulent fluctuations in both temperature and water vapor concen-N 2

trations. As the comparisons are based on optical wavelength CN the contribution

of water vapor must be removed from the radar C N.

35

lam

WAV .O IC/N

Vetr ha. h soel;ao t -2.5 1Figure.14. Poe SpcrlDniyAayi s fHrzna ,-

Page 36: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

The fluctuations of the refractive index across a layer is given 1' 15 as:

M x -77. 6 X10' 6 1+ 15,50i4 - 15, 5004j 8

where

j

P x pressure (mb)

T g temperature (Kelvin)g , gravity (m •s2

q s specific humidity (gm/gm)2 = squared Brunt-Vaisala frequency (s-2) r (g/6) 0'

qI = vertical gradient of specific humnidity (m" ')0' = vertical gradient of potential temperature (Kelvin/m)

The radar CN can be corrected to dry conditions, CN (dry) by evaluating thebracketed terms in Eq. (8) on the basis of the sonde measurements of P, T, and q.

2 2 1 _ _rC'N(dry) - CN(rmdar) ft1,00 -15, 500g ý j2

2

The comparison between the CN (dry) derived from radar measurements and the

optical scintillometer is shown in Figure 19. The optical scintillometer 1 3 obtains1 ata over very large weighting iunctions. The scintillometer i/e half-width varies

from 1.4 km at an altitude of 2.2 to 4. 9 km at an altitude of 14 km. The weighting

functions are shown in Figure 20. The comparison between radar and scintiliom-

eter shown in Figure 19 is obtained by passing the C2 (dry) through the six weight-

ing functions.

A comparison of thermnosonde data and the scintillometer is shown in Fig-

ure 2 1. Here the thermosonde data shown in Figure 15 is passed through thescintillometer weighting functions. This agreement is good. The large smoothing

of the weighting functions hides whatever variations may exist due to the space andtime differences in the respective measurements. The scintillometer viewed the

sky vertically while the thermosonde followed a slant path.Thermosonde and radar comparison can be made over very nearly the same

volume and space by the fact that the radar can be pointed in the direction of the

sonde. The radar C 2 (dry) is obtained over one-minute periods and averaged over

15. VanZandt, T. E., Gage, KS.., and Wjirnock, J.M. (1981) An Improved Modelfor the Calculation of Profiles of CN and e in the Free Atmosphere fromBackground Profiles of Ternerature, and Humidity, 20th conf. onRadar Meteorology, (3" Nov--3 Dee181

36

4j

L -,o -,, .

Page 37: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

five minutes. A composite of the radar results is made to match the sonde altitude

and times. The comparison of radar and thermosonde CN values is presented in

Figure 22. The thermosonde data has been averaged over 0. 50-krn intervals.

The comparisons shown indicate the thermosonde radar and scintilloneter

are in quite good agreement. The data shown represents the results from just

one day's measurements. Detailed comparisons involving all the data sets will

be analyzed and presented in separate scientific reports.

26.2-

22.&

15.t

11.2

•- 7. 5-,I-- 7*

3.7-

c? (RAW)2

Figure 15. ]Raw Thermosonde C Analysis - Profile Plot. Low andhigh gain measurements have bein combj~ned into a single best meas-urement. The thermosode measures Cfq from ground level to 30 krn.C is calculated from CN and the radiosonde measurements of pres-sure and temperature

37

"l aI" " " . -

Page 38: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

F ----.--.--. O--

01(20

14 ,

12.

r't. i i [•

k--

10.

1071

c (RAW)N2

Figure 16. Expanded View of Raw Thertnosoride CN Profile plot. TheI altituide r-esolution of (~is about 10 m. Bach data point is, a result ofthe rms value of CT taken over 1 sec

38

Page 39: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

11.*1-j 9.%

C],Cps

12.7.

• 11.4-

S10.2

I,--

-J 6.

7.6

CN2 (SMOOTHED)

Figure 17. Smoothed Thermosonde CN Profile Plot.CK is smoothed over 120 rn

39

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I4<NSTRUMENTNOISE LEVEL

-44

-3-

cli

X

0

0.00-00-0-2 .5 2 1 203040 0 0 7 8 9095 98 9 9ý899

CUMULTIVEPROBAIL-T

8a C uaiePc'c'Jlt itiuinC.-eo ,G TenuTc

l~itur obbi .t Cu2 ltv Prbblt Ditiuio uw x O i.. Tero

probbiliy cT is 4. 5 X( 1Uo-0U

40)

Page 41: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

15.0

5 MIN AVERAGE0205-0210

12.5

.- '--- .

€.,. * ! .c4 (DRY)

RADAR WITHPATH AVERAGING

5,0 .. "', .

STELLAR -'•42.5 02-08 ",

0020

-o_-0 -19.0 -io o170 16.0 -15.0 -14.0LOG C11

2 (rr2/ 3 )

Figure 19. Comparison of lBadar C and Seintillometer C2Profiles. The path averaged radar and scintillometer pro-fiJes show good agreement. T'he points depict radar(Cn measurements. The solid line through the radar pointsrerqwsent 5 -min radar averages. The seven scintillometerineasurements are shown as • with straight lines drawnb'tween thejn. 'Fhe dashed curve represents the radaraveragId C, corrected for moisture and passed through thescintiliometir weighting functions of Figure 19

41

Page 42: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

FILTER PEAK ALTITUDE2 2 3.4 525 73 94 41•

1.0.

4x

.2;

0 2 4 6 to 12 14 1 8 2

ALTITUDE {km)

Figure 20. Scintillometer Weighting Functions. The optical scintillom

eter obtains data over these large weighting functions

42

Page 43: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

20.00

17.50

OX20

15.00 I

12.50 - h THERMOSONDE

10.00W

;d 7.5f STELLAR

5.00

2.50

0.00 . • -... .- -

-20.00 -19.00 -18.00 -17.00 -16.00 -15.00

LOG C2 (m-2/3

Figure 2 1. Corn arison of Thermosond C2 andScintillometer C1, and ScirtillometernCa Profiles.The Thermosonde "raw" C.1 data was passedthrough the ocintillometer weighting functions ofFigurC 1n. Although the scint!1orneter vie-wed thesky vertically while the thermosonde followed aslant path, the agreement is good

"4I3

Page 44: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

0238

/ • _ ozz620 0234

0230

/ •.-" MIN 0223

TH[ERiOSOWDE R - RADAR AVtRAGE 0

50015 COMPOSITE OF 029,

LOG AVERAGE r 5 PROFILES/ _0215

0210

0206

bE

0204

LAUNCH: OsbO r

- o 0020

II

31 JUL 01Th e•0o d -0 1e50 1

0-GZ RADAR

:* (DRY) 01,67

-15-20

LOG CN ( 2~

C2 2

Figure 22. Comparison of Tberrnosorlde 1 1, and Radar CN Profiles.

The herosode data is averaged over 0. 50 Ian. The R adar data is

D, time and space composite which attempts to sYnchronize the ie

space coordinates of the Radar and Thermosonde.

44

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I

References

1. Tatarski, V.1. (1961) Wave Propagation in a Turbulent Medium, McGraw-HillCo., New York.

2. Titterton, P..T. , Mallery, L.E., and Arken, T.A. (1971) LightweightThermosonde .System, GTE Sylvania, Inc., Final Report, NAS5-11493.

3. GTE Sylvania, Inc. (1972) Lightweight Thermosonde System Model 140(Instruction Manual), Mountain View, California, B440.

4. Bufton, J. L. (1973) Correlation of microthermal turbulence data wi'th

meteorological soundings in the troposphere, J. Atmos. Sci. 30:83-87.

5. Bufton, J. L. (1975) A Radiosonde Thermal Sensor Technique For Measure-ment of Atmospheric Turbulence, NASA TN D-7867.

6. Curatola, C. (1975) Modifications to GTE Sylvania Thermesonde For ImprovedOperation, Final Report, AFWL-TR-75-180, ADA 018227.

7. Murphy, G. P. (1981) New Techniques and Devices For Measuring StratosphericTurbulence, AFGL-T---81-0128, ADA 102680.

8. Smithells, C.J. (1952) Tungsten, A Treatise on Its Metallurgy, PropertiesAnd Applicationc, Chapman & Hall, LozAdun, 3rd ed.

9. Marton, L. (1981) Fluid Dynamics, Academic Press, New York, Vol. 18,Part A, p. 271.

10. Dushman, S. (1962) Scientific Foundations of Vacuum Techniques, John Wiley,New York, p. 47, 2nd ed.

11. Jakob, M. (1949) Eeat Transfer, John Wiley, New York, Vol. 1, p. 291.

12. Watkins, B. J. (1981) Millstone Hill Doppler Radar Observations of Winds andTurbulence. Middle ,tmospheric Program, HandbooFfor MAP, Exte-Te--deabstracts from Int. Sym. on Middle Atm. Dyn. 2:30-36.

13. Ochs, G. R. , Lawrence, B.S., and Wang, T. (1976) Stellar scintillationmeasurement of the vertical profile of refractive - index turbulence in theatmosphere, Proc. Soc. of Photo-optical Inst. Eng. 75:48-54.

45

Page 46: Sonde Experiments for Comparative Measurements of Optical Turbulence · Sonde Experiments for Comparative Measurements of Optical Turbulence J.H. BROWN R.E. GOOD P.M. BENCH G. FAUCHER

14. Endlich, R. M. , and Singleton, R. C. (1969) Spectral analysis of detailedvertical wind speeds profiles, J. Atmos. Sci. 26:1030-1041.

15. VanZandt, T.E., Gage, K.S., and Warnock, J.M. (1981) An Improved Modelfor the Calculation of Profiles of C2 and i in the Free Atmosphere from IBackground Profiles of Wind, Temperature, and Humidity, 20th Conf. onRadar Meteorology, (30 Nov. - 3 Dec. 1981).

416

III

if