Photometric tracings of infrared solar spectrum from NASA CV-990 jet during July-August 196

Cruikshank, D. P.

Kuiper, G. P.

English

NASA Technical Reports Server

No. 123 ARIZONA-NASA ATLAS OF INFRARED SOLAR SPECTRUM 
A PRELIMINARY REPORT 
by G. P. KUIPER AND D. P. CRUIKSHANK 
September 24,1968 
ABSTRACT 
This paper shows a sample (about 5%) of a set of photometric tracings of the infrared solar spectrum obtained from 
the NASA CV-990 Jet during nine flights in July-August 1968. Two 12-inch telescopes were used, one feeding a 4.2-meter 
spectrometer of special design, the other the LPL B-spectrometer. The $-meter spectrometer records extend from 0.85-3.3 
microns; the B-spectrometer records, from 0.85-5.1 microns. Supplementary flights with the NASA Lear Jet are scheduled 
to extend the spectrum beyond. 
The present paper reproduces the 4.2-meter records between 0.85-0.97 microns. Some runs were made in duplicate 
because of occasional troubles with the heliostat controls which account for the gaps in the records. The resolution is about 
0.3 A or 30,000 in the region shown. In the remaining 4.2-meter records the resolution varies from 20,000-60,000. In this 
preliminary paper, matching portions of the Michigan Atlas, “Photometric Atlas of the Near Infrared Solar Spectrum, 
h8465 to h25,242,” are reproduced to facilitate comparisons of resolution and in particular to demonstrate the value of 
high-altitude flights in very nearly eliminating the telluric water-vapor spectrum. 
ystematic observations of the infrared solar spec- S trum with resolutions of 10,000-60,000 were 
undertaken in conjunction with the ongoing program 
of infrared spectroscopy of planets and red stars from 
the NASA CV-990 Jet. Equipment now under devel- 
opment at the Laboratory is designed to achieve reso- 
lutions from 1,000-200,000, depending on the in- 
tensity of the source. It is obvious that a good set of 
solar spectra with different resolutions, taken from 
the same altitude, was essential for purposes of wave- 
length identification and spectral interpretation. 
The present series of high-altitude solar flights 
were proposed to NASA in “Program of High-Alti- 
tude Infrared Spectroscopy of Sun, Planets, and 
Stars: III,” by G. P. Kuiper, J. R. Percy, F. F. 
Forbes, and H. L. Johnson, dated March 21, 1968, 
in continuation of a set of experimental flights that 
took place early October 1967, based on Hickham 
Field, Hawaii. These earlier flights were limited to 
the use of the B-spectrometer and owing to the pre- 
valence of high tropical cirrus during the period of 
observation, yielded only 1-2 hours of net observa- 
tions. Nevertheless, reasonably satisfactory results 
were obtained for the interval 1.24-2.04 p with a 
resolution of approximately 8000. During these 1967 
flights also, a simple method was devised for flushing 
the spectrometer and the telescope-heliostat area 
with exceedingly-dry outside air, thereby reducing 
the remaining precipitable water-vapor content in 
the instrumental air path to about 1 or 2 p. For the 
4-meter instrument this problem was especially criti- 
cal since the air path within the spectrometer alone 
179 
https://ntrs.nasa.gov/search.jsp?R=19690005870 2020-03-12T08:24:21+00:00Z
180 G .  P. KUIPER A N D  D. P. CRUIKSHANK 
is 17 meters (Ebert design) to which must be added 
the air path from the optical aircraft window to the 
spectrometer entrance slit via the Cassegrain tele- 
scope, approximately 4 meters. With normal dry 
laboratory conditions, a 20-meter air path contrib- 
utes about 120-150 p precip. H20, as compared to 
only 8-12 p in the entire atmospheric path above the 
aircraft. Flushing the equipment with dry nitrogen 
was attempted in the Hawaii flights but proved cum- 
bersome and less effective than the simple device 
referred to, of using compressed dry outside air. 
The outside temperatures at the operating level of 
40,000-42,000 f t  are normally between -55" and 
-60" C. The ambient frost point is usually around 
-70°C. By enclosing the optical path, window-helio- 
stat-telescope-spectrometer, with plastic sheets and 
flushing the air with the compressed dry air from the 
ventilation system, the ambient dew point within the 
spectrometer was kept below -30°C. After most 
solar runs, comparison spectra were made under 
identical operating conditions within the aircraft 
which gave direct information on the contributions 
to the telluric spectrum (H20, Cog, N20, CH4) by 
the spectrometer air. These records are of special 
interest for the stronger H20 bands at 1.4, 1.9, and 
2.6 p; and the COz bands at 2.0 and 2.6-2.7 p. 
Figure l a  shows the 4-meter spectrometer in the 
CV-990 Jet, with the 12-inch feeder telescope situ- 
ated beyond. The view is looking forward in the air- 
craft. Figure l b  shows the opposite aspect; the opti- 
cal window is seen above the heliostat (both above 
center) and the horizontal Cassegrain telescope be- 
yond. Telescope and heliostat are bolted on a sturdy 
support frame fastened to both the seat rail (nor- 
mally used for chairs) and the side rail, by means of 
shock mounts. The spectrometer was designed by 
Mr. Ferdinand de Wiess in consultation with the 
authors; it will be described in a separate publica- 
tion. The frame design resembles a radio tower, with 
8 cables under tension made to keep the end plates 
of the spectrometer parallel to each other in spite 
of aircraft vibrations due to engines and air turbu- 
lence. The tensions in the cables were made equal 
within about 1 % and kept at about 260 Ibs (120 kg.) 
This high tension served to increase the frequency 
and therefore the damping of the vibrations, both of 
which will diminish their amplitude. Since the instru- 
ment was normally used with both the entrance slit 
and the detector only 0.10 mm wide, it was neces- 
sary to keep the oscillations in the 17-meter light 
path to within 1 arc seconds. With the oscillations 
of the plane sometimes amounting to 2" or more, 
this requirement was really severe; and it is a tribute 
to the designer that at no time during the nine opera- 
tional flights, each lasting 150-170 minutes, did we 
find evidence of instrumental distortion. Only when 
the plane turned sideways in a steep bank (which 
of course did not occur during the level solar runs 
but only occasionally during comparison runs) would 
the amplitude of the signal change appreciably, indi- 
cating a twisting of the entire spectrometer, which 
is not surprising because of its four-point support 
to the fuselage (cf. Fig. l a ) .  
The detectors used up to 3.3 p were PbS cells, 
cooled with dry ice. Beyond 3.3 p, PbSe cells were 
used, also dry-ice cooled, which is satisfactory up 
to about 5.3 p (beyond this limit we will use liquid- 
nitrogen cooled PbSe up to about 6.3 p, and beyond 
this the Germanium bolometer, liquid-helium 
cooled). The solar signal was chopped at 60 cps. 
The preamplifier is seated close to the detector and 
has a gain of 30. The amplifier was mounted oppo- 
site the spectrometer on the starboard side of the air- 
craft in a rack also containing the power supply and 
the strip-chart recorder. The signal was synchro- 
nously rectified and amplified in the DC mode. The 
time constant was adjustable. Most records were 
obtained with 7 = 0.12 sec. This rapid response 
made it possible to record up to four spectral ele- 
ments per second which was important in the econ- 
omy of the program, there being some 100,000 spec- 
tral elements to record in a necessarily-limited flight 
time. The recorder used was a Sanborn 7701A, 
shock-mounted in its rack to minimize the effects 
of aircraft vibrations. The spectral trace is produced 
with an electrically-heated stylus on heat-sensitive 
paper. This ensures extremely low inertia and a very- 
short time constant of the recorder itself, about 0.01 
sec. 
The spectral interval selected for reproduction 
was obtained with a 128 x 154 mm Bausch and Lomb 
grating having 1200 grooves per mm. The grating 
was blazed for 1 .O p and was used as far as 1.43 p, 
where the angle of incidence had become about 70". 
The resulting resolution in the 1.4 p region was 
therefore exceptionally good, about 60,000. The 
region from 1.22-3.00 p was obtained with gratings 
of similar size but 600 lines per mm, the region 2.90- 
3.30 p with 300 lines per mm. With the B-spectrom- 
eter, designed to use interchangeably the same grat- 
ings as the 4.2 meter, the entire interval 0.85-5.1 
microns was recorded in a separate, independent 
INFRARED SOLAR SPECTRUM 181 
installation with its own 12-inch telescope. The part 
up to 3.0 p has resolutions 8,000-12,000; the region 
beyond, 2,000-5,000. 
The 4.2-meter spectrometer had 6-inch mirrors 
to fit the 5 x 6 inch gratings used. The effective 
F-ratio was therefore F/32, matched by the F/30 
Cassegrain telescope. The original secondary mirror 
was replaced by a newly-produced Cervit mirror. 
It was found that this allowed the use of the full 
solar beam from the 12-inch primary (intensity 50- 
60 times that of normal sunlight), which, of course, 
improved the quality of the spectral records. 
Figures 2-7 give photographic reproductions of 
all spectral records obtained with the 4-meter spec- 
trometer from hh8487-9725. The wavelength scales 
are based on the catalog by H. B. Babcock and C. M. 
Moore, “The Solar Spectrum, ~ 6 6 0 0  to A13495” 
(Carnegie 1947), derived from photographic records 
obtained at the Mt. Wilson Observatory. Our CV-990 
records attain about the same limit at h9000 A, 
Rowland intensity -3. At longer wavelengths our 
records show fainter lines presumably because of 
the lower photographic resolutions there. The telluric 
water-vapor lines with Mt. Wilson Rowland intensi- 
ties < 20 or 30 are usually invisible on our spectra 
(Le., have Rowland intensity -3 or less). Only some 
3 dozen very strong lines, up to Rowland intensity 
150, are recorded here, with intensities correspond- 
ing to -3 to 0. These lines are indicated by dots 
above the spectra. If only part of the absorption fea- 
ture is due to H20, the dot is placed in ( ) . 
For ready orientation we have added the identi- 
fications of all solar lines having Rowland intensity 
0 or above in the Babcock-Moore catalog, taken from 
this catalog. Some of these lack identification and 
other prominent lines are included although they had 
no Rowland intensity assigned to them (usually be- 
cause of blending with telluric lines). The very wide 
solar Paschen lines PS-Plo have not before been re- 
corded without the telluric disturbances. Two small 
regions show a shallow depression (marked G )  due 
to imperfect guiding (away from the center of the 
disk). 
Table 1 gives descriptive data of the high-alti- 
tude spectral records here shown. It includes the 
wavelength interval, the date and UT, the aircraft 
altitude during the observations, the outside tempera- 
ture, the cabin pressure inside the aircraft (which 
affects the pressure broadening of the residual water- 
vapor absorption produced in the cabin air path), 
and the gain-setting of the amplifier. The slit width 
in the present records was 0.10 mm; the cell width 
was the same; the time constant of the amplifier, 
0.12 sec; the grating was blazed for 1 micron, 1200 
lines per mm; the filter used to cut out higher orders, 
RG 8 (h>.68 p) .  Some gaps occur in the (dupli- 
cate) records, due to troubles with the heliostat con- 
trol (which happened all for A <  1 p)  . The absorp- 
tion lines regarded real on the basis of the records 
themselves (or, in some cases, by supporting data 
such as the Libge solar atlas) are marked with a dot, 
with a running number assigned for each spectral 
strip to facilitate further reference. In the Atlas, 
larger-scale reproductions will be used and sup- 
porting laboratory and ground-based solar spectra 
added. 
We are making a comparison here with the Mich- 
igan Atlas (1950), Figures 2M-7M, rather than 
with the more recent and improved Libge Atlas 
(L. Delbouille and R. Roland, 1963), because the 
former extends to 2.5 p, nearly as far as our records, 
whereas the Libge Atlas terminates at 1.2 p. It is 
seen that the dots above the spectral records in Fig- 
ures 2-7 all correspond to nearly-saturated telluric 
lines in Figures 2M-7M. 
The wavelength identifications of the weaker 
solar lines shown in our figures were verified with 
the aid of the Likge Atlas on which all the Babcock- 
Moore identifications were entered. Some of these 
weaker lines are not found in the Babcock-Moore 
catalog but were recorded in the Libge Atlas. A few 
puzzling cases were noted, the most striking of which 
is h9438.7 listed as “-1N Atm.,” while our records 
show it to be about 5 0. Numerous uncertainties in 
identification, sun or Atm., could be settled. These 
systematic comparisons have brought out clearly the 
immense value for subsequent identification work 
of high-resolution infrared solar spectra (R >> 
100,000) taken from a very dry mountain observa- 
tory. Preparations have been made for observing the 
sun in this manner with the 4.2-meter spectrometer 
as a first step. 
The spectrometer tests preceding the solar flights 
were made by Dr. Cruikshank, assisted by Mr. A. 
Thomson. They and Messrs. de Wiess and Kuiper 
optimized the equipment in the CV-990 during an 
engineering flight on July 2, 1968. The wavelength 
scales and water-vapor identifications in Figures 2-7 
were compiled by Dr. Kuiper, in the manner de- 
scribed above, and verified by him on the basis of 
post-flight laboratory runs on water vapor, made in 
collaboration with Dr. Uwe Fink. In  the A9350 
region these runs proved indispensable to resolve 
some remaining ambiguities. A brief report on the 
182 G. P. K U I P E R  A N D  D .  P. C R U I K S H A N K  
Fig. l a  4.2-meter solar spectrometer in NASA CV-990 Jet, with 12-inch feeder telescope beyond. Note shock-mount 
attachments to seat rail; central extended frame with 8 cables for keeping heavy end-plates of spectrometer parallel. Ver- 
tical tube supplying dry outside air to spectrometer seen beyond central frame. Adjustment screws at left, control focus and 
orientation of collimator and camera mirrors. (NASA Photograph) 
I N F R A R E D  S O L A R  SPECTRUM 183 
Fig. l b  12-inch horizontal Cassegrain telescope, fed with heliostat (elliptical mirror in white frame). Control of heliostat 
gyroscopic, with electronics in rack below. Optical window, with safety covers front and back, above heliostat mount. 4-meter 
spectrometer beyond, at left. During operations entire unit enveloped in plastic sheet, ventilated with dry outside air. (NASA 
Photograph) 
184 G .  P. K U I P E R  A N D  D. P. CRUIKSHANK 
INFRARED SOLAR SPECTRUM 185 
186 G .  P. KUIPER A N D  D .  P. CRUIKSHANK 
I N F R A R E D  S O L A R  SPECTRUM 187 
188 G .  P. KUIPER A N D  D .  P. CRUIKSHANK 
INFRARED SOLAR SPECTRUM 189 
190 G .  P. K U I P E R  A N D  D. P. CRUIKSHANK 
INFRARED SOLAR SPECTRUM 191 
192 G. P. K U I P E R  A N D  D. P. C R U I K S H A N K  
INFRARED SOLAR SPECTRUM 193 
194 G .  P. KUIPER A N D  D .  P. CRUIKSHANK 
I I I I I I I I I L i = c R = k  I I I I I 
INFRARED SOLAR SPECTRUM 195 
196 G. P. K U I P E R  A N D  D. P. CRUIKSHANK 
solar flights is found in Sky and Telescope, October 
1968, based on a University news release dated 
August 12, 1968. The nine operational flights were 
made on July 15, 17, 18, 19, 30, and August 1 ,2 ,6 ,  
and 7. AI1 records were made on East-West flights 
somewhat south of the Canadian border, between 
Minnesota and Seattle, Washington, at latitudes to 
achieve solar elevations of 6.5" =k 2'. 
Acknowledgments - We are greatly indebted 
to NASA Hq. and NASA-Ames, especially Dr. M. 
Bader and Mr. R. Cameron, for their interest in the 
high-altitude program and their invaluable advice 
and assistance throughout; to Mr. J. Percy for sev- 
eral design features of the electronics system in the 
vibrating aircraft and for his participation in about 
half the flights; to Mr. B. McClendon for assistance 
with the electronics during the other flights; and to 
Mr. C. Titulaer, Mr. A. Thomson, and Rev. G. Sill 
of LPL and Mr. D. Olsen of NASA-Ames for their 
important assistance during the flights in the solar 
guiding and the taking of spectral records. Mrs. 
A. Agnieray ably assisted in the preparation of the 
figures. This research was supported by NASA 
through Grant NsG 161-61 and the University of 
Arizona Institutional Grant NGR-03-002-09 1. 
TABLE 1 
SOLAR SPECTRUM RECORDS, 4.2-METER SPECTROMETER, NASA CV-990 JET 
1968 ALT. TEMP. ALT. (FT) 
FIG. MA) DATE UT (FT) ( " C )  CABIN GAIN 
2. a 8487-8569 Aug 2 18:26 4 1,000 -57 8900 5-4 
b 8569-8653 Aug 2 18:29 41,000 -57 8900 5-4 
C 8653-8739 Aug 2 18:32 4 1,000 -57 8900 5-4 
d 87 39-88 1 5 Aug 2 18:36 41,000 - 57 8900 5-4 
3. a 88 14-8902 Aug 2 18:42 41,500 -57.5 8900 5-4 
b 88 15-8850 Aug 2 4 1,000 
C 8902-8983 Aug 2 41,500 
d 8983-9064 Aug 2 41,500 
4. a 9064-9 150 Aug 6 41,000 
b 9064-9 150 Aug 2 41,500 
C 9 150-9234 AUP 6 4 1,000 -57.5 
d 41,500 -57.5 
41,500 - 59 
41,500 -57 
41,500 -59 
41 SO0 -57 
-59 
5. a 
b 
18:39 
18:45 
18:48 
20: 3 1 
18:52 
-57.5 
-57.5 
-57.5 
-57.5 
-57.5 
20: 34 
18:56 
20:38 
18:59 
20 : 42 
19:02 
20 : 45 411500 
19:05 41,500 
20:48 41,500 
19:08 41,500 
19:11 41.500 
8900 5-4 
8900 5-4 
8900 5-(4,3) 
8900 5-2 
8900 5-3 
8900 5-2 
8900 5-3 
8800 5-2 
8900 5-3 
8800 5-2 
8900 5-3 
8800 5-2 
9 150-9232 Aug 2 
9234-9316 Aug 6 
9232-9300 Aug 2 
C 93 16-9402 Aug 6 
d 93 15-9402 Aug 2 
6. a 9402-948 1 Aug 6 
b 9402-9480 Aug 2 
C 9481-9563 Aug 6 
d 9480-9563 Aug 2 
7. a 9563-9645 Aug 2 
b 9563-9646 Aug 6 20:51 41,500 -59 8800 5- 1 
d 9646-9725 Aug 6 20 : 55 41,500 - 59 8800 5- 1 
C 9645-9725 Aug 2 19: 14 41,500 - 57 8900 5-3 


Arizona-NASA Atlas of infrared solar spectrum, a preliminary report, number 123

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