Airborne photometer instrumentation and measurement data on high latitude hydroxyl airglow emissio

Brown, N. B.

Romick, G. J.

English

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GEOPHYSICAL INSTITUTE
of the 
UNIVERSITY OF ALASKA 
A LATITUDINAL SURVEY OF THE HYDROXYL AIRGLOW EMISSIONS 
Final Report
Grant No. NCR 02-001-058 
April 1 9 1969 - March 31 9 1970 
Prepared for 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
Principal Investigator 
Gerald J. Romick 
,X9QS.. o 
Co-Principal Investigator 
Neal B. Brown 
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Report Approved by: 
,-r Keith B. Mather I	 Director 
Geophysical Institute 
CA r"%, R.".. orma F L C 4*11^ upy
https://ntrs.nasa.gov/search.jsp?R=19710015735 2020-03-11T20:52:36+00:00Z
INTRODUCTION 
Under NASA Grant NCR 02-001-058, a multi-filtered, spatially scanning 
photometer sy stem was placed aboard the NASA Convair 990 aircraft Galileo, 
and successfully operated through-out the NASA 1969 Auroral Expedition. 
The primary objective of this grant was to support the construction of 
equipment, its testing and operation during the NASA 1969 Auroral Expedition, 
and a cursory evaluation of the data. The analysis of the data is the 
subject of a proposal which was submitted to NASA in February, 1971. 
This final technical report describes both the instrumentation which was 
assembled for the experiment and the overall success of the airborne 
operational experiment, and includes a brief summary of some of the data 
which has been reviewed to date. 
It should be noted that the instrumentation installed in the aircraft 
was used to carry out the University of Alaska programs under both NASA 
Grant NCR 02-001-058 as well as NASA Grant NCR 02-001-060. 
The primary goals of the proposed airborne experiment were to acquire 
geographically widespread observational data on the emission intensities of 
hydroxyl (OH) and related airglow emission features, particularly at high 
latitudes. These data would then be analyzed for the purposes of ascertain-
ing the relative importance of atmospheric dynamical processes, including 
those of a meteorological origin, as well as possible variations from the 
basic hydrogen-ozone reaction excitation mechanism to the production of 
hydroxyl airglow emissions. A concerted effort was also made to further 
establish the relationship between sudden increases in the intensity of the 
OH emissions from nominal polar airgiow levels by the presence of active 
aurora, as noted by Brown and Belon (1969) 
1
Instrumentation 
The proposed experiment required data pertaining to both the spatial 
distribution and temporal variations of several airgiow emission features. 
The modifications required to use an existing photometer system for these 
studies were mainly confined to the choice of a suitable detector for the 
near infrared and the signal detection and processing subsystems. From the 
outset there was considerable interest in obtaining and using an S-25 photo-
cathode photornultiplier tube (PMT) which would have a certain prescribed level 
of sensitivity out to at least 9350A when moderately cooled, as opposed to a 
standard S-l(RCA 7102) PMT detector which would have required liquid nitrogen 
cooling. 
An experimental S-25 PMT was ordered from IT&T(F-4075), with sensitivity 
specifications adequate for the planned observations. Production problems 
at IT&T left the final decision between the S-I and the S-25 PMT open until 
early September 1969 when a low sensitivity S-25 IT&T (F-4085) was delivered 
on consignment for evaluation. A careful laboratory test bench comparison 
of the S-25 with the S-i under simulated observational conditions proved that 
this tube would be adequate for the proposed observational program. Subse-
quently this PMT was integrated into the package and the pulse discrimination 
electronics adjusted accordingly. A second S-25 IT&T PMT, meeting initial 
specifications arrived at NASA Ames Research Center, Moffett Field, California 
just after the checkout flight and was installed, while the F-4085 was re-
tained as a spare. Subsequent operation showed little difference in sensi-
tivity between this S-25 PMT and that which had been thoroughly tested, how-
ever in view of its slightly higher sensitivity, as measured at the factory, 
it was used throughout the flights and upon completion of the expedition, 
the first tube (F-4085) was returned to IT&T. 
2
From a knowledge of the operational characteristics of the basic optical 
system when used at shorter wavelengths for other types of auroral and air-
glow studies, a decision was made to use pulse counting signal detection 
techniques. In order to retain flexibility under a variety of possible obser-
vational conditions, and also to interface smoothly with the existing analog 
recording instrumentation, the raw pulse data were converted to analog voltage 
levels. These were then passed into four separate amplifiers that resulted 
in four separate decades of signal level which were available simultaneously, 
ranging from 0 - 200 cps to 0 ­200,000 cps. In operation, pulse pile up 
occurred at approximately 40,000 cps. A manual multipole switch placed a 
load resistor chain with these same four amplifiers across the anode if ana-
log detection were desired over the range of lO
	 to 10- 4 amperes full scale. 
This feature was used successfully for a short period during a day to night 
transitional flight which occurred during passage from Ft. Churchill to Bodç, 
Norway. 
The remaining modifications were minor, consisting for the most part of 
installing a 10 resolution shaft encoder assembly on the optical field of 
view scanning system, reprogramming the filter wheel movement circuitry for 
positive filter identification and stop-motion movement, and general con-
struction for aircraft mounting. The full specifications of the instrument 
follow: 
The filtered photometer system consisted of a single optical system 
whose field of view was spatially scanned in elevation angle through a "60° 
window" of the aircraft and in which narrow band interference filters were 
programmed to move sequentially into the optical path. 
3
Optics: The objective was an achromat with an entrance aperture of 4.75" 
and focal length of 15.6" which was followed by a Ross Corrector 
inserted 11.75" behind objective to accomodate 2.8" diameter in-
terference filters. 
Instantaneous Field of View: 6.0 x 10 	 steridians (0.5° circular) 
Effective spatial regions viewed: Elevation angle scans were made from a 
zenith angle of 50° to the zenith at right angles to the flight 
path of aircraft. 
Field of View-Scanning Rate: 
Mode 1 - stationary or manual set point control to within 1° 
accuracy, with a shaft encoder readout on the operator's panel. 
- Mode 2 - motor driven with set point speed control 
a. set-point variable, 0°/sec to 450°/sec. 
b. discrete, 6 0 , 12°, 30°, 60°, 150°, 300°, 450°/sec. 
Filter wheel: 
Up to eight separate interference filters were mounted on a pro-
grammable wheel with an access plate which permitted changing 
interference filters during flight conditions if necessary. A 
discrete eight level electronic code for positive filter identi-
fication was displayed on the front panel for the operator and 
recorded for analysis. 
Filter Change Rates: 
Mode 1 - manual-pushbutton CW or CW 
Mode 2 - internal timer which permitted observing time with a 
given filter of 1, 10 or 25 seconds. 
Mode 3 - Filter change initiated by pulse derived from elevation 
scanning optical assembly. 
The minimum time between filters was 0.12 sec. 
4
Signal detection: 
Pulse counting followed by digital to analog conversion using 
a simple R-C integrator. The output of the integrator being 
fed to four separate amplifiers resulting in four discrete 
decades of output signal corresponding to: 
0- 2x102 cps 
o - 2 x 1O 3 cps 
0- 2x10 cps 
o - 2 x 1O 5 cps 
with a basic time constant of the integrator as 180 Hz. 
Detector: 
- IT&T F-4075 (SIN 096904) S-25 photocathode, 
0.2" diameter effective photocathode, 16 dynodes, operated 
at 2100 vdc. 
Detector Cooler: 
Products for Research model TE-102S, operated at set-point of 
-10°C with a stability of 0.1°C. 
Recording:
Analog output signals were recorded on seven channels of one 
of the two available NASA CP 100 Ampex 14 track recorders. 
These were; 
Channel	 Data	 Level 
1	 0 - 2 x 10  cps 	 -10 to + 10 volts 
2	 0 - 2 x 10 cps	 -10 to + 10 volts 
3	 0 - 2 x 1O 4 cps	 -10 to + 10 volts 
4	 0 - 2 x 1O 5 cps	 -10 to + 10 volts 
5	 Elevation angle position 	 0 to + 10 volts 
6	 8 level filter identification	 0 to + 10 volts 
7	 IRIG B time code	 (supplied by NASA) 
5
In addition, a two channel Sanborn chart recorder was installed 
in the equipment rack with multipole data access switches, so that the per-
formance of the system could be monitored and checked in flight. 
Operation 
The airborne operation of the instrumentation built by the University 
of Alaska for this work was remarkably trouble free and stable throughout 
the expedition, and at no time were data lost due to an instrumentation fail
-
ure. Post flight analysis of the data has revealed a few occasions during 
which the NASA CP 100 tape recorder failed to function properly, notably 
during the ferry flight to Ft. Churchill, Canada from-Moffett Field, California 
Fortunately the monitoring data acquired with the supplemental two channel 
Sanborn recorder presents good coverage so that the information gained during 
this flight is not totally lost. 
A summary of the operation of the instrument is listed in Table I. In 
Table II, the channel wavelengths are listed along with the emission feature 
that was observed.
6
TABLE I
Operation Resume 
1969 
Date 
UT
Flight Mode of 
Scanning
Operation 
Zenith
Time Interval 
U.T.
Recording 
Mode 
Tape-Chart 1
Channel Wavelength 
2	 3	 4	 5 6 7 8 
1 / / Test Flight  
Nov.24 2 / 0806 1231 1 4278 5893 5577 6300 8630 7250 8345 9350 
Nov.26 3 V' 0042 0133 / / 4278 7250 4861 6772 8911 8630 8345 9350 
/ 0133 0239 / 1 - / 0239 0307  
/ 0307 0319  
/ 0319 0437 1 v 
/ 0437 0611  
Nov.27 4 / 0033 0225 / / 4278 7250 6772 8911 8630 8345 9550 4861 
/ 0225 0230 / 1 / 0230 0450  
/ 0450 0532  
Nov.29 5 / 0225 0620 / / 4278 7250 6772 8911 8630 8345 9350 4861 
Dec.	 3 6 / 0513 0536 / / 4278 7250 6772 8911 8630 8345 9350 4861 
/ 0536 1025  
Dec. 4 7 / 0450 0930 / / 4278 7250 6772 8911 8630 8345 9350 4861 
-8 / 06100640 1. / 
Dec.	 5 / 0640 0756 1 1 / 0756 0850  
/ 0850 1000  
/ 1000 1127 1 1 
Dec.	 7 9 v' 0515 0600 / / 4278 7250 6772 8911 8630 8345 9350 4861 
/ 0600 0744  
/ 0744 1016 / 1 
Dec.	 8 10 0745 1245 V' 4278 7250 6772 8911 8630 8345 9350 4861 
Dec.11 11 1850 2135 1 / 4278 7250 6772 8911 8630 8345 9350 4861 
/ 21352230 / 1 
Dec.13 12 / 0630 1130 / / 5577 4278 5000 4861 6300 8911 8345 8630 
Dec.14 13 / 0530 1030 / / 5577 4278 5000 4861 6300 8911 8345 8630 
Dec.16 14 / 0120 0203 / 1 5577 4278 5000 4861 6300 8911 8345 8630 1 0203 0550 1 / / 0550 0553  
/	 - 05530804  
Dec.18 15 / 0817 0933 / / 5577 4278 9350 4861 6300 8911 8345 8630 
/ 09331028  
/ 1028 1426
7
[1 
TABLE II 
Wavelength Emission Feature 
in Angstroms Airglow Auroral 
4278 Background 1 NG (N2) 
4861 Background H8 
5577 [Oil [01] 
5893 Na Nz/02* 
6300 [01] [01] 
6772 Background/OH* 1PG (N2) 
7250 OH (8-3) Meinel 
8345 OH (6-2) Meinel N/OH* 
8645 02	 (0-1) 02/1PG (N2) 
8911 OH (7-3) 1PG (N2) 
9350 OH (8-4) OH
* Blend
8 
A Brief Summary of the Data Reviewed to Date 
We have been fortunate to have Mr. Robert Henderson, who is attending 
the University of Alaska on a NASA Fellowship, involved in the analysis of 
some of the data acquired during the expedition. He is now completing his 
analysis of the cross latitudinal, auroral zone and polar cap airgiow levels 
of OH and 02 observed during seven of the fifteen flights, during which 
auroral activity was the lowest. Further analysis has been hindered by 
lack of funding and the recent move of all data processing instrumentation 
to the new Geophysical Institute building at the University of Alaska. 
Briefly, from Mr. Henderson's work, we have been unable to find any 
qualitative or quantative difference in the emission intensities of OH which 
can be related to latitude or longitude effects. During these seven flights 
the diurnal variations that were observed were very similar in nature to 
those which have been reported for low latitude observations. In total, 
the worldwide undisturbed airgiow OH emissions seem surprisingly stable with 
little evidence to suggest that any peculiar variations might occur at high 
latitude, although it should be recognized that these are the first such 
observations and they are limited to a very short seasonal period during 
November and December future extension of this work over a larger period may 
reveal gross changes. 
The initial selection of data covering relatively undisturbed periods 
at high latitude included, as it later developed, at least one instance of a 
marked increase in the OH emission intensities. During flight 1/14 which 
originated in Bod3, Norway, the aircraft passed through the auroral zone into 
the polar cap and out again, terminating at Ft. Churchill, Canada. In reviewing 
the flight plan it was noted that the aircraft took off early in the morning 
sector (local time) and advanced in local time gradually overtaking the midnight 
sector near Ft. Churchill. The OH emission intensities showed a steady rise
starting near the mid-point of the flight, when the aircraft was over Greenland 
and within the polar cap. The intensity enhancement was nearly a factor of two 
and seems clearly related to the meteorology of the upper atmosphere. 
Suggestions for future work 
The instrumentation designed and built by the University of Alaska operated 
reliably throughout the expedition and was successful in that observational 
data which had not previously been available was acquired from both low and 
high latitudes. This was due in part to the design concept employed, the 
prior experience of Dr. Romick aboard the NASA 990 aircraft and to the tech-
nical and operational support provided by the personnel of the Airborne Science 
Office of NASA, Ames Research Center. 
The work which was initiated and carried out under this NASA Grant is 
one of the first attempts to document geographically large scale OH airglow 
phenomena on a consistent basis. The capability to observe OH airglow 
emissions at high latitude in close proximity to aurora, which has been firmly 
established through the work of Brown and Belon (1969) and more recently by 
Harrison (1970), should now permit a truly global picture of OH airglow 
phenomena to emerge. The importance of such studies are two-fold; initially 
it is well recognized that auroral zone and polar data do not exist and that 
they form a significant part of the overall phenomenology of OH airglow, 
with implications for polar upper atmospheric meteorological processes, and 
second, the spectacular perturbation of the nominally airglow emissions, such 
as OH and 02 tg by the aurora have implications for many current and future 
studies of the photo and ion chemistry of the D and E regions of the earth's 
upper atmosphere.
10
Therefore we can recommend that whenever possible, hydroxyl airglow 
emissions should be studied from an airborne platform with these purposes 
in mind. As spectral discrimination of the aurora from the airgiow has been 
achieved we can now also suggest that should funding be available, these 
studies should be expanded to cover the measurement of the effective rotational 
temperatures of OH as well as the diurnal, seasonal, and latitudinal variations. 
The extension of this work would also permit better coverage of one of the 
main comparative points between present theoretical studies and observations, 
that is, the variation in the intensities and effective rotational temperatures, 
which occur in twilights as a result of the changing height of the effective 
emitting layers, as well as the transitions from dayglow to purely nightglow 
excitation mechanisms. 
In reviewing this particular experiment, there is also one unique aspect 
which these experimentors feels merits attention with respect to many types 
of future auroral expedition experiments, and that is the capability to scan 
the optical system spatially. 
This capability greatly aids subsequent data analysis in terms of dis-
criminating between various spectral, temporal and spatial variations during 
the periods when the observations were made. 
During the course of the expedition, with the low level of auroral 
activity encountered, little data would have been obtained from fixed field 
of view observations, relating to the dynamic enhancements of OH which are 
typically associated with relatively bright auroral forms. 
In general, the magnitude and reliability of data acquired with nearly 
any optical instrument used in auroral and airglow studies is greatly en-
hanced by a pointing capability.
11
While this is not always efficiently possible with any given experiment 
and instrument, it is deemed in general to be a desirable factor. 
Other aspects of the total expedition seem worthy of special recommen-
dation and acknowledgement. The importance of planning and carrying out a 
coordinated inter-calibration should not be overlooked in future expeditions, 
particularly when such a relatively diverse group of auroral investigators 
meet. In addition, the Dr. William Fastie "hot seat" procedure of requesting 
inflight cross checks during actual observations shakes many a "gremlin" from 
the calculations, as witnessed during these flights. 
The second aspect deemed worthy of favorable mention is the inclusion 
of a low light level real time imaging system, wide field of view experiment 
whose monitors are placed throughout the aircraft interior for the various other 
experimentors to view. In the active semi-lit environment of the aircraft cabin, 
where most overhead hatches are filled with instrumentation, these monitors 
served an invaluable purpose in establishing the operational procedures or 
program changes necessary to acquire high quality data for various experiments 
during the expedition.
12
REFERENCES 
Brown, N. B. and A. E. Belon, Trans-Amer. Ceophys. Union 50, 258, 1969. 
Harrison, A. W., J. Geophys. Res., 75, 1330, 1970.


A latitudinal survey of hydroxyl airglow emissions Final report, 1 Apr. 1969 - 31 Mar. 1970

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