Ionizable constituent density measurement of D region using Lyman-alpha source and blunt prob

Hale, L. C.

Pontano, B. A.

English

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MEASUREMENTS OF AN IONIZABLE CONSTITUENT 
OF THE L O W  IONOSPHERE USING A LYMAN-(21 SOURCE 
AND BLUNT PROBE 
U 
ABSTRACT 
B. A. PONTANO and L. C. HALE 
Ionosphere Res ear  ch Laboratory 
The Pennsylvania State University 
niversity Park,  Pennsylvania, U .  S 
An experiment which measures  the density of an ionizable constituent 
of the D-region (presumably nitric oxide), has been flown successfully 
on September 22, 1968, December 6 ,  .1968 and December 12, 1968. This 
experiment uses a blunt probe to detect the changes in conductivity 
produced by Lyman-a ionizing radiation produced by a flashing micro- 
wave discharge in hydrogen behind a lithium fluoride window. The 
sensitivity of the experiment, which is inversely dependent on velocity, 
is enhanced by the use of a parachute. 
positive result, and an analysis of the data yields densities of the 
Gonizable constituent greater  than 10 /cm3 in the 40 - 63 km altitude 
range. 
The experiment yielded a very 
8 
IN TR ODUC TION 
This paper describes recent measurements of a neutral constituent 
(presumably nitric oxide) which have been made in the 40 - 63 km altitude 
range. 
Basically, the experiment consists of sending a source of radiation 
The experiment was originally proposed by R. A. Young in 1963. 
into the D-region and measuring the ionization caused by the source. 
https://ntrs.nasa.gov/search.jsp?R=19690018779 2020-03-12T03:22:16+00:00Z
2 
The changes in  conductivity caused by the flashing source are 
measured by a blunt probe. 
been summarized previously by Hale, Hoult, and Baker (1968). The 
blunt probe utilizes continuium principles to measure polar conductivitiees 
of the surrounding medium, the positive conductivity being due to positive 
The basis of the blunt probe technique has 
ions and 
ions and 
mobility 
vs. EIP 
the negative conductivity due to contributions from both negative 
electrons. Using charge neutrality, an assumed reduced 
for positive and negative ions, drift velocity data for electrons 
ratios,  and an appropriate model atmosphere such as CIRA, 1965, 
the data can be converted to positive and negative ion and electron 
densities. 
So that no major constituents including the O,('Ag) becomes ionized, 
the source must radiate above 11 18 A. 
the source has to radiate below 1340 A which leads to the choice of a 
Lyman-a! source (1216 A). 
be flown as par t  of a small rocket experiment was designed and built 
by Gee (1966). 
a 
However, to ionize the nitric oxide, 
The f i r s t  prototype of such a source that could 
The original calculations by Gee showed, for the simplest case 
one in  which no electron interactions occur, that the electron production 
by a rocket borne Lyman-a source is given by: 
where 
-1 -2 n = Lyman-a! f l u x  a t  the source in photons sec cm 
N(NO) = Concentration of NO molecules per cm 
0 
3 
3 
= Photo-ionization cross-section-of NO ."NO 
V = Normal velocity of the source. 
Since the sensitivity of the experiment is inversely proportional to 
velocity (eq. l ) ,  a parachute was deployed during descent a t  which time 
subsonic measurements were made. 
DESCRIPTION OF THE EXPERIMENT 
A block diagram of the entire probe system is shown in Fig. 1. 
The discharge lamp system consists of the Lyman-a'  source 
(discharge lamp) which is powered by-the lamp generator, a 1680 mc 
integral tube and cavity oscillating triode. 
coaxial cylinder shorted at one end. 
quarter wavelength long; therefore, when excited a t  the shorted end a 
voltage maximum occurs a t  the open end. When filled with hydrogen 
at a pressure  of about 1 mm of Hg, a discharge occurs a t  the voltage 
maxir-um (open end) behind a lithium flouride window. The spectrum 
&of the UV source is shown in Fig. 2 displaying no detectable radiation 
below about 1150 A. 
-2 c m  . 
at 5 sec.  intervals. 
The source consists of a right 
The lamp cavity was made a 
\ -1 The source intensity is about 1014 photons 8ec 
The activating circuit i s  used to turn the source on and off 
After every "on-off" cycle of the lamp, the probe voltage circuit 
changes the collection mode between positive and negative conductivity 
detection. 
collector ring (Fig. 3)  by a feedback electrometer.  The electrometer 
In either mode of operation, current  is measured at the 
output feeds a voltage controlled oscillator which i s  used to modulate 
the transmitter.  
4 
r----- 
w 
w 
FIGURE 1 
5 
5.c 
a' 
W '  a 
W a 
0 - 
0 - 
% 
3. a 
P- z 
W 
3 
0 
0 
W 
3 
v) 
a a 
2.6 
a 
a 
( L w  z 1.c 
I100 1200 1300 1400 
0 
WAVELENGTH I N  ANGSTROMS 
SPECTRUM OF ULTRAVIOLET LAMP USING HYD N 
FIGURE 2 
6 
LY LA 
NYLON INSUL 
RING 
ELECTRONICS 
HOUSING 
-SLOT A ~ T E N ~ A  
POWER CABLE 
- RETURN ELECTRODE 
BASE PLATE- 
EXTERNAL PROBE ASSEMBLY 
FIGURE 3a 
7 
NITRIC OXIDE PROBE 
FIGURE 3b 
8 
Two power supply converters and a board converter furnish all 
power and necessary voltages to the probe. 
The major portion of electronics is built into a 4" x 3" diameter 
drawn aluminum can, shown in F i g .  3 .  
mounted above the aluminum can within the nylon insulating ring. 
Positioned above the insulating ring is the Lyman-a, lamp, housed 
within 'the charged particle collecting assembly. 
collector assembly enables uniform illumination of the media directly 
in front of the collector ring while keeping all Lyman-cr radiation off 
of the collector surface. The probe and associated electronics are 
mounted atop the probe power suppiies,. Copper foil surrounds the 
power supplies thus forming the return electrode, which furnishes 
The feedback electrometer is 
The design of the 
a return current  path to the media. 
The total weight of the payload, including nose cone and parachute, 
The entire is about 14 1/2 pounds with the overall length of 16 inches. 
probe system consumes about 1 wat t  of tot31 power. 
FaLIGHT HISTORY L 
The initial attempt a t  measuring NO using this technique was from 
White Sands Missile Range aboard an Arcas rocket in July of 1968. 
An equipment failure prior to launch time aborted the flight. 
A second t ry  was made on September 24, 1968, a t  1840 R. M. S. T. 
f rom White Sands Missile Range yielding the f i r s t  useful data (PSU-NO-1). 
A radar  failure during the greater par t  of this flight required recon- 
structing the descent trajectory. 
f 30% uncertainty into the data. 
This introduced an additional 
9 
On December 6 ,  1969, at 1805 R. M.S. T . ,  a second successful 
shot (PSU-NO-2) w a s  flown from White Sands Missile Range. The 
data indicated a parachute malfunction, causing a high descent velocity. 
Although this reduced the instrument sensitivity, changes in ionization 
were still detectable. 
Additional useful data was  acquired below 50 km on December 12, 1968, 
at 1805 R .  M. S. T. by PSU-NO-3 showing a close repeatability with the 
first two shots. 
DATA ANALYSIS 
The experiment was flown after sunset to prevent solar radiation 
from striking the instrument and contaminating the data. 
was believed to be quickly destroyed after sunset below 70 km, 
Nicolet (1965), all three shots were flown within a half an hour after 
sunset a t  80 km. Although all three shots were launched after optical 
sunset a t  80 km, the data indicated an abundance of photo-electrons 
which can only be explained by the presence of scattered solar 
iadiation. 
of several  volts a t  the higher altitudes, causing the instrument to go 
off scale; hence, no data was  obtained above 63 km. 
altitudes, the electric field present a t  the collector ring (necessary 
for data reductionj could not be uniquely determined because of the 
potential shift. Therefore, a blunt probe was fired on December 17, 
1968, a t  1805 R. M. S. T. f rom White Sands Missile Range to provide 
environmental ion densities. 
f rom the lamp "off" condition when the NO probe measured the 
environmental ion densities. 
Since the NO 
The photo-electrons produced a shift in the probe potential 
At the lower 
The NO probe potential was then determined 
10 
Data reduction in the region above 50 km was straight forward since 
the newly created electrons were collected before interacting with 
other particles. 
the NO density was obtained by Eq. 1 where P now equals ANe, the 
number of electrons produced by the source. 
By measuring the electrons produced by the source, 
In the region below 50 km, attachment of electrons to neutrals 
must be considered because of the increase in attachment 
and collection time of the probe. 
is given by Gee (1966): 
coefficient 
In this case the electron production 
where 
and 
noN(No)(r NO . 
Y - V Ane - 
Y = (1-Ant) 
A = attachment coefficient (Cole and Pierce) 
At = collection time of the probe (about 
a The results of the three shots a r e  shown in F i g .  4. 
DATAACCURACY 
Scaling e r r o r s  on all three shots a r e  believed to be about f 5 % . 
Lamp calibration introduces another f 10% uncertainty into the 
calculation. 
of 2570 (Hale 1967). 
believed to be known within f 5 70 certainty. E r r o r s  in altitude of 
*2 km f o r  shot PSU-NO-1 introduces t 2070 e r r o r  into the determination 
of the environmental ion density and t 10% e r r o r  in the probe velocity. 
Uncertainties in the negative ion densities a r e  on the order 
The ratio of (p- / pe) ion to electron mobilities is 
- 
- 
11 
b 
a 
0 
O O  
a 
a 
Q 
0 
0 
0 
00 
0 
00 a 
0 00 O 
0 0  
00 0 
0 
00 
0 
L 
- c u m  
0 0 0  z z z  
I I 
0 0 C 
(0 ln t 
(wy)  3an i i i iw  
FIGURE 4 
12 
Thus, the absolute accuracy of the nitric oxide density is about *'7570 
for  PSU-NO-1 and *457'0 for PSU-NO-2 and PSU-NO-3. An additional 
f 10% of uncertainty is introduced, below 50 km, for all three shots 
in estimating the probe collection time and accuracy of the attachment 
coefficient. 
DISCUSSION OF THE DATA 
In the region of 60 km the data appears to be nearly an order  
of magnitude less  than the values of Pearce  (19691, which were obtained 
f rom rocket measurements of the nitric oxide fluorescence. At 
this altitude, the data matches well with the values of Baker and Hale 
(1969), which was calculated f rom blunt probe positive ion densities 
made during the course of 1966 solar eclipse. 
Although the data tends toward a constant mixing ratio, large 
deviations exist. These can be explained by the present belief (Nicolet, 
1969 and Pearce,  1969) that this region is a sink for NO. 
oxide is transported downward into this region and is destroyed by 
the reaction: 
Nitric 
B 
NO t O3 - NO2 f O2 
In view of the fact that the NO profile depends on both the downward 
transport  and the ozone distribution a simple mixing process need 
not predominate. 
In the future, this experiment will be launched later after sunset 
to avoid the photo-effects and obtain additional data a t  the higher 
altitudes. 
(3) 
13 
ACKNOWLEDGEMENT 
This work was supported by the National Aeronautics and Space 
Administration Grant NGR 39-009-015 and by the U. S. Army Research 
Office, Durham, N. C . ,  Grant DAHC04-68-C-0034. 
REFERENCES 
Baker,' D. C . ,  Ph. D. Thesis, Ionosphere Research Laboratory, The 
Pennsylvania State University. 
Baker, D. C .  and L. C .  Hale, 1969 COSPAR Paper ,  Ionosphere Research 
Laboratory, The Pennsylvania State University (1969). 
Gee, E. L. , Thesis, Ionosphere Research Laboratory, The Pennsylvania 
State University (1966). 
Hale, L. C . ,  Space Research VII,  Vol. I, North-Holland, Amsterdam, 
1967. 
Hale, L. C . ,  D. P. Hoult and D. C 4  Baker, Space Research VIII, North- 
Holland, Amsterdam, 1968. 
Nicolet, M. Private communication (1969): 
Nicolet, M . ,  J Geophys. Res. ,  - 70,  (1965). 
Pearce,  J . B . ,  J .  Geophys. R e s . ,  - 74, 853 (1969). 
Whitten, R .  C.  and I. G. Poppoff, Physics of the Lower Ionosphere, 
a Prentice-Hall, Inc. ,  Englewood Cliffs, New Je r sey  (1965). 


Measurements of an ionizable constituent of low ionosphere using a Lyman-alpha source and blunt probe

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