Airborne photoelectric particle counter for mapping clear air turbulenc

Rosen, J. M.

Sadler, R. A.

English

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https://ntrs.nasa.gov/search.jsp?R=19710010923 2020-03-11T20:44:48+00:00Z
AN AIRCRAFT BORNE RUST PARTICLE COUNTER AND 
ITS ~ P P ~ ~ e A T I O ~ S  T  THE STURY OF 
EAR A I R  TURBULENCE 
By James M. Rosen and Robert A. Sadler 
Physics Department 
University o f  Wyoming 
Distribution o f  th is  report i s  provided i n  the interest  
o f  i n f  orma ti on exchange. 
Prepared under Contract No. NAS 1-9592 
for 
A ~ R ~ N A U ~ I C S  AND SPACE A 
OU ND 
ITS A P P ~ I C A T ~ O ~  T  THE STUDY 0 
AR A I R  TURBU~ENC& 
By James M. Rosen and Robert A. Sadler 
Physics Department, University of 
Wyoming taramie Wyoming 82070 
Met~rological parameters are often used t o  map and study regions of atmos- 
pheric turbulence tha t  are otherwise invisible to the eye. Trace atmospheric 
constituents such a s  aerosols can also be mapped, thereby i n  a sense rendering 
the turbulence visible, T h i s  approach can provide physical insight f o r  develop- 
ing  models of turbulence, 
The m a p p ~ n ~  o f atmospheric aerobols i n  the past has been hindered somewhat 
Recent years have seen increasing y more interest i 
. Mi%h the adven large a i r c ra f~  the inter tween the a i  rcraf 
structure and CAT becomes even more important. Yet under~tanding 
could perhaps be avoided altogether. 
effort has been made t o  develop remote sensors which detect some parameter 
thought t o  be associated w i t h  CAT. T h i s  approach is somewhat unsatisfactory 
because the relation between the measured, parameter and CAT fs_generally not 
well understood, both from a theoretical and experimental standpaint. The 
prospect of  developing a useful remote sensor of CAT or an accurate forecasting 
method would be greatly enhanced if  the detailed structure of the atmosphere i n  
and around regions of CAT could be adequately probed. The knowledge of the set- 
t i n g  i n  which CAT occurs is  fundamental t o  its understanding. 
The long range goal of  the research described here is a detailed mapping of 
the aerosol concentration i n  a region of turbulence. By using the naturalKy 
occurring aerosol as a short term tracer;the actual physical motions o f  the 
atmosphere can be inferred or reconstructed, T h i s  "visible" picture along 
w i t h  the associated met~oro~ogical parameters \.r1'1l lead t o  a better physica 
u n d e r s ~ ~ d i ~ g  of CAT and i t s  deveKo~en 
must be developed a ten§~vely tested. the ~ o l l Q ~ ~ i n g  report 
deals w i t h  this begin~ing effort. ~as ica l ly  there were three develo~ent  stages 
associated w i ~ h  t h i s  research: o f  the a i r  borne instru- 
mentation~ 2, @ n v i ~ o  
esearck C ~ n ~ e r  
an adequate level e I more were known about this phen~enon, i t  
The aircraft is s t i l l  the only recognized detector o CAT, b u t  considerable 
Before this go an be achteved, how ever^ he necessary nstrumentation 
on a j e t  a i r ~ r a f t  
-2- 
INSTRUMENTAT ION 
Many types 
1s changing in si 
The response of the i n s t r ~ e n t  i 
even w i t h  h i g h  speed aircraft. I f  the response time were of the order of two or  
three seconds for instance, the resolution u l d  be several thousand feet. The 
actual response time of the instrument i s  about . I  second, giving a resolution o 
80 feet or better. 
able, b u t  none of them are suitable for direct applicatjon t o  high performance 
aircraft. The commercial instruments are not designed t o  opeiate over the re- 
quired temperature and pressure range or  sustain the vibrational environment. In 
add i t ion ,  these instruments respond i n  an unsatisfactory manner t o  the cosmic 
ray maximum near 50,000 feet. An instrument designed specifically for aircraft 
use i s  therefore necessary. 
The photoelectric particle counter developed under this contract i s  very 
similar t o  the one used by the author (Rosen 1968) for high a l t i t ude  balloon 
borne measurements. By preserving the geometry of the detector i tself  i n  the 
aircraft application, the ambiguity i n  a comparison of the balloon sounding w i t h  
the aircraft sounding can be eliminated. The basic detector i s  schematically 
shown i n  figure 
plier as the sensing de ice. Air being sampled is directed i n  a well-defined 
stream through the foca the condenser lens here ~ n d i v i d u a  
scatter 1 i g h t  into the micro$copes an The p h o t ~ ~ l  t i p 1  ier 
i t s  index of re 
Several commercial versions of the photoelectric particle counter are avail-  
and is essentially a dark field microscope i t h  a photomulti-  
se h e i g h t  is t h  n a funct io~ of  article ss’ze 
requires simul~ane~us pulses fr 
be regi stered . 
  ti pliers for a par- 
to  noise r a t i o  
ccr 
0 
4 
-4 - 
I S  
s t s  were per thers Research Gorp 
i n  Boulder, Colorado. The ins~rument was first subje~ted t o  simultaneous temper- 
ature and pressure extremes * The ~emperature s varied Prom 60°F t o  -65OFs 
while the pressure varied from sea leve t o  70,000 f t .  A cold soak temperature 
of -65OF a t  a pressure equivalent to  70,000 f t .  was maintained over a 
four hours. During this time the internal temperature of the instrume 
decreased w i t h  a several hour time constant and f inal ly  ceased to  function nor- 
mally. Since the expected f l i g h t  time o f  the instrument was only one half houro 
addi tional heating for the instrument was not considered necessary. 
The vibration test was performed i n  accordance w i t h  NASA FRC Process Speci- 
fication No. 21-2, Curve 8, figure 1. T h i s  curve requires tha t  the instrument 
be subjected t o  a one to  5 g acceleration between 5 and 50 H t  and 5 g accelera- 
t i o n  between 50 and 500 Ht. The frequency sweep rate was such as t o  require 15 
minutes on each axis and a two minute dwell on each resonance. The response of 
the instrument to this d r iv ing  force was similar to  t h a t  of a driven damped har- 
monic oscillator w i t h  the resonance between 30 and 50 Hz depending on the axis 
of vibration. 
six shock mounts supporting the instrument. Superimposed on the basic response 
curve are various resonance peaks due to internal resonances of the components, 
The presence of resonances are undesirabl e because the instrument can respond 
w i t h  more than  50 g 's  a t  these p a r t i c u ~ ~ r  frequencies. However, the primary re- 
In this case the restoring force and damping are attributed to  the 
ever be avoided when shock mounts are 
After the first shake tes t  the ~nstrument was mod~fied i n  order to  e ~ ~ m i n a t ~  
some of the resonances a ce the ~ r i ~ a  ~es~nance  due t o  %hoc 
mounts. The response of the i n s t ~ ~ e n t  d u r i n ~  the second shake tes t  was adequate 
ew minor exceptions~ S 
the age and cond i t i  
w i th  problems. Dur 
the mountain lee  wave a c t i v i t y  had ceased. A f te r  f i v e  successful f l i g h t s  the 
amount o f  ground support required t o  keep the c r a f t  a i r  r t h y  had increased con- 
siderably, which i n  tu rn  necessitated the decision t o  terminate the project. 
However, a considerable amount was learned from the f i v e  successful f l i g h t s .  
The instrument i t s e l f  was mounted i n  the nose o f  the a i r c r a f t  and a short  
probe led  d i r e c t l y  t o  the outside a i r f low.  The geometry of the probe i s  shown 
i n  f igure 2. Ambient a i r  enters a small hole. i n  the end o f  the tube and deccel 
erates as the tube becomes larger i n  diameter. The holes i n  the tube near the 
aerosol counter aesure a continuous f low of ambient a i r  and prevent the counter 
from becoming pressurized e 
The four channels o f  information from the aerosol counter were tape re -  
corded by on-board instrumentation provided by FRC. I n  addition, pressure, tem- 
perature and accelerat ion were also measured by sensors provided by FRC. The 
p i l o t ' s  remarks were recorded during the f l i g h t  and l a t e r  correlated with the 
data. 
i s  s ign i f i can t  enough t o  reproduce here. A discussion o f  the en t i re  set  o f  data 
would only serve t o  obscure the few important resul ts.  
A l l  o f  the data received has been reduced, but only a small por t ion o f  i t  
The specif ic ob~ec t i ves  of the a i r c r a f t  f l i g h t s  were two 
ef for t  was devoted t o  tes t ing  the instrumen i n  atmospheric condi- 
d: f i r s t ,  a 
und~rstood i n  ~ r d e r  t o  conf i  
The second object ive was t o  p 
Figure 2, A schematic diagram of the sampling probe used for he aircraft f i e l d  
t es t s  e 
-7 - 
(u 
cc- 
0 
I 
CL 
c 
0 
C, 
(d 
I cr c 
(u 
V 
I= 
0 
V 
?-- 
.r 
.I- 
-8- 
The data Prom a descent 
through a cirrus cloud i s  presented i n  figure 4. The position of the cloud as 
determined by the aerosol concentration profile agrees very well w i t h  the pilot's 
remarks concerning the position of the cloud. Several maneuvers o f  this type 
were performed and the results were a l l  very similar. 
Figure 5 i s  a comparison between a typical lloon sounding and two vertical 
soundings obtained w i t h  the aircraft, The difference i n  concentration between 
the two profiles is due largely to  the difference i n  particle size: .2 microns 
diameter for  the balloon ascent and .53 microns diameter for the aircraft ascent. 
The general agreement of the two types of soundings i s  considered very good for 
the troposphere (below 35,000 feet). Above 35,000 f t .  the balloon entered the 
stratosphere, whereas the aircraft d i d  not. Thus a comparison of the two sound- 
ing methods a t  the higher altitudes cannot be made from this data.  
ed to  have sane effect on the measured concentration and size distribution of 
the aerosols. An attempt was made to  estimate the size of this effect by making 
several passes through the same area a t  different speeds. The results of this 
effort are shown i n  figure 6, b u t  unfortunately are highly suspect. If the i n -  
strument had been functioning properly, the aerosol concentration during each 
pass should have remained constant rather than decreasing. Before this problem 
could be fu l ly  investigated, the project was terminated. Thus the affect of the 
In general the sampling probe and the speed of the aircraft would be expect- 
probe on the measured aerosol has not yet  been satisfactorily investigated. 
rough moun ta i~  lee waves, but  t h i ~  type 
of atmospheric condition was almost non-existe dur ing  the time of year i n  which 
the flights were made. igure 7 shows the res ts obtai~ed from a consta 
tude data run  dur ing  a time when meteorologica con~itions were fa~orable for lee 
wave d e v e l o ~ e n t ~  The results suggest t e lee wave was de 
The large ~luctuations i n  the aerosol co 
temperature f 1 uc 
Several attempts were made t o  f 
correspond close 
o t  's efforts t o  s tant  a9 ti tude seem t o  corres- 
w i t h  the o t h ~ r  pa~ame~er$~ The Lions are associated 
44. 
43- 
42 - 
io3  
11. 
41- 
$0- 
39- 
38- 
37- 
36- 
3- 
2- 
1- - - - - *) 
E .5- < 
w -  
w 
-I 
c- 
B1 
2 -  
2 -  
1 - I 
'1 '2 I3 14 
TIME INTO RUN (min.) 
-1 
G 'S 
- 0  
_- 1 
,-56 
--58 
--60 
--62 
OC 
.-64 
--66 
--68 
. 
Figure 4.  A d a t a  r u n  taken through a c i r r u s  cloud by the instrumented a i r c r a f t .  
-1 0- 
200 - 
50- 
10- 
5- 
m 
E .< . 
M 
w 
-I 1- 2 
2 .5- 
c. 
M 
.I - 
.OS- 
.01- 
12 24 36 48 72 84 
Figure 5. A comparison of  typical results obtained by the balloon sounding 
technique and the instrumented aircraft e 
-11- 
1- 
.5- 
m 
E < 
m 
w 
-I 
U 
e 
4 a 
is= .1 - 
.05 - 
.01- 
- .  
\ - .  4 
Figure 6, The effect of the aircraft speed on the dust concentration measured 
at a fixed location, 
-1 2- 
G 's 
N O T  N O T E D  BY PILOT 
TEMP E R ATU R E 
O C  
m 
E 
AEROSOL COUNT, CHANNEL I 
\ GOOD -UPDRAFT 
I I ,  S W P N E  '\. . .Q1 I 1 I 1 I I I 
12 8 4  0 4  8 12 16 20 Distance from 
Site (naut. mi.) 
Figure 7, The s t ructure  o f  t h e  aerosol concentration i n  a probable mountain 
l e e  wave condition. 
-13- 
ts of the field tests show that a t  least a qualitative measurement 
of atmospheric aerosols can be made using an a i r  borne particle counter. 
testing was not extensive enough t o  adequately assess the quantitative accuracy 
of the instrument. The effect o f  the sampling technique on the ambient aerosol 
concentration and size distribution needs to be further investigated because the 
results obtained during the present testing were not conclusive. The major pro- 
blems of adopting a photoelectric particle counter for use on high performance 
aircraft have been solved, and another useful atmospheric probe is now closer to 
a reality. 
References 
Rosen, J. M, Simultaneous Dust and 020 e Soundings over ~ o r t ~  and Centra 
America J e Res. 3, 1968, pp. 479-486. 
Rosen, J.  The Vertfcal Distribution of Dust Near the Surface of the Earth, 
3 .  Air Pollution Control, - 19, 1969, pp. 105-108. 


An aircraft borne dust particle counter and its applications to the study of clear air turbulence

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