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Variations with iititude of the Spectral Transmittance of the Atmosphere from 3350 to 3150 cm . (See Table I for identification of record numbers) ... 11

Variations with Altitude of the Spectral Transmittance of the Atmosphere from 3550 to 3350 cm . (See Table I for identification of record numbers) .

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Variations with Altitude of the Spectral Transmittance of the Atmosphere fr >m 3550 to 3350 cm' 1 . (See Table I for identification of record numbers)

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Variations with Altitude of the Spectral Transmittance of the Atmosphere from 3750 to 3550 cm (See Table I 
INTRODUCTION
In previous studies we have presented data concerniuj the spectral transmittance of the earth's atmosphere in seve.al spectral regions as observed at various altitudes. These data have been obtained with a balloon borne system designed to study the variation of the infrared solar spectrum with altitude. A small Littrow type prism instrument has been used as the spectrometer for obtaining these data. With the development of large computers it has become feasible to theoretically predict the spectral transmittance one would observe under high resolution. In addition while the extreme detail one observes in high resolution data is not desirable in some studies there are other studies in which high resolution experimental data are necessary. In view of this the prism spectrometer used in the balloon borne system was replaced with a double pass l/2 meter Czerny-Turner type grating instrument designed specifically for balloon use. This instrument was flown foi the first time on March 26, 1964. The results of the flight are the subject of thib report. n 2.
INSTRUMENTATION

1 Grating Spectrometer
The spectrometer is a l/2 meter grating spectrometer of Czerny-Turner design equipped with a 75 line per mm Bausch and Lomb grating blazed for lZ\x. The orders are separated by mef ns of a small Littrow type prism predisperser. The position of the Littrow prism and hence the wavelength of the radiation which is allowed to reach the entrance slit of the grating spectrometer is controlled by means of a cam which is coupled to the grating drive system. Cams have been ground on a single blank which allow the grating spectrometer to be used in the 3rd, 4th, 5th, 6th and 25th order and it is possible to operate the instrument in any of these orders by rotating the cam to the proper position. The grating position is also controlled by a cam. This cam was ground so that as near as possible the recorded spectra are linear in wavelength. The position of the motor shaft used to drive the grating cam is monitored by means of a 13 bit shaft position encoder. This aids in reducing the data automatically.
1 Grating Spectrometer
The radiation illuminating the exit slit of the grating spectrometer is brought out the side of the instrument where it is focused by an auxiliary optical system onto the detector (a Schwarz rapid response thermocouple). This detector optical unit is built as a separate unit; thus it is possible to change the detector being used with the instrument without disturbing the spectrometer optical system. The radiation is interrupted mechanically at 100 cps after its first pass through the spectrometer by means of a tuning fork chopper. The 100 cps signal generated by the detector is amplified by a low noise transistorized preamplifier designed specifically for use with the thermocouple.
2 Auxiliary Instrumentation
The solar radiation is reflected by a plane mirror into a telescope (diameter 10 in. , focal length 5 ft,) which focuses the radiation on the spectrometer slit. The plane mirror or heliostat is oriented by means of a biaxial pointing control which is a modification of one described by Goddard, Juza, Maher and Speck.
2 Auxiliary Instrumentation
The modifications are too extensive to discuss here; they will be detailed in a separate report.
2 Auxiliary Instrumentation
The amplified detector output and auxiliary information necessary to ascertain the performance of the equipment during flight were recorded on board by means of an FM magnetic tape recorder and aloo transmitted to the ground by means of an FM/FM telemetry system. This flight was launched from Holloman Air Foice Base and the ground station for telemetry was provided as a part of the range facilities.
2 Auxiliary Instrumentation
Primary power for the various units was supplied by means of a 28 vdc silver-zinc battery. All mechanical operations were accomplished by means of 400 cycle single phase synchronous niotors. The 400 cycle power was derived from the 28 vdc by meaas of a transistorized sine wave inverter. The power required by the electronics was supplied by means of mercury batteries.
2 Auxiliary Instrumentation
The various components were mounted into a gondola system constructed from pieces of electrical conduit brazed together to form a unit of the desired configuration. The spectrometer and biaxial pointing control unit were mounted on an octagonal plate which was attached to the gondola by means of a spring suspension system. This system reduces accelerations which these units suffer when the equipment is returned to the ground by parachute. mm 3.
2 Auxiliary Instrumentation
FLIGHT DETAILS
2 Auxiliary Instrumentation
The polyethylene balloon used to carry the instrumentation to high altitude was of taped design and when fully inflated was 172. 6 feet in diameter with a volume of two million cubic feet. The instrumentation including the Air Force command package weighed 800 pounds. The balloon was launched from Holloman Air Force Base near Alamogordo, New Mexico at 0826 M. 5. T. , March 26, 1964 . The balloon ascended with an average ascent rate of 200 m/min and reached a floating altitude of 31. 6 km. The instrumentation was separated from the balloon at 1204 M. S. T. to facilitaie recovery. The equipment was recovered in excellent condition.
RESULTS
All of the instrumentation operated properly and excellent spectra were obtained trom the ground through floating altitude.
RESULTS
The spectral data are the continuous record of the output voltage from the detector. This iecord of output voltage versus time readily transforms to a record of output voltage versus wavelength since the scan mechanism is powered by a 400 cycle synchronous motor. The wavelength calibration of individual spectra were based on absorption features which are well known from laboratory studies.
RESULTS
Information on the relative output of the detector as a function of wavelength is sufficient for some purposes. It provides informrtion on the relative absorption by the atmosphere above the balloon at various altitudes from 1. 6 km to 31. 6 km. More than such relative information about transmittance can be derived from these data. By studying the variations of the detector output with altitude it is possible to determine the detector voltage that one would observe if no absorption were present. Once this so-called vacuum envelope has been determined it is possible to convert all spectra to the form of percent transmission versus wavelength. In the past this data reduction has been performed using desk calculators. With the increased resolution achieved with the grating spectrometer it was obvious that such manual reduction would not be economical. In view of this an automatic method of data reduction was devised. As a first step the data were converted from analog to digital form. The vacuum envelope was also converted to digital form and the computations necessary to reduce the data to percent transmission were performed by means of an IBM 7094 computer. Selected spectra were plotted by means of a digital plotter. Seventeen of these spectra are presented in Figures 1 through 8 . Each of the spectra presented are separated into four parts according to wave number intervals. The distribution of the spectral intervals among the nine figures is given in Table I . Observations of some parts of the spectra are lacking when the pointing control momentarily lost the sun, elsewhere they may be omitted for clarity.
RESULTS
Most of the strong atmospheric absorptions in this region are due to water vapor and carbon dioxide. The amount of water vapor present in the atmosphere decreases rapidly with altitude and except for the strongest lines most of the water vapor absorption has disappeared by the time the balloon reached an altitude of 13 km. These strong lines persist and at floating altitude a major portion of the residual absorption is due to water vapor. 
COMPARISON WITH THEORETICAL PREDICTIONS
In a previous report it was shown that the slant path transmiUance predicted by Plass for the CO2 absorption in the 4. 3|JI region agreed fairly well with the transmittance observed at the higher altitudes. It was also shown that the theoretical transmittance given by Plass for the 6. 3\i H2O absorption did not agree with the observed transmittances. This lack of agreement appeared to be due to an overestimate of the amount o f water vapor present at the higher altitudes. The absorptions in the wavelength region scanned during this flight are duo to CC2 and H2O with the water vapor lines occurring throughout the region. As mentioned above many of the water vapor absorption lines have disappeared from the spectra obtained above 13 km. In view of this the spectrum barrnatasha@example.org. 6 km altitude and a solar elevation angle of 46° was compared with that given by Plass for CO2 absorption only for 15 km and a solar elevation angle of 45°. The spectrum barrnatasha@example.org km and a solar elevation angle of 57. 8° was compared with that given by Plass for 30 km and a solar elevation angle of 60°.
COMPARISON WITH THEORETICAL PREDICTIONS
The result of these co.nparisons are given in Figure 9 . In comparing the theoretical and experimental results allowance must be made for the fact that the experimental data are taken with a higher resolution that that given for the theoretical data, JI addition the experimental curves contain the water vapor absorptions which are not considered in the theoretical data. Taking these factors into consideration the agreement between the theoretical and experimental results is fairly good in the case of the lower altitude spectrum. This agreement is no longer present at the higher altitude. This is not unexpected since at these altitudes the H2O absorption is approximately er^ual to the CO2 absorption. In addition the percentage error in the experimental data are much worse for small absorptions since any error in determining the vacuum envelope will result in a larger percentage error in this case than in the case for larger absorptions.
COMPARISON WITH THEORETICAL PREDICTIONS
There are a number of strong H2O absorption lines which occur outside of the region where CO2 absorption is significant at the higher altitudes. Comparisons were made between the theoretical transmittance c _ta of Plass for 15 km and the absorptions observed at 15 km. These comparisons indicate that the theoretical results predict considerably more absorption than was observed. It is felt that the discrepancy is due to an overestimate by Plass of the amount of water vapor present at the higher altitudes.
COMPARISON WITH THEORETICAL PREDICTIONS
The water vapor absorption in the v "inity of 3854 cm has been studied in detail. The variation of this absorption with altitude was used to determine the average water vapor mixing ratio in various layers in the stratosphere. The results of this analysis and a discussion of the results are given in a separate publication. 
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